The Messenger 172
The Messenger 172
The Messenger 172
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Telescopes and Instrumentation DOI: 10.18727/0722-6691/5073
Martino Romaniello 1 and the Atacama Pathfinder Experiment the characteristics and limitations of
Stefano Zampieri 1 (APEX) antenna at Chajnantor. Also each collection of processed data. This
Nausicaa Delmotte 1 available through the archive are data is p articularly important, as it enables
Vincenzo Forchì 1 from selected non-ESO instruments at users to decide whether the data are
Olivier Hainaut 1 La Silla, for example, the Gamma-Ray suitable for their specific science goals.
Alberto Micol 1 burst Optical/Near-infrared Detector The systematic archive publication of such
Jörg Retzlaff 1 (GROND), the Fibre-fed Extended Range processed data dates back to 25 July
Ignacio Vera 1 Echelle Spectrograph (FEROS) and the 2011, with the first products produced by
Nathalie Fourniol 1 Wide Field Imager (WFI). It also includes the Public Surveys conducted with the
Mubashir Ahmed Khan 1 raw data for UKIDSS, the infrared deep Visible and Infrared Survey Telescope
Uwe Lange 1 sky survey using the wide-field camera for Astronomy (VISTA) infrared camera
Devendra Sisodia 2 WFCAM at the United Kingdom Infrared VIRCAM (Arnaboldi & Retzlaff, 2011).
Malgorzata Stellert 3 Telescope (UKIRT) in Hawaii. In addition, Processed data that were generated at
Felix Stoehr 1 ESO hosts and operates the European ESO have been available since September
Magda Arnaboldi 1 copy of the ALMA Science Archive 2013. An up-to-date overview of the
Chiara Spiniello 1, 4 (Stoehr et al., 2017). The integration of released data is available online for con-
Laura Mascetti 5 archive services for LPO and ALMA data tributed and pipeline processed data 2, 3.
Michael Fritz Sterzik 1 is discussed here.
The number of users accessing pro-
Over the years, the archive has steadily cessed data in the archive has grown
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ESO grown into a powerful scientific resource steadily over time (Figure 1). At the cur-
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Pactum Limited, London, UK for the ESO astronomical community. rent rate, an average of 2.2 new users
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TEKOM Industrielle Systemtechnik As processed data are routinely included, are added every working day, with each
GmbH, Gautin, Germany they can be used directly for scientific user placing 11 requests on average.
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INAF–Osservatorio Astronomico di measurements, thus alleviating the need Given the growing popularity within the
Capodimonte, Naples, Italy for users to carry out data processing community, and the increasing volume
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Terma GmbH, Darmstadt, Germany on their own. An in-depth analysis of the and complexity of the archive holdings —
archive usage and user community is and taking into account the recommen-
presented in Romaniello et al. (2016). dations of advisory bodies, such as the
The archive of the La Silla Paranal Users Committee, the Public Survey
Observatory is a powerful scientific The archive is populated with processed Panel, and the results of the community
resource for the ESO astronomical data through two channels. For the first working group report on science data
community. It stores both the raw data channel, data-processing pipelines are management (STC Report 580 4) — it has
generated by all ESO instruments and run at ESO for selected instrument modes become necessary to upgrade the ways
selected processed data. We present to generate products that are free from in which users can access the ESO
new capabilities and user services that instrumental and atmospheric signatures Science Archive in order to enhance data
have recently been developed in order and that have been calibrated. They discovery and usage.
to enhance data discovery and usage cover virtually the entire data history of
in the face of the increasing volume the corresponding instrument modes and The trajectory of contemporary astro-
and complexity of the archive holdings. are generated by automatic processing, nomical research increasingly involves
Future plans to extend the new services with no knowledge of the associated multi-epoch, multi-messenger, multi-
to processed data from the Atacama science case. Checks are in place to wavelength, multi-facility science, in
Large Millimeter/submillimeter Array identify quality issues with the products. which data are plentiful and varied. At
(ALMA) are also discussed. The s econd channel involves data prod- the same time, data acquired from
ucts that have been contributed by the different facilities are becoming ever
community, which have been generated more complex, yet have to be combined
Background and motivation with processing schemes optimised to in order to tackle increasingly challenging
serve specific science cases. In most scientific questions. In this context, the
The ESO Science Archive 1 began oper cases, they have already been used to role of science data archives is to lower
ating in its current form in 1998, a few derive published results (see Arnaboldi the access threshold that separates
months ahead of the start of science et al., 2014). These contributed datasets, researchers from acquiring and being
operations of the Very Large Telescope, which are validated via a joint effort able to work with the data that they are
the VLT (see Pirenne et al., 1998). It is between the providers and ESO before interested in. The average astronomer
the operational, technical and science ingestion into the archive, often include cannot be expected to be intimately
data archive of the La Silla Paranal advanced products like mosaiced familiar with the details of each archive
Observatory (LPO). As such, it stores all images, source catalogues and spectra. and, even less, with the details of the
of the raw data, including the ambient instruments that produced the datasets
weather conditions, from the LPO, i.e., Thorough user documentation is also concerned. The access layer to the data
the telescopes at Paranal and La Silla, provided for all data releases, detailing therefore has to be as self-explanatory as
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Different types of user interaction are Figure 2. The landing web page of the ESO Archive coordinate or name, as resolved by the CDS’s
supported: Science Portal. The celestial sphere is colour-coded Sesame service 8. In order to serve different use
according to the types of ESO data contained at cases, they are a combination of physical charac
– Interactive access: web pages through
each position (the sky viewer is CDS’ AladinLite 6, the teristics of the data (e.g., signal-to-noise ratio,
which users can browse and explore web version of Aladin). The entire content of sens itivity, spectral range covered, spectral reso
the assets with interactive, iterative the archive is presented through aggregations of lution), the observational setup (e.g. filter name,
queries. The results of such queries 17 parameters, which can also be used to enter exposure time) and the ESO observing process
query constraints, in addition to querying by object (e.g. PI name, Programme ID).
are presented in real time in various
tabular and/or graphic forms, allowing
an evaluation of the usefulness of
the data which can then be selected
for retrieval.
– Programmatic access: whereby
users are able to formulate complex
queries through their own programmes
and scripts, obtain the list of matching
assets, and retrieve them.
– Access by tools: whereby data are
discovered, selected and accessed
through tools normally developed by
third parties, which are external to
the web access channel. These tools
often implement sophisticated data
handling capabilities, such as TOPCAT 5
for catalogues, or Aladin 6 for images.
1e–11
thus providing direct access to the ESO
8e–11 database tables 13. By adhering to widely
6e–11 recognised standards developed by the
International Virtual Observatory Alliance
4e–11
470 475 480 485 490 495 500 505 510 (IVOA) 14, the ESO data can be queried
alongside data from other observatories
and data centres. This brings the ESO
data into the appropriate general context
of multi-wavelength, multi-messenger
science.
Programmatic access
Users can specify their own custom
queries via a standard service protocol
using the IVOA’s Astronomical Data
Query Language, ADQL15. The service
Tool access
Bruno Leibundgut 1 Proposal solicitation and submission onds). The image quality throughout was
Pascale Hibon 1 quite good (0.5 arcseconds), and nearly
Harald Kuntschner 1 The call for HAWK-I/GRAAL Science Veri- independent of the outside seeing with
Cyrielle Opitom 1 fication proposals and the corresponding occasionally spectacular image quality in
Jérôme Paufique 1 web page were published on 2 October the fast photometry mode (0.2 arcsec-
Monika Petr-Gotzens 1 2017 1. The call was announced through onds in K). In rare cases, an elongation
Ralf Siebenmorgen 1 the ESO Science Newsletter on 17 Octo- of the images was observed, which was
Elena Valenti 1 ber 2017 2 with a deadline for proposal probably not related to the adaptive
Anita Zanella 1 submission of 31 October 2017. Nineteen optics, as it has also been observed with
proposals were received by the deadline other instruments on UT4. The only notice-
and evaluated by the Science Verification able instrument issue during the run was
1
ESO team over the following 2.5 weeks. A total a systematic instrument configuration
allocation of 35.5 hours was chosen, a tool error, revealed for non-zero position
slight oversubscription compared to the angles and corrected during the run.
Science Verification observations with available observing time (30 hours in total
the High Acuity Wide field K-band over four summer nights). This resulted The observations essentially followed the
Imager (HAWK-I) instrument enhanced in 14 projects being selected for schedul- priority given by the ranking of the pro-
by the ground-layer adaptive optics ing. All Principal Investigators (PIs) were posals. The seven top-ranked projects
module (GRAAL) were obtained during informed of the outcome of this selection were completed fully within the requested
4.5 nights from 2 to 6 January 2018. process on 27 November, and the constraints. Some data were obtained
Fourteen projects were selected from a successful applicants were given a dead- for three programmes, and for one pro-
total of 19 submitted proposals. The line for submission of the Phase 2 material ject, the data did not comply within the
total time scheduled for these 14 pro- of 14 December 2017. All PIs complied requested constraints. The lowest-ranked
jects was 35.5 hours, which represents with this deadline and the submitted three projects could not be started.
a slight oversubscription for the four material was verified by the User Support
allocated summer nights. The seven top- Department before 22 December, so
ranked projects were completed, three the HAWK-I/GRAAL Science Verification Archive and data processing
more programmes received some data, queue was ready by 31 December.
one was observed outside the requested All raw and pipeline-reduced data are
constraints, and three projects were not The scheduled projects covered a range publicly available through the ESO science
started. The Science Verification nights of topics, including: the characterisation archive. The ESO data quality c ontrol
were affected by various technical of a Solar System binary object — the group reduced all Science Verification
problems, mostly unrelated to GRAAL, dwarf planet Eris and its moon Dysnomia; data and the resulting products are avail-
which resulted in a total loss of 10 hours. observations of the mass function and able from the ESO Phase 3 data product
Half a night was allocated on 6 January dynamics of young clusters; pairs of stellar form 3. A new version of the HAWK-I/
to compensate for some of the lost time. clusters and their origins; and a massive GRAAL data reduction pipeline has been
The atmospheric conditions were rather embedded cluster. Star formation projects released. The HAWK-I/GRAAL Science
variable with occasionally excellent included an investigation into the infrared Verification web page also contains direct
natural seeing (0.3 arcseconds). The excess emission of pre-main-sequence links to the Science Verification data in
ground layer turbulence fraction varied stars in the Large Magellanic Cloud (LMC) the archive 1.
from 40% to 85% during these nights. and observations of molecular hydrogen
The best performance in terms of in a Herbig Haro object. Extragalactic
improved image quality was observed topics included a potentially binary active Some early science results
when the ground layer fraction was galactic nucleus in a merging galaxy sys-
above 70%, as expected for the system. tem, and multi-epoch observations of Solar System objects: Eris and
The image quality in the K filter ranged luminous infrared galaxies to search for Dysnomia
between 0.2 arcseconds (in excellent core-collapse supernovae. Trans-Neptunian objects (TNOs) are icy/
conditions) to about 0.5 arcseconds (with rocky bodies located beyond the orbit
mediocre seeing, > 0.8 arcseconds), of Neptune, which are believed to be rem-
and a small fraction of ground-layer tur- Observations nants of the building blocks from which
bulence. The delivered image quality planets formed. The dwarf planet
was very stable, but in some cases an All observations were made without tip- (136199) Eris is one of the largest TNOs
asymmetric point spread function was tilt stars and using only the four laser known in the Solar System, with a size
observed. beacons provided by the Adaptive Optics similar to that of Pluto. During the HAWK-I/
Facility (AOF). Various technical problems GRAAL Science Verification, high-
led to a loss of several hours during the precision photometric observations of Eris
Science Verification nights. At the same were obtained at near-infrared wave-
time some very good seeing conditions lengths. The aim of the observations was
were encountered (down to 0.3 arcsec- to characterise the surface heterogeneity
–47°19ಿ40.0ೀ –47°19ಿ40.0ೀ
20ಿ00.0ೀ 20ಿ00.0ೀ
Declination (J2000)
Declination (J2000)
20.0ೀ 20.0ೀ
40.0ೀ 40.0ೀ
21ಿ00.0ೀ 21ಿ00.0ೀ
Stellar outflows from young stars Young star cluster RCW38 early evolution of stars in such an
Herbig-Haro objects are massive outflows RCW 38 is the youngest (< 1 Myr) of the environment.
driven by stellar systems in the making. Milky Way’s 13 super star clusters (Fukui
They are large objects on the sky, extend- et al., 2016), and the densest stellar sys- Stellar cluster pairs in the LMC
ing over several arcminutes (~ 1 parsec), tem within 4 kpc of the Sun (Kuhn et al., The LMC possibly hosts the largest
and appear mostly diffuse, although they 2015). The cluster contains hundreds of number of candidate stellar cluster pairs
also contain point-like substructures, protostars, pre-main sequence stars, and within the Local Group. These systems
which evolve on timescales of years. In OB-star candidates (Winston et al., 2011), are extremely interesting as their study
fact, time evolution is key to understand- along with a substantial substellar candi- can provide a fresh look at the mecha-
ing the physics of outflows, and in par- date population revealed in the cluster nisms of cluster formation and evolution.
