Patrick Rabou

Bio: Patrick Rabou is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Adaptive optics & Exoplanet. The author has an hindex of 28, co-authored 79 publications receiving 4756 citations. Previous affiliations of Patrick Rabou include Institut Universitaire de France.

SPHERE: A ‘Planet Finder’ Instrument for the VLT

Abstract: Direct detection and spectral characterization of extra-solar planets is one of the most exciting but also one of the most challenging areas in modern astronomy. The challenge consists in the very large contrast between the host star and the planet, larger than 12.5 magnitudes at very small angular separations, typically inside the seeing halo. The whole design of a "Planet Finder" instrument is therefore optimized towards reaching the highest contrast in a limited field of view and at short distances from the central star. Both evolved and young planetary systems can be detected, respectively through their reflected light and through the intrinsic planet emission. We present the science objectives, conceptual design and expected performance of the SPHERE instrument.

A probable giant planet imaged in the Beta Pictoris disk

Abstract: Since the discovery of its dusty disk in 1984, Beta Pictoris has become the prototype of young early-type planetary systems, and there are now various indications that a massive Jovian planet is orbiting the star at ~ 10 AU. However, no planets have been detected around this star so far. Our goal was to investigate the close environment of Beta Pic, searching for planetary companion(s). Deep adaptive-optics L'-band images of Beta Pic were recorded using the NaCo instrument at the Very Large Telescope. A faint point-like signal is detected at a projected distance of ~ 8 AU from the star, within the North-East side of the dust disk. Various tests were made to rule out with a good confidence level possible instrumental or atmospheric artifacts. The probability of a foreground or background contaminant is extremely low, based in addition on the analysis of previous deep Hubble Space Telescope images. The object L'=11.2 apparent magnitude would indicate a typical temperature of ~1500 K and a mass of ~ 8 Jovian masses. If confirmed, it could explain the main morphological and dynamical peculiarities of the Beta Pic system. The present detection is unique among A-stars by the proximity of the resolved planet to its parent star. Its closeness and location inside the Beta Pic disk suggest a formation process by core accretion or disk instabilities rather than a binary-like formation process.

Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70

Abstract: Young circumstellar disks are of prime interest to understand the physical and chemical conditions under which planet formation takes place. Only very few detections of planet candidates within these disks exist, and most of them are currently suspected to be disk features. In this context, the transition disk around the young star PDS 70 is of particular interest, due to its large gap identified in previous observations, indicative of ongoing planet formation. We aim to search for the presence of planets and search for disk structures indicative for disk-planet interactions and other evolutionary processes. We analyse new and archival near-infrared (NIR) images of the transition disk PDS 70 obtained with the VLT/SPHERE, VLT/NaCo and Gemini/NICI instruments in polarimetric differential imaging (PDI) and angular differential imaging (ADI) modes. We detect a point source within the gap of the disk at about 195 mas (about 22 au) projected separation. The detection is confirmed at five different epochs, in three filter bands and using different instruments. The astrometry results in an object of bound nature, with high significance. The comparison of the measured magnitudes and colours to evolutionary tracks suggests that the detection is a companion of planetary mass. We confirm the detection of a large gap of about 54 au in size within the disk in our scattered light images, and detect a signal from an inner disk component. We find that its spatial extent is very likely smaller than about 17 au in radius. The images of the outer disk show evidence of a complex azimuthal brightness distribution which may in part be explained by Rayleigh scattering from very small grains. Future observations of this system at different wavelengths and continuing astrometry will allow us to test theoretical predictions regarding planet-disk interactions, planetary atmospheres and evolutionary models.

SPHERE: the exoplanet imager for the Very Large Telescope

Abstract: Observations of circumstellar environments to look for the direct signal of exoplanets and the scattered light from disks has significant instrumental implications. In the past 15 years, major developments in adaptive optics, coronagraphy, optical manufacturing, wavefront sensing and data processing, together with a consistent global system analysis have enabled a new generation of high-contrast imagers and spectrographs on large ground-based telescopes with much better performance. One of the most productive is the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE) designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE includes an extreme adaptive optics system, a highly stable common path interface, several types of coronagraphs and three science instruments. Two of them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared (NIR) range in a single observation for efficient young planet search. The third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to look for the reflected light of exoplanets and the light scattered by debris disks. This suite of three science instruments enables to study circumstellar environments at unprecedented angular resolution both in the visible and the near-infrared. In this work, we present the complete instrument and its on-sky performance after 4 years of operations at the VLT.

