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Register a new userPerformance of the VLT Planet Finder SPHERE II. Data analysis and Results for IFS in laboratory
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We present the performance of the Integral Field Spectrograph (IFS) of SPHERE, the high-contrast imager for the ESO VLT telescope designed to perform imaging and spectroscopy of extrasolar planets, obtained from tests performed at the Institute de Planetologie et dAstrophysique de Grenoble facility during the integration phase of the instrument.} {The tests were performed using the instrument software purposely prepared for SPHERE. The output data were reduced applying the SPHERE data reduction and handling software, adding an improved spectral deconvolution procedure. To this aim, we prepared an alternative procedure for the spectral subtraction exploiting the principal components analysis algorithm. Moreover, a simulated angular differential imaging procedure was also implemented to estimate how the instrument performed once this procedure was applied at telescope. The capability of the IFS to faithfully retrieve the spectra of the detected faint companions was also considered.} {We found that the application of the updated version of the spectral deconvolution procedure alone, when the algorithm throughput is properly taken into account, gives us a $5sigma$ limiting contrast of the order of 5$times$$10^{-6}$ or slightly better. The further application of the angular differential imaging procedure on these data should allow us to improve the contrast by one order of magnitude down to around 7$times$$10^{-7}$ at a separation of 0.3 arcsec. The application of a principal components analysis procedure that simultaneously uses spectral and angular data gives comparable results. Finally, we found that the reproducibility of the spectra of the detected faint companions is greatly improved when angular differential imaging is applied in addition to the spectral deconvolution.
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Aims. We present simulations of the perfomances of the future SPHERE IFS instrument designed for imaging extrasolar planets in the near infrared (Y, J, and H bands). Methods. We used the IDL package code for adaptive optics simulation (CAOS) to prepare a series of input point spread functions (PSF). These feed an IDL tool (CSP) that we designed to simulate the datacube resulting from the SPHERE IFS. We performed simulations under different conditions to evaluate the contrast that IFS will be able to reach and to verify the impact of physical propagation within the limits of the near field of the aperture approximation (i.e. Fresnel propagation). We then performed a series of simulations containing planet images to test the capability of our instrument to correctly classify the found objects. To this purpose we developed a separated IDL tool. Results. We found that using the SPHERE IFS instrument and appropriate analysis techniques, such as multiple spectral differential imaging (MDI), spectral deconvolution (SD), and angular differential imaging (ADI), we should be able to image companion objects down to a luminosity contrast of ? 10-7 with respect to the central star in favorable cases. Spectral deconvolution resulted in the most effective method for reducing the speckle noise. We were then able to find most of the simulated planets (more than 90% with the Y-J-mode and more than the 95% with the Y-H-mode) for contrasts down to 3 times 10-7 and separations between 0.3 and 1.0 arcsec. The spectral classification is accurate but seems to be more precise for late T-type spectra than for earlier spectral types. A possible degeneracy between early L-type companion objects and field objects (flat spectra) is highlighted. The spectral classification seems to work better using the Y-H-mode than with the Y-J-mode.
SPHERE is an instrument designed and built by a consortium of French, German, Italian, Swiss and Dutch institutes in collaboration with ESO. The project is currently in its Phase B. The main goal of SPHERE is to gain at least one order of magnitude with respect to the present VLT AO facility (NACO) in the direct detection of faint objects very close to a bright star, especially giant extrasolar planets. Apart from a high Strehl ratio, the instrument will be designed to reduce the scattered light of the central bright star and subtract the residual speckle halo. Sophisticated post-AO capabilities are needed to provide maximum detectivity and possibly physical data on the putative planets. The Integral Field Spectrograph (IFS), one of the three scientific channels foreseen in the SPHERE design, is a very low resolution spectrograph (R~20) which works in the near IR (0.95-1.35 micron), an ideal wavelength range for the ground based detection of planetary features. Its goal is to suppress speckle to a contrast of 10^7, with a goal of 10^8, and at the same time provide spectral information in a field of view of about 1.5 x 1.5 arcsecs^2 in proximity of the target star. In this paper we describe the overall IFS design concept.
The system of four planets around HR8799 offers a unique opportunity 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). In this paper (paper IV), we compare the available spectra and photometry of the planets to known objects and atmospheric models (BT-SETTL14, Cloud-AE60, Exo-REM) to characterize the atmospheric properties of the planets. 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 two planets. Our analysis confirms that only the Exo-REM models with thick clouds fit (within 2{sigma}) the whole set of spectrophotometric datapoints available for HR8799 d and e for Teff = 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. We conclude that an enhanced content in dust and decreased CIA of H2 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.
The planetary system discovered around the young A-type HR8799 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. We present and exploit new near-infrared images and integral-field spectra of the four gas giants surrounding HR8799 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 of these bodies in the 1.0-2.5 $mu$m range. We also provide new astrometric data, in particular for planet e, to further constrain the orbits. We used the infrared dual-band imager and spectrograph (IRDIS) subsystem to obtain pupil-stabilized, dual-band $H2H3$ (1.593 $mu$m, 1.667 $mu$m), $K1K2$ (2.110 $mu$m, 2.251 $mu$m), and broadband $J$ (1.245 $mu$m) images of the four planets. IRDIS was operated in parallel with the integral field spectrograph (IFS) of SPHERE to collect low-resolution ($Rsim30$), near-infrared (0.94-1.64 $mu$m) spectra of the two innermost planets HR8799d and e. The data were reduced with dedicated algorithms, such as the Karhunen-Lo`eve 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.
Until now, just a few extrasolar planets (~30 out of 860) have been found through the direct imaging method. This number should greatly improve when the next generation of High Contrast Instruments like Gemini Planet Imager (GPI) at Gemini South Telescope or SPHERE at VLT will became operative at the end of this year. In particular, the Integral Field Spectrograph (IFS), one of the SPHERE subsystems, should allow a first characterization of the spectral type of the found extrasolar planets. Here we present the results of the last performance tests that we have done on the IFS instrument at the Institut de Planetologie et dAstrophysique de Grenoble (IPAG) in condition as similar as possible to the ones that we will find at the telescope. We have found that we should be able to reach contrast down to 5x10$^{-7}$ and make astrometry at sub-mas level with the instrument in the actual conditions. A number of critical issues have been identified. The resolution of these problems could allow to further improve the performance of the instrument.
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