On a clear night, our home galaxy, the Milky Way, is visible as a starry ribbon across the sky. I... more On a clear night, our home galaxy, the Milky Way, is visible as a starry ribbon across the sky. Its core is located in the constellation of Sagittarius, approximately where the bright glow is interrupted by the darkest dust filaments. There, hidden, lies a massive black hole. To peer through the obscuring clouds and see the stars and gas near the black hole we use GRAVITY. The main GRAVITY results are the detection of gra- vitational redshift, the most precise mass- distance measurement, the test of the equivalence principle, and the detection of orbital motion near the black hole.
Ground-based and Airborne Instrumentation for Astronomy V, 2014
The instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), recently installed... more The instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), recently installed on the VLT-UT3, aims to detected and characterize giant extra-solar planets and the circumstellar environments in the very close vicinity of bright stars. The extreme brightness contrast and small angular separation between the planets or disks and their parent stars have so far proven very challenging. SPHERE will meet this challenge by using an extreme AO, stellar coronagraphs, an infrared dual band and polarimetric imager called IRDIS, an integral field spectrograph, and a visible polarimetric differential imager called ZIMPOL. Polarimetry allows a separation of the light coming from an unpolarized source such as a star and the polarized source such as a planet or protoplanetary disks. In this paper we present the performance of the infrared polarimetric imager based on experimental validations performed within SPHERE before the preliminary acceptance in Europe. We report on the level of instrumental polarization in the infrared and its calibration limit. Using differential polarimetry technique, we quantify the level of speckle suppression, and hence improved sensitivity in the context of imaging extended stellar environments.
Observing at high angular resolution from the ground is not made possible with Adaptive Optics al... more Observing at high angular resolution from the ground is not made possible with Adaptive Optics alone, and besides the turbulence residuals, atmospheric refraction, thermal background or instrument's mechanical flexures may also severely limit the gain of optical quality that AO techniques are supposed to provide. We describe here how NAOS, the newly installed AO system on the VLT, has been
Fundamental limitations of the concept of a laser reference star are reviewed: the wavefront meas... more Fundamental limitations of the concept of a laser reference star are reviewed: the wavefront measurement accuracy is discussed, Rayleigh, Mie and resonance backscattering link budgets are evaluated.
ABSTRACT The use of a Laser Guide Star (LGS) in an Adaptive Optics system in order to increase th... more ABSTRACT The use of a Laser Guide Star (LGS) in an Adaptive Optics system in order to increase the sky coverage, leads to a degradation of correction performances caused by the focus anisoplanatism, or cone effect, the LGS upward tilt indetermination and the defocusing produced by the non-constant altitude of the LGS. If the Adaptive Optics system has the typical configuration of a Shack-Hartmann wavefront sensor and a piezo-stack deformable mirror, a possible partial solution to solve the problem is to add a low order curvature wavefront sensor able to look at an off-axis a natural guide star close enough to the observed object. In fact the very low order modes (tip-tilt, defocus and astigmatism) are the most degraded by the LGS use but they have also the largest isoplanatic patch especially in the near infrared (H,K bands) wavelengths. With this configuration the Shack-Hartmann sensor provides the coefficients for the higher order modes while the curvature sensor provide the coefficients for the lower order ones. In this way the tilt and conical anisoplanatisms are partially reduced and there is also a continuos monitoring of the sodium layer altitude. Furthermore another aspect is the comparison of the performances at very faint magnitudes between a Shack-Hartmann and a low order curvature sensor in order to check if the reduced pupil sampling provides a better correction. In this framework a simulation work has been developed to study the coupling performances of a curvature sensor with a piezo-stack mirror; the code has been written in IDL.
In this paper, we simulate different possibilities to upgrade the Adaptive Optics Facility (AOF) ... more In this paper, we simulate different possibilities to upgrade the Adaptive Optics Facility (AOF) of the VLT, to reach the diffraction limit in the near infrared. We present simulations of Ground Layer AO, Laser Tomography AO, Multi-Conjugate AO, Dual AO and a hybrid system which is a simplified version of MCAO. We describe the strengths and weaknesses of each approach and summarize the studies to be still carried out.
