Fabrice Madec

First light of the VLT planet finder SPHERE III. New spectrophotometry and astrometry of the HR 8799 exoplanetary system

Context. The planetary system discovered around the young A-type HR 8799 provides a unique laboratory to: a) test planet formation theories; b) probe the diversity of system architectures at these separations, and c) perform comparative (exo)planetology. Aims. We present and exploit new near-infrared images and integral-field spectra of the four gas giants surrounding HR 8799 obtained with SPHERE, the new planet finder instrument at the Very Large Telescope, during the commissioning and science verification phase of the instrument (July–December 2014). With these new data, we contribute to completing the spectral energy distribution (SED) of these bodies in the 1.0–2.5 μm range. We also provide new astrometric data, in particular for planet e, to further constrain the orbits. Methods. We used the infrared dual-band imager and spectrograph (IRDIS) subsystem to obtain pupil-stabilized, dual-band H2H3 (1.593 μm, 1.667 μm), K1K2 (2.110 μm, 2.251 μm), and broadband J (1.245 μm) images of the four planets. IRDIS was operated in parallel with the integral field spectrograph (IFS) of SPHERE to collect low-resolution (R ~ 30), near-infrared (0.94–1.64 μm) spectra of the two innermost planets HR 8799 d and e. The data were reduced with dedicated algorithms, such as the Karhunen-Loeve image projection (KLIP), to reveal the planets. We used the so-called negative planets injection technique to extract their photometry, spectra, and measure their positions. We illustrate the astrometric performance of SPHERE through sample orbital fits compatible with SPHERE and literature data. Results. We demonstrated the ability of SPHERE to detect and characterize planets in this kind of systems, providing spectra and photometry of its components. The spectra improve upon the signal-to-noise ratio of previously obtained data and increase the spectral coverage down to the Y band. In addition, we provide the first detection of planet e in the J band. Astrometric positions for planets HR 8799 bcde are reported for the epochs of July, August, and December 2014. We measured the photometric values in J, H2H3, K1K2 bands for the four planets with a mean accuracy of 0.13 mag. We found upper limit constraints on the mass of a possible planet f of 3–7 MJup . Our new measurements are more consistent with the two inner planets d and e being in a 2d:1e or 3d:2e resonance. The spectra of HR 8799 d and e are well matched by those of L6-8 field dwarfs. However, the SEDs of these objects are redder than field L dwarfs longward of 1.6 μm.

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.

First light of the VLT planet finder SPHERE IV : Physical and chemical properties of the planets around HR8799

Context. The system of fourplanets discovered around the intermediate-mass star HR8799 offers a unique opportunity to test planet formation theories at large orbital radii and to probe the physics and chemistry at play in the atmospheres of self-luminous young (~30 Myr) planets. We recently obtained new photometry of the four planets and low-resolution (R ~ 30) spectra of HR8799 d and e with the SPHERE instrument (Paper III). Aims. In this paper (Paper IV), we aim to use these spectra and available photometry to determine how they compare to known objects, what the planet physical properties are, and how their atmospheres work. Methods. We compare the available spectra, photometry, and spectral energy distribution (SED) of the planets to field dwarfs and young companions. In addition, we use the extinction from corundum, silicate (enstatite and forsterite), or iron grains likely to form in the atmosphere of the planets to try to better understand empirically the peculiarity of their spectrophotometric properties. To conclude, we use three sets of atmospheric models (BT-SETTL14, Cloud-AE60, Exo-REM) to determine which ingredients are critically needed in the models to represent the SED of the objects, and to constrain their atmospheric parameters (T_(eff), log g, M/H). Results. We find that HR8799d and e properties are well reproduced by those of L6-L8 dusty dwarfs discovered in the field, among which some are candidate members of young nearby associations. No known object reproduces well the properties of planets b and c. Nevertheless, we find that the spectra and WISE photometry of peculiar and/or young early-T dwarfs reddened by submicron grains made of corundum, iron, enstatite, or forsterite successfully reproduce the SED of these planets. Our analysis confirms that only the Exo-REM models with thick clouds fit (within 2σ) the whole set of spectrophotometric datapoints available for HR8799 d and e for T_(eff) = 1200 K, log g in the range 3.0−4.5, and M/H = +0.5. The models still fail to reproduce the SED of HR8799c and b. The determination of the metallicity, log g, and cloud thickness are degenerate. Conclusions. Our empirical analysis and atmospheric modelling show that an enhanced content in dust and decreased CIA of H_2 is certainly responsible for the deviation of the properties of the planet with respect to field dwarfs. The analysis suggests in addition that HR8799c and b have later spectral types than the two other planets, and therefore could both have lower masses.

