MNRAS 515, 1380–1391 (2022) https://doi.org/10.

1093/mnras/stac1552
Advance Access publication 2022 June 13

Discovering vanishing objects in POSS I red images using the Virtual

Observatory
Enrique Solano,1 ‹ B. Villarroel2,3 and C. Rodrigo1
1 Centro ˜
de Astrobiologı́a (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, E-28692, Villanueva de la Canada, Madrid, Spain
2 Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-106 91 Stockholm, Sweden
3 Instituto de Astrofı́sica de Canarias, Avda Vı́a Láctea S/N, La Laguna, E-38205 Tenerife, Spain

Accepted 2022 May 31. Received 2022 May 3; in original form 2022 March 8

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ABSTRACT
In this paper, we report a search for vanishing sources in POSS I red images using virtual observatory (VO) archives, tools, and
services. The search, conducted in the framework of the VASCO project, aims at finding POSS I (red) sources not present in
recent catalogues like Pan-STARRS DR2 (limiting magnitude r = 21.4) or Gaia EDR3 (limiting magnitude G = 21). We found
298 165 sources visible only in POSS I plates, out of which 288 770 had a cross-match within 5 arcsec in other archives (mainly
in the infrared), 189 were classified as asteroids, 35 as variable objects, 3592 as artefacts from the comparison to a second
digitization (Supercosmos), and 180 as high proper motion objects without information on proper motion in Gaia EDR3. The
remaining unidentified transients (5399) as well as the 172 163 sources not detected in the optical but identified in the infrared
regime are available from a VO compliant archive and can be of interest in searches for strong M-dwarf flares, high-redshift
supernovae, asteroids, or other categories of unidentified red transients. No point sources were detected by both POSS-I and
POSS-II before vanishing, setting the rate of failed supernovae in the Milky Way during 70 yr to less than one in one billion.
Key words: astronomical data bases: surveys – astronomical data bases: virtual observatory tools.

an automated search for vanishing object using the digitized plates

1 I N T RO D U C T I O N
of the First Palomar Sky Survey (POSS I) and the Pan-STARRS
Transients can be defined as astrophysical phenomena whose dura- (DR2) and Gaia EDR3 catalogues taking advantage of the virtual
tion is significantly lower than the typical time-scale of the stellar observatory (VO) tools and services.2
and galactic evolution (from seconds to years in contrast to millions POSS I was conducted between 1949 and 1956 (99 per cent of the
or billions of years). Supernovae, novae, gamma-ray bursts, etc., are plates) and 1956–1958 (1 per cent of the plates) using the 48-inch
some examples of transient events. Oschin Schmidt telescope at Mount Palomar in southern California
While most of the modern surveys have developed robust and (Minkowski & Abell 1963). The survey covers the entire sky north of
well-tested facilities to discover transients [ASAS (Pojmanski 1997), −45◦ declination and was carried out using photographic plates, later
OGLE (Udalski, Szymański & Szymański 2015), ZTF (Bellm et al. converted into a digital format. In order to obtain colour information,
2019) or Gaia (Gaia Collaboration et al. 2021), to name a few], the each region of the sky was photographed twice, once using a blue-
same level of attention is not paid to vanishing events, that is, objects sensitive Kodak 103a-O plate, and once with a red-sensitive Kodak
detected in old surveys but that are not identified in more recent ones. 103a-E plate, peaking at ∼4 100 and ∼6 400 Å, respectively.3 The
In this context, vanishing refers both to known types of objects faded limiting photographic magnitudes of the blue and red plates are 21.1
below the detection limits (e.g. large-amplitude variables) as well to and 20.0 mag, respectively.
unknown physical phenomena non predicted before. Objects that do In this paper, we made use of the digitization of the POSS I
not appear in the same position because they have moved in the sky red plates available from the Digitized Sky Survey from ESO4 and
(e.g. Solar system objects) do not belong to this category. produced at the Space Telescope Science Institute through its Guide
VASCO1 (Vanishing and Appearing Sources during a Century Star Survey group.5
of Observations) is a project to search for vanishing and appearing The Panoramic Survey Telescope and Rapid Response System
sources using existing survey data. Examples of exceptional astro- (Pan-STARRS6 ) is a system for wide-field astronomical imaging de-
physical transients found with VASCO are given in Villarroel et al. veloped and operated by the Institute for Astronomy at the University
(2020b). VASCO also runs a citizen science project that investigates
150 000 candidates visually (Villarroel et al. 2020a). This paper,
2 https://www.ivoa.net/
conceived in the frame of the VASCO project, aims at performing
3 https://authors.library.caltech.edu/31250/1/Palomar Observatory Sky Atl
as.pdf
4 http://archive.eso.org/dss/dss/
 E-mail: esm@cab.inta-csic.es 5 http://gsss.stsci.edu/Catalogs/Catalogs.htm
1 https://vasconsite.wordpress.com/ 6 https://panstarrs.stsci.edu/

© 2022 The Author(s)