ticular the link to their driving source: the core (Muzic et al., 2017). With HAWK-I/ As part of a larger effort aimed at provid-
planet-forming young stellar disc. Efficient GRAAL data (see the cover image), one ing an independent characterisation of
mapping of Herbig-Haro objects requires can directly study several key aspects of cluster pairs in the LMC (Dalessandro et
wide-field, high-spatial-resolution data; star formation: massive star birth; low- al., 2018; Mucciarelli et al., 2012) this
this is exactly what HAWK-I provides in mass star and brown dwarf formation in a study exploited the wide field of view and
the near-infrared, where extinction effects dense environment and under the influ- the enhanced spatial resolution available
are mitigated. Molecular hydrogen emis- ence of photoionisation fronts from mas- with HAWK-I/GRAAL to observe the clus-
sion at 2.12 μm was observed in the sive stars; the initial mass function (IMF) ter pair NGC 2136 and NGC 2137 in the
Herbig-Haro object HH 212 using HAWK-I on an unprecedented sample spanning J- and H-bands. The high-quality colour-
in 2007. The driving source of HH 212 three orders of magnitudes in mass; and magnitude diagrams for the two clusters
is a low-mass protostar located in the mass segregation in young clusters. (Figure 5) will yield accurate cluster ages
Orion star-forming region at a distance of from the main-sequence turnoff luminosity,
about 400 pc. The new HAWK-I/GRAAL Star-forming complex in the LMC the structure of the systems from accurate
Science Verification image of HH 212 Pre-main-sequence candidate stars in star counts, and density profiles and the
shows all the characteristics of Herbig- the LMC often show near-infrared degree of mutual interaction. This informa-
Haro objects: well developed bow excesses compared to theoretical model tion will, in turn, yield clues as to the origin
shocks, where the outflowing gas inter- predictions. This was discovered using and final fate of these stellar systems.
acts with the ambient medium; jet-like VISTA images from the VISTA Magellanic
features closer to the source, tracing the Cloud survey (VMC; Cioni et al., 2011). Supernovae in the cores of galaxies
largely undisturbed flow originating in However, the VISTA images are affected Luminous infrared galaxies are highly
the star-disc system; and structure at by crowding and photometric uncertain- star-forming and dust-obscured galaxies.
essentially all scales. The new data (Fig- ties, which could also mimic this excess. While relatively rare in the local Universe,
ure 3) compared with the archival HAWK-I The HAWK-I/GRAAL Science Verification they start to dominate the total core-
image will enable proper motions to be observations targeted the central area collapse supernova rates at z ~ 1. Two
measured with high accuracy, i.e., down of the star-forming complex N44 to obtain luminous infrared galaxies were observed
to 20 km s –1, over the entire length of a colour-magnitude diagram to well during HAWK-I/GRAAL Science Verifica-
HH 212 — a fraction of the typical flow below 1 solar mass. The increased angu- tion. This resulted in the discovery of a
velocity of 300 km s –1. A detailed com- lar resolution has resolved the crowding new supernova, SN 2018ec (Kankare et
parison between the dynamics of the problem — almost 3 times as many al., 2018; Figure 6), in NGC 3256, which
blue- and red-shifted lobes is especially stars were detected in the densest young is only the second reported supernova
interesting because, although HH 212 star cluster areas (Figure 4) — and also in this luminous infrared galaxy, with an
appears symmetrical, its lobes show sub- helped with independent photometry. If expected intrinsic core-collapse super-
stantially different space velocities, some- the near-infrared excess persists in these nova rate of about one per year. Optical
thing that is challenging to explain with HAWK-I/GRAAL data as well, then it may transient surveys did not discover this
current jet launching models. be that the low metallicity in the LMC is nearby supernova — at a distance of only
responsible for significant changes in the 37 Mpc — owing to a combination of
10 arcseconds 10 arcseconds
the high extinction (AV ~ 2 magnitudes) A dual active galactic nucleus? nucleus system are crucial to character
along the line of sight of the host galaxy Recent observations using the VLT instru- ising the coordinated assembly of the
and the high background. SN 2018ec ment Multi Unit Spectroscopic Explorer galaxies and the supermassive black
was classified as a Type I c supernova by (MUSE) uncovered a potential dual active holes. The goal of obtaining the Ks-band
the survey “extended-Public ESO Spec- galactic nucleus candidate at redshift image (Figure 7) was to detect the host
troscopic Survey for Transient Objects” z = 3.3 with a separation of only 20 kpc. galaxy of the obscured active galactic
(ePESSTO; Berton et al., 2018). The study The merging of supermassive black nucleus. Indeed, the host galaxy was
of SN 2018ec will contribute to the long- holes in galaxy mergers is expected in detected at the expected location (thanks
term aim of deriving missing fractions for the h
ierarchical formation of galaxies. to the exquisite image quality, of 0.4 arc
core-collapse supernovae from the local HAWK-I/GRAAL follow-up observations seconds, and depth delivered by the
to the high-redshift Universe. of this high-redshift dual active galactic adaptive optics system). After de-blending
image of supernova
tem using the software package GALFIT3
SN 2018ec in NGC 3256
in a Ks image. (Peng et al., 2010), Ks-band magnitudes
of 19.2 (Vega magnitudes) for the quasar
host galaxy and 20.6 magnitudes for
the companion galaxy were derived. At
z = 3.3 the Ks-band corresponds nearly
to the rest-frame velocity, and stellar
masses of log(M∗ /M⊙) ~ 11.4 and ~ 10.9
were derived for the quasar host and
the companion, respectively (adopting a
mass-to-light ratio of ~ 0.1 for a 200 Myr-
old stellar population). The host galaxies
are both very massive and probably trace
one of the most massive dark matter
halos at that epoch of the Universe
(Husemann et al., 2018).
Acknowledgements
22
4
We are grateful to Hervé Bouy, Christian Schneider,
Σk s (magnitudes [Vega] arcsec –2)
Zhi-Yu Zhang 1, 2 and evolution, such as star formation (for example, in excess of 1000 M⊙ yr –1,
Donatella Romano 3 rates, and the timescales for gas deple- see Ivison et al., 1998) — have their
Rob J. Ivison 2, 1 tion and dust formation. ultraviolet and optical stellar light heavily
Padelis P. Papadopoulos 4, 5 obscured by dust (see Figure 1). How-
Francesca Matteucci 6, 7, 8 ever, according to theories and cosmo-
The stellar initial mass function logical simulations, it is in exactly these
systems where the most extreme IMF
1
Institute for Astronomy, University of First introduced by Edwin Salpeter variations would arise. Are there any other
Edinburgh, Royal Observatory (Salpeter, 1955), the stellar initial mass sensible, indirect methods to probe the
Edinburgh, UK function is an empirical probability func- IMF in these important, dust-shrouded
2
ESO tion which describes the relative numbers systems?
3
INAF–Osservatorio di Astrofisica e of stars that form in different mass ranges
Scienza dello Spazio di Bologna, Italy during a single star formation episode. Luckily, carefully selected chemical
4
Department of Physics, Aristotle Univer- The determination of the shape of the abundances (see the next sections) can
sity of Thessaloniki, Greece IMF — whether it is constant and universal be measured at millimetre/submillimetre
5
Research Center for Astronomy, or it depends on the physical conditions wavelengths — a regime relatively free
Academy of Athens, Greece in the interstellar medium (ISM) out of from the pernicious effects of dust; these
6
Department of Physics, University of which the stars form — is of the utmost provide a fossil imprint of the chemical
Trieste, Italy importance for modern astrophysics, enrichment processes and an indirect
7
INAF–Osservatorio Astronomico di because of its fundamental role in all constraint on the prevailing stellar IMF in
Trieste, Italy theories of star and galaxy formation. those extreme environments. It is well
8
INFN, Sezione di Trieste, Italy known (for example, Tinsley, 1980) that
Though neatly defined (more or less) stars in different mass ranges produce
from a theoretical point of view (Kroupa, different elements in different proportions
The stellar initial mass function (IMF) is 2001), the IMF is not easily derived from and on different timescales, with the
fundamental to all measurements of direct star counts (Bastian et al., 2010). initial chemical composition of the stars
cosmic star formation, which involves Many challenges must be overcome in also playing a role. Indeed, in the last
an extrapolation from rare, massive order to convert the observed stellar three decades, systemic variations of the
stars (M∗ > 8 M⊙) to the full stellar mass luminosities into stellar masses, where IMF slope have been explored with the aid
spectrum. Classical determinations of uncertainties in stellar distances, ages, of increasingly refined galactic chemical-
a galaxy’s IMF are limited to ultraviolet, metallicities, extinctions and the possibility evolution models. These attempt to
optical and near-infrared wavelengths, of unresolved binary systems severely explain, for instance, the overabundance
and these cannot be adopted for dust- hamper our ability to measure the present- of magnesium with respect to iron in local
obscured galaxies with intense, ongo- day mass function of a given stellar popu- elliptical galaxies, where magnesium is
ing star formation, even in the local lation. Furthermore, the effects of a com- synthesised on short timescales by mas-
Universe. The unprecedented sensi- plex star formation history and finite stel- sive stars and iron is produced mostly
tivity of the Atacama Large Millimeter/ lar lifetimes must be taken into account on long timescales by type I a supernovae
submillimeter Array (ALMA) allows us to to recover the IMF from the present-day with relatively low-mass progenitors, or
detect weak emission from 13CO and mass function. For example, the more the low metallicities measured in gas-rich,
C18O isotopologues, which offer a sen- massive a star, the less time it takes to star-forming dwarf galaxies. However,
sitive, relatively dust-free, probe of the evolve off the main sequence; at the same differences in star formation timescales
IMF. Globally low 13CO/C18O ratios for time, low-mass stars — with lifetimes and/or galactic outflows have sometimes
all our targets — dusty starburst galax- comparable to the age of the Universe — shown to act in a similar way, making it
ies at redshifts ~ 2–3 — alongside a continue to populate the present-day very difficult to prefer a variable IMF over
detailed chemical evolution model imply mass function. This readily introduces a other possibilities (Matteucci, 1994).
that stars formed in extreme starburst bias against high-mass objects.
environments are significantly biased
towards massive stars compared to Carbon, nitrogen and oxygen production
ordinary star-forming spiral galaxies. Deducing the shape of the IMF from its in stars, and mixing in the ISM
We have combined information from the chemical imprint
coldest interstellar medium (at tens The seven stable isotopes of carbon,
of Kelvins) with the physics of nucleo- Estimating the IMF directly is therefore nitrogen and oxygen (the CNO elements)
synthesis in hot stars (at tens of millions anything but a trivial task. On top of this, are produced solely by nucleosynthesis
of Kelvins), to delineate the formation direct observations of stellar light are not in stars. On galactic scales, 13C and 18O
and evolution of g alaxies. This opens up always possible. are released predominately by low- and
a new window to probe the stellar IMF intermediate-mass stars (M∗ < 8 M⊙) and
of galaxies with ALMA and it challenges The most massive and luminous galaxies massive stars (M∗ > 8 M⊙), respectively
our understanding of fundamental that shine at high redshift — for instance, (Kobayashi et al., 2011). This is due to
parameters governing galaxy formation those producing stars at tremendous rates the differing energy barriers in nuclear
reactions and the mass-dependent evo- isotopes. Measurements of 13CO and ALMA observations of 13CO and C18O
lution of stars. C18O — isotopologues of carbon towards dusty starbursts
monoxide, 12C16O or CO — in the ISM
13
C is mostly synthesised as a secondary can thus be used to trace the relative Starburst galaxies in the local Universe
13
element, i.e., its production needs the C and 18O abundances produced by most likely had prior episodes of cosmo-
pre-existing seed of the primary element, successive generations of stars. logical evolution, so the elementary abun-
12
C, to be present at a star’s birth. How- dances in their ISM could be affected by
ever, 13C also has a primary production In theoretical work by Romano et al. a complex star formation history may not
channel, if synthesised directly from 12C (2017), we reassessed the relative roles strictly be related to the current episode
produced through helium burning in the of stars in different mass ranges in the of star formation. We selected a sample
star itself. This may happen at the base production of the rare CNO isotopes, of dusty starburst galaxies at z ~ 2–3,
13
of the convective envelopes of asymptotic C, 15N, 17O and 18O, along with the more with less than 3 Gyr of cosmic time avail-
giant branch (AGB) stars going through abundant 12C, 14N and 16O. We used a able for prior episodes of evolution. So
periodic episodes of dredge-up (Renzini proprietary galactic chemical evolution they are expected to have relatively clean
& Voli, 1981), or in low-metallicity, fast- code for the Milky Way and stellar yields and simple star formation histories.
rotating, massive stars, in which rotation from the literature for massive stars, AGB Owing to the weakness of the isotopo-
triggers the production of primary 13C stars and novae to show that the available logue lines (13CO and C18O), we selected
by allowing the diffusion of 12C produced isotopic data for the local ISM, proto- the four strongest CO emitters in the liter-
in He-burning zones into zones burning solar nebula, metal-poor stars and abun- ature, which are all gravitationally lensed
hydrogen (Chiappini et al., 2008). dance gradients across the Galactic systems with their signals amplified by
disc can be reproduced satisfactorily factors of ~ 3–10.
Massive stars dominate the production of with a suitable choice of yields. Moreover,
18
O (Timmes et al., 1995), which is mostly we showed that our models could be We performed simultaneous observations
synthesised as a secondary element in extended to constrain the stellar IMF of of 13CO and C18O emission lines, using
the early stages of helium burning, start- star-forming galaxies across cosmic time. ALMA in its relatively compact array con-
ing from any pre-existing 16O. Therefore Among the remaining uncertainties, an figurations, in the spring of 2015 (Zhang
18
O production is strongly dependent on unknown star formation history is particu- et al., 2018). Between 10 and 30 minutes
the initial stellar metallicity. larly tricky to deal with. However, if gal were spent on each target per observa-
axies are caught during the earliest stages tion. We manually calibrated all data
These isotopes are then ejected into the of their evolution, the uncertainties are using the Common Astronomy Software
ISM via stellar winds, where they form significantly reduced. Applications (CASA) package 1 (v. 4.7.1)
molecules in the same way as their major following standard procedures. The final
(Jy beam –1 km s –1 )
Declination (J2000)
observations and in the data reduction, 0.32
so the final images have limited angular 56.0ೀ 0.24
resolution — most targets are unresolved
0.16
or only marginally resolved.
