References of "Absil, Olivier"
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See detailExoplanet detection yield of a space-based Bracewell interferometer from small to medium satellites
Dandumont, Colin ULiege; Defrere, Denis ULiege; Kammerer, Jens et al

in Journal of Astronomical Telescopes, Instruments, and Systems (2020), 6(3),

Space-based nulling interferometry is one of the most promising solutions to spectrally characterize the atmosphere of rocky exoplanets in the mid-infrared (3 to 20  μm). It provides both high angular ... [more ▼]

Space-based nulling interferometry is one of the most promising solutions to spectrally characterize the atmosphere of rocky exoplanets in the mid-infrared (3 to 20  μm). It provides both high angular resolution and starlight mitigation. This observing capability depends on several technologies. A CubeSat (up to 20 kg) or a medium satellite (up to a few hundreds of kg), using a Bracewell architecture on a single spacecraft could be an adequate technological precursor to a larger, flagship mission. Beyond technical challenges, the scientific return of such a small-scale mission needs to be assessed. We explore the exoplanet science cases for various missions (several satellite configurations and sizes). Based on physical parameters (diameter and wavelength) and thanks to a state-of-the-art planet population synthesis tool, the performance and the possible exoplanet detection yield of these configurations are presented. Without considering platform stability constraints, a CubeSat (baseline of b  ≃  1  m and pupils diameter of D  ≃  0.1  m) could detect ≃7 Jovian exoplanets, a small satellite (b  ≃  5  m  /  D  ≃  0.25  m) ≃120 exoplanets, whereas a medium satellite (b  ≃  12.5  m  /  D  ≃  0.5  m) could detect ∼250 exoplanets including 51 rocky planets within 20 pc. To complete our study, an analysis of the platform stability constraints (tip/tilt and optical path difference) is performed. Exoplanet studies impose very stringent requirements on both tip/tilt and OPD control. [less ▲]

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See detailDesign, pointing control, and on-sky performance of the mid-infrared vortex coronagraph for the VLT/NEAR experiment
Maire, Anne-Lise ULiege; Huby, Elsa; Absil, Olivier ULiege et al

in Journal of Astronomical Telescopes, Instruments, and Systems (2020), 6

Vortex coronagraphs have been shown to be a promising avenue for high- contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design ... [more ▼]

Vortex coronagraphs have been shown to be a promising avenue for high- contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of the mid-infrared extremely large telescope imager and spectrograph. To ensure good performance of these coronagraphs, a precise control of the centering of the star image in real time is needed. We previously developed and validated the quadrant analysis of coronagraphic images for tip-tilt sensing estimator (QACITS) pointing estimator to address this issue. While this approach is not wavelength-dependent in theory, it was never implemented for mid-IR observations, which leads to specific challenges and limitations. Here, we present the design of the mid-IR vortex coronagraph for the "new Earths in the α Cen Region (NEAR) experiment with the Very Large Telescope (VLT)/Very Large Telescope imager and spectrometer for the mid-infrared (VISIR) instrument and assess the performance of the QACITS estimator for the centering control of the star image onto the vortex coronagraph. We use simulated data and on-sky data obtained with VLT/VISIR, which was recently upgraded for observations assisted by adaptive optics in the context of the NEAR experiment. We demonstrate that the QACITS-based correction loop is able to control the centering of the star image onto the NEAR vortex coronagraph with a stability down to 0.015 λ / D rms over 4 h in good conditions. These results show that QACITS is a robust approach for precisely controlling in real time the centering of vortex coronagraphs for mid-IR observations. [less ▲]

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See detailExocomets: A spectroscopic survey
Rebollido, I.; Eiroa, C.; Montesinos, B. et al

in Astronomy and Astrophysics (2020), 639

Context. While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events, which are interpreted to be exocomets ... [more ▼]