Published by Oxford University Press on behalf of Royal Astronomical Society
 POSS I vanishing objects 1381
of Hawaii. Pan-STARRS1 (PS1) is the first part of Pan-STARRS.
PS1, located at Haleakala Observatory, started operation in 2010 and
have surveyed the sky in five bands (g, r, i, z, y) at declinations higher
than −30◦ using a 1.8-m telescope and a 1.4 Gigapixel camera. The
PS1 Second Data Release (DR2) survey contains almost 2 billion
objects and was released on 2019 January 28. PS1 (DR2) was queried
using the corresponding Virtual Observatory ConeSearch service.7
Gaia is a European space mission providing astrometry, pho-
tometry and spectroscopy of more than 1 500 million stars in the
Milky Way. Also, data for significant samples of extragalactic and
Solar system objects are made available. Photometric information is
provided in three bands: G, GBP , and GRP with a limiting magnitude
of G ∼ 21 mag.8 Gaia EDR3 (Gaia Collaboration et al. 2021) is based

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on data collected between 2014 July 25 and 2017 May 28, spanning
a period of 34 months. Gaia EDR3 data were gathered through the
Vizier (Ochsenbein, Bauer & Marcout 2000) service.
This article is organized as follows: In Section 2, we describe the
methodology followed to identify candidates to vanishing objects
while, in Section 3, we assess the different hypotheses to explain the Figure 1. Example of a POSS I image with a bright source showing
physical nature of those candidates. After Sections 4 and 5, where diffraction spikes. Green squares correspond to USNO B-1.0 sources.
we report the discovery of a brown dwarf candidate in POSS I and
give an estimation of the number of vanishing stars, respectively,
we summarized the main results of the paper in Section 6. A
brief description of the VO-compliant archive than contains detailed
information on the candidates is given in the appendix.

2 C A N D I DAT E S E L E C T I O N
We built a VO-workflow consisting in the following steps:

(i) Sky tessellation: To avoid memory overflow problems associ-

ated to the data processing of large volumes of data, we made use of
the scripting capabilities of Aladin9 (Bonnarel et al. 2000; Boch &
Fernique 2014), to tessellate the sky covered by POSS I in circular Figure 2. Example of a POSS I image showing a cane-shaped artefact
regions of 30-arcmin radius. (located at the centre-right of the image), which is removed from the
(ii) Source extraction: For each one of these regions, we run SEXTRACTOR catalogue according to its anomalous values of FWHM and
SEXTRACTOR (Bertin & Arnouts 1996) to build a catalogue of elongation. SEXTRACTOR sources are overplotted as red dots.
sources. To minimize the number of false sources in noisy images and
detect only sources well above the noise level, the DETECT− THRESH (a) For each SEXTRACTOR source, we look for counterparts
parameter was set to five and only sources with SNR− WIN>30 and in the USNO B-1.011 (Monet et al. 2003) in a circular region of
FLAG = 0 were kept. 90-arcmin radius.
(iii) Cross-matching: We made use of the CDSSkymatch func- (b) SEXTRACTOR sources having a USNO counterpart fulfill-
tionality implemented in STILTS10 (Taylor 2006) to cross-match the ing any of the following two conditions were rejected.
catalogue of sources obtained in the previous step with the Gaia
(1) Rmag1 or Rmag2 < 12.4;
EDR3 and Pan-STARRS DR2 catalogues. Sources in the SExtractor
(2) Rmag1 or Rmag2 < −0.09 × d + 15.3,
catalogue not having counterparts either in Gaia or Pan-STARRS in a
where d is the angular separation in arcsec between the
5-arcsec radius were kept. The adopted radius is a good compromise
SEXTRACTOR and the USNO B-1.0 source and Rmag1 and
to ensure that not many high proper motion were left out while, at
Rmag2 are the USNO magnitudes in the red band at two
the same time, avoiding an unmanageable number of false positives.
different epochs (Fig. 1).
(iv) Spikes’ removal: Spurious detections appearing on the diffrac-
tion spikes of very bright sources in POSS I images must be
identified and removed. After some trial and error, we implemented (v) Other artefacts’ removal: Morphometric parameters like the
the following empirical procedure to remove them: full width at half-maximum (FWHM) or the elongation were used
to clean the SEXTRACTOR catalogue from spurious sources. For
each image, we computed the median and the absolute deviation
of the median of the FWHM and the elongation of the sources in
order to remove sources deviating more than 2σ from the median
7 http://gsss.stsci.edu/webservices/vo/CatalogSearch.aspx?&CAT=PS1V3
values (Fig. 2). Additionally, we also applied the following filtering
OBJECTS&RA=&DEC=&SR = conditions:
8 https://www.cosmos.esa.int/web/gaia/earlydr3
9 https://aladin.u-strasbg.fr/
10 http://www.star.bris.ac.uk/∼mbt/stilts/ 11 https://cdsarc.cds.unistra.fr/viz-bin/cat/I/284

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Figure 3. Example of a high proper motion source (centre of the image). Red open circles represent Gaia counterparts at J2016.0 epoch. Solid blue diamonds
indicate the position of the same sources at the POSS I epoch. The isolated red circle at the lower left of centre really coincides with the POSS I source at the
centre of the image if the POSS I epoch is considered (blue diamond inside the inner circle). The outer and inner black circles correspond to the 3-arcmin and
5-arcsec search radius, respectively.

