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Stellar activity patterns are responsible for jitter effects that areobserved at different timescales and amplitudes. These effects are currently inthe focus of many exoplanet search projects, since the lack of a well-definedcharacterization and correction strategy hampers the detection of the signalsassociated with small exoplanets. Accurate simulations of the stellarphotosphere can provide synthetic time series data. These may help toinvestigate the relation between activity jitter and stellar parameters whenconsidering different active region patterns. Moreover, jitters can be analysedat different wavelength scales in order to design strategies to remove orminimize them. In this work we present the StarSim tool, which is based on amodel for a spotted rotating photosphere built from the integration of thespectral contribution of a fine grid of surface elements. The model includesall significant effects affecting the flux intensities and the wavelength ofspectral features produced by active regions and planets. A specificapplication for the characterization and modelling of the spectral signature ofactive regions is considered, showing that the chromatic effects of faculae aredominant for low temperature contrasts of spots. Synthetic time series aremodelled for HD 189733. Our algorithm reproduces both the photometry and theRVs to good precision, generally better than the studies published to date. Weevaluate the RV signature of the activity in HD 189733 by exploring a grid ofsolutions from the photometry. We find that the use of RV data in the inverseproblem could break degeneracies and allow for a better determination of somestellar and activity parameters. In addition, the effects of spots are studiedfor a set of simulated transit photometry, showing that these can introducevariations which are very similar to the signal of an atmosphere dominated bydust.

Modelling the photosphere of active stars for planet detection and characterization