P. Ballerini, G. Micela, A. F. Lanza, I. Pagano
Stellar magnetic activity is a source of noise in the study of the transits
of extrasolar planets. It induces flux variations which affect significantly
the transit depth determination and the derivations of planetary and stellar
parameters. Furthermore, the colour dependence of stellar activity may
significantly influence the characterization of planetary atmospheres. Here we
present a systematic approach to quantify the corresponding stellar flux
variations as a function of wavelength bands. We consider a star with spots
covering a given fraction of its disc and model the variability in the UBVRIJHK
photometric system and in the Spitzer/IRAC wavebands for dwarf stars from G to
M spectral types. We compare activity-induced flux variations in different
passbands with planetary transits and quantify how they affect the
determination of the planetary radius and the analysis of the transmission
spectroscopy in the study of planetary atmospheres. We suggest that the
monitoring of the systems by using broad band photometry, from visible to
infrared, helps to constraining activity effects. The ratio of the relative
variations of the stellar fluxes in short wavelength optical bands (e.g., U or
B) to near infrared ones (e.g., J or K) can be used to distinguish starspot
brightness dips from planetary transits in a stellar light curve. In addition
to the perturbations in the measurement of the planetary radius, we find that
starspots can affect the determination of the relative semimajor axis and the
inclination of the planetary orbit which have a significant impact on the
derivation of the stellar density from the transit light curves.
View original:
http://arxiv.org/abs/1201.3514
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