(a) SPREAD− MODEL > −0.002 mas yr−1 may lie outside our 5-arcsec radius searches becoming,
(b) 2 < FHWM < 7 thus, potential candidates. To identify and remove them from the list
(c) ELONGATION<1.3 of candidates, we made use of the observing epoch of the POSS I
(d) abs((XMAX− IMAGE - XMIN− IMAGE) - images (keyword: EPOCH).
(YMAX− IMAGE - YMIN− IMAGE)) < 2 For each one of the SEXTRACTOR sources fulfilling all the conditions
(e) XMAX− IMAGE - XMIN− IMAGE > 1 described in the previous steps, we cross-matched them with Gaia
(f) YMAX− IMAGE - YMIN− IMAGE > 1 EDR3 in a 180 arcmin radius, keeping all the counterparts in that
radius. For these Gaia counterparts, we kept those having proper
SPREAD− MODEL is a SEXTRACTOR parameter intended to be a motion information, which was used to correct the position of the
point/extended source classifier. By construction, SPREAD− MODEL Gaia counterparts to the POSS I epoch. The adopted epoch for
is close to zero for point sources, positive for extended sources Gaia was J2016.0. SEXTRACTOR sources having a Gaia counterpart
(galaxies), and negative for detections smaller than the PSF, such (corrected at POSS I epoch) at less of 5 arcsec were flagged as
as cosmic-ray hits. XMAX/XMIN/YMAX/YMIN indicate the maxi- high proper motion sources and, therefore, removed from the list of
mum/minimum x/y coordinate among detected pixels. Our condition candidates (Fig. 3).
forces the source to be larger than one pixel and of similar size in (vii) Concatenation: The lists of sources fulfilling all the previous
both directions. steps were concatenated into a single table and removed duplicated
(vi) Identification of high proper motion objects: The ∼60-yr time instances as tessellated images may overlap. After all this process,
baseline between the POSS I images and Gaia and Pan-STARRS we ended up with a list of 298 165 POSS I sources not seen either in
leads that objects with proper motions typically higher than 80 Gaia EDR3 or Pan-STARRS DR2.

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Figure 4. Detection of the asteroid 1998 XR77 (centre of the image). Its elongated, striped shape is clearly visible. The predicted position by Skybot (∼35 arcsec
south-east from the real position) as well as its trajectory are plotted in red. Yellow shapes indicate the sources identified by SEXTRACTOR.

3 A N A LY S I S We also queried the Astrographic Catalogue (Urban et al. 1998) to

look for observations previous to POSS I epoch finding no results.
In the previous section, we obtained a total of 298 165 potential
(ii) Asteroids: The typical exposure time of the POSS I red images
sources that do not have counterparts either in Pan-STARRS DR2 or
(45–60 min) and the mean daily motion of Main Belt asteroids (0.1–
Gaia EDR3 within a certain distance (5 arcsec). In what follows we
0.3 deg d−1 , larger for nearer asteroids) make that most of these
will study the possible nature of these sources.
objects leave a stripe on the POSS I red images (Fig. 4). Although
(i) Objects not present either in Gaia EDR3 or Pan-STARRS but due to its elongated shape, most of them are discarded in the search
present in other astronomical surveys. To check this possibility, we procedure, very slow asteroids mimicking point-like sources could
looked for counterparts in the catalogues available from the CDS escape from the filtering criteria. In order to also discard these
Upload X-match utility implemented in TOPCAT (Taylor 2005) and sources, we made use of the SkyBoT13 VO service (Berthier et al.
from IRSA (Neowise, PTF). These searches were complemented 2006) to look for known asteroids lying in the POSS I field of view
with a search in the catalogues available from VOSA (Bayo et al. at the time when the image was observed. Sources lying at less than
2008).12 Sources with counterparts at less than 5 arcsec in any of 1 arcmin from the predicted position of the asteroid were removed.
the queried photometric catalogues were removed from our list of In total, 189 asteroids were found leaving us with 9 206 (9 395-189)
candidates to vanishing objects. candidates.
These searches significantly reduced the number of candidates (from (iii) Stellar variability: It might happen that our candidates are
298 165 to 9 395). A significant number (∼59 per cent) of the not visible either in Gaia EDR3, Pan-STARRS or other catalogues
identified sources were visible in infrared catalogues (Neowise, simply because they are large-amplitude variable objects reaching
CatWISE2020, unWISE, and the infrared catalogues included in their faintest magnitudes at the time when they were observed in
VOSA) but not in the optical (KIDS, Skymapper, and the optical those surveys. Gaia EDR3 and Pan-STARRS are deeper surveys
catalogues included in VOSA) or the ultraviolet (GALEX). The than POSS I but, how much deeper are they? In order to estimate
sources detected in the infrared but not in the optical/ultraviolet the limiting magnitude of our POSS I candidates in the Gaia EDR3
are available from the online archive (see Appendix). and Pan-STARRS photometric systems, we randomly selected 100
candidates. Centred on each one of them, we cutout a POSS I image of
15 × 15-arcmin radius and, using SeXTRACTOR, compiled the sources

12 The list of catalogues consulted by VOSA can be found at http://svo2.cab

.inta-csic.es/theory/vosa/help/star/credits/. 13 https://vo.imcce.fr/webservices/skybot/

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1384 E. Solano, B. Villarroel and C. Rodrigo
2001), FUORs (Hartmann & Kenyon 1996), RCB stars (Benson
et al. 1994), ILRTs (Cai et al. 2021), K giants (Tang et al. 2010),
cataclysmic objects like novae or pulsating variables like Miras
(Reid & Goldston 2002), RV Tau stars (de Ruyter et al. 2005) or
Cepheids (Klagyivik & Szabados 2009). Other potential types of
variable objects can be found in Byrne & Fraser (2022). Moreover,
extragalactic transients that can be associated with rare blazars or
accretion outbursts in active galactic nuclei (Lawrence et al. 2016) or
highly variable quasars or microlensing events (Nagoshi et al. 2021)
can also contribute.
In order to assess whether our candidates to vanishing objects
were already known variable objects, we searched for them in the
International Variable Star Index15 (Watson, Henden & Price 2006)
and in the Transient Name Server.16 In both cases no counterparts

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were found at less than 5 arcsec. We also queried the PTF object
catalogue available at IRSA17 finding 62 counterparts, out of which
Figure 5. Distribution of the Gaia EDR3 (blue) and Pan-STARRS (red) 35 were flagged as good (ngoodobs > 0). This reduced the number
magnitudes of a randomly selected sample of POSS I sources. Limiting of candidates to 9 171 (9 206-35).
magnitudes of POSS I sources at Gaia EDR3 and Pan-STARRS are G = 18.5 (iv) Supernovae, hypernovae and failed supernovae: Much less
and r = 19, respectively. frequent but still possible is that some of our candidates may be
ascribed to explosions of very luminous supernovae and hypernovae.
If these objects are hosted in very faint galaxies, they will be
present in them. A total of ∼22 000 sources were obtained. These visible just at the time of explosion keeping no track in images
sources were cross-matched with Gaia EDR3 and Pan-STARRS with taken subsequently. ASASSN-15lh / SN 2015L, the most luminous
a 5 arcsec search radius to look for counterparts in these catalogues. supernovae observed so far thought to be originated by the tidal
We got 19 804 and 20 784 counterparts in Gaia EDR3 and Pan- disruption of a star when crossing the tidal radius of a supermassive
STARRS, respectively. Fig. 5 shows the distribution of the Gaia black hole (Leloudas et al. 2016), or GRB171205A a hypernovae
EDR3 (G band) and Pan-STARRS (r band) magnitudes. We see caused by the explosion of a very massive star (Izzo et al. 2019)
how completeness is reached for POSS I sources at G = 18.5 in could be examples of the objects belonging to this category.
Gaia EDR3 and r = 19 in Pan-STARRS. The limiting magnitude Failed supernovae, on its part, have been proposed to explain
of Gaia EDR3 (G = 21) (Gaia Collaboration et al. 2021) and Pan- the absence of Type IIP core-collapse supernovae arising from
STARRS (r = 21.8)14 imply that, for a source not to be visible in progenitors above 17 M . In this scenario, the stellar cores will
Gaia EDR3 and Pan-STARRS, the drop in magnitude should be collapse directly to form a black hole without producing the explosion
larger than 2.5 mag approximately. of the star (Byrne & Fraser 2022). As for supernovae and hypernovae,
Flare stars are objects with spectral types later than late-K that failed supernovae occurring at POSS-I epoch will not be visible in
can undergo unpredictable dramatic increases in brightness for a modern archives. Different candidates to failed supernovae have been
few minutes or hours before returning to their quiescent state (e.g. proposed in the literature (Kochanek et al. 2008; Reynolds, Fraser &
Greiner & Motch 1995). The relatively little time spent at the Gilmore 2015; Neustadt et al. 2021) but the real nature of these
brightest magnitude (the flare duty cycle for M dwarfs is found objects is still far from being confirmed.
to increase from 0.02 per cent for early M dwarfs to 3 per cent for (v) Artefacts: Could artefacts resemble point-like sources and,
late M dwarfs (Hilton et al. 2010). The duty cycle is defined as the thus, escape from our morphometric criteria? Small dust particles
percentage of time in an entire period of observation where flares sticking to the plate during exposures or microspots originated over
occur), their unpredictable occurrence together with the fact that M the years may produce this type of point-like features (Villarroel
stars are the most numerous objects in the galaxy (Cifuentes et al. et al. 2020b). Clearly, a human inspection of the POSS I plates could
2020), make flare stars good candidates to explain the nature of, solve the problem. However, the original plates of old sky surveys
at least, a significant part of our sources. Nevertheless, differences are treated like gold and accessing those plates is extraordinarily
in the type of data used to estimate the frequency of flares – time- rare. An alternative to remove candidates artefacts originated during
resolved photometric (Kowalski et al. 2009) or spectroscopic (Hilton the scanning process is to compare the images digitized at STSCI
et al. 2010) surveys –, in the wavelength range (near UV, optical), with those digitized by SuperCosmos.18 The comparison was carried
in the magnitudes used to count the number of flares (duty cycle, out using the table access protocol (TAP) service implemented in
flares per hour), in the parameters used for flare identification – flare the GAVO Data Centre.19 Candidates having a counterpart in the
variability index (Kowalski et al. 2009), flare line index (Hilton et al. Supercosmos digitization at less than 5 arcsec were kept. After this
2010) –, or the existing correlation with spatial distribution, spectral comparison, 5579 candidates still remain.
type or age – begin more frequent close to the Galactic plane, at later
spectral types and at younger ages (Hilton et al. 2010) –, makes it
quite difficult to give a realistic estimation of the number of flaring
objects among our final list of unidentified transients. 15 https://cdsarc.cds.unistra.fr/viz-bin/cat/B/vsx
Other (although less numerous) types of stellar objects triggering 16 https://www.wis-tns.org/
large amplitude variations are, for instance, LBVs (van Genderen 17 https://irsa.ipac.caltech.edu/cgi- bin/Gator/nph- scan?mission=irsa&submi

