SOAP 2.0: A tool to estimate the photometric and radial velocity variations induced by stellar spots and plages

TL;DR

SOAP 2.0 is a new tool that accurately estimates and helps correct photometric and radial velocity variations caused by stellar spots and plages, considering convective blueshift inhibition and limb effects.

Contribution

The paper introduces SOAP 2.0, enhancing previous models by including convective blueshift inhibition, limb brightening, and realistic contrast ratios for better activity signal estimation.

Findings

SOAP 2.0 accurately reproduces activity variations for spots and plages.

The ratio of FWHM to RV amplitude indicates the active region type.

SOAP 2.0 can correct activity-induced signals in stellar observations.

Abstract

This paper presents SOAP 2.0, a new version of the SOAP code that estimates in a simple way the photometric and radial velocity variations induced by active regions. The inhibition of the convective blueshift inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the convective blueshift effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the full width at half maximum (FWHM) and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with \vsini$\le8$\kms. A ratio smaller than three implies a spot, while a larger ratio implies a plage. Using the observation of HD189733, we show that SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star $\alpha$ Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation.