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See detailThe VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits. IV. Gravitational instability rarely forms wide, giant planets
Vigan, A.; Bonavita, M.; Biller, B. et al

in Astronomy and Astrophysics (2017), 603

Understanding the formation and evolution of giant planets (≥1 M[SUB]Jup[/SUB]) at wide orbital separation (≥5 AU) is one of the goals of direct imaging. Over the past 15 yr, many surveys have placed ... [more ▼]

Understanding the formation and evolution of giant planets (≥1 M[SUB]Jup[/SUB]) at wide orbital separation (≥5 AU) is one of the goals of direct imaging. Over the past 15 yr, many surveys have placed strong constraints on the occurrence rate of wide-orbit giants, mostly based on non-detections, but very few have tried to make a direct link with planet formation theories. In the present work, we combine the results of our previously published VLT/NaCo large program with the results of 12 past imaging surveys to constitute a statistical sample of 199 FGK stars within 100 pc, including three stars with sub-stellar companions. Using Monte Carlo simulations and assuming linear flat distributions for the mass and semi-major axis of planets, we estimate the sub-stellar companion frequency to be within 0.75-5.70% at the 68% confidence level (CL) within 20-300 AU and 0.5-75 M[SUB]Jup[/SUB], which is compatible with previously published results. We also compare our results with the predictions of state-of-the-art population synthesis models based on the gravitational instability (GI) formation scenario with and without scattering. We estimate that in both the scattered and non-scattered populations, we would be able to detect more than 30% of companions in the 1-75 M[SUB]Jup[/SUB] range (95% CL). With the threesub-stellar detections in our sample, we estimate the fraction of stars that host a planetary system formed by GI to be within 1.0-8.6% (95% CL). We also conclude that even though GI is not common, it predicts a mass distribution of wide-orbit massive companions that is much closer to what is observed than what the core accretion scenario predicts. Finally, we associate the present paper with the release of the Direct Imaging Virtual Archive (DIVA), a public database that aims at gathering the results of past, present, and future direct imaging surveys. Based on observations collected at the European Southern Observatory, Chile (ESO Large Program 184.C-0157 and Open Time 089.C-0137A and 090.C-0252A). [less ▲]

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See detailThe VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits . III. The frequency of brown dwarfs and giant planets as companions to solar-type stars
Reggiani, Maddalena ULg; Meyer, M. R.; Chauvin, G. et al

in Astronomy and Astrophysics (2016), 586

Context. In recent years there have been many attempts to characterize the occurrence and distribution of stellar, brown dwarf (BD), and planetary-mass companions to solar-type stars with the aim of ... [more ▼]

Context. In recent years there have been many attempts to characterize the occurrence and distribution of stellar, brown dwarf (BD), and planetary-mass companions to solar-type stars with the aim of constraining formation mechanisms. From radial velocity observations a dearth of companions with masses between 10-40 M[SUB]Jupiter[/SUB] has been noticed at close separations, suggesting the possibility of a distinct formation mechanism for objects above and below this range. <BR /> Aims: We present a model for the substellar companion mass function (CMF). This model consists of the superposition of the planet and BD companion mass distributions, assuming that we can extrapolate the radial velocity measured CMF for planets to larger separations and the stellar companion mass-ratio distribution over all separations into the BD mass regime. By using both the results of the VLT/NaCo large program (NaCo-LP) and the complementary archive datasets, which probe the occurrence of planets and BDs on wide orbits around solar-type stars, we place some constraints on the planet and BD distributions. <BR /> Methods: We developed a Monte Carlo simulation tool to predict the outcome of a given survey, depending on the shape of the orbital parameter distributions (mass, semimajor axis, eccentricity, and inclination). Comparing the predictions with the results of the observations, we calculate the likelihood of different models and which models can be ruled out. <BR /> Results: Current observations are consistent with the proposed model for the CMF, as long as a sufficiently small outer truncation radius (≲100 AU) is introduced for the planet separation distribution. Some regions of parameter space can be excluded by the observations. <BR /> Conclusions: We conclude that the results of the direct imaging surveys searching for substellar companions around Sun-like stars are consistent with a combined substellar mass spectrum of planets and BDs. This mass distribution has a minimum between 10 and 50 M[SUB]Jupiter[/SUB], in agreement with radial velocity measurements. In this picture the dearth of objects in this mass range would naturally arise from the shape of the mass distribution, without the introduction of any distinct formation mechanism for BDs. This kind of model for the CMF allows us to determine the probability for a substellar companion as a function of mass to have formed in a disk or from protostellar core fragmentation, as such mechanisms overlap in this mass range. Based on observations collected at the European Southern Observatory, Chile (ESO Large Program 184.C-0157 and Open Time 089.C-0137A and 090.C-0252A). [less ▲]