t=Select&projshort = PTF
18 https://www.roe.ac.uk/ifa/wfau/cosmos/scosmos.html
14 https://panstarrs.stsci.edu/ 19 http://dc.zah.uni-heidelberg.de/tap

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Figure 6. LP 371-1, the object marked with a cross in the SDSS image, is a high proper motion star as reported in Simbad (PMRA: −154 mas yr−1 ; PMDEC:
−140 mas yr−1 ; red line) but without proper motion information in Gaia EDR3 (table shown at the bottom panel). See the text for more details.

(vi) Wrong astrometry: If the POSS I red images from where the the reader that the launch of the first satellite happened in 1957, when
candidates to vanishing objects were extracted have poor astrometry, most of the POSS I survey was already completed.
then, the extracted sources will appear displaced from the Gaia EDR3 (viii) High proper motion objects without proper motion infor-
and Pan-STARRS positions being, thus, flagged as candidates. mation in Gaia EDR3. Not all sources included in Gaia EDR3 have
To check this possibility, we randomly selected a subsample of associated an estimation of their proper motion. If this is the case and
∼400 000 sources extracted from POSS I images, sources that were the object has a significant proper motion, it could be wrongly flagged
cross-matched with Gaia EDR3. The mean and median values for the as candidate to vanishing object. In order to identify these fast-
differences in position were 0.97 and 0.91 arcsec, respectively, with moving objects, we carried out a visual inspection using Aladin. First,
a standard deviation of 0.5 arcsec. Thus, we can conclude that wrong we made use of the proper motion information available in Simbad
astrometry cannot explain the number of candidates to vanishing for objects at small angular distances from our candidates. This way
objects we have found. we discarded 178 objects (Fig. 6). For the remaining 5401 (5579-
(vii) Technosignatures: Technosignatures can be defined as prop- 178) candidates, we looked for sources at close angular distances in
erties or effects that cannot be ascribed to natural phenomena and, catalogues with different time coverage (2MASS, SDSS, UKIDSS,
thus, may indicate an artificial origin (e.g. artificial communication ZTF) aiming at finding a clear linear displacement between images
lasers, Dyson spheres and megastructures. In particular, the latter (Fig. 7). After this visual inspection, we ended up with a final list
two could make a dim or even vanish entirely the star). The of 5399 candidates to vanishing objects. A flowchart summarizing
role of vanishing stars in searches for technosignatures was first the selection and analysis process is shown in Fig. 8. The spatial
presented in Villarroel, Imaz & Bergstedt (2016). A general overview distribution in galactic coordinates of the final list of candidates as
describing the possibilities of technosignature searches in time- well the distribution of their magnitudes (R Supercosmos) are given
domain astronomy is given in Davenport (2019) while concrete in Figs 9 and 10, respectively.
examples can be found in Villarroel et al. (2020b). Human satellites
at the geostationary orbit could be argued as a possibility to explain
the glints found in POSS I images, glints that could be caused by 4 B ROW N DWA R F S I N P O S S I I M AG E S
reflections of the Sun. This glints would be bright, have a PSF-like As pointed out in Section 3, most of the 298 165 candidates were
shape and short duration (Villarroel et al. 2022). However, we remind discarded because they were detected in catalogues other than Gaia

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1386 E. Solano, B. Villarroel and C. Rodrigo

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Figure 7. Example of a high proper motion object not reported either in Gaia EDR3 or Simbad. The blue/green/red/black crosses mark the position of the
source in POSS I/2MASS/UKIDSS/ZTF images, respectively.

EDR3 or Pan-STARRS. Since most of the discarded sources were

detected in the infrared, we looked into this sample to identify
candidate brown dwarfs in POSS I images. This is relevant because
it would imply that this class of objects was already recorded in
photographic plates 40 yr before the confirmation of its first member
(Rebolo, Zapatero Osorio & Martı́n 1995).
For this, we made a spectral energy distribution fitting using VOSA
and the BT-Settl CIFITS grid of model atmospheres (Baraffe et al.
2015). A candidate brown dwarf with an effective temperature of
2 400 K (M9 V according to the Mamajek’s Color and Effective
Temperature Sequence20 ) was found. The SED fitting as well the
position of the candidate brown dwarf in POSS I, 2MASS, and Pan-
STARRS images is shown in Fig. 11.