The aim of the Multi-Conjugate Adap-tive Optics Demonstrator (MAD) is to correct for atmospheric ... more The aim of the Multi-Conjugate Adap-tive Optics Demonstrator (MAD) is to correct for atmospheric turbulence over a field of view which is much larger than the one typically covered by the exist-ing adaptive optics systems installed on 8-m-class telescopes. After a long period of ...
The 4LGSF is to be installed as a subsystem of the ESO Adaptive Optics Facility (AOF, [1]) on Uni... more The 4LGSF is to be installed as a subsystem of the ESO Adaptive Optics Facility (AOF, [1]) on Unit Telescope 4 (UT4) of the VLT, to provide the AO instruments GALACSI/MUSE and GRAAL/HAWK-I with four sodium laser guide stars. The 4LGSF will deploy four modular LGS Units at the UT4 Centrepiece. Two key aspects of the 4LGSF design are: (i) new industrial laser source (fibre lasers) with reduced volume, reduced need of maintenance, higher reliability, simpler operation and optimised spectral format for highly efficient sodium excitation, (ii) modular structure of the four LGS Units, composed of the laser and laser launch telescope, capable to operate independently of the others. The final design of the 4LGSF is now complete and the project has entered the manufacturing, assembly, integration and test phase. Furthermore, modular LGS units containing the laser emitter integrated on the launch telescope have already been demonstrated at ESO in the past years [2, 3]. We believe that having ...
More than 4000 exoplanets are known to date in systems that differ greatly from our Solar System.... more More than 4000 exoplanets are known to date in systems that differ greatly from our Solar System. In particular, inner exoplanets tend to follow orbits around their parent star that are much more compact than that of Earth. These systems are also extremely diverse, covering a range of intrinsic properties. Studying the main physical processes at play in the innermost regions of the protoplanetary discs is crucial to understanding how these planets form and migrate so close to their host. With GRAVITY, we focused on the study of near-infrared emission of a sample of young intermediatemass stars, the Herbig Ae/Be stars.
The Messenger 178 – Quarter 4 | 2019 hole and are consistent with a small region of heated electr... more The Messenger 178 – Quarter 4 | 2019 hole and are consistent with a small region of heated electrons (a “hot spot”), moving in an orbit around the black hole. The GRAVITY observations also revealed changes in the polarisation angle over the course of the flare. In particular, as the centroid of the emission region completes one orbit around the black hole, the polarisation angle also makes a single loop. These polarisation measurements indicate the presence of a strong magnetic field in the immediate vicinity of the black hole and might indicate a magnetic origin of the flare. What’s next?
We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the... more We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the GRAVITY instrument on the European Southern Observatory Very Large Telescope Interferometer. The extensive baseline coverage from 5 to 60 Mλ allowed us to reconstruct a continuum image of the nucleus with an unrivaled 0.2 pc resolution in the K-band. We find a thin ring-like structure of emission with a radius r = 0.24 ± 0.03 pc, inclination i = 70 ± 5°, position angle PA = −50 ± 4°, and h/r < 0.14, which we associate with the dust sublimation region. The observed morphology is inconsistent with the expected signatures of a geometrically and optically thick torus. Instead, the infrared emission shows a striking resemblance to the 22 GHz maser disc, which suggests they share a common region of origin. The near-infrared spectral energy distribution indicates a bolometric luminosity of (0.4–4.7) × 1045 erg s−1, behind a large AK ≈ 5.5 (AV ≈ 90) screen of extinction that also appears to...
Context. The tip-tilt stabilisation system of the 1.8 m Auxiliary Telescopes of the Very Large Te... more Context. The tip-tilt stabilisation system of the 1.8 m Auxiliary Telescopes of the Very Large Telescope Interferometer was never dimensioned for robust fringe tracking, except when atmospheric seeing conditions are excellent. Aims. Increasing the level of wavefront correction at the telescopes is expected to improve the coupling into the single-mode fibres of the instruments, and enable robust fringe tracking even in degraded conditions. Methods. We deployed a new adaptive optics module for interferometry (NAOMI) on the Auxiliary Telescopes. Results. We present its design, performance, and effect on the observations that are carried out with the interferometric instruments.