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See detailThe VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits. II. Survey description, results, and performances
Chauvin, G.; Vigan, A.; Bonnefoy, M. et al

in Astronomy and Astrophysics (2015), 573

Context. Young, nearby stars are ideal targets for direct imaging searches for giant planets and brown dwarf companions. After the first-imaged planet discoveries, vast efforts have been devoted to the ... [more ▼]

Context. Young, nearby stars are ideal targets for direct imaging searches for giant planets and brown dwarf companions. After the first-imaged planet discoveries, vast efforts have been devoted to the statistical analysis of the occurence and orbital distributions of giant planets and brown dwarf companions at wide (≥5-6 AU) orbits. <BR /> Aims: In anticipation of the VLT/SPHERE planet-imager, guaranteed-time programs, we have conducted a preparatory survey of 86 stars between 2009 and 2013 to identify new faint comoving companions to ultimately analyze the occurence of giant planets and brown dwarf companions at wide (10-2000 AU) orbits around young, solar-type stars. <BR /> Methods: We used NaCo at VLT to explore the occurrence rate of giant planets and brown dwarfs between typically 0.1 and 8''. Diffraction-limited observations in H-band combined with angular differential imaging enabled us to reach primary star-companion brightness ratios as small as 10[SUP]-6[/SUP] at 1.5''. Repeated observations at several epochs enabled us to discriminate comoving companions from background objects. <BR /> Results: During our survey, twelve systems were resolved as new binaries, including the discovery of a new white dwarf companion to the star HD 8049. Around 34 stars, at least one companion candidate was detected in the observed field of view. More than 400 faint sources were detected; 90% of them were in four crowded fields. With the exception of HD 8049 B, we did not identify any new comoving companions. The survey also led to spatially resolved images of the thin debris disk around HD 61005 that have been published earlier. Finally, considering the survey detection limits, we derive a preliminary upper limit on the frequency of giant planets for the semi-major axes of [10, 2000] AU: typically less than 15% between 100 and 500 AU and less than 10% between 50 and 500 AU for exoplanets that are more massive than 5 M[SUB]Jup[/SUB] and 10 M[SUB]Jup[/SUB] respectively, if we consider a uniform input distribution and a confidence level of 95%. <BR /> Conclusions: The results from this survey agree with earlier programs emphasizing that massive, gas giant companions on wide orbits around solar-type stars are rare. These results will be part of a broader analysis of a total of ~210 young, solar-type stars to bring further statistical constraints for theoretical models of planetary formation and evolution. Based on observations collected at the European Southern Observatory, Chile (ESO Large Program 184.C-0157 and Open Time 089.C-0137A and 090.C-0252A).Tables 2 and 6 are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201423564/olm">http://www.aanda.org</A> [less ▲]

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See detailFundamental Limitations of High Contrast Imaging Set by Small Sample Statistics
Mawet, D.; Milli, J.; Wahhaj, Z. et al

in Astrophysical Journal (2014), 792

In this paper, we review the impact of small sample statistics on detection thresholds and corresponding confidence levels (CLs) in high-contrast imaging at small angles. When looking close to the star ... [more ▼]