24ಿ00.0ೀ 0.08
Most targeted lines are detected robustly 0.00
with signal-to-noise (S/N) > 5. Only two 04.0ೀ
–0.08
targeted lines are marginally detected 08.00s 07.50s 07.00s 1h25m06.50s 07.50s 07.00s 1h25m06.50s
at ~ 4-σ level; J = 3 → 2 from SDP.17b Right ascension (J2000) Right ascension (J2000)
(HATLAS J090302.9–014127) and
J = 5 → 4 from SPT 0103–45 (SPT-S Figure 2. Velocity-integrated flux map (zero moment) emission. Black contours show the high-resolution
of 13CO and C18O for the J = 3 → 2 transition in 336-GHz continuum image, obtained from the
J010312−4538.8). However, the high-J
SPT 0125–47. White contours show the low-resolution ALMA archive, presenting the Einstein ring structure
transitions show consistent results at 94-GHz continuum, tracing the rest-frame cold dust produced by the gravitational lensing effect.
higher S/N, so we can be confident about
the observed line ratios. See Figure 2 Global ratio or nuclei
SMC
for an example of our ALMA detections of Discs
13
CO and C18O, J = 3 → 2. IRAS 13120-5453 centre SMC, LMC, dwarfs
LMC IRAS 13120-5453 global
SMGs (this work)
Literature data on 13CO and C18O in
IC 10
various galaxies
10
Milky Way, discs,
I( 13 CO)/I(C18 O)
100 Bottom-heavy
Big Bang, grew to a total stellar mass of 1011 M⊙
Kroupa and stopped forming stars 1 Gyr later. SFR is the
10 Top-heavy star formation rate. b) Corresponding 13CO/C18O (as
Ballero a proxy of 13C/18O) abundance ratio as a function
1
of redshift, following different IMFs. Our lensed star-
burst sample is plotted with red symbols. Blue
dots show the 13CO/C18O ratios measured in a few
b representative local galaxies.
100 SMC SMC, LMC, dwarfs
C/ 18 O
LMC
Milky Way Milky Way, discs
13
question, we adopt a galactic chemical IMF can reproduce the I(13CO)/I(C18O) Acknowledgements
evolution model that accurately includes observed in starburst galaxies, near and Zhi-Yu Zhang, Rob J. Ivison and Padelis P.
the isotopic yields across the full range far. The extremely low I(13CO)/I(C18O) ratio Papadopoulos acknowledge support from the Euro-
of stellar mass, taking into account the measured in the centre of IRAS 13120– pean Research Council in the form of the Advanced
differential release of different elements 5453 can be explained with the top- Investigator Programme, 321302, COSMICISM. This
research was supported by the Munich Institute for
into the ISM as a function of a star’s life- heavy and the B allero IMF (Ballero et al., Astro- and Particle Physics (MIAPP) of the German
time, and the initial metallicity, as well 2007), which could reproduce the chemi- Research Foundation (DFG) cluster of excellence
as any prior galactic evolution. We have cal abundances of stars in the Galactic “Origin and Structure of the Universe”. This work also
benchmarked the model against the rich bulge. benefited from the International Space Science Insti-
tute (ISSI) in Bern, thanks to the funding of the team
isotopic datasets of the Milky Way and “The Formation and Evolution of the Galactic Halo”
shown it can reproduce the Galacto (Principal Investigator Donatella Romano). This paper
centric gradients of isotopic abundance Outlook and implication makes use of ALMA data.
ratios, and all the relevant local disc data
(Romano et al., 2017). Our results — finding a top-heavy IMF in References
dusty starburst systems across cosmic
With such a well-calibrated model, we time, where classical IMF measurement Ballero, S. K. et al. 2007, A&A, 467, 123
can safely build up an extreme case for methods cannot be applied — are con- Bastian, N., Covey, K. R. & Meyer, M. R. 2010,
ARA&A, 48, 339
the evolution of the 13C/18O abundance sistent with the results from other, less Chiappini, C. et al. 2008, A&A, 479, L9
ratio for a pure starburst, as shown in dusty, less extreme starburst systems, Danielson, A. L. R. et al. 2013, MNRAS, 436, 2793
Figure 4. To do that, we evolve a galaxy such as ultra-compact dwarf galaxies, Henkel, C. et al. 2014, A&A, 565, A3
from z ~ 3 (2 Gyr after the Big Bang) for progenitors of early-type galaxies, and Ivison, R. J. et al. 1998, MNRAS, 298, 583
Jiménez-Donaire, M. J. et al. 2017, ApJL, 836, L29
a span of 1 Gyr, with a high star formation compact starbursting stellar associations Kobayashi, C., Karakas, A. I. & Umeda, H. 2011,
rate, until it reaches a total stellar mass of in the Large Magellanic Cloud. MNRAS, 414, 3231
1011 M⊙. Star formation is stopped com- Kroupa, P. 2001, MNRAS, 322, 231
pletely after that, and the relic evolves The systematic variation of the IMF in Matteucci, F. 1994, A&A, 288, 57
Renzini, A. & Voli, M. 1981, A&A, 94, 175
passively to z ~ 0. This model was different galaxy types has an obvious Romano, D. et al. 2017, MNRAS, 470, 401
repeated with four different types of IMF, dependency on their star formation Salpeter, E. E. 1955, ApJ, 121, 161
from bottom-heavy (biased towards low- properties. The IMF can no longer be Sliwa, K. et al. 2017, ApJL, 840, L11
mass stars) to top-heavy (biased towards assumed to be universal, with a constant Timmes, F. X., Woosley, S. E. & Weaver, T. A. 1995,
ApJS, 98, 617
massive stars), including the canonical canonical form, as commonly applied in Tinsley, B. M. 1980, Fundamentals of Cosmic
Kroupa IMF that can reproduce average most cosmological simulations. More Physics, 5, 287
Galactic conditions (K roupa, 2001). over, all measurements of cosmic star Zhang, Z.-Y. et al. 2018, Nature, DOI: 10.1038/s41586-
formation rate and stellar mass, and their 018-0196-x
With the Kroupa IMF, the evolved 13C/18O derivatives, must be re-assessed urgently.
ratio reaches the range observed in the For example, the star formation rates in Links
discs of the Milky Way and nearby normal starburst galaxies are derived from classi-
1
spiral galaxies. However, only a top-heavy cal tracers, which extrapolate observables CASA software: https://casa.nrao.edu/index.shtml
Francesco R. Ferraro 1, 2 black holes in star clusters can finally Thus, despite its importance, our empiri-
Alessio Mucciarelli 1, 2 be addressed, impacting our under- cal knowledge of globular cluster internal
Barbara Lanzoni 1, 2 standing of the formation and evolution- kinematics from the very centre (where
Cristina Pallanca 1, 2 ary processes of globular clusters and the most interesting dynamical phenom-
Livia Origlia 2 their interactions with the Galactic tidal ena occur) to the tidal radius (where the
Emilio Lapenna 1, 2 field. effects of the Galactic tidal field are visible)
Emanuele Dalessandro 2 is still critically inadequate. In particular, a
Elena Valenti 3 detailed knowledge of the velocity disper-
Giacomo Beccari 3 Galactic Globular Clusters are gas-free sion profile and the (possible) rotation
Michele Bellazzini 2 stellar systems, made up of a few times curve is still missing in the majority of the
Enrico Vesperini 4 105 stars of different masses (typically cases. This is essentially due to observa-
Anna Lisa Varri 5 from ~ 0.1 to 0.8 M⊙ ). They are the tional difficulties.
Antonio Sollima 2 most populous, and the oldest stellar
systems in which stars can be individually In principle, velocity dispersion and
observed. Moreover they are the sole rotation can be obtained from different
1
Dipartimento di Fisica e Astronomia, cosmic structures that, within the times- approaches. In practice, however, the
Università degli Studi di Bologna, Italy cale of the age of the Universe, undergo standard methodology commonly used in
2
INAF–Osservatorio di Astrofisica e nearly all of the physical processes known extra-galactic astronomy (i.e., measuring
Scienza dello Spazio di Bologna, Italy in stellar dynamics. Galactic globular radial velocities from Doppler shifts and
3
ESO clusters are true touchstones for astro- velocity dispersions from the line broad-
4
Department of Astronomy, Indiana physics. The study of their stellar popula- ening of integrated-light spectra) can
University, Bloomington, USA tions is crucial to validating predictions suffer from severe shot-noise bias in
5
Institute for Astronomy, University of from stellar evolution theory, and they are Milky Way globular clusters, because the
Edinburgh, Royal Observatory, UK invaluable laboratories for multi-body acquired spectrum can be dominated by
dynamics. Surprisingly, while remarkable the contribution of just a few bright stars
progress has been made in the study (for example, Dubath et al., 1997). In the
Globular clusters are collisional systems, of Galactic globular cluster s tellar popu case of resolved stellar populations, a
where stars of different masses orbit lations (see Carretta et al., 2009 and safer approach is to determine velocity
and mutually interact. They are the best Piotto et al., 2015), the kinematical charac- dispersion and rotation from the veloci-
“natural laboratories” in the Universe terisation of these systems is just in its ties of individual stars. By combining
for studying multi-body dynamics and infancy and the modelling often relies on the line-of-sight information (measured
their (reciprocal) effects on stellar evolu- a set of over-simplified assumptions. through resolved spectroscopy) with the
tion. Although these objects have been two velocity components on the plane
studied since the very beginning of In general, globular clusters are assumed of sky (from internal proper motions), a
modern astrophysics, little is known to be quasi-relaxed, non-rotating stellar full 3D view of the velocity space of the
observationally about their internal kine- systems, characterised by spherical system can be obtained. This begins to
matics, thus preventing a complete symmetry and orbital isotropy, with struc- be feasible in Galactic globular clusters.
understanding of their dynamical state, tural and kinematical properties (surface
and of their formation and evolutionary brightness and velocity dispersion pro- Internal proper motions require high-
history. We present the first results from files) that are well captured by a truncated precision photometry and astrometry on
the Very Large Telescope (VLT) Multi- Maxwellian distribution function (for relatively long time baselines. These are
Instrument Kinematic Survey of Galactic example, King, 1966). However, growing finally achievable thanks to multi-epoch
globular clusters (MIKiS), which is spe- observational evidence demonstrates HST and Gaia observations. The former
cifically designed to provide line-of-sight that although this scenario is correct to are providing the necessary information
velocities of hundreds of individual a first approximation, it is largely over- on the centres of Galactic globular clus-
stars over the entire radial extension simplified. Indeed, there is accumulating ters (even if the innermost regions of the
of a selected sample of clusters. The evidence of significant deviations from densest systems might still be missed;
survey allows the first kinematical sphericity (Chen & Chen, 2010), and from for example, see Bellini et al., 2014 and
exploration of the innermost regions of a King density profile, a profile used to Watkins et al., 2015 for recent results). In
high-density globular clusters. When fit the observed distribution of stars within the meantime, Gaia is providing the com-
combined with proper motion measure- a globular cluster as a function of their plementary measures in the outskirts.
ments, it will provide the full 3D view in distance from the centre (see Carballo- The line-of-sight kinematical information
velocity-space for each system. Long- Bello et al., 2012; Lane et al., 2010). Sig- over the entire radial extension of Galactic
running open issues, such as the accu- natures of systemic rotation and pressure globular clusters is still largely missing,
rate shapes of the velocity dispersion anisotropy have been detected in several because it requires the collection of large
profiles, the existence of systemic rota- clusters (for example, Watkins et al., 2015; samples of individual stellar spectra, both
tion and orbital anisotropy (and thus Kamann et al., 2018; and references in highly crowded regions — the central
the level of relaxation), and the contro- therein). density of the Milky Way globular clusters
versial presence of intermediate-mass can reach up to 7 × 105 L⊙ parsec –3 (see
HST/ACS-HRC SINFONI
1
Figure 3. Distribution of the targets selected for the
–10 MIKiS survey (large circles) showing the height on
0.5 the Galactic plane z vs. absolute integrated V-band
magnitude MV (left) and the King concentration
parameter c vs. core relaxation time tc (right). The
–7 –8 –9 7 8 9
total Galactic globular cluster population is also
MV log tc (years)
plotted for reference (small dots).
10
5
the innermost core regions of high-
SINFONI KMOS FLAMES
SINFONI KMOS FLAMES density systems, thus finally opening up
(790) (96) (700)
(52) (82) (276) the p
ossibility of properly exploring the
kinematics of Galactic globular clusters
0 1 2 0 1 2 3 at sub-arcsecond scales (see Figures 1
log r (arcseconds) log r (arcseconds) and 4). For comparison, note that no
proper motions have been determined in
of the red giant branch with good signal- knowledge of the visible matter density the innermost 10 arcseconds of these
to-noise in reasonable exposure times, distribution and the kinematic profiles dense globular clusters. For example, in
the horizontal branch level is always can provide reliable estimates of the the case of NGC 6388, proper motions
brighter than I = 16.5 (i.e., all the targets stellar densities, mass-to-light ratios, have been measured at only r > 20 arcsec-
are located at distances < 16 kpc). More- and total cluster masses. onds (Watkins et al., 2015).
over, we included only globular clusters 3. T he exploration of the kinematics in
with [Fe/H] > –1.8, showing metallic lines the proximity of the cluster tidal radius, Figure 5 summarises the results obtained
deep enough to guarantee a few km s –1 which has major implications for the from the analysis of 6275 stars sampling
accuracy in the radial velocities measure- understanding of the physical origin of the entire radial extension of 11 Galactic
ments obtained from low-resolution recently claimed “extra-tidal structures”, globular clusters (Ferraro et al., 2018). This
spectra. the interplay with the external tidal dataset allowed us to accurately deter-
field, as well as the possible presence mine the systemic velocity and velocity
As a first step, the MIKiS survey is of small dark matter halos or modifica- dispersion profile of each system, as well
expected to provide the full characteri tions to the theory of gravity. as to investigate the presence of ordered
sation of the line-of-sight internal kine- 4. A detailed characterisation of the kine- motions. It also provides the first kine-
matics of each target cluster, from the matics of multiple populations with matical information for two poorly investi-
innermost to the outermost regions. different light-element content, to gated clusters: NGC 1261 and NGC 6496.
