Patrice Martinez

First light of the VLT planet finder SPHERE I. Detection and characterization of the substellar companion GJ 758 B

GJ 758 B is a brown dwarf companion to a nearby (15.76%) solar-type, metal-rich (M/H = +0.2 dex) main-sequence star (G9V) that was discovered with Subaru/HiCIAO in 2009. From previous studies, it has drawn attention as being the coldest (similar to 600 K) companion ever directly imaged around a neighboring star. We present new high-contrast data obtained during the commissioning of the SPHERE instrument at the Very Large Telescope (VLT). The data was obtained in Y-, J-, H-, and K-s-bands with the dual-band imaging (DBI) mode of IRDIS, thus providing a broad coverage of the full near-infrared (near-IR) range at higher contrast and better spectral sampling than previously reported. In this new set of high-quality data, we report the re-detection of the companion, as well as the first detection of a new candidate closer-in to the star. We use the new eight photometric points for an extended comparison of GJ 758 B with empirical objects and four families of atmospheric models. From comparison to empirical object, we estimate a T8 spectral type, but none of the comparison objects can accurately represent the observed near-IR fluxes of GJ 758 B. From comparison to atmospheric models, we attribute a T-eff = 600 +/- 100 K, but we find that no atmospheric model can adequately fit all the fluxes of GJ 758 B. The lack of exploration of metal enrichment in model grids appears as a major limitation that prevents an accurate estimation of the companion physical parameters. The photometry of the new candidate companion is broadly consistent with L-type objects, but a second epoch with improved photometry is necessary to clarify its status. The new astrometry of GJ 758 B shows a significant proper motion since the last epoch. We use this result to improve the determination of the orbital characteristics using two fitting approaches: Least-Squares Monte Carlo and Markov chain Monte Carlo. We confirm the high-eccentricity of the orbit (peak at 0.5), and find a most likely semi-major axis of 46.05 AU. We also use our imaging data, as well as archival radial velocity data, to reject the possibility that this is a false positive effect created by an unseen, closer-in, companion. Finally, we analyze the sensitivity of our data to additional closer-in companions and reject the possibility of other massive brown dwarf companions down to 4-5 AU.

EPICS: direct imaging of exoplanets with the E-ELT

Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to discover and explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m ground-based telescopes, the Extremely Large Telescopes (ELTs), have the potential to dramatically enlarge the discovery space towards older giant planets seen in reflected light and ultimately even a small number of rocky planets. EPICS is a proposed instrument for the European ELT, dedicated to the detection and characterization of Exoplanets by direct imaging, spectroscopy and polarimetry. ESO completed a phase-A study for EPICS with a large European consortium which - by simulations and demonstration experiments - investigated state-of-the-art diffraction and speckle suppression techniques to deliver highest contrasts. The paper presents the instrument concept and analysis as well as its main innovations and science capabilities. EPICS is capable of discovering hundreds of giant planets, and dozens of lower mass planets down to the rocky planets domain.

Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE

Context. 51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, which was recently discovered by direct imaging. It is one of the closest direct imaging planets in angular and physical separation (~0.5′′, ~13 au) and is well suited for spectroscopic analysis using integral field spectrographs. Aims. We aim to refine the atmospheric properties of the known giant planet and to constrain the architecture of the system further by searching for additional companions. Methods. We used the extreme adaptive optics instrument SPHERE at the Very Large Telescope (VLT) to obtain simultaneous dual-band imaging with IRDIS and integral field spectra with IFS, extending the spectral coverage of the planet to the complete Y - to H -band range and providing additional photometry in the K12-bands (2.11, 2.25 μ m). The object is compared to other known cool and peculiar dwarfs. The posterior probability distributions for parameters of cloudy and clear atmospheric models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. We used archival VLT-NACO ( L ′) Sparse Aperture Masking data to probe the innermost region for additional companions. Results. We present the first spectrophotometric measurements in the Y and K bands for the planet and revise its J -band flux to values 40% fainter than previous measurements. Cloudy models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity, and cloud sedimentation parameter f sed . We find that the atmosphere is highly super-solar ([Fe/H] = 1.0 ± 0.1 dex), and the low \hbox{