In this paper, we review the impact of small sample statistics on detection thresholds and corresponding confidence levels (CLs) in high-contrast imaging at small angles. When looking close to the star, the number of resolution elements decreases rapidly toward small angles. This reduction of the number of degrees of freedom dramatically affects CLs and false alarm probabilities. Naively using the same ideal hypothesis and methods as for larger separations, which are well understood and commonly assume Gaussian noise, can yield up to one order of magnitude error in contrast estimations at fixed CL. The statistical penalty exponentially increases toward very small inner working angles. Even at 5-10 resolution elements from the star, false alarm probabilities can be significantly higher than expected. Here we present a rigorous statistical analysis that ensures robustness of the CL, but also imposes a substantial limitation on corresponding achievable detection limits (thus contrast) at small angles. This unavoidable fundamental statistical effect has a significant impact on current coronagraphic and future high-contrast imagers. Finally, the paper concludes with practical recommendations to account for small number statistics when computing the sensitivity to companions at small angles and when exploiting the results of direct imaging planet surveys. [less ▲]

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See detailCompanion search around β Pictoris with the newly commissioned L'-band vector vortex coronagraph on VLT/NACO
Mawet, D.; Absil, Olivier ULg; Milli, J. et al

in Booth, Mark; Matthews, Brenda; Graham, James (Eds.) Exploring the Formation and Evolution of Planetary Systems (2014, January 01)

Here we present the installation and successful commissioning of an L'-band Annular Groove Phase Mask (AGPM) coronagraph on VLT/NACO. The AGPM is a vector vortex coronagraph made from diamond ... [more ▼]

Here we present the installation and successful commissioning of an L'-band Annular Groove Phase Mask (AGPM) coronagraph on VLT/NACO. The AGPM is a vector vortex coronagraph made from diamond subwavelength gratings tuned to the L' band. The vector vortex coronagraph enables high contrast imaging at very small inner working angle (here 0''.09, the diffraction limit of the VLT at L'), potentially being the key to a new parameter space. During technical and science verification runs, we discovered a late-type companion at two beamwidths from an F0V star (Mawet et al. 2013), and imaged the inner regions of β Pictoris down to the previously unexplored projected radius of 1.75 AU. The circumstellar disk was also resolved from ~= 1'' to 5'' (see J. Milli et al., these proceedings). These results showcase the potential of the NACO L-band AGPM over a wide range of spatial scales. [less ▲]

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See detailHigh Contrast Imaging with the New Vortex Coronagraph on NACO
Mawet, D.; Absil, Olivier ULg; Girard, J. H. et al

in The Messenger (2013), 152

The installation and successful commissioning of an L'-band annular groove phase mask (AGPM) coronagraph on VLT/NACO is presented. The AGPM is a vector vortex coronagraph made from diamond sub-wavelength ... [more ▼]

The installation and successful commissioning of an L'-band annular groove phase mask (AGPM) coronagraph on VLT/NACO is presented. The AGPM is a vector vortex coronagraph made from diamond sub-wavelength gratings tuned to the L'-band. The vector vortex coronagraph enables high-contrast imaging at very small inner working angles (here 0.09 arcseconds, the diffraction limit of the VLT at L'), potentially opening up a new parameter space in high-resolution imaging. During technical and science verification runs, we discovered a late-type companion at two beamwidths from an F0V star, and imaged the inner regions of β Pictoris down to the previously unexplored projected radius of 1.75 astronomical units. The circumstellar disc of β Pic was also resolved from 1 to 5 arcseconds. These results showcase the potential of the NACO L'-band AGPM over a wide range of spatial scales. [less ▲]