Once combined with measurements of provide crucial constraints to globular In the majority of the surveyed systems
proper motion, the global project will cluster formation scenarios. we find evidence of rotation within a few
provide the full 3D view of the velocity half-mass radii from the centre. These
space of each system, obtained from results are in overall agreement with the
hundreds individual stars, with crucial MIKiS first results predictions of recent theoretical studies,
impact on many hot topics of globular suggesting that the detected signals
cluster science. In particular, the MIKiS The results obtained so far clearly could be the relics of significant internal
survey will provide: demonstrate the revolutionary potential rotation that was set at the epoch of the
1. The very first sub-arcsecond kinematic of the approach adopted in the MIKiS cluster’s formation. This evidence, com-
exploration of Galactic globular cluster survey to study the kinematics of colli- bined with other recent results in the
cores, thus allowing a systematic search sional systems. In this section, we give literature (see for example, Kamann et
for signatures of systemic rotation an overview of the first set of results. We al., 2018), suggests that the vast majority
and intermediate-mass (103 –104 M⊙ ) find that the AO-corrected SINFONI of Galactic globular clusters (if not all of
black holes, providing crucial new observations attained an angular resolu- them) display some level of internal rota-
insights into the physics and formation tion comparable with that of the HST, thus tion. This might be the remnant signal of
processes of both globular clusters allowing us to extract individual spectra a much larger amount of ordered motion
and these elusive dark compact for 700 resolved stars within 10 arcsec- imprinted at birth (at the end of the initial
objects. onds from the centre of NGC 2808 (see violent relaxation phase) which gradually
2. T he determination of the mass distri- Figure 1), and even 52 individual star dissipated via two-body relaxation (see
bution and the global amount of spectra within the central 2 arcseconds Tiongco et al., 2017).
mass in dark remnants (white dwarfs, of the high-density cluster NGC 6388 (see
neutron stars, stellar mass black Lanzoni et al., 2013). This is indeed an Figure 6 shows the unprecedented rota-
holes), since the kinematic profiles are unprecedented achievement; for the very tion curve derived for M5 (Lanzoni et al.,
sensitive to the whole mass enclosed first time, the radial velocities of hundreds 2018a). The velocity dispersion profile
within stellar orbits. The simultaneous of individual stars have been measured in and the rotation curve in this cluster were
cluster. The rotation axis has been 2 NGC 6723 NGC 1261
NGC 3201
measured in distinct concentric annuli at
different distances from the cluster centre
and it turns out to be strikingly stable
(having a constant position angle of 145 6
degrees with respect to the north-south
direction at all surveyed radii). The well- 4
defined shape of the rotation curve is fully
consistent with cylindrical rotation. The 2 NGC 1904 NGC 6254 NGC 5927
star density distribution shows a clear
10 10 100 1000
flattening in the direction perpendicular to
the rotation axis, with the ellipticity (e) 8
increasing with increasing distance from
the cluster centre, reaching a maximum 6
of e ~ 0.14 at r > 80 arcseconds. The peak 4
of the projected rotation velocity curve NGC 5272 NGC 362
(~ 3 km s−1) has been found at ~ 0.6 half- 2
mass radii, and its ratio with respect to 10 100 1000 10 100 1000
the central velocity dispersion is Vpeak /σ0 r (arcseconds)
~ 0.4. All of these results suggest that
M5 is an oblate rotator that is seen
almost edge on. 4
Figure 6. The unprece-
dented rotation curve
M5
obtained for M5 (L anzoni
Figure 7 shows the results obtained in et al., 2018a). The blue
another intriguing cluster: NGC 5986 2 circles mark the mean
(Lanzoni et al., 2018b). The velocity dis- stellar velocity as a
Vrot (XR) (km s –1)
8
2
–2
σP(r) (km s –1)
–4
– 200 0 200
XR (arcseconds)
4
Figure 7. Left panel: Velocity dispersion profile of
NGC 5986, showing a clear increasing trend in the
outskirts. Right panel: Rotation curve of NGC 5986.
The blue circles mark the mean s tellar velocity as
a function of the projected distance on either side of
the rotation axis (XR). The solid line is the best least-
squares fit to the observed points (from Lanzoni et
1.5 2 2.5 al., 2018b).
log r (arcseconds)
on the complex interplay between g lobular Ferraro, F. R. et al. 2018, ApJ, 860, 50 Tiongco, M. A. et al. 2018, MNRAS, 475, L86
Harris, W. E. 1996, AJ, 112, 1487 Watkins, L. L. et al. 2015, ApJ, 803, 29
cluster internal evolution and the tidal
Kamann, S. et al. 2018, MNRAS, 473, 5591
field of the Galaxy. King, I. R. 1966, AJ, 71, 64
Lane, R. R. et al. 2010, MNRAS, 406, 2732 Notes
Lanzoni, B. et al. 2013, ApJ, 769, 107
a
References Lanzoni, B. et al. 2018a, ApJ, in press, he shape of the profile is fixed by the concentration
T
arXiv:1804.10509 parameter c, defined as c = log(r t /rc), where rc is
Bellini, A. et al. 2014, ApJ, 797, 115 Lanzoni, B. et al. 2018b, ApJ, submitted the core radius of the model (roughly correspond-
Carballo-Bello, J. A. et al. 2012, MNRAS, 419, 14 Lapenna, E. et al. 2015, ApJ, 798, 23 ing to the cluster-centric distance at which the
Carretta, E. et al. 2009, A&A, 505, 117 Lutzgendorf, N. et al. 2011, A&A, 533, A36 p rojected density of stars drops to half of its central
Chen, C. W. & Chen, W. P. 2010, ApJ, 721, 1790 Piotto, G. et al. 2015, AJ, 149, 91 value), and rc is the tidal radius (at which the stellar
Dubath, P. et al. 1997, A&A, 324, 505 Tiongco, M. A. et al. 2016, MNRAS, 461, 402 density becomes zero).
Tiongco, M. A. et al. 2017, MNRAS, 469, 683
G. Hüdepohl (atacamaphoto.com)/ESO
Claudia Paladini 1 between stellar parameters and con- 2013). At this stage the need for high
Fabien Baron 2 vective sizes, which are determined on angular resolution images became clear.
Alain Jorissen 3 the basis of three-dimensional stellar
Jean-Baptiste Le Bouquin 4 convection models. Our results open
Bernd Freytag 5 up a new era for the characterisation Stellar surfaces with PIONIER
Sophie Van Eck 3 of stellar convection in stars other than
Markus Wittkowski 1 the Sun. The PIONIER instrument (Le Bouquin et
Josef Hron 6 al., 2009) combines the light of four tele-
Andrea Chiavassa 7 scopes (the four Auxiliary Telescopes, or
Jean-Philippe Berger 4 The surface of the Sun is populated by the four Unit Telescopes) in the H-band.
Christos Siopis 3 about two million convective cells that PIONIER is very stable and efficient, and
Andreas Mayer 6 are roughly 2000 km in size. According is best suited to imaging bright targets
Gilles Sadowski 3 to the theory outlined by Schwarzschild (see for example, Wittkowski et al., 2017).
Kateryna Kravchenko 3 (1975), when the Sun evolves towards
Shreeya Shetye 3 the red giant branch, its atmosphere will The semi-regular variable π1 Gruis, an
Franz Kerschbaum 6 inflate and, because of the lower surface evolved star with a period of 195 days
Jacques Kluska 8 gravity, only a few convective cells will and a parallax of 6.13 ± 0.76 milliarcsec-
Sofia Ramstedt 5 survive at the surface. On the other hand, onds, was observed with PIONIER in
it is known that stars evolving along the September 2014 (Figure 1). Given the
giant branch lose mass via stellar winds. complexity of the target, we collected
1
ESO Mass loss from evolved stars is one of as many uv points as possible, which
2
Department of Physics and Astronomy, the c rucial processes for galactic chemis- resulted in a total of two nights of obser-
Georgia State University, USA try. Stellar convection is one of the vations. The data were obtained using
3
Institut d’Astronomie et d’Astrophysique, dynamical processes that plays a crucial the compact and the medium arrays of
Université libre de Bruxelles, Belgium role in shaping the inner atmospheres the VLTI, which are best suited to imaging
4
Université Grenoble Alpes, CNRS, of evolved stars. In particular, through its targets with a diameter of about 20 milli-
IPAG, France interplay with dust formation, it contrib- arcseconds, as in the case of π1 Gruis.
5
Department of Physics and Astronomy, utes to the mass-loss process. The switch between the array configura-
Uppsala University, Sweden tions was done within one week to mini-
6
Department of Astrophysics, University The angular resolution of optical interfer- mise the effect of variability of the star.
of Vienna, Austria ometry allows the stellar discs of evolved The H-band (like the K-band) gives access
7
Université Côte d’Azur, Observatoire de stars to be resolved, as well as smaller to the photospheres of evolved stars.
la Côte d’Azur, CNRS, Lagrange, Nice, structures such as convective granulation. AGB stars with oxygen-rich chemistry,
France However, for several years we have been such as π1 Gruis, are ideal candidates for
8
Institute of Astronomy, KU Leuven, limited by the number of available aper- studies of the stellar surface convection,
Belgium tures. Several papers have reported as oxygen-rich dust is transparent at
asymmetric structures in evolved giants. those wavelengths.
The departure from spherical symmetry
We used the Precision Integrated-Optics was measured either by comparing We collected 303 spectrally dispersed
Near-infrared Imaging ExpeRiment visibilities observed at different position visibilities (three spectral channels at
(PIONIER) at the Very Large Telescope angles, or via measurements of closure 1.625, 1.678, and 1.730 micrometers) and
Interferometer (VLTI) to image the stellar phase different from zero or ±180 degrees. 201 closure phases. Model-independent
surface of the S-type Asymptotic Giant The observations were then interpreted images have been reconstructed for
Branch (AGB) star π1 Gruis. The angular by superimposing bright spots with vary- each spectral channel using the software
resolution of two milliarcseconds allowed ing contrasts on limb-darkened discs packages SQUEEZE (Baron et al., 2010),
us to observe the surface of this giant (Young et al., 2000; Ragland et al., 2006; and the Multi-aperture image Reconstruc-
star in unprecedented detail. At the Montarges et al., 2016, 2017). In other tion Algorithm (MiRA, Thiebaut, 2008).
observed wavelength the stellar disc cases, the interpretation was done using Figure 2 shows the result of the recon-
appears circular and dust-free. More physical models including radiative trans- struction algorithms, which use d ifferent
over, the disc is characterised by a few fer (for example Cruzalebes et al., 2013, principles but give two very robust and
bubbles of a convective nature. We Arroyo-Torres et al., 2015). However, similar results in this case. The stellar
determine the contrast, and the charac- because of the scarce uv coverage, the disc is nearly round, populated by several
teristic horizontal length-scale of the interpretation of the data was highly non- patterns of a convective nature.
convective granules. The latter is deter- unique, and asymmetric structures could
mined, for the first time, directly from also be interpreted as indications of the
the image, without involving the usual presence of a binary companion (Mayer Characterising stellar convection
geometric modelling that has been used et al., 2014), or even an increase of the
in the literature. The measurements density scale-height in the equatorial The three quantities characterising con-
fall along empirical scaling relations plane due to rotation (van Belle et al., vective granules are the contrast, the size
C. Paladini
Figure 1. (Above) Left: λcentre = 1.625 µm λcentre = 1.678 µm λcentre = 1.730 µm
Declination (mas)
Declination (mas)
configuration. 5 5 5
0.6
0 0 0
0.4
–5 –5 –5
0.2
–10 –10 –10
0.0
–10 –5 0 5 10 –10 –5 0 5 10 –10 –5 0 5 10
Right ascension (mas) Right ascension (mas) Right ascension (mas)
1.0
aಿ) bಿ) cಿ)
10 10 10
0.8
Figure 2. (Right) Upper
Declination (mas)
Declination (mas)
Declination (mas)
of the granules, and their characteristic derived the power spectrum density of that best fits the spectral energy distri
lifetime. The last of these cannot be the image; this method is commonly used bution; 2) a Gaussian profile; and 3)
determined as we currently only have in several fields of astronomy, especially a square mask that excludes the steep
observations obtained at one epoch. when modelling stellar convection. How- decrease in brightness of the limb
The contrast was obtained for every ever, a mere power spectrum of our darkening in the image.
individual spectral channel after correct- image would simply provide the diameter
ing the image for limb darkening. We of the star. As we are interested in the After subtracting the limb darkening,
obtained a contrast between 12% and characteristic size of granulation, we sub- we scaled the background of the image
13%, with a slight increase towards short tracted the stellar disc from the image using the average over the image, and
wavelengths where the contamination using dedicated masks. Three masks then added space around the image to
from molecular opacities becomes more were designed: 1) a limb darkening profile better isolate the maximum power scale.
significant. To derive the characteristic obtained from the Model Atmospheres The resulting power spectrum density is
scales of the granules in the images, we in Radiative and Convective Scheme shown in Figure 3. The maximum power
did not use any geometric model, but (MARCS) model (Van Eck et al., 2017) corresponds to a typical granulation size
Christian Ginski 1, 2 With the Spectro-Polarimetric High- The SPHERE instrument (Beuzit et al.,
Rob van Holstein 1 contrast Exoplanet REsearch (SPHERE) 2008) is perfectly suited to this task.
