Exploring the Potential of Integral Field Spectroscopy Observing Extrasolar Planet Transits: Ground Based Observations of the Atmospheric Na in HD209458b

Abstract

We explore the use of Integral Field Spectroscopy (IFS) to observe extrasolar planet transits. Although this technique should find its full potential in space observations (e.g. JWST, TPF), we have tested its basics with ground based time series observations of HD209458b obtained with WHT+INTEGRAL during a transit. For this analysis we used 5550 spectra, obtained in 150 exposures during a period of >7 hours. We found that IFS offers 3 fundamental advantages with respect to previously used methods. (i) It improves the effective S/N in photon limited observations by distributing the light coming from the star into the 2 dimensions of the detector. (ii) This type of IFS data allows to 'auto-calibrate' instrumental and background effects. (iii) Since the star image characteristics as well as its photometric properties are extracted from the same data-cube, it is possible to decorrelate photometric instabilities induced by PSF variations. These data have also allowed us to explore the accuracy limits of ground based 'relative' spectrophotometry. This was done using a photometric index that probes the NaD lines, for which we obtained a nominal 1-sigma error of ~1.0x10^-4. This result, based on observations of only 1 transit, indicates that this type of ground observation can constrain the characterization of the transmission spectrum of extrasolar planets. The present observations are compatible with no extra NaD depression during the transit. Though this result seems to be inconsistent with the recently reported HST-STIS findings we point out its limited statistical meaning: the results disagree within 1-sigma, but agree within 2-sigma. We also give some recommenda-tions to instrument developers in order to enhance the efficiency of the method.

15 pages, 2 tables, 10 figures. To appear in PASP (January 2006)

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• Light pollution at the Roque de los Muchachos Observatory

Cited by in corpus (5)

• Sodium Absorption From the Exoplanetary Atmosphere of HD189733b Detected in the Optical Transmission Spectrum
• The Broadband Infrared Emission Spectrum of the Exoplanet HD 189733b
• Determining atmospheric conditions at the terminator of the hot-Jupiter HD209458b
• GTC OSIRIS transiting exoplanet atmospheric survey: detection of sodium in XO-2b from differential long-slit spectroscopy
• Toroidal Atmospheres around Extrasolar Planets