NAOS, the first AO system of the VLT: on-sky performance

Abstract: NAOS is the first adaptive optics system installed at the VLT 8m telescopes. It was designed, manufactured and tested by a french Consortium under an ESO contract, to provide compensated images to the high angular resolution IR spectro-imaging camera (CONICA) in the 1 to 5 μ m spectral range. It is equipped with a 185 actuator deformable mirror, a tip/tilt mirror and two wavefront sensors, one in the visible and one in the near IR spectral range. It has been installed in November at the Nasmyth focus B of the VLT UT4. During the first light run in December 2001, NAOS has delivered a Strehl ratio of 50 under average seeing conditions for bright guide stars. The diffraction limit of the telescope has been achieved at 2.2 μ m . The closed loop operation has been very robust under bad seeing conditions. It was also possible to obtain a substantial correction with m V=17.6 and m K=13.1 reference stars. The on-sky acceptance tests of NAOS-CONICA were completed in May 2002 and the instrument will be made available to the European astronomical community in October by ESO. This paper describes the system and present the on-sky performance in terms of Strehl ratio, seeing conditions and guide star magnitude.

Monthly Notices of the Royal Astronomical Society

Abstract: Monthly Notices is one of the three largest general primary astronomical research publications. It is an international journal, published by the Royal Astronomical Society. This article 1 describes its publication policy and practice.

Stellar Multiplicity

Abstract: Stellar multiplicity is an ubiquitous outcome of the star formation process Characterizing the frequency and main characteristics of multiple systems and their dependencies on primary mass and environment is therefore a powerful tool to probe this process While early attempts were fraught with selection biases and limited completeness, instrumentation breakthroughs in the last two decades now enable robust analyses In this review, we summarize our current empirical knowledge of stellar multiplicity for Main Sequence stars and brown dwarfs, as well as among populations of Pre-Main Sequence stars and embedded protostars Clear trends as a function of both primary mass and stellar evolutionary stage are identified that will serve as a comparison basis for numerical and analytical models of star formation

A Giant Planet Imaged in the Disk of the Young Star β Pictoris

Abstract: Here, we show that the ~10-million-year-old β Pictoris system hosts a massive giant planet, β Pictoris b, located 8 to 15 astronomical units from the star. This result confirms that gas giant planets form rapidly within disks and validates the use of disk structures as fingerprints of embedded planets. Among the few planets already imaged, β Pictoris b is the closest to its parent star. Its short period could allow for recording of the full orbit within 17 years.

The Occurrence of Potentially Habitable Planets Orbiting M Dwarfs Estimated from the Full Kepler Dataset and an Empirical Measurement of the Detection Sensitivity

Abstract: We present an improved estimate of the occurrence rate of small planets orbiting small stars by searching the full four-year Kepler data set for transiting planets using our own planet detection pipeline and conducting transit injection and recovery simulations to empirically measure the search completeness of our pipeline. We identified 156 planet candidates, including one object that was not previously identified as a Kepler Object of Interest. We inspected all publicly available follow-up images, observing notes, and centroid analyses, and corrected for the likelihood of false positives. We evaluated the sensitivity of our detection pipeline on a star-by-star basis by injecting 2000 transit signals into the light curve of each target star. For periods shorter than 50 days, we find Earth-size planets (1−1.5 R⊕) and super-Earths (1.5−2 R⊕) per M dwarf. In total, we estimate a cumulative planet occurrence rate of 2.5 ± 0.2 planets per M dwarf with radii 1−4 R⊕ and periods shorter than 200 days. Within a conservatively defined habitable zone (HZ) based on the moist greenhouse inner limit and maximum greenhouse outer limit, we estimate an occurrence rate of Earth-size planets and super-Earths per M dwarf HZ. Adopting the broader insolation boundaries of the recent Venus and early Mars limits yields a higher estimate of Earth-size planets and super-Earths per M dwarf HZ. This suggests that the nearest potentially habitable non-transiting and transiting Earth-size planets are 2.6 ± 0.4 pc and pc away, respectively. If we include super-Earths, these distances diminish to 2.1 ± 0.2 pc and pc.

The Occurrence and Architecture of Exoplanetary Systems

Abstract: The basic geometry of the Solar System—the shapes, spacings, and orientations of the planetary orbits—has long been a subject of fascination as well as inspiration for planet-formation theories. For exoplanetary systems, those same properties have only recently come into focus. Here we review our current knowledge of the occurrence of planets around other stars, their orbital distances and eccentricities, the orbital spacings and mutual inclinations in multiplanet systems, the orientation of the host star's rotation axis, and the properties of planets in binary-star systems.