We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT... more We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT/SPHERE during the SHINE exoplanet survey. The host is a B9.5V member of the Lower-Centaurus-Crux subgroup of the Scorpius Centaurus OB association. The measured angular separation of the companion (1.2705 ± 0.0023”) corresponds to a projected distance of 159 ± 12 AU. We observed the target with the dual-band imaging and long-slit spectroscopy modes of the IRDIS imager to obtain its spectral energy distribution (SED) and astrometry. In addition, we reprocessed archival NACO L-band data, from which we also recover the companion. Its SED is consistent with a young (<30 Myr), low surface gravity object with a spectral type of M9γ ± 1. From comparison with the BT-Settl atmospheric models we estimate an effective temperature of Teff = 2600 ± 100 K, and comparison of the companion photometry to the COND evolutionary models yields a mass of ~29−37 MJ at the estimated age of 16−7+15 Myr for t...
Context. With an orbital distance comparable to that of Saturn in the solar system, β Pictoris b ... more Context. With an orbital distance comparable to that of Saturn in the solar system, β Pictoris b is the closest (semi-major axis ≃9 au) exoplanet that has been imaged to orbit a star. Thus it offers unique opportunities for detailed studies of its orbital, physical, and atmospheric properties, and of disk-planet interactions. With the exception of the discovery observations in 2003 with NaCo at the Very Large Telescope (VLT), all following astrometric measurements relative to β Pictoris have been obtained in the southwestern part of the orbit, which severely limits the determination of the planet’s orbital parameters. Aims. We aimed at further constraining β Pictoris b orbital properties using more data, and, in particular, data taken in the northeastern part of the orbit. Methods. We used SPHERE at the VLT to precisely monitor the orbital motion of beta β Pictoris b since first light of the instrument in 2014. Results. We were able to monitor the planet until November 2016, when it...
On a clear night, our home galaxy, the Milky Way, is visible as a starry ribbon across the sky. I... more On a clear night, our home galaxy, the Milky Way, is visible as a starry ribbon across the sky. Its core is located in the constellation of Sagittarius, approximately where the bright glow is interrupted by the darkest dust filaments. There, hidden, lies a massive black hole. To peer through the obscuring clouds and see the stars and gas near the black hole we use GRAVITY. The main GRAVITY results are the detection of gra- vitational redshift, the most precise mass- distance measurement, the test of the equivalence principle, and the detection of orbital motion near the black hole.
Ground-based and Airborne Instrumentation for Astronomy V, 2014
The instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), recently installed... more The instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), recently installed on the VLT-UT3, aims to detected and characterize giant extra-solar planets and the circumstellar environments in the very close vicinity of bright stars. The extreme brightness contrast and small angular separation between the planets or disks and their parent stars have so far proven very challenging. SPHERE will meet this challenge by using an extreme AO, stellar coronagraphs, an infrared dual band and polarimetric imager called IRDIS, an integral field spectrograph, and a visible polarimetric differential imager called ZIMPOL. Polarimetry allows a separation of the light coming from an unpolarized source such as a star and the polarized source such as a planet or protoplanetary disks. In this paper we present the performance of the infrared polarimetric imager based on experimental validations performed within SPHERE before the preliminary acceptance in Europe. We report on the level of instrumental polarization in the infrared and its calibration limit. Using differential polarimetry technique, we quantify the level of speckle suppression, and hence improved sensitivity in the context of imaging extended stellar environments.
Observing at high angular resolution from the ground is not made possible with Adaptive Optics al... more Observing at high angular resolution from the ground is not made possible with Adaptive Optics alone, and besides the turbulence residuals, atmospheric refraction, thermal background or instrument&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s mechanical flexures may also severely limit the gain of optical quality that AO techniques are supposed to provide. We describe here how NAOS, the newly installed AO system on the VLT, has been
Fundamental limitations of the concept of a laser reference star are reviewed: the wavefront meas... more Fundamental limitations of the concept of a laser reference star are reviewed: the wavefront measurement accuracy is discussed, Rayleigh, Mie and resonance backscattering link budgets are evaluated.