Context. While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events, which are interpreted to be exocomets (falling evaporating bodies) around β Pic in the early 1980s, only ∼20 stars have been reported to host exocomet-like events. <BR /> Aims: We aim to expand the sample of known exocomet-host stars, as well as to monitor the hot-gas environment around stars with previously known exocometary activity. <BR /> Methods: We have obtained high-resolution optical spectra of a heterogeneous sample of 117 main-sequence stars in the spectral type range from B8 to G8. The data were collected in 14 observing campaigns over the course of two years from both hemispheres. We analysed the Ca II K&H and Na I D lines in order to search for non-photospheric absorptions that originated in the circumstellar environment and for variable events that could be caused by the outgassing of exocomet-like bodies. <BR /> Results: We detected non- photospheric absorptions towards 50% of the sample, thus attributing a circumstellar origin to half of the detections (i.e. 26% of the sample). Hot circumstellar gas was detected in the metallic lines inspected via narrow stable absorptions and/or variable blue- and red-shifted absorption events. Such variable events were found in 18 stars in the Ca II and/or Na I lines; six of them are reported in the context of this work for the first time. In some cases, the variations we report in the Ca II K line are similar to those observed in β Pic. While we do not find a significant trend in the age or location of the stars, we do find that the probability of finding CS gas in stars with larger v sin i is higher. We also find a weak trend with the presence of near-infrared excess and with anomalous (λ Boo-like) abundances, but this would require confirmation by expanding the sample. <P />Table C.1 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/639/A11">http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/639/A11</A> [less ▲]

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See detailSPHERE+: Imaging young Jupiters down to the snowline
Boccaletti, A.; Chauvin, G.; Mouillet, D. et al

E-print/Working paper (2020)

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating ... [more ▼]

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating modes, primarily in the field of direct imaging of exoplanetary systems, focusing on exoplanets as point sources and circumstellar disks as extended objects. The achievements obtained thus far with SPHERE (~200 refereed publications) in different areas (exoplanets, disks, solar system, stellar physics...) have motivated a large consortium to propose an even more ambitious set of science cases, and its corresponding technical implementation in the form of an upgrade. The SPHERE+ project capitalizes on the expertise and lessons learned from SPHERE to push high contrast imaging performance to its limits on the VLT 8m-telescope. The scientific program of SPHERE+ described in this document will open a new and compelling scientific window for the upcoming decade in strong synergy with ground-based facilities (VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and WFIRST). While SPHERE has sampled the outer parts of planetary systems beyond a few tens of AU, SPHERE+ will dig into the inner regions around stars to reveal and characterize by mean of spectroscopy the giant planet population down to the snow line. Building on SPHERE's scientific heritage and resounding success, SPHERE+ will be a dedicated survey instrument which will strengthen the leadership of ESO and the European community in the very competitive field of direct imaging of exoplanetary systems. With enhanced capabilities, it will enable an even broader diversity of science cases including the study of the solar system, the birth and death of stars and the exploration of the inner regions of active galactic nuclei. [less ▲]

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See detailA dusty benchmark brown dwarf near the ice line of HD 72946
Maire, Anne-Lise ULiege; Baudino, J.-L.; Desidera, S. et al

in Astronomy and Astrophysics (2020), 633

Context. HD 72946 is a bright and nearby solar-type star hosting a low- mass companion at long period (P ̃ 16 yr) detected with the radial velocity (RV) method. The companion has a minimum mass of 60.4 ± ... [more ▼]

Context. HD 72946 is a bright and nearby solar-type star hosting a low- mass companion at long period (P ̃ 16 yr) detected with the radial velocity (RV) method. The companion has a minimum mass of 60.4 ± 2.2 M[SUB]J[/SUB] and might be a brown dwarf. Its expected semi-major axis of ̃243 mas makes it a suitable target for further characterization with high-contrast imaging, in particular to measure its inclination, mass, and spectrum and thus definitely establish its substellar nature. <BR /> Aims: We aim to further characterize the orbit, atmosphere, and physical nature of HD 72946B. <BR /> Methods: We present high-contrast imaging data in the near-infrared with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. We also use proper motion measurements of the star from HIPPARCOS and Gaia. <BR /> Results: The SPHERE data reveal a point source with a contrast of ̃9 mag at a projected separation of ̃235 mas. No other point sources are detected in the field of view. By jointly fitting the RV, imaging, and proper motion data, we constrain all the orbital parameters of HD 72946B and assess a dynamical mass of 72.4 ± 1.6 M[SUB]J[/SUB] and a semi-major axis of 6.456.45[SUP]+0.08[/SUP][SUB]-0.07[/SUB] au. Empirical comparison of its SPHERE spectrum to template dwarfs indicates a spectral type of L5.0 ± 1.5. The J-H3 color is close to the expectations of the DUSTY models and suggests a cloudy atmosphere. Comparison with atmospheric models of the spectrophotometry suggests an effective temperature of ̃1700 K. The bolometric luminosity (log(L/L[SUB]☉[/SUB]) = -4.11 ± 0.10 dex) and dynamical mass of HD 72946B are more compatible with evolutionary models for an age range of ̃0.9-3 Gyr. The formation mechanism of the companion is currently unclear as the object appears slightly away from the bulk of model predictions. HD 72946B is currently the closest benchmark brown dwarf companion to a solar-type star with imaging, RV, and proper motion measurements. <P />Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 0102.C-0781. [less ▲]