Prime focus spectrograph: Subaru's future

The Prime Focus Spectrograph (PFS) is a new multi-fiber spectrograph on Subaru telescope. PFS will cover around 1.4 degree diameter field with ~2400 fibers. To ensure precise positioning of the fibers, a metrology camera is designed to provide the fiber position information within 5 {\mu}m error. The final positioning accuracy of PFS is targeted to be better than 10 {\mu}m. The metrology camera will locate at the Cassegrain focus of Subaru telescope to cover the whole focal plane. The PFS metrology camera will also serve for the existing multi-fiber infrared spectrograph FMOS.The Prime Focus Spectrograph (PFS) of the Subaru Measurement of Images and Redshifts (SuMIRe) project has been endorsed by Japanese community as one of the main future instruments of the Subaru 8.2-meter telescope at Mauna Kea, Hawaii. This optical/near-infrared multi-fiber spectrograph targets cosmology with galaxy surveys, Galactic archaeology, and studies of galaxy/AGN evolution. Taking advantage of Subaru’s wide field of view, which is further extended with the recently completed Wide Field Corrector, PFS will enable us to carry out multi-fiber spectroscopy of 2400 targets within 1.3 degree diameter. A microlens is attached at each fiber entrance for F-ratio transformation into a larger one so that difficulties of spectrograph design are eased. Fibers are accurately placed onto target positions by positioners, each of which consists of two stages of piezo-electric rotary motors, through iterations by using back-illuminated fiber position measurements with a widefield metrology camera. Fibers then carry light to a set of four identical fast-Schmidt spectrographs with three color arms each: the wavelength ranges from 0.38 μm to 1.3 μm will be simultaneously observed with an average resolving power of 3000. Before and during the era of extremely large telescopes, PFS will provide the unique capability of obtaining spectra of 2400 cosmological/astrophysical targets simultaneously with an 8-10 meter class telescope. The PFS collaboration, led by IPMU, consists of USP/LNA in Brazil, Caltech/JPL, Princeton, and JHU in USA, LAM in France, ASIAA in Taiwan, and NAOJ/Subaru.

A narrow, edge-on disk resolved around HD 106906 with SPHERE

Context. HD 106906AB is the only young binary system so far around which a planet has been imaged and a debris disk has been shown to exist, thanks to a strong IR excess. As such, it represents a unique opportunity for studying the dynamics of young planetary systems. Aims. We aim at further investigating the close (tens of au scales) environment of the HD 106906AB system. Methods. We used the extreme adaptive-optics-fed, high-contrast imager SPHERE that has recently been installed on the VLT to observe HD 106906. Both the IRDIS imager and the Integral Field Spectrometer were used. Results. We discovered a highly inclined, ring-like disk at a distance of 65 au from the star. The disk shows a strong brightness asymmetry with respect to its semi-major axis. It shows a smooth outer edge, compatible with ejection of small grains by the stellar radiation pressure. We show furthermore that the planets projected position is significantly above the PA of the disk. Given the determined disk inclination, it is not excluded, however, that the planet could still orbit within the disk plane if at a large separation (2000 3000 au). We identified several additional point sources in the SPHERE /IRDIS field of view that appear to be background objects. We compare this system with other debris disks sharing similarities, and we briefly discuss the present results in the framework of dynamical evolution.

Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor - II. Concept validation with ZELDA on VLT/SPHERE

Warm or massive gas giant planets, brown dwarfs, and debris disks around nearby stars are now routinely observed by dedicated high-contrast imaging instruments on large, ground-based observatories. These facilities include extreme adaptive optics (ExAO) and state-of-the-art coronagraphy to achieve unprecedented sensitivities for exoplanet detection and spectral characterization. However, differential aberrations between the ExAO sensing path and the science path represent a critical limitation for the detection of giant planets with a contrast lower than a few

Prime Focus Spectrograph for the Subaru telescope: massively multiplexed optical and near-infrared fiber spectrograph

10^{-6}

High contrast polarimetry in the infrared with SPHERE on the VLT

at very small separations (<0.3\as) from their host star. In our previous work, we proposed a wavefront sensor based on Zernike phase contrast methods to circumvent this issue and measure these quasi-static aberrations at a nanometric level. We present the design, manufacturing and testing of ZELDA, a prototype that was installed on VLT/SPHERE during its reintegration in Chile. Using the internal light source of the instrument, we performed measurements in the presence of Zernike or Fourier modes introduced with the deformable mirror. Our experimental and simulation results are consistent, confirming the ability of our sensor to measure small aberrations (<50 nm rms) with nanometric accuracy. We then corrected the long-lived non-common path aberrations in SPHERE based on ZELDA measurements. We estimated a contrast gain of 10 in the coronagraphic image at 0.2\as, reaching the raw contrast limit set by the coronagraph in the instrument. The simplicity of the design and its phase reconstruction algorithm makes ZELDA an excellent candidate for the on-line measurements of quasi-static aberrations during the observations. The implementation of a ZELDA-based sensing path on the current and future facilities (ELTs, future space missions) could ease the observation of the cold gaseous or massive rocky planets around nearby stars.

Prime Focus Spectrograph (PFS) for the Subaru telescope: overview, recent progress, and future perspectives

Abstract. The Prime Focus Spectrograph (PFS) is an optical/near-infrared multifiber spectrograph with 2394 science fibers distributed across a 1.3-deg diameter field of view at the Subaru 8.2-m telescope. The wide wavelength coverage from 0.38  μm to 1.26  μm, with a resolving power of 3000, simultaneously strengthens its ability to target three main survey programs: cosmology, galactic archaeology and galaxy/AGN evolution. A medium resolution mode with a resolving power of 5000 for 0.71  μm to 0.89  μm will also be available by simply exchanging dispersers. We highlight some of the technological aspects of the design. To transform the telescope focal ratio, a broad-band coated microlens is glued to each fiber tip. A higher transmission fiber is selected for the longest part of the cable system, optimizing overall throughput; a fiber with low focal ratio degradation is selected for the fiber-positioner and fiber-slit components, minimizing the effects of fiber movements and fiber bending. Fiber positioning will be performed by a positioner consisting of two stages of piezo-electric rotary motors. The positions of these motors are measured by taking an image of artificially back-illuminated fibers with the metrology camera located in the Cassegrain container; the fibers are placed in the proper location by iteratively measuring and then adjusting the positions of the motors. Target light reaches one of the four identical fast-Schmidt spectrograph modules, each with three arms. The PFS project has passed several project-wide design reviews and is now in the construction phase.

Apodization in high-contrast long-slit spectroscopy. II. Concept validation and first on-sky results with VLT/SPHERE

The instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), recently installed on the VLT-UT3, aims to detected and characterize giant extra-solar planets and the circumstellar environments in the very close vicinity of bright stars. The extreme brightness contrast and small angular separation between the planets or disks and their parent stars have so far proven very challenging. SPHERE will meet this challenge by using an extreme AO, stellar coronagraphs, an infrared dual band and polarimetric imager called IRDIS, an integral field spectrograph, and a visible polarimetric differential imager called ZIMPOL. Polarimetry allows a separation of the light coming from an unpolarized source such as a star and the polarized source such as a planet or protoplanetary disks. In this paper we present the performance of the infrared polarimetric imager based on experimental validations performed within SPHERE before the preliminary acceptance in Europe. We report on the level of instrumental polarization in the infrared and its calibration limit. Using differential polarimetry technique, we quantify the level of speckle suppression, and hence improved sensitivity in the context of imaging extended stellar environments.