Bibcode
Murgas, F.; Chen, G.; Pallé, E.; Nortmann, L.; Nowak, G.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 622, id.A172, 12 pp.
Fecha de publicación:
2
2019
Revista
Número de citas
13
Número de citas referidas
12
Descripción
Context. Rayleigh scattering in a hydrogen-dominated exoplanet
atmosphere can be detected using ground- or space-based telescopes.
However, stellar activity in the form of spots can mimic Rayleigh
scattering in the observed transmission spectrum. Quantifying this
phenomena is key to our correct interpretation of exoplanet atmospheric
properties. Aims: We use the ten-meter Gran Telescopio Canarias
(GTC) telescope to carry out a ground-based transmission spectra survey
of extrasolar planets to characterize their atmospheres. In this paper
we investigate the exoplanet HAT-P-11b, a Neptune-sized planet orbiting
an active K-type star. Methods: We obtained long-slit optical
spectroscopy of two transits of HAT-P-11b with the Optical System for
Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS)
on August 30, 2016 and September 25, 2017. We integrated the spectrum of
HAT-P-11 and one reference star in several spectroscopic channels across
the λ 400-785 nm region, creating numerous light curves of the
transits. We fit analytic transit curves to the data taking into account
the systematic effects and red noise present in the time series in an
effort to measure the change of the planet-to-star radius ratio
(Rp/Rs) across wavelength. Results: By
fitting both transits together, we find a slope in the transmission
spectrum showing an increase of the planetary radius towards blue
wavelengths. Closer inspection of the transmission spectrum of the
individual data sets reveals that the first transit presents this slope
while the transmission spectrum of the second data set is flat.
Additionally, we detect hints of Na absorption on the first night, but
not on the second. We conclude that the transmission spectrum slope and
Na absorption excess found in the first transit observation are caused
by unocculted stellar spots. Modeling the contribution of unocculted
spots to reproduce the results of the first night we find a spot filling
factor of δ = 0.62-0.17+0.20 and a
spot-to-photosphere temperature difference of ΔT =
429-299+184 K.
Transit light curves are only available at the CDS via anonymous ftp to
http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A172
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