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See detailMachine learning for image-based wavefront sensing
Vanberg, Pierre-Olivier; Orban De Xivry, Gilles ULiege; Absil, Olivier ULiege et al

Conference (2019, December 14)

High-contrast imaging systems in ground-based astronomy rely on a precise control of the wavefront. On one hand, atmospheric turbulence distorts the wavefront which is corrected by a dedicated adaptive ... [more ▼]

High-contrast imaging systems in ground-based astronomy rely on a precise control of the wavefront. On one hand, atmospheric turbulence distorts the wavefront which is corrected by a dedicated adaptive optics system. On the other hand, non-common path aberrations between wavefront sensor and scientific paths can also overwhelm a putative scientific signal and need to be corrected. Hence, measuring precisely the wavefront at the scientific focal plane is of prime interest for applications such as direct imaging of exoplanets. While early attempts using neural networks showed some successful results, the latest advances in machine learning have yet to be fully exploited for the problem of focal plane wavefront sensing. In this paper, we explore the use of convolution neural networks to perform image-based wavefront sensing. Based on simulated data, we evaluate neural architectures on two different data sets, one with only low order aberrations (20 Zernike modes) and one including higher orders modes (100 Zernike modes). We discuss the accuracy reached in both cases, and we show that direct phase map reconstruction outperforms classical modal approaches. The precision achieved ranges typically between 1% and 10% of the injected wavefront. Finally, we explore the impact of phase diversity, and we compare our optimized CNN model to a standard iterative phase retrieval algorithm. [less ▲]

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See detailImaging Extrasolar Planetary Systems
Absil, Olivier ULiege

Scientific conference (2019, December 13)

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See detailNEAR: First Results from the Search for Low-Mass Planets in α Cen
Kasper, Markus; Arsenault, Robin; Käufl, Ulli et al

in Messenger (2019), 178

ESO, in collaboration with the Breakthrough Initiatives, has modified the VLT mid-infrared imager VISIR to greatly enhance its ability as a planet finder. It has conducted a 100-hour observing campaign to ... [more ▼]

ESO, in collaboration with the Breakthrough Initiatives, has modified the VLT mid-infrared imager VISIR to greatly enhance its ability as a planet finder. It has conducted a 100-hour observing campaign to search for low-mass planets around both components of the binary a Centauri, part of the closest stellar system to the Earth. Using adaptive optics and high-performance coronagraphy, the instrument reached unprecedented contrast and sensitivity allowing it to see Neptune-sized planets in the habitable zone, if present. The experiment allowed us to characterise the current limitations of the instrument. We conclude that the detection of rocky planets similar to Earth in the habitable zone of the a Centauri System is already possible with 8-metre-class telescopes in the thermal infrared. [less ▲]

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See detailTechnological challenges for the Large Interferometer For Exoplanets (LIFE)
Defrere, Denis ULiege; Quanz, Sascha; Absil, Olivier ULiege et al

Scientific conference (2019, November 04)

LIFE is a project initiated in 2017 and officially kicked-off in 2019 to develop the science, technology and a roadmap for an ambitious space mission that will allow mankind for the first time to detect ... [more ▼]

