Aims. 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 Institut de Planetologie et d'Astrophysique de Grenoble facility during the integration phase of the instrument. Methods. 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 component 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. Results. 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 x 10 super(-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 x 10 super(-7) at a separation of 0.3 arcsec. The application of a principal component 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.
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.
Warm or massive gas giant planets, brown dwarfs, and debris disks around nearby stars are now routinely observed by dedicated high-contrast imaging instruments that are mounted 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 their spectral characterization. However, low spatial frequency differential aberrations between the ExAO sensing path and the science path represent critical limitations for the detection of giant planets with a contrast lower than a few 10 super(-6) at very small separations (<0.3'') from their host star. In our previous work, we proposed a wavefront sensor based on Zernike phase-contrast methods to circumvent this problem 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 first performed measurements in the presence of Zernike or Fourier modes introduced with the deformable mirror. Our experimental results are consistent with the results in simulations, confirming the ability of our sensor to measure small aberrations (<50 nm rms) with nanometric accuracy. Following these results, we corrected the long-lived non-common path aberrations in SPHERE based on ZELDA measurements and estimated a contrast gain of 10 in the coronagraphic image at 0.2'', reaching the raw contrast limit set by the coronagraph in the instrument. In addition to this encouraging result, the simplicity of the design and its phase reconstruction algorithm makes ZELDA an excellent candidate for the online 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 facilitate the observation of cold gaseous or massive rocky planets around nearby stars.
The young systemsPZ Tel and HD 1160, hosting known low-mass companions, were observed during the commissioning of the new planet finder of the Very Large Telescope (VLT) SPHERE with several imaging ...and spectroscopic modes. We aim to refine the physical properties and architecture of both systems. We use SPHERE commissioning data and dedicated Rapid Eye Mount (REM) observations, as well as literature and unpublished data from VLT/SINFONI, VLT/NaCo, Gemini/NICI, and Keck/NIRC2. We derive new photometry and confirm the short-term (P = 0.94 d) photometric variability of the star PZ Tel A with values of 0.14 and 0.06 mag at optical and near-infrared wavelengths, respectively. SPHERE opens new horizons in the study of young brown dwarfs and giant exoplanets using direct imaging thanks to high-contrast imaging capabilities at optical and near-infrared wavelengths, as well as high signal-to-noise spectroscopy in the near-infrared domain from low resolutions (R ~ 30-50) to medium resolutions (R ~ 350).
Context. The next generation of exoplanet hunters will be targeting hot Jupiter-like exoplanets orbiting around nearby stars through direct imaging. The high contrast needed for such planet finders ...requires optical surfaces free of high spatial frequency ripples that might remain in the post-coronagraphic image as quasi-static speckles. Aims. We report results on the manufacturing of three supersmooth aspherical mirrors for the ESO/VLT-SPHERE instrument. The excellent optical quality obtained will allow the future planet hunter to increase the level of achievable contrast by a strong reduction of the noise level and residual quasi-static speckles on the image plane. Methods. The stress polishing method used on these mirrors is well suited to superpolishing aspheric components for astronomy. The main advantage of this technique is the very high optical quality obtained either on the form errors or on the high spatial frequency errors. Furthermore, the roughness can be decreased to a few angstroms, thanks to the classical polishing with a large pitch tool. Results. Interferograms obtained during polishing and in the final stage show the supersmooth quality of each mirror. Errors in the high spatial frequency range are lower than 4 nm rms WF, thereby avoiding the degradation of the post-coronagraphic image. A comparison of the power spectral density (PSD) obtained by stress polishing and the PSD of the VLT-UT3 primary mirror demonstrates that the contrast capabilities will not be limited by the aspherical mirrors.
We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT/SPHERE during the SHINE exoplanet survey. The host is a B9.5V member of the Lower-Centaurus-Crux ...subgroup of the Scorpius Centaurus OB association. The measured angular separation of the companion (1.2705 ± 0.0023”) corresponds to a projected distance of 159 ± 12 AU. We observed the target with the dual-band imaging and long-slit spectroscopy modes of the IRDIS imager to obtain its spectral energy distribution (SED) and astrometry. In addition, we reprocessed archival NACO L-band data, from which we also recover the companion. Its SED is consistent with a young (<30 Myr), low surface gravity object with a spectral type of M9γ ± 1. From comparison with the BT-Settl atmospheric models we estimate an effective temperature of Teff = 2600 ± 100 K, and comparison of the companion photometry to the COND evolutionary models yields a mass of ~29−37 MJ at the estimated age of 16−7+15 $16^{+15}_{-7}$16−7+15 Myr for the system. The star HIP 64892 is a rare example of an extreme-mass ratio system (q ~ 0.01) and will be useful for testing models relating to the formation and evolution of such low-mass objects.
The new planet finder for the Very Large Telescope (VLT), the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE), just had its first light in Paranal. A dedicated instrument for the ...direct detection of planets, SPHERE, is composed of a polametric camera in visible light, the Zurich IMager POLarimeter (ZIMPOL), and two near-infrared sub-systems: the Infra-Red Dual-beam Imager and Spectrograph (IRDIS), a multi-purpose camera for imaging, polarimetry, and long-slit spectroscopy, and the integral field spectrograph (IFS), an integral field spectrograph. We present the results obtained from the analysis of data taken during the laboratory integration and validation phase, after the injection of synthetic planets. Since no continuous field rotation could be performed in the laboratory, this analysis presents results obtained using reduction techniques that do not use the angular dierential imaging (ADI) technique. With IFS, we could retrieve a spectrum with error bars of about 0.15 mag on each channel and astrometric relative position error of 0.6 mas. For a fainter object such as HR8799d, a 13 MsubJup planet at a distance of 27 AU, IRDIS could obtain a relative astrometric error of 3 mas.
Context.Optical long-baseline interferometry is moving a crucial step forward with the advent of general-user scientific instruments that equip large aperture and hectometric baseline facilities, ...such as the Very Large Telescope Interferometer (VLTI). Aims.AMBER is one of the VLTI instruments that combines up to three beams with low, moderate and high spectral resolutions in order to provide milli-arcsecond spatial resolution for compact astrophysical sources in the near-infrared wavelength domain. Its main specifications are based on three key programs on young stellar objects, active galactic nuclei central regions, masses, and spectra of hot extra-solar planets. Methods.These key science goals led to scientific specifications, which were used to propose and then validate the instrument concept. AMBER uses single-mode fibers to filter the entrance signal and to reach highly accurate, multiaxial three-beam combination, yielding three baselines and a closure phase, three spectral dispersive elements, and specific self-calibration procedures. Results.The AMBER measurements yield spectrally dispersed calibrated visibilities, color-differential complex visibilities, and a closure phase allows astronomers to contemplate rudimentary imaging and highly accurate visibility and phase differential measurements. AMBER was installed in 2004 at the Paranal Observatory. We describe here the present implementation of the instrument in the configuration with which the astronomical community can access it. Conclusions.After two years of commissioning tests and preliminary observations, AMBER has produced its first refereed publications, allowing assessment of its scientific potential.
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