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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.
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.
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.

Table C.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/639/A11 [less ▲]Detailed reference viewed: 36 (1 ULiège) SPHERE+: Imaging young Jupiters down to the snowlineBoccaletti, A.; Chauvin, G.; Mouillet, D. et alE-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 ▲]Detailed reference viewed: 25 (1 ULiège) A dusty benchmark brown dwarf near the ice line of HD 72946Maire, Anne-Lise ; Baudino, J.-L.; Desidera, S. et alin Astronomy and Astrophysics (2020), 633Context. 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.
Aims: We aim to further characterize the orbit, atmosphere, and physical nature of HD 72946B.
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.
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.

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 ▲]Detailed reference viewed: 23 (1 ULiège) Atmospheric characterization of terrestrial exoplanets in the mid-infared: biosignatures, habitability & diversityQuanz, Sascha P.; Absil, Olivier ; Angerhausen, Daniel et alE-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 ▲]Detailed reference viewed: 47 (13 ULiège) Development of a space-based nulling interferometer to detect and characterize exoplanetsSchifano, Luca; Defrere, Denis ; Absil, Olivier et alin 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 ▲]Detailed reference viewed: 49 (7 ULiège) Separating extended disc features from the protoplanet in PDS 70 using VLT/SINFONIChristiaens, V.; Casassus, S.; Absil, Olivier et alin Monthly Notices of the Royal Astronomical Society (2019), 486Transition 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 ▲]Detailed reference viewed: 34 (3 ULiège) Exoplanet Characterization with the VLTIDefrere, Denis ; Ireland, Michael; Martinache, Frantz et alScientific conference (2019, June 20)Detailed reference viewed: 28 (2 ULiège) The METIS high contrast imaging modes: concept, performance, and perspectivesAbsil, Olivier ; Kenworthy, Matthew; Carlomagno, Brunella et alConference (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 ▲]Detailed reference viewed: 31 (0 ULiège) Evidence for a circumplanetary disc around protoplanet PDS 70 bChristiaens, V.; Cantalloube, F.; Casassus, S. et alin Astrophysical Journal. Letters (2019), 877We 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 ▲]Detailed reference viewed: 17 (4 ULiège) Simultaneous detection and characterisation of exoplanets using machine learningNath, Rakesh ; Absil, Olivier 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?Detailed reference viewed: 38 (3 ULiège) STIM map: detection map for exoplanets imaging beyond asymptotic Gaussian residual speckle noisePairet, Benoît; Cantalloube, Faustine; Gomez Gonzalez, Carlos A. et alin Monthly Notices of the Royal Astronomical Society (2019), 487Direct 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 ▲]Detailed reference viewed: 13 (3 ULiège)