Bibcode
Yan, F.; Pallé, E.; Fosbury, R. A. E.; Petr-Gotzens, M. G.; Henning, Th.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 603, id.A73, 10 pp.
Fecha de publicación:
7
2017
Revista
Número de citas
72
Número de citas referidas
68
Descripción
Transit spectroscopy is one of the most commonly used techniques for
exoplanet atmosphere characterisation. This technique has been used to
detect ionised and neutral species in exoplanet atmospheres by comparing
the observed stellar lines in and out of transit. The centre-to-limb
variation (CLV) of the stellar lines across the stellar disk is an
important effect for transmission spectroscopy, since it results in a
change of stellar line depth when the planet transits different parts of
the stellar disk. We reanalysed the transit data of HD 189733b taken
with the HARPS spectrograph to study the CLV effect during transit. The
transmission light curve of the Na i D line so obtained shows a clear
imprint of the CLV effect. We used a one-dimensional non-LTE stellar
spectral model to simulate the CLV effect. After applying the
correction, the measurement of the Na i absorption in the atmosphere of
HD 189733b becomes better determined. We compared the CLV effect of HD
189733b to that of HD 209458b. The CLV effects are different for these
two benchmark planetary systems and this is attributed to their
different stellar effective temperatures and transit impact parameters.
We then explored the general CLV effect that occurs during exoplanet
transits. Normally, a star with a lower effective temperature exhibits a
stronger CLV effect and its CLV feature extends over a relatively broad
wavelength range. The transit impact parameter (b) describes the transit
trajectory on the stellar disk and thus determines the actual
manifestation of the CLV effect. We introduced a b-diagram which
describes the behaviour of the CLV effect as the function of different
impact parameters. With improving observational precision, a careful
modelling and correction of the CLV effect is necessary for exoplanet
atmosphere characterisation using transit spectroscopy.
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