LIFE is a project initiated in 2017 and officially kicked-off in 2019 to develop the science, technology and a roadmap for an ambitious space mission that will allow mankind for the first time to detect and characterize the atmospheres of dozens of warm, terrestrial extrasolar planets. Thanks to NASA's Kepler mission and dedicated, long-term exoplanet searches from the ground, we know that rocky exoplanets are ubiquitous in the Milky Way and very likely also in the immediate Solar neighbourhood. Detecting these nearest planets, understanding the (atmospheric) diversity of other worlds and searching for indications of habitability and biological activity is a cornerstone of 21st century astrophysics and will provide us a new perspective on our place in this Universe. After a brief introduction on the scientific objectives, we present in this talk the recent technology developments required for LIFE and present the main technological challenges to tackle before launching such a mission. [less ▲]

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See detailThe game-changing promises of ELT/METIS for exoplanet imaging
Absil, Olivier ULiege

Poster (2019, October 21)

METIS, the mid-infrared ELT imager and spectrograph, is one of the three first-generation instruments of the Extremely Large Telescope. It recently passed its preliminary design review, and is expected to ... [more ▼]

METIS, the mid-infrared ELT imager and spectrograph, is one of the three first-generation instruments of the Extremely Large Telescope. It recently passed its preliminary design review, and is expected to see first light in 2027. Specifically designed to deliver high-contrast imaging capabilities, METIS features advanced coronagraphic concepts such as a ring-apodized vortex coronagraph and an apodizing phase plate. It also comprises a high-resolution (R=100,000) integral field spectrograph covering wavelengths from 3 to 5 µm, which can be combined with the coronagraphic observing modes. Using the full resolving power of the ELT thanks to a high-performance adaptive optics module, METIS promises to reach game-changing performance in the field of exoplanet imaging. In this talk, I will review the design and expected performance of METIS high-contrast imaging modes. I will then describe some of the most appealing science cases that will be addressed by METIS in the field of exoplanet imaging, including the possible discovery of temperate rocky planets in the alpha Centauri system, the high-spectral resolution study of Proxima b, or the spectral characterization of exoplanets discovered by radial velocities or astrometry (Gaia follow-up). I will conclude this talk by decribing our plans to deploy machine learning techniques in the operation and data analysis of the METIS high contrast imaging modes. [less ▲]

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See detailThe Potential of Exozodiacal Disks Observations with the WFIRST Coronagraph Instrument
Mennesson, B.; Bailey, V.; Kasdin, J. et al

E-print/Working paper (2019)

The Wide Field Infrared Survey Telescope (WFIRST) Coronagraph Instrument (CGI) will be the first high-performance stellar coronagraph using active wavefront control for deep starlight suppression in space ... [more ▼]

The Wide Field Infrared Survey Telescope (WFIRST) Coronagraph Instrument (CGI) will be the first high-performance stellar coronagraph using active wavefront control for deep starlight suppression in space, providing unprecedented levels of contrast, spatial resolution, and sensitivity for astronomical observations in the optical. One science case enabled by the CGI will be taking images and(R~50)spectra of faint interplanetary dust structures present in the habitable zone of nearby sunlike stars (~10 pc) and within the snow-line of more distant ones(~20pc), down to dust density levels commensurate with that of the solar system zodiacal cloud. Reaching contrast levels below~10-7 for the first time, CGI will cross an important threshold in debris disks physics, accessing disks with low enough optical depths that their structure is dominated by transport phenomena than collisions. Hence, CGI results will be crucial for determining how exozodiacal dust grains are produced and transported in low-density disks around mature stars. Additionally, CGI will be able to measure the brightness level and constrain the degree of asymmetry of exozodiacal clouds around individual nearby sunlike stars in the optical, at the ~10x solar zodiacal emission level. This information will be extremely valuable for optimizing the observational strategy of possible future exo-Earth direct imaging missions, especially those planning to operate at optical wavelengths, such as Habitable Exoplanet Observatory (HabEx) and the Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR). <P /> [less ▲]

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See detailHR 10: a main-sequence binary with circumstellar envelopes around both components. Discovery and analysis
Montesinos, B.; Eiroa, C.; Lillo-Box, J. et al

in Astronomy and Astrophysics (2019), 629

Context. This paper is framed within a large project devoted to studying the presence of circumstellar material around main sequence stars, and looking for exocometary events. The work concentrates on HR ... [more ▼]

Context. This paper is framed within a large project devoted to studying the presence of circumstellar material around main sequence stars, and looking for exocometary events. The work concentrates on HR 10 (A2 IV/V), known for its conspicuous variability in the circumstellar narrow absorption features of Ca II K and other lines, so far interpreted as β Pic-like phenomena, within the falling evaporating body scenario. <BR /> Aims: The main goal of this paper is to carry out a thorough study of HR 10 to find the origin of the observed variability, determine the nature of the star, its absolute parameters, and evolutionary status. <BR /> Methods: Interferometric near-infrared (NIR) observations, multi-epoch high-resolution optical spectra spanning a time baseline of more than 32 yr, and optical and NIR photometry, together with theoretical modelling, were used to tackle the above objectives. <BR /> Results: Our results reveal that HR 10 is a binary. The narrow circumstellar absorption features superimposed on the photospheric Ca II K lines - and lines of other species - can be decomposed into two or more components, the two deep ones tracing the radial velocity of the individual stars, which implies that their origin cannot be ascribed to transient exocometary events, their variability being fully explained by the binarity of the object. There does not appear to be transient events associated with potential exocomets. Each individual star holds its own circumstellar shell and there are no traces of a circumbinary envelope. Finally, the combined use of the interferometric and radial velocity data leads to a complete spectrometric and orbital solution for the binary, the main parameters being: an orbital period of 747.6 days, eccentricities of the orbits around the centre of mass 0.25 (HR 10-A), 0.21 (HR 10-B) and a mass ratio of q = M[SUB]B[/SUB]/M[SUB]A[/SUB] = 0.72-0.84. The stars are slightly off the main sequence, the binary being 530 Myr old. <P />Partially based on observations obtained with PIONIER/VLT (ESO, Paranal, Chile), FIES/NOT, HERMES/Mercator, HARPS-N/TNG and UES/WHT (La Palma, Spain), FEROS/2.2-m ESO-MPIA (La Silla, Chile), CS21/Harlan J. Smith Telescope (McDonald Observatory, US) and UHRF/3.6-m AAT (Anglo Australian Observatory), and archival data from HARPS/3.6-m ESO and UVES/VLT (ESO archive), and HIRES/Keck 1 (Keck archive). [less ▲]

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See detailAtmospheric characterization of terrestrial exoplanets in the mid-infared: biosignatures, habitability & diversity
Quanz, Sascha P.; Absil, Olivier ULiege; Angerhausen, Daniel et al

E-print/Working paper (2019)

Exoplanet science is one of the most thriving fields of modern astrophysics. A major goal is the atmospheric characterization of dozens of small, terrestrial exoplanets in order to search for signatures ... [more ▼]

Exoplanet science is one of the most thriving fields of modern astrophysics. A major goal is the atmospheric characterization of dozens of small, terrestrial exoplanets in order to search for signatures in their atmospheres that indicate biological activity, assess their ability to provide conditions for life as we know it, and investigate their expected atmospheric diversity. None of the currently adopted projects or missions, from ground or in space, can address these goals. In this White Paper we argue that a large space-based mission designed to detect and investigate thermal emission spectra of terrestrial exoplanets in the MIR wavelength range provides unique scientific potential to address these goals and surpasses the capabilities of other approaches. While NASA might be focusing on large missions that aim to detect terrestrial planets in reflected light, ESA has the opportunity to take leadership and spearhead the development of a large MIR exoplanet mission within the scope of the "Voyage 2050'' long-term plan establishing Europe at the forefront of exoplanet science for decades to come. Given the ambitious science goals of such a mission, additional international partners might be interested in participating and contributing to a roadmap that, in the long run, leads to a successful implementation. A new, dedicated development program funded by ESA to help reduce development and implementation cost and further push some of the required key technologies would be a first important step in this direction. Ultimately, a large MIR exoplanet imaging mission will be needed to help answer one of mankind's most fundamental questions: "How unique is our Earth?'' [less ▲]