Attila Juhász 3 instrument at ESO’s Very Large Tele- Recently van Holstein et al. (2017) were
Myriam Benisty 4, 5 scope (VLT) we can study the linear able to constrain the polarisation degree
Tobias Schmidt 6 polarisation of directly detected planets of the planets around HR 8799 to be lower
Gaël Chauvin 4, 5 and brown dwarfs, to learn about their than 1% and the companion to PZ Tel
Jos de Boer 1 atmospheres and immediate environ- to be lower than 0.1% with measurements
Mike Wilby 1 ments. We summarise here the recent performed with the SPHERE Infra-Red
Carlo F. Manara 7 discovery of a low-mass companion in Dual Imaging and Spectrograph (IRDIS).
Philippe Delorme 4 polarised light by Ginski et al. (2018). Here, we highlight another recent result:
Francois Ménard 4 The object shows an extreme degree of the first detection of a new substellar
Gabriela Muro-Arena 2 polarisation, indicating the presence of companion to a young nearby star in
Paola Pinilla 8 a circumplanetary disc. polarised light.
Til Birnstiel 9
Mario Flock 10
Christoph Keller 1 High-resolution polarimetry of Observations of the CS Cha system
Matthew Kenworthy 1 substellar companions
Julien Milli 7 The CS Cha system contains a spectro-
Johan Olofsson 11, 12 In the past 15 years, numerous substellar- scopic binary, both components of
Laura Pérez 13 mass companions to young nearby stars which appear to be solar-type pre-main-
Frans Snik 1 have been discovered with high-contrast sequence stars (called T Tauri stars).
Nikolaus Vogt 11 and high-angular-resolution imaging. The system is located in the nearby
Using resolved photometry and spectros- Chamaeleon I molecular cloud at a dis-
copy we can study the atmospheres of tance of 165 pc and was previously
1
Sterrewacht Leiden, the Netherlands these objects, which range from plane- studied by means of unresolved photo-
2
Anton Pannekoek Institute for Astron- tary to brown dwarf masses. This makes metric measurements, which revealed a
omy, University of Amsterdam, the them especially interesting targets to test large infrared excess. This suggests
Netherlands planet formation theories. At the same the presence of a circumstellar disc (see,
3
Institute of Astronomy, University of time, the formation of these objects at a for example, Espaillat et al., 2007). The
Cambridge, UK few tens or hundreds of astronomical observed spectral energy distribution
4
Université de Grenoble Alpes, CNRS, units is particularly challenging, given the shows a dip at 10 microns, which hints at
IPAG, France limited spatial extent and lifetime of circum- the presence of a large cavity in the disc,
5
Unidad Mixta Internacional Franco- stellar discs. a possible sign of ongoing evolution.
Chilena de Astronomía, CNRS/INSU
UMI 3386 and Departamento de High-spatial-resolution polarimetry is a On 18 February 2017 we used SPHERE/
Astronomía, Santiago, Chile powerful tool that can provide a plethora IRDIS to observe the CS Cha system
6
LESIA, Observatoire de Paris, PSL of information about these companions. in near-infrared polarised light with the
Research University, CNRS, Sorbonne While the thermal emission of substellar aim of resolving its surrounding disc for
Universités, UPMC Université Paris 06, objects is not usually intrinsically polar- the first time. Our observation resolved
Université Paris Diderot, Sorbonne ised, scattering by patchy clouds or a circumbinary disc with a diameter of
Paris Cité, France atmospheric haze can introduce an over- ~ 110 astronomical units (au). We show
7
ESO all linear polarisation. Rotational flattening, this disc in Figure 1a.
8
Department of Astronomy, Steward the presence of orbiting moons, magnetic
Observatory, The University of Arizona, fields, or circumplanetary discs can also However, the disc was not the only
Tucson, USA cause polarisation. By measuring the detection made that night. We noticed
9
University Observatory Munich, degree and angle of linear polarisation that a faint companion candidate was
Faculty of Physics, Ludwig-Maximilians- with high accuracy we can distinguish visible at approximately 1.3 arcseconds
University, Munich, Germany between these effects and extract atmos- to the west of the primary stars. Remark-
10
Max-Planck-Institut für Astronomie, pheric parameters as well as information ably, this companion is not only visible
Heidelberg, Germany about the circumplanetary environment. in intensity (see Figure 1c), but also in
11
Instituto de Física y Astronomía, polarised light (see Figure 1a). It is
Universidad de Valparaíso, Chile Polarisation has been measured in the extremely faint, with an apparent magni-
12
Núcleo Milenio Formación Planetaria – past for field brown dwarfs, but only tude of 19.2 magnitudes in the J-band.
NPF, Universidad de Valparaíso, Chile the latest generation of extreme adaptive- Such flux levels are predicted by planetary
13
Departamento de Astronomía, optics imagers at large aperture tele- atmosphere models for objects with a
Universidad de Chile, Santiago, Chile scopes are allowing us now to open the few times the mass of Jupiter. A particu-
parameter space to detect these interest- larly intriguing property of this companion
ing low-mass companions to nearby is its high level of polarisation. In our
stars. J-band data we measured a degree of
baseline, we could then show that CS Cha 0.5 c) VLT/SPHERE/J-band The position of the
and the companion have nearly the same c entral binary is marked
with a star s ymbol.
proper motion on the sky (see Figure 2).
The small differential motion that we
0.0
found is consistent with the orbital motion
that is expected for a low mass com
panion. This makes it very likely that this
object is gravitationally bound to CS Cha. –0.5 02/2017
A planet with a disc? –1.0 –0.5 0.0 0.5 1.0 1.5 2.0
ΔRight ascension (arcseconds)
Since we have multiple observations of
the companion in various photometric tude relative to the host star. We then phere models for substellar objects.
bands we can attempt a characterisation. use the known brightness of the host to In Figure 3, we show two model spectra,
In particular, we are interested in con- translate these relative measurements obtained for an object of 5 Jupiter
straining its mass and determining the into absolute fluxes. The SPHERE H-band masses (MJup) and one of 20 MJup. These
causes of its high degree of polarisation. photometry has larger uncertainties model spectra include clouds in the
because the observations were taken in atmosphere models, but do not include
In Figure 3 we show all the available poor weather conditions. circumplanetary material.
photometric measurements along with
upper limits for non-detections. We We compared the companion photometry We found that the J-H colour of the com-
always measure the companion magni- to PHOENIX (Helling et al., 2008) atmos- panion is somewhat consistent with a
SPHERE/BB–H
WFPC2/F814W
SPHERE/BB–J
NACO/Lಿ
~ 165 pc
ESO/P. Horálek
Upper: A planetarium show at the ESO Supernova Lower: ESO and VDL ETG Projects B.V. (the
Planetarium & Visitor Centre, which opened its N etherlands) sign a contract for the manufacture,
doors to the public on Saturday 28 April 2018. assembly, testing and delivery of the Segment
Support Mechanics, responsible for holding and
controlling the 798 mirror segments of the primary
mirror of the Extremely Large Telescope.
Bruno Leibundgut 1 gamma-ray burst (GRB170817A) two events. The programmatic aspects of
Ferdinando Patat 1 seconds later, the search for an optical/ ESO observations were also exhaustively
infrared counterpart was on. Within a explored.1
few hours, an optical counterpart was
1
ESO detected in the galaxy NGC 4993. Spec- The first session was focused on
troscopic follow-up observations began GW170817 observations. The gravita-
immediately, resulting in a detailed record tional wave signal was presented
Understanding the nature and results of the evolution of the event over the fol- and compared to that from black hole
of black hole and neutron star mergers lowing two weeks. mergers by Sarah Antier (Laboratoire de
has become a hot topic in astrophysics. l’Accélérateur Linéaire Orsay), followed
The combination of gravitational wave ESO and ESA telescopes and instru- by a description of the event as seen
and electromagnetic observations of ments participated in this global observ- at optical and near-infrared wavelengths
GW170817/GRB 170817A has triggered ing campaign. Parts of the community (Stephen Smartt, Queen’s University
new and exciting science projects. The focused on the search of the optical Belfast), in X-rays (Maria Grazia Bernardini,
timeline for observations of gravitational counterpart with ESO’s Visible and Infra- Laboratoire U nivers et Particules de
wave events lies between seconds and red Survey Telescope for Astronomy Montpellier) and in gamma rays (Roland
days, and coordinated observations (VISTA) and the VLT Survey Telescope Diehl, Max Planck Institute for Extrater-
of electromagnetic radiation are critical (VST), but as soon as the GRB detected restrial Physics [MPE] in Garching).
when probing the nature of these events. by the ESA INTErnational Gamma-Ray
The great success of the observations Astrophysics Laboratory (INTEGRAL) Marina Rejkuba (ESO) reported on the
of GW170817/GRB 170817A from more satellite and its optical counterpart had ESO observations and the activities
than 50 observatories has highlighted been identified, the event was followed up associated with the release of the data
the importance of coordination between using several spectrographs and imagers. to the community. Optical observations
different instruments and facilities. This of GW170817 could only be conducted
two-day workshop focused on what has for a couple of hours before the object
been learned from ESO observations of Workshop goals set each evening in Chile, with several
GW170817/GRB 170817A, and discussed instruments being used simultaneously
strategies for coordinating observations The goal of the workshop was to bring on the VLT. The ESA satellites INTEGRAL
of future events. the community together to discuss the and X-ray Multi-Mirror satellite (XMM-
best way to obtain ESO observations of Newton) also participated in the observ-
future gravitational wave events. Despite ing campaign, and Peter K retschmar
Background the speed with which the workshop was (European Space Agency, ESA) gave
organised — it was announced in the an account of the activities required at
The first detection of an electromagnetic ESO Science Newsletter on 20 December the operations centres in order to obtain
counterpart of a gravitational wave event 2017 — 55 participants had registered these data at short notice.
had a historic dimension, as it connected by the deadline in early January.
two seemingly separate “universes”. Since it is still very early days for the
Several mergers of black holes had been The speaker list was partially defined electromagnetic observation of gravita-
observed prior to that, indicating black through the Principal Investigators (PIs) tional wave events, Anders Jerkstrand
holes of several tens of solar masses; this of exisiting proposals. Eight of the 26 (Max Planck Institute for Astrophysics,
presented a puzzle, as black holes of speakers were female (corresponding to Garching) gave a theorist’s view of what
these sizes had not previously been antici- 31%), which reflected the gender distribu- we should expect and how to make
pated. The detection of gravitational tion amongst the registered participants sense of the observations of GW170817.
waves — a technical feat requiring meas- (29% female). The first day of the pro- He gave a comprehensive overview of
urements of strains of a few times 10 –20 gramme was dedicated to assessing the what the signatures of the r-process ele-
— in 2015 was epochal, and was recog- status of the gravitational wave detec- ments would look like in the optical and
nised with the Nobel Prize in Physics in tions and their follow-up observations, near-infrared spectral sequences, and
2017. While black hole mergers are not in particular for GW170817; while the sec- outlined where we still have significant
expected to carry an electromagnetic ond day focused on the planning and gaps in our interpretation of the spectra.
signal, theoretical modelling predicted that coordination of future observations. Each There remains plenty of room for future
the merger of two neutron stars would day finished with an extensive discussion observations to clarify the many questions
lead to short gamma-ray bursts (GRBs), session. On 31 January, the past and and uncertainties we still have in respect
and would potentially be site of the current ESO observations of (fast) tran- of these events. The session ended with
formation of heavy elements through sients were discussed, and potential a presentation by Nial Tanvir (University
the r-process. lessons for future observations debated. of Leicester) on his experience of ESO
The afternoon of 1 February was entirely observations of fast transient phenomena,
When, on 17 August 2017, an unusal devoted to a community discussion of focusing on gamma-ray bursts. Target
gravitational event (GW170817) was the best strategies for future electromag- of Opportunity observations have been
observed that coincided with a short netic observations of gravitational wave offered at the VLT since the beginning of
operations, with the addition of refine- The discussion session covered past mean a serious interruption to the
ments such as the rapid response mode ESO observations, and aimed to identify uploaded schedule, requiring the corre-
about 10 years ago. This frank presenta- what worked and where difficulties were sponding recovery of the schedule time-
tion was an excellent basis for a discus- encountered. The panel members were line afterwards. There may also be point-
sion on how ESO operations could help Stefano Covino, Marina Rejkuba, Steven ing constraints for satellites which need
to secure critical data for similar events in Smartt and Nial Tanvir. The open discus- to be evaluated before schedule interrup-
the future. sion yielded some interesting comments, tions. Aitor Ibarra (ESA) and Richard
and comparisons were made with the Saxton (ESA) set out a new tool for the
The afternoon session was reserved for experience of using ESO telescopes for improved coordination of observations
presentations of ongoing projects dedi- observations of gamma-ray bursts. It and information sharing.
cated to the follow-up of transient events. was concluded that overall ESO provided
ESO is supporting several such pro- valuable — and sometimes unique — The afternoon was devoted to a discus-
grammes, either with its own telescopes resources that can be essential, providing sion centred on the optimal planning of
or by hosting dedicated experiments at insights in areas where theoretical predic- future observations, including the best
its sites. These include the following tions are lacking. Recommendations possible coordination of ESO telescopes
projects: the public survey called VIsta were made to strengthen the communi- and instruments. Ferdinando Patat, Enzo
Near-infraRed Observations Unveiling cations between various observatories Brocato, Peter Jonker and Erik Kuulkers
Gravitational wave Events (VINROUGE), and facilities in order to avoid duplication were the panel members, and a lively
which uses VISTA to obtain infrared and to increase synergies. discussion ensued between the panel
light curves (Andrew Levan, University and the audience. Several important
of W
arwick); the extended Public ESO The second day of the workshop con- points were raised, among them the wish
Spectroscopic Survey of Transient centrated on the planning of future that ESO accept Large Programmes
Objects (ePESSTO), which uses the ESO observations. The schedule of science with Target of Opportunity observations.
Faint Object Spectrograph and Camera 2 observations with the Laser Interfer Additionally ESO was asked to provide
(EFOSC2) at the New Technology Tele- ometer Gravitational-wave Observatory rapid delivery of pre-reduced data so that
scope (NTT) to provide optical spectros- (LIGO)-Virgo collaboration was presented quick assessments and scientific deci-
copy (Maria Teresa Botticella, INAF– by Marica Branchesi (Gran Sasso Science sions can be made, potentially to then
Osservatorio di Capodimonte); the Rapid Institute). The next science run is planned interactively modify observation blocks
Eye Mount telescope (REM) at La Silla, to start in October 2018 and is scheduled for follow-up observations. ESO will have
which is part of a larger collaboration set to last for approximately one year. The to investigate which of these requests
up to follow the optical counterparts of principal investigators of the current ESO can be implemented operationally. As a
gravitational wave events (Eliana Palazzi, programmes to search for and follow first step, Target of Opportunity Large
INAF–IASF Bologna); and the Gamma- up electromagnetic signals from gravita- Programmes were accepted again for
Ray burst Optical/Near-infrared Detector tional wave events then presented their ESO Period 102 (from October 2018 to
(GROND) instrument on the Max-Planck- plans for the next semester. Elena Pian March 2019). An important discussion
Gesellschaft/ESO 2.2-metre telescope (INAF–IASF Bologna) and Paolo D’Avanzo point was whether the (European) com-
at La Silla, which obtains photometry in (INAF–Osservatorio Astronomico di Brera) munity could agree to submitting a single
seven filters simultaneously (Janet Chen, presented their VLT proposals. A proposal ESO proposal for observations of future
MPE Garching). to obtain spectropolarimetry of such gravitational wave events. As a result of
events was detailed by Stefano Covino this discussion one single Period 102
A new project that is just starting opera- (INAF–Osservatorio Astronomico di proposal was submitted before the dead-
tions is the Gravitational-wave Optical Brera). Aniello Grado (INAF–Osservatorio line of 28 March 2018. ESO was also
Transient Observer (GOTO), which was Capodimonte) then presented two ongo- invited to attend the LIGO–Virgo town hall
described by Danny Steeghs (University ing programmes with the VST. meeting in April 2018 in Amsterdam,
of Warwick). In addition, the long-running where these discussions will continue.
Télescopes à Action Rapide pour les A special session on the observing
Objets Transitoires (TAROT) project was opportunities with ESA satellites followed.
presented by Michel Boer (Centre National The capabilities of INTEGRAL, and in Acknowledgements
de la Recherche Scientifique, CNRS). particular its operational constraints, We thank Svea Teupke for providing logistical sup-
Future facilities to detect and characterise were introduced by Erik Kuulkers (ESA), port at very short notice. We would also like to thank
the electromagnetic counterparts of followed by a presentation on XMM- all of the speakers for providing the slides ahead
gravitational wave events are: BlackGEM, Newton by Norbert Schartel (ESA). Jan- of their presentations so that a seeing-impaired
c olleague could follow them on his own laptop.
to be installed at La Silla (Paul Groot, Uni- Uwe Ness (ESA) described some pro-
versity of Nijmegen); the Son Of X-Shooter grammatic aspects of the planning and
(SOXS), to be installed on the NTT in 2020 coordination of space-based observa- Links
(Sergio Campana, INAF–Osservatorio tions. The INTEGRAL and XMM-Newton 1
Workshop programme: http://www.eso.org/sci/
Astronomico di Brera); and the Zwicky schedules are built well in advance of meetings/2018/gw2018.html
Transient Facility in California (Ulrich he observations and the rapid observa-
Feindt, Oskar Klein Centre Stockholm). tion of an unexpected transient may
Markus Wittkowski 1
Liz Humphreys 1
1
ESO
and dynamics that they produce. Sven supergiant stars. She described how these dynamical processes. Kateryna
Wedemayer then outlined what can be spatially resolved spectra reveal complex Kravchenko and Gioia Rau showed
learnt from solar observations using ALMA structure in these extended stellar atmos- comparisons between 3D models and
in an invited talk (Figure 2). pheres that we do not understand, and observations using both the tomographic
which impacts our understanding of method and near-infrared interferometry
The radiation observed by ALMA origi- stellar activity, magnetic fields, angular with the GRAVITY instrument. Gioia
nates mostly from the chromosphere — momentum loss, and stellar cluster Rau also showed modelling of ultraviolet
a complex and dynamic layer between populations. spectra that contain chromospheric
the photosphere and corona that plays emission lines.
a crucial role in the transport of energy Agnes Lèbre (in an invited talk), and the
and matter and, ultimately, in the heating next speakers described the techniques
of the outer solar atmosphere. The ses- and recent results from spetropolarimetry, Imaging results
sion ended with a presentation by Oskar detecting magnetic fields and star spots
von der Lühe, in which he described the on the surfaces of Sun-like stars (Emre A major theme of the meeting centred on
facilities for the high-angular-resolution Isik, Torsten Böhm) a giant and super- recent imaging results of stellar surfaces
imaging of the Sun. Bringing together giant stars (Agnes Lèbre, Arturo López obtained at visible/infrared and radio/
solar and stellar physicists at this work- Ariste). Susanne Höfner (in an invited talk) millimetre wavelengths, and comparing
shop proved to be particularly fruitful. and Bernd Freytag presented the recent them with models and other complemen-
Throughout the meeting, discussions fre- status of 3D simulations of convection tary observations. Gail Schaefer started
quently revealed the increasing similarities for different types of stars, and in particu- this session by providing an invited over-
between these fields. lar, the extension of those simulations view on imaging stellar surfaces with the
from solar-type stars to red giant and red CHARA array. This included imaging
supergiant stars. gravity darkening on rapid rotators, star
From the Sun towards evolved stars spots on magnetically active stars, con-
Basic physical considerations and vective cells on red supergiants, winds
The workshop programme continued to detailed numerical simulations predict from massive stars, and observations of
illustrate the application of physical con- a dramatic increase in the sizes of con- tidal distortions from Roche lobe filling in
cepts from the Sun towards evolved stars, vection cells during the late phases of interacting binaries.
including processes such as chromo- stellar evolution. The interplay of large
spheric activity, surface magnetic fields, and small convection cells, waves, pulsa- In an invited talk, Rachael Roettenbacher
pulsation and convection. In an invited tions, and shocks can give the surface concentrated on active giants, which
talk, Andrea Dupree highlighted the of an AGB star an appearance that is have been imaged using photometry,
ubiquitous signatures of chromospheric very different from the granulation pattern spectroscopy, and, only recently, interfer-
activity, variable outflows, and winds in across the solar surface. Detailed time- ometry (Figure 3). Here, interferometry
spatially unresolved spectra of giant and resolved imaging is needed to constrain has provided a way to unambiguously
of the magnetically
ies of red supergiant stars obtained with
active star ζ And.
the PIONIER instrument in an invited talk,
and emphasised the different techniques
used to analyse these observations,
including intriguing comparisons of inter-
ferometric results with spectropolarimetry
— as presented earlier in the workshop
by Arturo López Ariste and Agnes Lèbre.
Claudia Paladini presented stellar surface
imaging of the asymptotic giant branch
star π1 Gruis in the PIONIER spectral
channels (Figure 5; also see Claudia’s
article on p. 24). The images of this star
are relatively uncontaminated by molecular
ESO/K. Ohnaka
W Hya, and reveals unexpected lines in Finally, Liz Humphreys described how potential impact on the physical interpre-
most of the sources, as well as possible ALMA long-baseline observations had tation of the results. His talk was illustrated
fast rotation in the atmosphere of one of revealed an unusual morphology for the with examples of stellar surface imaging
the stars. Lynn Matthews described their SiO maser emission towards the binary from real datasets.
JVLA and ALMA studies, which reveal system Mira AB. The effect of binary
the evolving shapes of the radio photo- companions on the near-circumstellar For the radio to millimetre regime, Bill
spheres of AGB stars. The data provide environment of AGB stars is, in general, Cotton gave an invited talk on radio imag-
evidence that the shapes of the radio an open question. The ALMA data ing of the envelopes of evolved stars,
photospheres of AGB stars change on probed this region of Mira A using SiO paying particular attention to the technical
timescales of several months or more. emission. Most importantly, the data differences between radio and optical/
Additionally, the data reveal signatures locate SiO masers with respect to the infrared interferometry. He described how
of brightness asymmetries and non- star, unlike with lower-frequency obser milliarcsecond resolution of very bright,
uniformities. The results are consistent vations. They also indicate an impact i.e., non-thermal, emission from molecular
with manifestations of large-scale irregular of the binary companion on gas within masers in the envelopes of evolved stars
convective flows on the stellar surfaces. about 10 stellar radii of Mira A. These can be achieved using VLBI techniques
types of studies, using high-frequency with baselines of thousands of kilometres.
The application of new imaging tech- SiO masers, can provide a new avenue
niques to the interpretation of these data for understanding the influence of binaries
was also discussed. Ka Tat Wong out- on AGB mass loss and shaping their Prospects
lined a recent study of the non-equilibrium envelopes.
chemistry of oxygen-rich AGB stars, Gioia Rau started the session on future
performed using ALMA. Chemical models prospects with an invited talk about
suggest that pulsation-driven shocks Image reconstruction techniques imaging the surfaces of stars from space.
propagating from the stellar surfaces of She reviewed results obtained so far from
oxygen-rich evolved stars to the dust John Young was invited to provide an space with the benefit of extending the
formation zone trigger non-equilibrium overview of the various available algo- wavelength coverage, including ultraviolet
chemistry in the shocked gas near the rithms for synthesis imaging at visible spectra taken with the International Ultra-
star, including the formation of carbon- and infrared wavelengths. He described violet Explorer (IUE), as well as ultraviolet
bearing molecules in the stellar winds reconstruction biases that can follow images obtained with the Hubble Space
dominated by oxygen-rich chemistry. The from non-optimal choices of regularisation Telescope (HST) of Mira and Betelgeuse.
talk focused on observations of IK Tau functions and their strengths, and their She then investigated the prospects for
Andrea Bianco 1 ground-based facilities, the current The focus was mainly on dispersing
Rebecca Bernstein 2 Extremely Large Telescope (ELT) projects elements based on gratings and prisms;
Antonio de Ugarte Postigo 3, 4 provide clear evidence for this, and spec- alternative approaches such as Fabry-
Francisco Garzon 5 trographs play an essential role in their Perot interferometry or Fourier-transform
Wayne Holland 6 planned instrument suites. Dispersing spectrometers were not considered. The
Antonio Manescau 7 elements are at the core of these instru- workshop was organised into the follow-
Ramon Navarro 8 ments, since they define the spectral ing three main sessions:
Marco Riva 1 resolution and dispersion of the spectro- – A n overview of the scientific questions
graph and hence the final performance to be addressed, both with large and
of the instrument. On the other hand, small ground-based astronomical facili-
1
INAF–Osservatorio Astronomico di because of their nature, dispersing ele- ties. In this session, the status of the
Brera, Merate, Italy ments are often the least efficient optical three ELTs currently under construction
2
Carnegie Observatories, Pasadena, elements of the whole spectrograph, was presented, including their instru-
USA and therefore dominate the final instru- mentation programmes.
3
Instituto de Astrofísica de Andalucía mental throughput. This, of course, also – Properties of dispersing elements for
(IAA-CSIC), Granada, Spain holds true for smaller telescopes, which astronomy, their evolution, the issues
4
Dark Cosmology Centre, Niels Bohr can typically address a broad range and constraints of the optical design
Institute, University of Copenhagen, of science cases provided they have ade- of spectrographs for large telescopes
Denmark quate instrumentation. and, finally, their calibration.
5
Instituto de Astrofísica de Canarias, – Technologies for the production of
Tenerife, Spain Starting from the design phase of any gratings and prisms. This session was
6
UK Astronomy Technology Centre, spectrograph, it is crucial to be aware of divided according to the different manu-
Royal Observatory, Edinburgh, UK the different possibilities that are available facturing technologies and spectral
7
ESO on the market, including those that have range of use of the diffractive elements.