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See detailL'-band AGPM vector vortex coronagraph's first light on VLT/NACO: Discovery of a late-type companion at two beamwidths from an F0V star
Mawet, D.; Absil, Olivier ULg; Delacroix, Christian ULg et al

in Astronomy and Astrophysics (2013), 552

Context. High contrast imaging has thoroughly combed through the limited search space accessible with first-generation ground-based adaptive optics instruments and the Hubble Space Telescope. Only a few ... [more ▼]

Context. High contrast imaging has thoroughly combed through the limited search space accessible with first-generation ground-based adaptive optics instruments and the Hubble Space Telescope. Only a few objects were discovered, and many non-detections reported and statistically interpreted. The field is now in need of a technological breakthrough. Aim. Our aim is to open a new search space with first-generation systems such as NACO at the Very Large Telescope, by providing ground-breaking inner working angle (IWA) capabilities in the L' band. The L' band is a sweet spot for high contrast coronagraphy since the planet-to-star brightness ratio is favorable, while the Strehl ratio is naturally higher. Methods. An annular groove phase mask (AGPM) vector vortex coronagraph optimized for the L' band, made from diamond subwavelength gratings was manufactured and qualified in the lab. The AGPM enables high contrast imaging at very small IWA, potentially being the key to unexplored discovery space. Results. Here we present the installation and successful on-sky tests of an L'-band AGPM coronagraph on NACO. Using angular differential imaging, which is well suited to the rotational symmetry of the AGPM, we demonstrated a \Delta L' > 7.5 mag contrast from an IWA ~ 0".09 onwards, during average seeing conditions, and for total integration times of a few hundred seconds. [less ▲]

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See detailImage quality and high contrast improvements on VLT/NACO
Girard, J. H. V.; O'Neal, J.; Mawet, D. et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2012)

NACO is the famous and versatile diffraction limited NIR imager and spectrograph at the VLT with which ESO celebrated 10 years of Adaptive Optics. Since two years a substantial effort has been put in ... [more ▼]

NACO is the famous and versatile diffraction limited NIR imager and spectrograph at the VLT with which ESO celebrated 10 years of Adaptive Optics. Since two years a substantial effort has been put in understanding and fixing issues that directly affect the image quality and the high contrast performances of the instrument. Experiments to compensate the non-common-path aberrations and recover the highest possible Strehl ratios have been carried out successfully and a plan is hereafter described to perform such measurements regularly. The drift associated to pupil tracking since 2007 was fixed in october 2011. NACO is therefore even more suited for high contrast imaging and can be used with coronagraphic masks in the image plane. Some contrast measurements are shown and discussed. The work accomplished on NACO will serve as reference for the next generation instruments on the VLT, especially the ones working at the diffraction limit and making use of angular differential imaging (i.e. SPHERE, VISIR, and possibly ERIS). [less ▲]

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See detailDiversity among other worlds: characterization of exoplanets by direct detection (Update of a White Paper submitted to the ESA ExoPlanet Roadmap Advisory Team)
Schneider, J.; Boccaletti, A.; Aylward, A. et al

Report (2008)

The physical characterization of exoplanets will require to take spectra at several orbital positions. For that purpose, a direct imaging capability is necessary. Direct imaging requires an efficient ... [more ▼]

The physical characterization of exoplanets will require to take spectra at several orbital positions. For that purpose, a direct imaging capability is necessary. Direct imaging requires an efficient stellar suppression mechanism, associated with an ultrasmooth telescope. We show that before future large space missions (interferometer, 4-8 m class coronograph, external occulter or Fresnel imager), direct imaging of giant planets and close-by super-Earth are at the cross-road of a high scientific interest and a reasonable feasibility. The scientific interest lies in the fact that super-Earths share common geophysical attributes with Earths. They already begin to be detected by radial velocity (RV) and, together with giant planets, they have a larger area than Earths, making them detectable with a 1.5-2 m class telescope in reflected light. We propose such a (space) telescope be a first step before large direct imaging missions. [less ▲]

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