5 FA I L E D S U P E R N OVA E ?
In Villarroel et al. (2020b), the rate of failed supernovae was
estimated to be less than 1 in 90 million during a 70 yr of time
window. We investigate the list of 298 165 transient sources to see if
any of these can be found both in POSS I and in POSS II red images
before vanishing. We find five candidates that each one turns out to
be a superposition of a transient and artefact. Also, among the 5399
final candidates, we found only two sources almost simultaneously
observed in the POSS I blue and red images (the difference in

20 https://www.pas.rochester.edu/∼emamajek/EEM dwarf UBVIJHK color

Figure 8. Flowchart of the candidate selection and analysis. See Sections 2
and 3 for details. s Teff.txt

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Figure 9. Spatial distribution in galactic coordinates of the final list of 5399 candidates (blue dots). A coloured POSS-II images is displayed in the background.

exposure times (typically, 45–60 min in the red and 8–10 min in the
blue) which, despite some flux dilution due to the large observing
time, makes higher the likelihood of finding a transient in red
images.
The above results indicate that an entire disappearance of a
star might be rare, which agrees with some theoretical predictions
(Byrne & Fraser 2022). All-sky survey searches for failed supernovae
are more likely to succeed on declining brightness of an object within
m < 3 mag, rather than its entire disappearance. In order to reach
a final conclusion on the rate of failed supernovae, a future study
will carefully examine whether the complete list of 298 165 sources,
as well as the list of candidates emerging from the VASCO citizen
science project, contains candidates visible in both the blue and the
red band.

6 S U M M A RY
Figure 10. Distribution of the Supercosmos R magnitudes of the final sample Working with three large-area sky surveys (POSS I, Gaia EDR3
(5399 objects). It peaks at R ∼ 18, 5 with 80 per cent of the target with and Pan-STARRS DR2) and a workflow based on VO archives and
magnitudes in the range 17 ≤ R ≤ 19.
services, we have searched for sources identified in POSS I but not
seen either in Gaia or Pan-STARRS finding 298 165 sources. After
filtering sources found in other archives (mainly in the infrared),
observing time between the blue and red exposures is, typically, asteroids, high proper motion objects with no information on proper
∼30 min). Although, on the basis of the displacements of the sources motion in Gaia EDR3, known variables and artefacts, we ended
between the POSS I blue and red images, they could be classified up with a list of 5399 sources. Working with POSS I data has the
as non-catalogued asteroids, the fact that the two sources show a advantage of getting rid from contamination of artificial satellites
point-like shape might question this hypothesis since, as mentioned and, at the same time, opens the possibility of exploring long-term
in Section 3, asteroids are expected to show an elongated shape in (of the order of decades) variability phenomena.
the direction of the movement (Fig. 12). The small number of almost Although the origin of these 5399 vanishing sources is not
simultaneous transients in blue and red images can be, at least, partly clear, most of them might be associated to large amplitude (>
explained by the different wavelength coverage (very red sources 2.5 mag) variable stars like, for instance, flare stars. Other physical
may not be visible in the blue, and vice versa) and by the different (unknown asteroids, non-catalogued high proper motion objects

MNRAS 515, 1380–1391 (2022)

1388 E. Solano, B. Villarroel and C. Rodrigo

Figure 11. Top panel: spectral energy distribution fitting of the candidate brown dwarf (RA: 77◦. 7951, Dec. 8◦. 94396). The red dots represent the observed Downloaded from https://academic.oup.com/mnras/article/515/1/1380/6607509 by guest on 24 January 2024
photometry. Overplotted in blue is the best fitting CIFIST model. Photometric upper limits are plotted as inverted yellow triangles and are not considered in
the SED-fitting process. Bottom panel: the candidate brown dwarf as seen in POSS I (red cross) and Pan-STARRS (blue cross). The green cross in between
indicates the position of the source in an intermediate epoch (2MASS).

or exotic objects theoretically proposed like failed supernovae) sients. Follow-up observations with bigger telescopes will reveal
and artificial (technosignatures) mechanisms can also be proposed the presence/absence of an object in its place. Sources still missing
to explain the disappearance of our list of objects in modern after follow-up observations could also be useful for technosignature
archives. studies like, for instance, laser searches (Villarroel et al. 2020b;
The candidates to vanishing stars 5399 as well as the sources Marcy, Tellis & Wishnow 2022). The 298 165 sources will be further
detected in the infrared but not in the visible (172 163) are easily examined by the VASCO citizen science project (Villarroel et al.
accessible from a VO compliant archive. These sources can be 2020a). Finally, it is also important to stress the fundamental role
of interest in searches for strong M-dwarf flares, extreme stellar played by the VO in this paper. The discovery, access and analysis
variability on extended times-scales as well as extragalactic tran- of millions of objects coming from tens of archives covering the