8
NOVA Optical Infrared Instrumentation not specifically been developed for
Group, ASTRON, the Netherlands astronomy. Indeed, thanks to new tech-
nologies, the possibilities in the field Discussions and outcomes
of diffraction gratings and dispersing ele-
Astronomical spectrographs play an ments are increasing as a result of a In general, the instrumentation suites
important role in addressing some of number of different approaches, for proposed for the three ELT projects
the biggest challenges in modern example, holography, lithography and are similar, and require a wide range of
astronomy. One of the most critical micro-machining. This is not always easy, spectral and spatial resolutions. They
components of any spectrograph is its since the requirements can vary across resemble the instruments developed for
dispersing element, since it determines different fields. However, it can be possi- the 8–10-metre-class telescopes and all
the resolution and dispersion of the ble to adapt the latest technological face the challenges of wide focal planes
spectrograph, and is typically one of advances to specific scientific needs. On and the conservation of the “étendue” —
the least efficient optical components the other hand, it is also important for a property of the light used to character-
of the instrument. The aim of this work- companies and research institutes that ise the area and angle over which it is
shop was to bring together researchers are active in the design and production of spread out. Large-sized gratings/prisms
and engineers involved in the design, dispersing elements, and that are involved are required to reach the target resolu-
development and construction of in the design of the spectrographs, to tion, but it is important to keep the total
spectroscopic instrumentation, with understand how to adapt technological size of the instrument within bounds by
companies and institutes that produce developments towards becoming feasible means of strategic choices in the optical
dispersing elements and associated products for astronomical research. design (through pupil and image slicing).
optical components. The forum provided
the opportunity to discuss the scientific This workshop 1 brought together The 8–10-metre-class telescopes will
needs of future instruments, and to researchers and engineers involved in require new instrumentation and new
address the technological challenges the design, development and construc- concepts in the era of the ELTs. One
that will allow the development of new tion of spectroscopic instrumentation, example may be the efficient spectro-
types of dispersing elements in the as well as companies and institutes that scopic telescopes currently under study,
coming years. produce dispersing elements and asso which are designed to simultaneously
ciated optical components. The forum collect thousands of spectra of targets
provided an opportunity to discuss the that are fed from wide field surveys. The
In order to adequately address open scientific needs of current and future same approach applies to small- and
questions in astronomy, there is a drive instruments and to address the techno- medium-class telescopes, where the sci-
for the development of bigger, more logical challenges that will enable the entific cases are often diverse, and which
sensitive telescopes and instruments — community to progress with the develop- may also need to develop or focus on
both ground-based and in space — with ment of new types of dispersing elements specific science cases with very efficient,
a very wide spectral range. In respect of in the coming years. dedicated instruments.
Figure 1. Workshop participants. large formats, it is now feasible to reach The three days involved many animated
sizes of the order of a square metre, and discussions that extended beyond the
The dispersing elements for the spectro- these possibilities are worth considering workshop schedule. Indeed, there were
graphs have a large set of requirements. when designing future instrumentation. several opportunities to network and dis-
Aside from achieving the highest possible cuss a range of related topics, including
diffraction efficiency, it is also important specific projects as well as new ideas.
to understand and know their dispersion, Dispersing elements for the infrared
price, weight/size, availability on the One of the issues identified, was that
market, ghosts, wavefront error (WFE), In the infrared, immersed gratings have numerous large gratings would be
etc. Being able to obtain repeatable and become an interesting option since the required over the next years to satisfy the
consistent wavelength calibrations is availability of materials with high refractive requirements of the ELT instrumentation
essential to get the best out of the spec- index makes it possible to increase the programmes as well as other existing and
trographs, especially for highly stable high- resolution significantly while keeping the future spectroscopic facilities. Although
resolution spectrographs. size under control. Moreover, other tech- astronomy is not a big industrial market,
nologies, such as VPHGs, are not suitable it is clear that there is room for many
The different technologies discussed at for wavelengths above 2.5 µm (new players as the requirements are challeng-
the workshop related to the manufacture approaches based on direct laser inscrip- ing. The availability of many new tech
of diffraction gratings can be summed up tion are being developed to extend the nologies and capabilities will open up
under the following headings. range to longer wavelengths). Depending new alternatives, but in order to fully take
on the material, different spectral ranges advantage of all of the possibilities, inter-
can be covered and non-standard mate- actions between instrument designers,
High-performance first-order diffraction rials (like silicon, germanium, zinc selenide, industry and research institutes is crucial.
gratings indium phosphate) show excellent proper- This workshop was a successful first step
ties and results, especially in terms of in this direction.
Volume Phase Holographic Gratings roughness and WFE.
(VPHGs) are considered the baseline for Acknowledgements
instrumentation in the visible and near- High-precision machining techniques
infrared bands, on the basis of the excel- (in particular diamond turning) make it We are grateful for the financial and logistical sup-
lent results obtained over the last decade. possible to obtain unconventional gratings port that made this workshop possible. In particular,
we would like to mention the financial support
However, some limitations were appar- on curved surfaces or freeform gratings. received from ESO, INAF (Italian National Institute of
ent, such as their size, WFE, and their The benefit of this could be a simplification Astrophysics), and the Optical Infrared Coordination
efficiency at high dispersion. Other tech- of the optical design or an improvement Network for Astronomy (OPTICON; an EU Horizon
niques are becoming available, in particu- of the capabilities (such as in the case of 2020 research and innovation programme under
grant agreement No. 730890). We are also grateful
lar lithographic gratings based on either multi-blazed gratings). Moreover, such to the staff of the INAF–Osservatorio Astronomico
electron-beam lithography or on hologra- machines are suitable for working on large- di Brera for their consistent support over the course
phy. There are some degrees of freedom sized substrates, matching the require- of the workshop.
in the structure of the periodic pattern ments of modern telescopes and instru-
and in the material, which allow for the mentation. In the case of spectropolarim- Links
maximisation of the diffraction efficiency eters, the use of liquid crystal gratings
— even in the ultra-violet. As there are can provide interesting advantages, being 1
orkshop web page: http://www.brera.inaf.it/
W
markets that require such gratings in very able to control both the dispersion and DispersingElements2017
Carlos De Breuck 1
ESO/L. Calçada
Peter Teuben 2
Thomas Stanke 1
1
ESO
2
University of Maryland, USA
2 2
to observing with interferometers, where Intensity (k [Tmb ])
the spatially extended sky signal is re
solved, for single-dish telescopes, the sky 0
1 1
dominates over the source signal by
many orders of magnitude. Moreover, the
sky signal varies significantly on times- –50
cales on the order of seconds. Most of the 0 0
observing and data reduction techniques
therefore need to concentrate on the 100 50 0 –50 –100 60 80 100 120
removal of this bright sky emission. Addi-
tional challenges come from the atmos- 0.4
ΔDeclination (arcseconds)
15
Area (k [Tmb ] km s –1)
–5°15ಿ00ೀ –5°15ಿ00ೀ
10 2
200
–5°20ಿ00ೀ –5°20ಿ00ೀ
Declination
Declination
10 1
–5°30ಿ00ೀ –5°30ಿ00ೀ
0
10 –1
5 h35 m40 s 20 s 00 s 40 s 5 h35 m40 s 20 s 00 s 40 s
Right ascension (J2000) Right ascension (J2000)
Figure 3. Example from the ArTéMiS data reduction Figure 4. Top left: A channel from
tutorial. The image on the left shows the image after an ALMA total power observation
running through the basic ArTéMiS IDL pipeline. of CO from a small region in the
Note the negative bowls next to the bright emission, Small Magellanic Cloud. Overlayed
which are due to the over-subtraction of the sky on this greyscale are the pointing
signal. The image on the right shows the full reduction centres of the 12-metre array. For
using the Scanamorphos pipeline, which uses the one pointing, the true extent of the
full redundancy of the data. 12-metre field of view is given as
well with the larger green circle.
Top right: The reconstructed total
Millimétrique (IRAM) website for the power map from the pseudo-
visibilities generated from a virtual
Grenoble Image and Line Data Analysis
interferometer emulating the short
Software (GILDAS 2; Pety, 2005), or the spacings. Lower left: The pure
APEX ArTéMiS pages 3. interferometeric map combining
the 7- and 12-metre data. Lower
right: Combining the total power
One of the advantages of a single dish
visibilities with those of the 7- and
observation is that it can complement 12-metre data recovers the large-
interferometric data by supplying infor- scale flux as well as the fine scale
mation corresponding to short spacings structure. The size of each rectan-
gle is ~ 5 × 3 arcminutes and the
that are filtered out by the interferometer,
c olour scale is in Jy/beam.
but that are necessary to recover the 0.54 1.1 1.7 2.2 2.8 3.4 4 4.5 5.1
larger-scale emission. It is not uncommon
to miss half of the flux in a more extended
component when considering only inter- the single dish map with pseudo-visibilities References
ferometric data. that can be used in a standard joint
Pety, J. 2005, SF2A-2005, ed. Casoli, F. et al.,
deconvolution method to create images. EdP-Sciences, Conference Series, 721
The majority of the second day in the Roussel, H. 2013, PASP, 125, 1126
workshop was spent on a number of Talk slides, example scripts and example Schuller, F. 2012, SPIE, 8452, 84521T
techniques that have been developed and data are linked from the workshop web
fine-tuned over the past 30 to 40 years, page 1, the workshop Zenodo repository 4, Links
including a tutorial following the standard as well as via a github repository 5 that
example of the M100 spiral g alaxy using was updated throughout the workshop. 1
eeting web page: https://www.eso.org/sci/
M
meetings/2018/SingleDish2018.html
CASA, supplemented with two new tech- 2
IRAM GILDAS website:
niques. The default method in CASA is https://www.iram.fr/IRAMFR/GILDAS/
called “feather”, but two new techniques Acknowledgements 3
A PEX ArTéMiS pages 3: http://www.apex-telescope.
were also highlighted: Short Spacing This event received funding from the European
org/instruments/pi/artemis/data_reduction/
4
T he workshop Zenodo web page: https://zenodo.
Corrections (SSC) — which combines Union’s Horizon 2020 research and innovation org/communities/sd2018
two images — and the Total Power to p rogramme under grant agreement No. 730562. 5
G ithub repository for the material used in the
Visibility tool (TP2VIS) — which replaces m eeting: https://github.com/teuben/sd2018
Henri M. J. Boffin 1
Marina Rejkuba 1
1
ESO
possibility of making queries in a In the afternoon, participants were able future workshops were also received,
programmatic way. Lodovico Coccato to interact with ESO staff and discuss with opinions differing, depending on the
gave a demonstration of how to reduce topics of their choice, including help with previous experience and knowledge of
data with EsoReflex, as well as how to data reduction, help with proposal writing, participants. It is our aim to repeat this
use the software Molecfit to remove finding information on ESO web pages, workshop approximately every two years
atmospheric signatures from science installing ESO software, help with obser- to promptly address questions from the
spectra. Finally, John Pritchard showed vation preparations, and using the Science continuous flow of new users of ESO
how to modify EsoReflex workflows to Archive either to access data or to return facilities.
tailor them to the user’s aims. reduced data to the archive. At registra-
tion, participants were asked to indicate
One full day of the workshop was dedi- the area of the programme (proposal Acknowledgements
cated to hands-on sessions. In the first preparation, observing strategies and We would like to thank Véronique Ziegler for her help
part, on Wednesday morning, three tools usage, data reduction) they would with the practical organisation, Stuart Ryder from
parallel tutorial sessions were held, during like to explore further. Participants were the International Telescopes Support Office (ITSO)
which participants were guided in using then split into small groups with overlap- for setting up the remote participation via Zoom, and
Sandor Horvath and the Information Technology (IT)
EsoReflex for three instruments, MUSE, ping interests, or had scheduled one-to- staff for their help during the workshop. We most
the Ultraviolet and Visual Echelle Spectro- one sessions with the ESO staff member warmly thank all speakers and tutors for the great
graph (UVES) and X-shooter. These who was best placed to help with their effort they made to provide clear and instructive
instruments were chosen as the majority specific topic. talks or demonstrations and to efficiently help the
participants in individual sessions.
of the participants expressed an interest
in them when registering for the work- At the end of the workshop, the organisers
shop. In each case, after a first step-by- asked participants to provide feedback, Links
step demonstration, the participants and an extremely large number of people, 1
A ll presentations as well as some of the video
could choose to reduce a set of data more than 50% of the attendees, did so. recordings are available on the workshop web
provided by the organisers or to work on The feedback was unanimously positive page: https://www.eso.org/sci/meetings/2018/
their own data. Two or three tutors were with all respondents saying they would Users-Workshop/program.html
available for each session, helping and recommend such a workshop to their
advising the participants in this endeavour. colleagues. A few suggestions for similar
DOI: 10.18727/0722-6691/5084
Report on the
held at ESO Vitacura, Santiago & La Silla Observatory in Chile, 18 February–2 March 2018
Fernando Selman 1 During the two weeks between 19 Feb- scientific community at Vitacura. In
Claudio Melo 1 ruary and 2 March 2018, the Office addition to learning about the observing
Giacomo Beccari 1 for Science at Vitacura and the La Silla techniques that were used during
Henri M. J. Boffin 1 Observatory were the hosts of the the school, the students also attended
Valentin Ivanov 1 second ESO/NEON (Network of Euro- several lectures covering the current
Eleonora Sani 1 pean Observatories in the North) La Silla and future capabilities of the Atacama
Linda Schmidtobreick 1 Observing School. Thanks to the Large Millimeter/submillimeter Array
Michel Dennefeld 2 generous funding from ESO, the Optical (ALMA), the telescopes at Paranal, and
Heidi Korhonen 3 Infrared Coordination Network for the Extremely Large Telescope (ELT),
Astronomy (OPTICON), and the La Silla as well as talks on what makes a good
Observatory, a group of 20 students, scientific presentation, time manage-
1
ESO consisting of mostly PhD but also some ment, effective proposal writing, and
2
Institut d’Astrophysique de Paris (IAP), advanced MSc students, from different career choices.
