The first Doppler imaging of the active binary prototype RS Canum Venaticorum

Abstract

We present the first Doppler images of the prototypical active binary star RS CVn, derived from high-resolution spectra observed in 2004, 2016 and 2017, using three different telescopes and observing sites. We apply the least-squares deconvolution technique to all observed spectra to obtain high signal-to-noise line profiles, which are used to derive the surface images of the active K-type component. Our images show a complex spot pattern on the K star, distributed widely in longitude. All starspots revealed by our Doppler images are located below a latitude of about 70${}^{\circ }$. In accordance with previous light-curve modeling studies, we find no indication of a polar spot on the K star. Using Doppler images derived from two consecutive rotational cycles, we estimate a surface differential rotation rate of $\Delta \Omega =-0.039\pm 0.003rad{d}^{-1}$ and $\alpha =\Delta \Omega /{\Omega }_{eq}=-0.030\pm 0.002$ for the K star. Given the limited phase coverage during those two rotations, the uncertainty of our differential rotation estimate is presumably higher.

11 pages, 10 figures, accepted for publication in MNRAS

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