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See detailDevelopment of a space-based nulling interferometer to detect and characterize exoplanets
Schifano, Luca; Defrere, Denis ULiege; Absil, Olivier ULiege et al

in Proceedings of SPIE: The International Society for Optical Engineering (2019, July 12)

The development of small space-based platforms for nulling interferometric observations could be the pathfinder of a new era in exoplanetology. While planetary transit and radial velocity are the most ... [more ▼]

The development of small space-based platforms for nulling interferometric observations could be the pathfinder of a new era in exoplanetology. While planetary transit and radial velocity are the most productive ways to detect exoplanets, such techniques are indirect detections. For deeper characterization of exoplanets, direct detection techniques should be developed. By injecting direct light coming from exoplanets into spectrometers, we could study their chemical composition, search for biosignatures, and possibly infer the presence of life. The low number of photons to be gathered from the planets, high contrast with the star and small angular resolution are the major difficulties for a direct detection. However, nulling interferometry seems to be a solution to tackle these challenges. By combining the light of two or more telescopes, we would considerably increase the angular resolution, and thus could potentially lead to the detection of Earth-size rocky exoplanets around Solar-type stars. Moreover, with a π- phase shift between the two interferometer arms, the starlight is reduced which allows the detection of much fainter objects around the star. In this paper it will be presented the development of a new mission based on nulling interferometry and dedicated to the Alpha Centauri system. As our nearest stellar system, it is a prime target to investigate for the research of new worlds. Monte-Carlo simulations about potential exoplanet yield of such an interferometer will be described, for different assumptions such as the detection wavelength and telescope size. Single-mode fibers and integrated optics will also be investigated for this mission. This could lead to low-cost type missions with a high potential of scientific return. [less ▲]

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See detailSeparating extended disc features from the protoplanet in PDS 70 using VLT/SINFONI
Christiaens, V.; Casassus, S.; Absil, Olivier ULiege et al

in Monthly Notices of the Royal Astronomical Society (2019), 486

Transition discs are prime targets to look for protoplanets and study planet-disc interactions. We present VLT/SINFONI observations of PDS 70, a transition disc with a recently claimed embedded ... [more ▼]

Transition discs are prime targets to look for protoplanets and study planet-disc interactions. We present VLT/SINFONI observations of PDS 70, a transition disc with a recently claimed embedded protoplanet. We take advantage of the angular and spectral diversity present in our data for an optimal PSF modelling and subtraction using principal component analysis (PCA). We report the redetection of PDS 70 b, both the front and far side of the outer disc edge, and the detection of several extended features in the annular gap. We compare spectral differential imaging applied before (PCA-SADI), and after (PCA-ASDI) angular differential imaging. Our tests suggest that PCA-SADI better recovers extended features, while PCA-ASDI is more sensitive to point sources. We adapted the negative fake companion (NEGFC) technique to infer the astrometry of the companion, and derived r = 193.5 ± 4.9 mas and PA =158.7[SUP]°[/SUP] ± 3.0[SUP]°[/SUP]. We used both NEGFC and ANDROMEDA to infer the K-band spectro-photometry of the protoplanet, and found results consistent with recent VLT/SPHERE observations, except for their 2018/02 epoch measurement in the K2 filter. Finally, we derived an upper limit of \dot{M_b} < 1.26 × 10^{-7} \big [ 5 M_Jup/M_b \big ] \big [ R_b/R_Jup\big ] M_Jup yr[SUP]-1[/SUP] for the accretion rate of the companion based on an adaptation of PCA-SADI/PCA-ASDI around the Brγ line (assuming no extinction). [less ▲]

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See detailExoplanet Characterization with the VLTI
Defrere, Denis ULiege; Ireland, Michael; Martinache, Frantz et al

Scientific conference (2019, June 20)

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See detailThe METIS high contrast imaging modes: concept, performance, and perspectives
Absil, Olivier ULiege; Kenworthy, Matthew; Carlomagno, Brunella ULiege et al

Conference (2019, June 10)

METIS is one of the three scientific first-generation instruments for the ELT. Its main science goals are focused on exo-planetary systems, including the study of rocky planets around nearby stars. To ... [more ▼]