France parts of the world, were guided by five
3
Dark Cosmology Centre, Niels Bohr ESO tutors. The students prepared
Institute, University of Copenhagen, and carried out complex observations, Over the course of three nights at La Silla,
Denmark reduced and analysed the data, and the students used the ESO Faint Object
finally presented the results to the ESO Spectrograph and Camera (EFOSC2) and
the infrared spectrograph and imaging Giacomo Beccari guided a group study- nature of the accretors in the observed
camera SOFI attached to the New Tech- ing Ha-excess sources in the Orion objects spectroscopically. Similarly,
nology Telescope (NTT) as well as the nebula and in Chamaeleon. In particular, DFOSC was used to perform broad-band
Danish telescope, equipped with the the students acquired low-resolution V, R, I and narrow-band Ha imaging of
Danish Faint Object Spectrograph and spectra with EFOSC2 to study the equiva- young stars in Chamaeleon. The images,
Camera (DFOSC). Divided into five lent width of the Ha emission line of targeting a number of T Tauri stars with
groups, the students worked on a variety 12 young T Tauri stars in Orion. Such Ha emission studied by the Gaia–ESO
of astrophysical topics, supported by emission in young stars is typically used
Heidi Korhonen at the Danish telescope, to identify ongoing accretion from a Figure 2. Students getting real-life experience at the
and by Monica Castillo and Ariel Sanchez protoplanetary disc. The measurements consoles of the NTT (left), and the D anish telescope
at the NTT 1. allowed the students to confirm the (right).
S1 S2
0.2
δS(3839)
0.0
pec.
–0.2
C-N, Na-O are anti-correlated in typical “I want to thank the organisers and Acknowledments
GCs. A few anomalous clusters present tutors of the summer school. Both the
We would like to express our gratitude to ESO’s
multiple sequences of CN-CH anti- talks and the research projects were Director General, the La Silla Paranal Observatory
correlation, a proxy for C-N. These spe- tremendously interesting, and I am sure (LPO) Director and the Director for Science, without
cial GCs also share a few other odd they will be very useful in the future. I also whose unconditional support this school would not
have materialised. We would also like to thank the
characteristics; this is often interpreted as want to mention what was said among
invited speakers at the school: Michele Cirasuolo,
these GCs having originated in dwarf the students, that despite the level of Alain Gilliote, Pascale Hibon, Yara Jaffe, Bruno
galaxies that were captured and destroyed stress generated, the school exceeded Leibundgut, Adele Plunkett, Alain Smette and
by the Milky Way. Our results show that the expectations. This type of school Frédéric Vogt. Hans Zinnecker was a special con
tributor to the school, first with a lecture on star
NGC 3201 presents multiple sequences is extremely useful for any astronomer
formation, and second, contributing to lively dis
of CN-CH, however it does not show regardless of the area chosen in the cussions and debates about the different topics
other anomalous characteristics. We have future. All the activities, from the talks to c overed — heartfelt thanks to him! The logistical
therefore discovered the first GC that is the visit to the observatory motivate aspects of the school were handled by Paulina Jirón
and María Eugenia Gomez, to whom we extend our
neither completely typical nor completely us even more than we already are to con-
deep gratitude.
anomalous, which means that the extra- tinue doing research in our PhD.”
galactic origin scenario needs revision,
and likely requires new stellar evolution It was intense and exhausting but we all References
models that can better explain how the feel that the process was well worth the
Dias, B. et al. 2018, arXiv:1803.05124
CN-CH anti-correlation forms.” effort. With this and the previous version
of the school we have reached a total of
The spirit of the school was accurately 40 students who are now familiar with Links
summarised by an email from one of the the way ESO does astronomy at the 1
SO–NEON Observing School: https://www.eso.
E
students at the school, Gabriela Navarro observatories in Chile. More importantly, org/sci/meetings/2018/lasilla_school2018.html
from Universidad Andrés Bello (UNAB) in we have been able to share our passion 2
G aia–ESO Survey: https://www.gaia-eso.eu/
Santiago: and, hopefully, helped the next genera-
tion of astronomers.
Fellows at ESO
After graduating from high school, I hosted at the La Silla Observatory in first experience at Paranal in addition to
vacillated between biology and physics, Chile. my previous ones at La Silla (and the
but I finally decided to follow my first incomparable beauty of Chile) played
passion and to start a Bachelor in phys- I really enjoyed this first encounter with an important role in my decision to apply
ics, with the intention of specialising in research, especially with such fascinating for an ESO fellowship after the end of
astronomy. The choice of university was objects as comets. I was lucky enough my thesis.
easy since Liège University, which was to get a grant, so could start a PhD in
just next door, was the only one in the Liège, continuing with my Master’s thesis This is how I ended up in Chile, living
French-speaking part of Belgium to offer work to study and compare the chemical abroad for the first time. I have never
a Masters in space sciences. Because composition of a large number of comets regretted my decision to come to ESO
I enjoy sharing my passion for space and observed with the TRAPPIST telescope. Chile and highly appreciate the stimulating
astronomy, during my university years Less than two weeks after starting my multi-disciplinary environment and the
I had a summer job at the “Euro Space PhD, I flew to La Silla. This was a tech opportunity to learn about very different
Center” in Belgium, developing activities nical mission, and my first contact with a scientific topics. I also enjoy the freedom
aimed at kids and centred on the theme professional telescope was with a screw- that I have to pursue my own research,
of space exploration. This was a great driver in my hand. I immediately loved and to try to expand our understanding of
experience and encouraged me to con- being at an observatory, especially work- the composition of small bodies of the
tinue to do outreach. ing on a small telescope, where you can Solar System.
have direct contact with the instrument
During my Master’s degree, I took a class you are using. Being part of the TRAPPIST ESO offers a lot of opportunities that I
called “Small Bodies of the Solar Sys- team gave me the opportunity to have an would not have elsewhere, especially as
tem”. At that time, I became fascinated by overview and get involved in all aspects a young scientist; I get to mentor stu-
comets. In addition to being incredibly of the facility, from technical aspects to dents, define my own projects, take up
beautiful objects, they are types of fossils scheduling to observing. responsibilities, and organise confer-
that allow us to study the history of the ences. Thanks to my duties in Paranal, I
Solar System. There is a quote from From the scientific point of view, I am have learned a lot and gained familiarity
David Levy, which I think describes com- thankful to my supervisor because I was with new instruments and new tech-
ets particularly well: “Comets are like given a lot a freedom to work on the niques. Being assigned to the HAWK-I
cats; they have tails and they do precisely project my own way as well as pursue infrared imager, I have also participated in
what they want”. This summarises how, new ideas. One of the most exciting parts the commissioning of its adaptive optics
after studying them for more than a cen- of my thesis was my involvement in the module, working with a really great team.
tury, comets remain mysterious objects ground-based support campaign of the The teamwork is something I particularly
and keep surprising us; and it is the rea- ESA Rosetta mission. Sending a space appreciate about Paranal. In the future,
son I chose comets as the subject of my mission to orbit a comet, and eventually I hope I can continue to do research and
Master’s thesis, during which I had the landing on its surface was an incredible keep observing regularly, as I love being
chance to work with the TRAnsiting achievement, and it was a fabulous in an astronomical observatory. In any
Planets and PlanetesImals Small Tele- opportunity to follow the results and new case, I feel lucky to have a family who
scope (TRAPPIST) project, which consists developments of the mission while trying always encouraged me to pursue a career
of two 60-centimetre telescopes, one to link those to what we were observing in astronomy. It made it so much easier
each in the northern and southern hemi- from the ground. It is also in the frame- to get here.
spheres. At the time I worked on it, only work of this ground-based campaign that
the southern telescope existed, which is I came to Paranal for the first time. This
Martin Cullum 1
1
ESO
The ESO 3.6-metre telescope was Fortunately, Switzerland and Italy pro- Ray Wilson, changed the way future large
equipped with a so-called Hartmann vided the solution. In 1982, both coun- telescopes would be designed and fully
screen. This was a metal plate, the same tries became ESO Member States and validated the decision of the ESO Council
diameter as the primary mirror, with an with their entry fees ESO decided to to go ahead with the construction of the
array of high precision holes bored in it. build another telescope to ease the load Very Large Telescope (VLT).
This was placed just in front of the primary on the already oversubscribed 3.6-metre
mirror and a series of extra-focal photo- telescope. At the same time, this pro- Ray was a reluctant manager. He never
graphic images were taken at different vided the Organisation with the opportu- strived for power or influence and,
telescope positions. After scanning and nity to gain experience with innovative although justly proud of his achievements,
analysing these images, the optical aber- telescope technologies. Ray Wilson, by was always self-deprecating. But with
rations could be estimated. Not only now head of the ESO Telescope Group, his abundant enthusiasm he very effec-
was this a cumbersome and risky proce- saw the opportunity to design a modern tively led and inspired the dedicated
dure, but the possibilities of correction 3.5-metre alt-azimuth telescope that group of physicists, engineers and tech-
with the 3.6-metre telescope were limited eliminated some of the recognised prob- nicians who developed Active Optics
by the very heavy and stiff primary mirror. lems with the 3.6-metre. technology at ESO, implementing it on
Nevertheless, Ray’s position at ESO the NTT and later — in a more extreme
allowed him to develop the idea of Active Ray persuaded the then Director General, form — on the VLT. He was happy to give
Optics for future telescopes, and even Lodewijk Woltjer, to build the new tele- credit to his colleagues and was always
tually to provide solutions to these prob- scope with an actively controlled thin pri- willing to listen and explain. He could talk
lems. Even in the late 70s, ESO, along mary mirror. Woltjer agreed under the as naturally to the Director General as
with other major observatories, was condition that the New Technology Tele- he could to the ESO janitor and was thus
already thinking about the next generation scope (NTT), as it would be known, must greatly respected within the Organisation
of giant telescopes. have a performance no worse than the on a personal level as well as for his tech-
3.6-metre telescope even if the active nical expertise.
From 1979–1980, Ray spent a year at control did not work as planned. Another
La Silla working with the optical group to innovation of the NTT was the free air- During his final three years at ESO, and
gain experience in the operation and flow enclosure design. This concept had after he retired in 1993, Ray worked
maintenance of large telescopes. This been pioneered at the Multiple Mirror on a two-volume monograph “Reflecting
convinced him even more that future tele- Telescope on Mt. Hopkins in Arizona and Telescope Optics”. These two volumes,
scopes should have thin flexible primary differed markedly from that of classical published in 1996 and 1999 respectively,
mirrors with an active control system telescope domes, which had small aper- remain classical works on the develop-
that would be able to correct optical mis- tures to “protect” the telescope from the ment and design of optical telescopes
alignment and compensate for gravita- outside environment. Having a relatively that represent a lasting epitaph to Ray’s
tional and thermal mirror distortions. thin primary mirror and effective air flow lifetime achievements.
About this time, Ray visited a former stu- through the enclosure allowed the tele-
dent colleague from Imperial College, scope — and in particular the primary In the latter part of his career, Ray was
Roland Shack, who was now professor at mirror — to be in thermal equilibrium with awarded numerous prizes and honours
the Optical Sciences Center in Tucson, the ambient environment, instead of for his contributions to the advancement
Arizona. Shack had invented a compact being isolated from it. Ray recognised the of telescope technology. These include
and efficient optical test device that was importance of this development and the Medal of Geneva University in 1993,
based on the classical Hartmann test, it became an important feature of the the Karl Schwarzschild Medal of the
but could be mounted directly in the tele- NTT concept. German Astronomical Society in 2003,
scope focal plane. Ray immediately saw the Chevalier of the French Légion
the importance of this device for future The First Light of the NTT in March 1989 d’Honneur in 2004, the Prix Lallemand
telescopes and set about having one took place under excellent seeing condi- of the French Academy of Sciences in
built at ESO. The device became known tions, allowing the NTT to demonstrate its 2008, the Kavli Prize of the Norwegian
as the Shack–Hartmann wavefront sensor. performance to the full. This it certainly Academy of Science and Letters (together
When this was later coupled to a CCD did, producing probably the best images with Roger Angel and Jerry N elson), as
detector for image readout, ESO had a ever obtained from a ground-based tele- well as the Tycho Brahe Prize of the Euro-
practical device to measure telescope scope at that time, and three times better pean Astronomical Society in 2010.
aberrations in real time. However, to than had ever been obtained with ESO’s
actively correct aberrations would require 3.6-metre telescope. And all of this was He leaves his wife, Anne, and two sons
a telescope with a much thinner primary at a third of the cost of the 3.6-metre from his first marriage, Geoffrey and
mirror than classical large telescopes like telescope! Almost overnight, ESO’s repu- Peter.
the ESO 3.6-metre. But to propose the tation as an innovative and leading organ-
construction of a very large telescope isation for astronomical research was
based on untested technology would established. The overwhelming success
have been a giant leap of faith that would of the NTT, founded to a very large
hardly be accepted by the ESO Council. extent on the insight and perseverance of
Personnel Movements
Europe Europe
Chile Chile
Gallilee, Mark (UK) Mechanical Technical Lead Faez, Robinson (CL) Telescope Instruments Operator
Mejia-Restrepo, Julian (CO) Fellow
Sánchez Sáez, Paula (CL) Student
Wibowo, Ridlo (ID) Student
The Messenger:
Editors: Gaitee A. J. Hussain,
Anna M iotello;
Graphics, Layout, Typesetting:
Mafalda Martins;
Design, Production: Jutta B
oxheimer;
Proofreading: Peter Grimley;
w ww.eso.org/messenger/
Unless otherwise indicated, all images Front cover: JHK colour-composite image of the central
in The Messenger are courtesy of ESO, region of The massive star forming region RCW 38
except authored contributions which from HAWK-I using the ground-layer adaptive optics
are courtesy of the respective authors. module, enabling a study of the detailed influence
of photoionisation from massive stars on star formation
© ESO 2018 across a wide range of stellar masses down to brown
ISSN 0722-6691 dwarfs. Credit: ESO/Muzic et al.