ABSTRACT The use of a Laser Guide Star (LGS) in an Adaptive Optics system in order to increase th... more ABSTRACT The use of a Laser Guide Star (LGS) in an Adaptive Optics system in order to increase the sky coverage, leads to a degradation of correction performances caused by the focus anisoplanatism, or cone effect, the LGS upward tilt indetermination and the defocusing produced by the non-constant altitude of the LGS. If the Adaptive Optics system has the typical configuration of a Shack-Hartmann wavefront sensor and a piezo-stack deformable mirror, a possible partial solution to solve the problem is to add a low order curvature wavefront sensor able to look at an off-axis a natural guide star close enough to the observed object. In fact the very low order modes (tip-tilt, defocus and astigmatism) are the most degraded by the LGS use but they have also the largest isoplanatic patch especially in the near infrared (H,K bands) wavelengths. With this configuration the Shack-Hartmann sensor provides the coefficients for the higher order modes while the curvature sensor provide the coefficients for the lower order ones. In this way the tilt and conical anisoplanatisms are partially reduced and there is also a continuos monitoring of the sodium layer altitude. Furthermore another aspect is the comparison of the performances at very faint magnitudes between a Shack-Hartmann and a low order curvature sensor in order to check if the reduced pupil sampling provides a better correction. In this framework a simulation work has been developed to study the coupling performances of a curvature sensor with a piezo-stack mirror; the code has been written in IDL.
In this paper, we simulate different possibilities to upgrade the Adaptive Optics Facility (AOF) ... more In this paper, we simulate different possibilities to upgrade the Adaptive Optics Facility (AOF) of the VLT, to reach the diffraction limit in the near infrared. We present simulations of Ground Layer AO, Laser Tomography AO, Multi-Conjugate AO, Dual AO and a hybrid system which is a simplified version of MCAO. We describe the strengths and weaknesses of each approach and summarize the studies to be still carried out.
The aim of the Multi-Conjugate Adap-tive Optics Demonstrator (MAD) is to correct for atmospheric ... more The aim of the Multi-Conjugate Adap-tive Optics Demonstrator (MAD) is to correct for atmospheric turbulence over a field of view which is much larger than the one typically covered by the exist-ing adaptive optics systems installed on 8-m-class telescopes. After a long period of ...
The 4LGSF is to be installed as a subsystem of the ESO Adaptive Optics Facility (AOF, [1]) on Uni... more The 4LGSF is to be installed as a subsystem of the ESO Adaptive Optics Facility (AOF, [1]) on Unit Telescope 4 (UT4) of the VLT, to provide the AO instruments GALACSI/MUSE and GRAAL/HAWK-I with four sodium laser guide stars. The 4LGSF will deploy four modular LGS Units at the UT4 Centrepiece. Two key aspects of the 4LGSF design are: (i) new industrial laser source (fibre lasers) with reduced volume, reduced need of maintenance, higher reliability, simpler operation and optimised spectral format for highly efficient sodium excitation, (ii) modular structure of the four LGS Units, composed of the laser and laser launch telescope, capable to operate independently of the others. The final design of the 4LGSF is now complete and the project has entered the manufacturing, assembly, integration and test phase. Furthermore, modular LGS units containing the laser emitter integrated on the launch telescope have already been demonstrated at ESO in the past years [2, 3]. We believe that having ...
More than 4000 exoplanets are known to date in systems that differ greatly from our Solar System.... more More than 4000 exoplanets are known to date in systems that differ greatly from our Solar System. In particular, inner exoplanets tend to follow orbits around their parent star that are much more compact than that of Earth. These systems are also extremely diverse, covering a range of intrinsic properties. Studying the main physical processes at play in the innermost regions of the protoplanetary discs is crucial to understanding how these planets form and migrate so close to their host. With GRAVITY, we focused on the study of near-infrared emission of a sample of young intermediatemass stars, the Herbig Ae/Be stars.
