Paper: astro-ph/0509407
Date: Wed, 14 Sep 2005 20:32:46 GMT (353kb)

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

Authors: Santiago Arribas (1-4), Ronald L. Gilliland (1), William B. Sparks
(1), Luis Lopez-Martin (3), Evencio Mediavilla (3), and Pedro Gomez-Alvarez
(3). ((1)STScI, (2)ESA, (3)IAC, (4)CSIC.)

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

Report-no: ST ScI Eprint #1684
\\
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.

\\ ( http://arXiv.org/abs/astro-ph/0509407 , 353kb)