Bibcode
DOI
Arribas, Santiago; Gilliland, Ronald L.; Sparks, William B.; López-Martín, Luis; Mediavilla, Evencio; Gómez-Alvarez, Pedro
Referencia bibliográfica
The Publications of the Astronomical Society of the Pacific, Volume 118, Issue 839, pp. 21-36.
Fecha de publicación:
1
2006
Número de citas
9
Número de citas referidas
5
Descripción
We explore the use of integral field spectroscopy (IFS) for observing
extrasolar planet transits. Although this technique should find its full
potential in space-based observations (e.g., James Webb Space Telescope,
Terrestrial Planet Finder), we have tested its basics with ground-based
time-series observations of HD 209458b obtained with the William
Herschel Telescope optical fiber system INTEGRAL during a transit in
2004 August 17/18. For this analysis we have used 5550 spectra (from a
potential of ~30,000) obtained in 150 exposures during a period of more
than 7 hr. We have found that IFS offers three fundamental advantages
with respect to previously used methods (based on imaging or standard
slit spectroscopy). First, it improves the effective signal-to-noise
ratio in photon-limited observations by distributing the light coming
from the star into the two dimensions of the detector. Second, this type
of IFS data allows us to ``autocalibrate'' instrumental and background
effects. Third, since the star image characteristics (i.e., seeing,
spatial shifts, etc.) as well as its photometric properties are
extracted from the same data cube, it is possible to decorrelate
photometric instabilities induced by point-spread function (or
instrument) 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 Na D lines, for which we
obtained a nominal 1 σ error of ~1.0 × 10-4. This
result, based on observations of only one transit, indicates that this
type of ground observation can constrain the characterization of the
transmission spectrum of extrasolar planets, especially if they cover
multiple transits under good weather conditions. The present
observations are compatible with no extra Na D depression during the
transit. Although this result seems to be inconsistent with the recently
reported Hubble Space Telescope STIS findings, we point out its limited
statistical meaning: the results disagree within 1 σ, but agree
within 2 σ. This method requires careful and specific reductions,
and details about this process are given. We also give some
recommendations to instrument developers in order to enhance the
efficiency of the method.