Spectroscopy Of Extrasolar Planets Research Articles

Performance of the VLT Planet Finder SPHERE

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 Plan\'etologie et d'Astrophysique 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 $5\sigma$ 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.

Exoplanet Transit Spectroscopy and Photometry

Photometry and spectroscopy of extrasolar planets provides information about their atmospheres and surfaces. From extrasolar planet spectra and photometry we can infer the composition and temperature of the atmospheres as well as the presence of molecular species, including biosignature gases or surface features. So far photometry has been published for three different transiting hot Jupiters (gas giant planets in short-period orbits), opening the era of comparative exoplanetology.

Color-differential astrometry with the NGST. Application to the spectroscopy of giant extrasolar planets

The color-differential astrometry method consists in measuring the variations of the photocenter position with wavelength. This yields spectral information on the spatial structure of an unresolved source, and could allow, among other applications, the direct detection and spectroscopy of extrasolar planets. We give some estimates of signal-to-noise ratio for CDA using the the NGST mid-infrared instrument (MIRI) spectrograph, assuming for the planetary luminosity either black-body models or recent synthetic spectra. Giant Planets around nearby Sun-like stars are potentially observable over a wide-range of orbital distances, if the precision on the measurement is limited by the fundamental noises. Space-based CDA would then be complementary, in terms of star-planet separation, to ground based interferometry and to coronography. This assumes, though, a proper chromatic stability of the instrument. This note introduces some possible methods for instrumental internal calibration, and presents a possible spatial design for a calibration by spatial modulation.