METIS is one of the three scientific first-generation instruments for the ELT. Its main science goals are focused on exo-planetary systems, including the study of rocky planets around nearby stars. To enable key METIS science cases, high-contrast imaging (HCI) is at the heart of the instrument. Here, we review the concept and design of the METIS HCI modes as presented at the METIS Preliminary Design Review in May 2019. We present the expected performance of METIS HCI based on end-to-end simulations, and discuss the influence of various instrumental effects, including AO-related effects (influence of atmospheric parameters, lag, petal piston, etc). We also discuss our baseline strategy for the measurement and correction of non-common path aberrations (NCPA). Finally, we discuss the perspective of using advanced wavefront measurement and control to improve the METIS HCI performance, including the application of machine learning techniques to the correction of NCPA and to AO predictive control. [less ▲]

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See detailEvidence for a circumplanetary disc around protoplanet PDS 70 b
Christiaens, V.; Cantalloube, F.; Casassus, S. et al

in Astrophysical Journal. Letters (2019), 877

We present the first observational evidence for a circumplanetary disc around the protoplanet PDS 70b, based on a new spectrum in the $K$ band acquired with VLT/SINFONI. We tested three hypotheses to ... [more ▼]

We present the first observational evidence for a circumplanetary disc around the protoplanet PDS 70b, based on a new spectrum in the $K$ band acquired with VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric emission from the planet with either (1) a single value of extinction or (2) variable extinction, and (3) a combined atmospheric and circumplanetary disc model. Goodness-of-fit indicators favour the third option suggesting circumplanetary material contributing excess thermal emission --- most prominent at $2.3 \mu$m. Inferred accretion rates ($ 10^-7.8$--$10^-7.3 M_J$ yr$^-1$) are compatible with observational constraints based on the H$\alpha$ and Br$\gamma$ lines. For the planet, we derive an effective temperature of 1500--1600 K, surface gravity $\log(g) 4.0$, radius $ 1.6 R_J$, mass $ 10 M_J$ and possible thick clouds. Models with variable extinction lead to slightly worse fits. However, the amplitude ($\Delta A_V 3$mag) and timescale of variation ($\lesssim$ years) required for the extinction would also suggest circumplanetary material. [less ▲]

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See detailSimultaneous detection and characterisation of exoplanets using machine learning
Nath, Rakesh ULiege; Absil, Olivier ULiege

Scientific conference (2019, May 27)

Can we understand exoplanets better if we use both high res spectra and direct images in a machine learning pipeline?

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See detailSTIM map: detection map for exoplanets imaging beyond asymptotic Gaussian residual speckle noise
Pairet, Benoît; Cantalloube, Faustine; Gomez Gonzalez, Carlos A. et al

in Monthly Notices of the Royal Astronomical Society (2019), 487

Direct imaging of exoplanets is a challenging task as it requires to reach a high contrast at very close separation to the star. Today, the main limitation in the high-contrast images is the quasi-static ... [more ▼]

Direct imaging of exoplanets is a challenging task as it requires to reach a high contrast at very close separation to the star. Today, the main limitation in the high-contrast images is the quasi-static speckles that are created by residual instrumental aberrations. They have the same angular size as planetary companions and are often brighter, hence hindering our capability to detect exoplanets. Dedicated observation strategies and signal processing techniques are necessary to disentangle these speckles from planetary signals. The output of these methods is a detection map in which the value of each pixel is related to a probability of presence of a planetary signal. The detection map found in the literature relies on the assumption that the residual noise is Gaussian. However, this is known to lead to higher false positive rates, especially close to the star. In this paper, we re-visit the notion of detection map by analysing the speckle noise distribution, namely the Modified Rician distribution. We use non-asymptotic analysis of the sum of random variables to show that the tail of the distribution of the residual noise decays as an exponential distribution, hence explaining the high false detection rate obtained with the Gaussian assumption. From this analysis, we introduce a novel time domain detection map and we demonstrate its capabilities and the relevance of our approach through experiments on real data. We also provide an empirical rule to determine detection threshold providing a good trade-off between true positive and false positive rates for exoplanet detection. [less ▲]

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