Pupil stabilization for SPHERE's extreme AO and high performance coronagraph system

We propose a new concept of pupil motion sensor for astronomical adaptive optics systems and present experimental results obtained during the first laboratory validation of this concept. Pupil motion is an important issue in the case of extreme adaptive optics, high contrast systems, such as the proposed Planet Finder instruments for the ESO and Gemini 8-meter telescopes. Such high contrast imaging instruments will definitively require pupil stabilization to minimize the effect of quasi-static aberrations. The concept for pupil stabilization we propose uses the flux information from the AO system wave-front sensor to drive in closed loop a pupil tip-tilt mirror located in a focal plane. A laboratory experiment validates this concept and demonstrates its interest for high contrast imaging instrument.Comment: This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at http://www.opticsexpress.org/abstract.cfm?id=144687 on the OSA websit

Analysis of ground-based differential imager performance

In the context of extrasolar planet direct detection, we evaluated the performance of differential imaging with ground-based telescopes. This study was carried out in the framework of the VLT-Planet Finder project and is further extended to the case of Extremely Large Telescopes. Our analysis is providing critical specifications for future instruments mostly in terms of phase aberrations but also regarding alignments of the instrument optics or offset pointing on the coronagraph. It is found that Planet Finder projects on 8m class telescopes can be successful at detecting Extrasolar Giant Planets providing phase aberrations, alignments and pointing are accurately controlled. The situation is more pessimistic for the detection of terrestrial planets with Extremely Large Telescopes for which phase aberrations must be lowered at a very challenging level

A giant planet imaged in the disk of the young star Beta Pictoris

Here we show that the ~10 Myr Beta Pictoris system hosts a massive giant planet, Beta Pictoris b, located 8 to 15 AU 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, Beta Pictoris b is the closest to its parent star. Its short period could allow recording the full orbit within 17 years.Comment: 4 pages, 2 figures. Published online 10 June 2010; 10.1126/science.1187187. To appear in Scienc

beta Pic b position relative to the Debris Disk

Context. We detected in 2009 a giant, close-by planet orbiting {\beta} Pic, a young star surrounded with a disk, extensively studied for more than 20 years. We showed that if located on an inclined orbit, the planet could explain several peculiarities of {\beta} Pictoris system. However, the available data did not permit to measure the inclination of {\beta} Pic b with respect to the disk, and in particular to establish in which component of the disk - the main, extended disk or the inner inclined component/disk-, the planet was located. Comparison between the observed planet position and the disk orientation measured on previous imaging data was not an option because of potential biases in the measurements. Aims. Our aim is to measure precisely the planet location with respect to the dust disk using a single high resolution image, and correcting for systematics or errors that degrades the precision of the disk and planet relative position measurements. Methods. We gathered new NaCo data at Ks band, with a set-up optimized to derive simultaneously the orientation(s) of the disk(s) and that of the planet. Results. We show that the projected position of {\beta} Pic b is above the midplane of the main disk. With the current data and knowledge on the system, this implies that {\beta} Pic b cannot be located in the main disk. The data rather suggest the planet being located in the inclined component.Comment: 13 pages, 6 figures, to appear in Astronomy and Astrophysic

Collisional Cascades in Planetesimal Disks II. Embedded Planets

We use a multiannulus planetesimal accretion code to investigate the growth of icy planets in the outer regions of a planetesimal disk. In a quiescent minimum mass solar nebula, icy planets grow to sizes of 1000--3000 km on a timescale t = 15-20 Myr (a/30 AU)^3 where a is the distance from the central star. Planets form faster in more massive nebulae. Newly-formed planets stir up leftover planetesimals along their orbits and produce a collisional cascade where icy planetesimals are slowly ground to dust. The dusty debris of planet formation has physical characteristics similar to those observed in beta Pic, HR 4796A, and other debris disks. We derive dust masses for small particles, 1 mm and smaller, and large particles, 1 mm and larger, as a function of the initial conditions in the planetesimal disk. The dust luminosities derived from these masses are similar to those observed in Vega, HR 4796A, and other debris disks. The calculations produce bright rings and dark gaps. Bright rings occur where 1000 km and larger planets have recently formed. Dark gaps are regions where planets have cleared out dust or shadows where planets have yet to form.Comment: to be published in the Astronomical Journal, January 2004; 7 pages of text; 17 figures at http://cfa-www.harvard.edu/~kenyon/pf/emb-planet-figures.pdf; 2 animations at http://cfa-www.harvard.edu/~kenyon/pf/emb-planet-movies.htm

A probable giant planet imaged in the Beta Pictoris disk

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.Comment: 5 pages, 3 figures, 1 table. A&A Letters, in pres

Rings in the Planetesimal Disk of Beta Pic

The nearby main sequence star Beta Pictoris is surrounded by an edge-on disk of dust produced by the collisional erosion of larger planetesimals. Here we report the discovery of substructure within the northeast extension of the disk midplane that may represent an asymmetric ring system around Beta Pic. We present a dynamical model showing that a close stellar flyby with a quiescient disk of planetesimals can create such rings, along with previously unexplained disk asymmetries. Thus we infer that Beta Pic's planetesimal disk was highly disrupted by a stellar encounter in the last hundred thousand years.Comment: Accepted by ApJ Letters. LaTeX, 13 pages, 4 figures, full PostScript file available from http://www.maths.qmw.ac.uk/~jdl

Signatures of Planets in Spatially Unresolved Disks

Main sequence stars are commonly surrounded by debris disks, composed of cold dust continuously replenished by a reservoir of undetected dust-producing planetesimals. In a planetary system with a belt of planetesimals (like the Solar System's Kuiper Belt) and one or more interior giant planets, the trapping of dust particles in the mean motion resonances with the planets can create structure in the dust disk, as the particles accumulate at certain semimajor axes. Sufficiently massive planets may also scatter and eject dust particles out of a planetary system, creating a dust depleted region inside the orbit of the planet. In anticipation of future observations of spatially unresolved debris disks with the Spitzer Space Telescope, we are interested in studying how the structure carved by planets affects the shape of the disk's spectral energy distribution (SED), and consequently if the SED can be used to infer the presence of planets. We numerically calculate the equilibrium spatial density distributions and SEDs of dust disks originated by a belt of planetesimals in the presence of interior giant planets in different planetary configurations, and for a representative sample of chemical compositions. The dynamical models are necessary to estimate the enhancement of particles near the mean motion resonances with the planets, and to determine how many particles drift inside the planet's orbit. Based on the SEDs and predicted $\it{Spitzer}$ colors we discuss what types of planetary systems can be distinguishable from one another and the main parameter degeneracies in the model SEDs.Comment: 40 pages (pre-print form), including 16 figures. Published in ApJ 200

Dust disks around old Pre Main-Sequence stars: HST/NICMOS2 scattered light images and modeling

We present recent near-infrared detections of circumstellar disks around the two old PMS Herbig stars HD 141569 and HD 100546 obtained with the HST/NICMOS2 camera. They reveal extended structures larger than 350-400 AU in radius. While the HD 100546 disk appears as a continuous disk down to 40 AU, the HD 141569 environment seems more complex, splitted at least into two dust populations. As a convincing example, the full modeling of the disk surrounding HR 4796, another old PMS star, is detailed and confronted with more recent observations.Comment: 6 page