Speckle temporal stability in XAO coronagraphic images

{f_{\rm sed} = 1.26^{+0.36}_{-0.29}}

System study of EPICS: the exoplanets imager for the E-ELT

} value is indicative of a vertically extended, optically thick cloud cover with small sized particles. The model radius and surface gravity estimates suggest higher planetary masses of \hbox{

EPOL: the exoplanet polarimeter for EPICS at the E-ELT

{M_\mathrm{gravity} = 9.1^{+4.9}_{-3.3} \, {M}_\mathrm{J}}

Atmospheric image blur with finite outer scale or partial adaptive correction

}. The evolutionary model only provides a lower mass limit of > 2 M J (for pure hot-start). The cold-start model cannot explain the luminosity of the planet. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at solar system scales and exclude brown-dwarf companions more massive than 20 M J beyond separations of ~2.5 au and giant planets more massive than 2 M J beyond 9 au.

High order test bench for extreme adaptive optics system optimization

Context. The major source of noise limiting high-contrast imaging is caused by quasi-static speckles. Speckle noise originates from wavefront errors caused by various independent sources, and evolves on different timescales depending on their nature. An understanding of how quasi-static speckles originate from instrumental errors is paramount to the search for faint stellar companions. Instrumental speckles average to form a fixed pattern, which can be calibrated to a certain extent, but their temporal evolution ultimately limits this possibility. Aims. This study focuses on the laboratory evidence and characterization of the quasi-static pinned speckle phenomenon. Specifically, we examine the coherent amplification of the static speckle contribution to the noise variance in the scientific image, through its interaction with quasi-static speckles. Methods. The analysis of a time series of adaptively corrected, coronagraphic images recorded in the laboratory enables the characterization of the temporal stability of the residual speckle pattern in both direct and differential coronagraphic images. Results. We estimate that spoiled and rapidly evolving quasi-static speckles present in the system at the angstrom/nanometer level affect the stability of the static speckle noise in the final image after the coronagraph. The temporal evolution of the quasi-static wavefront error exhibits a linear power law, which can be used to first order to model quasi-static speckle evolution in high-contrast imaging instruments.

Design, analysis, and testing of a microdot apodizer for the apodized pupil Lyot coronagraph - III. Application to extremely large telescopes

ESO and a large European consortium completed the phase-A study of EPICS, an instrument dedicated to exoplanets direct imaging for the EELT. The very ambitious science goals of EPICS, the imaging of reflected light of mature gas giant exoplanets around bright stars, sets extremely strong requirements in terms of instrumental contrast achievable. The segmented nature of an ELT appears as a very large source of quasi-static high order speckles that can impair the detection of faint sources with small brightness contrast with respect to their parent star. The paper shows how the overall system has been designed in order to maximize the efficiency of quasi-static speckles rejection by calibration and post-processing using the spectral and polarization dependency of light waves. The trade-offs that led to the choice of the concepts for common path and diffraction suppression system is presented. The performance of the instrument is predicted using simulations of the extreme Adaptive Optics system and polychromatic wave-front propagation through the various optical elements.

Fine cophasing of segmented aperture telescopes with ZELDA, a Zernike wavefront sensor in the diffraction-limited regime

EPOL is the imaging polarimeter part of EPICS (Exoplanet Imaging Camera and Spectrograph) for the 42-m E-ELT. It is based on sensitive imaging polarimetry to differentiate between linearly polarized light from exoplanets and unpolarized, scattered starlight and to characterize properties of exoplanet atmospheres and surfaces that cannot be determined from intensity observations alone. EPOL consists of a coronagraph and a dual-beam polarimeter with a liquid-crystal retarder to exchange the polarization of the two beams. The polarimetry thereby increases the contrast between star and exoplanet by 3 to 5 orders of magnitude over what the extreme adaptive optics and the EPOL coronagraph alone can achieve. EPOL operates between 600 and 900 nm, can select more specific wavelength bands with filters and aims at having an integral field unit to obtain linearly polarized spectra of known exoplanets. We present the conceptual design of EPOL along with an analysis of its performance.