The Messenger 178 – Quarter 4 | 2019 hole and are consistent with a small region of heated electr... more The Messenger 178 – Quarter 4 | 2019 hole and are consistent with a small region of heated electrons (a “hot spot”), moving in an orbit around the black hole. The GRAVITY observations also revealed changes in the polarisation angle over the course of the flare. In particular, as the centroid of the emission region completes one orbit around the black hole, the polarisation angle also makes a single loop. These polarisation measurements indicate the presence of a strong magnetic field in the immediate vicinity of the black hole and might indicate a magnetic origin of the flare. What’s next?
We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the... more We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the GRAVITY instrument on the European Southern Observatory Very Large Telescope Interferometer. The extensive baseline coverage from 5 to 60 Mλ allowed us to reconstruct a continuum image of the nucleus with an unrivaled 0.2 pc resolution in the K-band. We find a thin ring-like structure of emission with a radius r = 0.24 ± 0.03 pc, inclination i = 70 ± 5°, position angle PA = −50 ± 4°, and h/r < 0.14, which we associate with the dust sublimation region. The observed morphology is inconsistent with the expected signatures of a geometrically and optically thick torus. Instead, the infrared emission shows a striking resemblance to the 22 GHz maser disc, which suggests they share a common region of origin. The near-infrared spectral energy distribution indicates a bolometric luminosity of (0.4–4.7) × 1045 erg s−1, behind a large AK ≈ 5.5 (AV ≈ 90) screen of extinction that also appears to...
Context. The tip-tilt stabilisation system of the 1.8 m Auxiliary Telescopes of the Very Large Te... more Context. The tip-tilt stabilisation system of the 1.8 m Auxiliary Telescopes of the Very Large Telescope Interferometer was never dimensioned for robust fringe tracking, except when atmospheric seeing conditions are excellent. Aims. Increasing the level of wavefront correction at the telescopes is expected to improve the coupling into the single-mode fibres of the instruments, and enable robust fringe tracking even in degraded conditions. Methods. We deployed a new adaptive optics module for interferometry (NAOMI) on the Auxiliary Telescopes. Results. We present its design, performance, and effect on the observations that are carried out with the interferometric instruments.
We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT... more We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT/SPHERE during the SHINE exoplanet survey. The host is a B9.5V member of the Lower-Centaurus-Crux subgroup of the Scorpius Centaurus OB association. The measured angular separation of the companion (1.2705 ± 0.0023”) corresponds to a projected distance of 159 ± 12 AU. We observed the target with the dual-band imaging and long-slit spectroscopy modes of the IRDIS imager to obtain its spectral energy distribution (SED) and astrometry. In addition, we reprocessed archival NACO L-band data, from which we also recover the companion. Its SED is consistent with a young (<30 Myr), low surface gravity object with a spectral type of M9γ ± 1. From comparison with the BT-Settl atmospheric models we estimate an effective temperature of Teff = 2600 ± 100 K, and comparison of the companion photometry to the COND evolutionary models yields a mass of ~29−37 MJ at the estimated age of 16−7+15 Myr for t...
Context. With an orbital distance comparable to that of Saturn in the solar system, β Pictoris b ... more Context. With an orbital distance comparable to that of Saturn in the solar system, β Pictoris b is the closest (semi-major axis ≃9 au) exoplanet that has been imaged to orbit a star. Thus it offers unique opportunities for detailed studies of its orbital, physical, and atmospheric properties, and of disk-planet interactions. With the exception of the discovery observations in 2003 with NaCo at the Very Large Telescope (VLT), all following astrometric measurements relative to β Pictoris have been obtained in the southwestern part of the orbit, which severely limits the determination of the planet’s orbital parameters. Aims. We aimed at further constraining β Pictoris b orbital properties using more data, and, in particular, data taken in the northeastern part of the orbit. Methods. We used SPHERE at the VLT to precisely monitor the orbital motion of beta β Pictoris b since first light of the instrument in 2014. Results. We were able to monitor the planet until November 2016, when it...
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Papers by N. Hubin