MNRAS 515, 1380–1391 (2022)

 POSS I vanishing objects 1389

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Figure 12. Two sources seen in POSS I red and blue images (differences in time ∼30 min) but not detected in more recent surveys.

electromagnetic spectrum from the ultraviolet to the mid-infrared AC K N OW L E D G E M E N T S

would have not been possible without the tools and services provided
This research has made use of the Spanish Virtual
by this e-infrastructure.
Observatory (https://svo.cab.inta-csic.es) project funded by

MNRAS 515, 1380–1391 (2022)

1390 E. Solano, B. Villarroel and C. Rodrigo
MCIN/AEI/10.13039/501100011033/ through grant PID2020- Bertin E., Arnouts S., 1996, A&AS, 117, 393
112949GB-I00 and MDM-2017-0737 at Centro de Astrobiologı́a Boch T., Fernique P., 2014, in Manset N., Forshay P., eds, ASP Conf. Ser. Vol.
(CSIC-INTA), Unidad de Excelencia Marı́a de Maeztu. BV is 485, Astronomical Data Analysis Software and Systems XXIII. Astron.
funded by the Swedish Research Council (Vetenskapsrådet, grant Soc. Pac., San Francisco, p. 277
Bonnarel F. et al., 2000, A&AS, 143, 33
no. 2017-06372) and is also supported by the The L’Oréal -
Byrne R., Fraser M., 2022, MNRAS, 512, 1188
UNESCO For Women in Science Sweden Prize with support of the
Cai Y. Z. et al., 2021, A&A, 654, A157
Young Academy of Sweden. She is also supported by Märta och Cifuentes C. et al., 2020, A&A, 642, A115
Erik Holmbergs donation. Davenport J. R. A., 2019, AJ, preprint (arXiv:1907.04443)
This work presents results from the European Space Agency de Ruyter S., van Winckel H., Dominik C., Waters L. B. F. M., Dejonghe H.,
(ESA) space mission Gaia. Gaia data are being processed by the 2005, A&A, 435, 161
Gaia Data Processing and Analysis Consortium (DPAC). Funding Gaia Collaboration et al., 2021, A&A, 649, A1
for the DPAC is provided by national institutions, in particular the Greiner J., Motch C., 1995, A&A, 294, 177
institutions participating in the Gaia MultiLateral Agreement (MLA). Hartmann L., Kenyon S. J., 1996, ARA&A, 34, 207
Hilton E. J., West A. A., Hawley S. L., Kowalski A. F., 2010, AJ, 140,

Downloaded from https://academic.oup.com/mnras/article/515/1/1380/6607509 by guest on 24 January 2024

