摘要：We observed the hot Jupiter HAT-P-32b (also
known as HAT-P-32Ab) to determine its optical transmission spectrum by measuring the
wavelength-dependent, planet-to-star radius ratios in the region between
518−918 nm. We used the
OSIRIS instrument at the Gran Telescopio CANARIAS (GTC) in long-slit spectroscopy mode,
placing HAT-P-32 and a reference star in the same
slit and obtaining a time series of spectra covering two transit events. Using the best
quality data set, we were able to yield 20 narrowband transit light curves, with each
passband spanning a 20 nm wide interval. After removal of all systematic noise signals and
light curve modeling, the uncertainties for the resulting radius ratios lie between 337
and 972 ppm. The radius ratios show little variation with wavelength, suggesting a high
altitude cloud layer masking any atmospheric features. Alternatively, a strong depletion
in alkali metals or a much smaller than expected planetary atmospheric scale height could
be responsible for the lack of atmospheric features. Our result of a flat transmission
spectrum is consistent with a previous ground-based study of the optical spectrum of this
planet. This agreement between independent results demonstrates that ground-based
measurements of exoplanet atmospheres can give reliable and reproducible results despite
the fact that the data often is heavily affected by systematic noise as long as the noise
source is well understood and properly corrected. We also extract an optical spectrum of
the M-dwarf companion HAT-P-32B. Using PHOENIX stellar atmosphere models we determine an
effective temperature of Teff = 3187+60-71 K, which is slightly colder than previous studies
relying only on broadband infrared data.
关键词：planets and satellites: atmospheres;techniques: spectroscopic