The Gaia mission website is https://www.cosmos.esa.int/gaia. The
1402
Gaia archive website is https://archives.esac.esa.int/gaia.
Izzo L. et al., 2019, Nature, 565, 324
The Pan-STARRS1 Surveys (PS1) and the PS1 public science
Klagyivik P., Szabados L., 2009, A&A, 504, 959
archive have been made possible through contributions by the Kochanek C. S., Beacom J. F., Kistler M. D., Prieto J. L., Stanek K. Z.,
Institute for Astronomy, the University of Hawaii, the Pan-STARRS Thompson T. A., Yüksel H., 2008, ApJ, 684, 1336
Project Office, the Max-Planck Society and its participating insti- Kowalski A. F., Hawley S. L., Hilton E. J., Becker A. C., West A. A.,
tutes, the Max Planck Institute for Astronomy, Heidelberg and the Bochanski J. J., Sesar B., 2009, AJ, 138, 633
Max Planck Institute for Extraterrestrial Physics, Garching, The Lawrence A. et al., 2016, MNRAS, 463, 296
Johns Hopkins University, Durham University, the University of Leloudas G. et al., 2016, Nat. Astron., 1, 0002
Edinburgh, the Queen’s University Belfast, the Harvard-Smithsonian Marcy G. W., Tellis N. K., Wishnow E. H., 2022, MNRAS, 509, 3798
Center for Astrophysics, the Las Cumbres Observatory Global Minkowski R. L., Abell G. O., 1968, in Strand K. A.ed., Basic Astronomical
Data: Stars and stellar systems, The National Geographic Society-Palomar
Telescope Network Incorporated, the National Central University
Observatory Sky Survey. University of Chicago Press, Chicago, IL USA,
of Taiwan, the Space Telescope Science Institute, the National Aero-
p. 481
nautics and Space Administration under Grant No. NNX08AR22G Monet D. G. et al., 2003, AJ, 125, 984
issued through the Planetary Science Division of the NASA Science Nagoshi S., Iwamuro F., Wada K., Saito T., 2021, PASJ, 73, 122
Mission Directorate, the National Science Foundation Grant No. Neustadt J. M. M., Kochanek C. S., Stanek K. Z., Basinger C., Jayasinghe T.,
AST-1238877, the University of Maryland, Eotvos Lorand Univer- Garling C. T., Adams S. M., Gerke J., 2021, MNRAS, 508, 516
sity (ELTE), the Los Alamos National Laboratory, and the Gordon Ochsenbein F., Bauer P., Marcout J., 2000, A&AS, 143, 23
and Betty Moore Foundation. Pojmanski G., 1997, Acta Astron., 47, 467
This publication makes use of VOSA, developed under the Spanish Rebolo R., Zapatero Osorio M. R., Martı́n E. L., 1995, Nature, 377, 129
Virtual Observatory project. This research has made use of Aladin Reid M. J., Goldston J. E., 2002, ApJ, 568, 931
Reynolds T. M., Fraser M., Gilmore G., 2015, MNRAS, 453, 2885
(Bonnarel et al. 2000; Boch & Fernique 2014), Simbad (Wenger
Tang S., Grindlay J., Los E., Laycock S., 2010, ApJ, 710, L77
et al. 2000), and Vizier (Ochsenbein et al. 2000), developed at CDS,
Taylor M. B., 2005, in Shopbell P., Britton M., Ebert R., eds, ASP Conf.
Strasbourg Observatory, France. TOPCAT (Taylor 2005) and STILTS Ser. Vol. 347, Astronomical Data Analysis Software and Systems XIV.
(Taylor 2006) have also been widely used in this paper. This research Astron. Soc. Pac., San Francisco, p. 29
has made use of the NASA/IPAC Infrared Science Archive, which is Taylor M. B., 2006, in Gabriel C., Arviset C., Ponz D., Enrique S., eds, ASP
funded by the National Aeronautics and Space Administration and Conf. Ser. Vol. 351, Astronomical Data Analysis Software and Systems
operated by the California Institute of Technology. This research has XV. Astron. Soc. Pac. San Francisco, p.666
also made use of IMCCE’s SkyBoT VO tool. Udalski A., Szymański M. K., Szymański G., 2015, Acta Astron., 65, 1
Urban S. E., Corbin T. E., Wycoff G. L., Martin J. C., Jackson E. S., Zacharias
M. I., Hall D. M., 1998, AJ, 115, 1212
DATA AVA I L A B I L I T Y van Genderen A. M., 2001, A&A, 366, 508
Villarroel B., Imaz I., Bergstedt J., 2016, AJ, 152, 76
The data underlying this article are available in the SVO archive of
Villarroel B. et al., 2020a, preprint (arXiv:2009.10813)
vanishing objects in POSS I red images available at http://svocats.ca Villarroel B. et al., 2020b, AJ, 159, 8
b.inta-csic.es/vanish/ Villarroel B., Mattsson L., Guergouri H., Solano E., Geier S., Dom O. N.,
Ward M. J., 2022, Acta Astron., 194, 106
Watson C. L., Henden A. A., Price A., 2006, Soc. Astron. Sci. Ann. Symp.,
REFERENCES
25, 47
Baraffe I., Homeier D., Allard F., Chabrier G., 2015, A&A, 577, A42 Wenger M. et al., 2000, A&AS, 143, 9
Bayo A., Rodrigo C., Barrado Y Navascués D., Solano E., Gutiérrez R.,
Morales-Calderón M., Allard F., 2008, A&A, 492, 277
Bellm E. C. et al., 2019, Publ. Astron. Soc. Pac., 131, 018002
Benson P. J., Clayton G. C., Garnavich P., Szkody P., 1994, AJ, 108, 247 A P P E N D I X A : VO C O M P L I A N T, O N L I N E
Berthier J., Vachier F., Thuillot W., Fernique P., Ochsenbein F., Genova F., C ATA L O G U E
Lainey V., Arlot J.-E., 2006, in Gabriel C., Arviset C., Ponz D., Enrique
In order to help the astronomical community on using our catalogue
S., eds, ASP Conf. Ser. Vol. 351, Astronomical Data Analysis Software
and Systems XV. Astron. Soc. Pac., San Francisco, p. 367
of candidates to vanishing objects, we developed an archive system

MNRAS 515, 1380–1391 (2022)

 POSS I vanishing objects 1391
that can be accessed from a webpage21 or through a Virtual Obser- Application Messaging) VO protocol. SAMP allows VO applications
vatory ConeSearch.22 to communicate with each other in a seamless and transparent manner
The archive system implements a very simple search interface for the user. This way, the results of a query can be easily transferred
that allows queries by coordinates and radius as well as by other to other VO applications, such as, for instance, Topcat.
parameters of interest. The user can also select the maximum number
of sources (with values from 10 to unlimited). The result of the query
is a HTML table with all the sources found in the archive fulfilling the
search criteria. The result can also be downloaded as a VOTable or a
CSV file. Detailed information on the output fields can be obtained
placing the mouse over the question mark located close to the name
This paper has been typeset from a TEX/LATEX file prepared by the author.
of the column. The archive also implements the SAMP23 (Simple

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21 http://svocats.cab.inta-csic.es/vanish/
22 for instance, http://svocats.cab.inta- csic.es/vanish- possi/cs.php?RA=0.70
8&DEC=47.155&SR=0.1&VERB = 2.
23 http://www.ivoa.net/documents/SAMP

MNRAS 515, 1380–1391 (2022)