Surface velocity network with anti-solar differential rotation on the active K-giant $\sigma$ Geminorum

TL;DR

This study applies local correlation tracking to stellar Doppler images of the active K-giant $\sigma$ Gem, revealing weak anti-solar differential rotation and poleward spot migration, advancing understanding of stellar surface flows.

Contribution

First application of local correlation tracking to stellar data, demonstrating surface flow patterns including anti-solar differential rotation and poleward migration.

Findings

Weak anti-solar differential rotation with α≈-0.0022

Poleward spot migration at 220 m/s

Consistent with previous studies and theoretical models

Abstract

We demonstrate the power of the local correlation tracking technique on stellar data for the first time. We recover the spot migration pattern of the long-period RS CVn-type binary $\sigma$ Gem from a set of six Doppler images from 3.6 consecutive rotation cycles. The resulting surface flow map suggests a weak anti-solar differential rotation with $\alpha\approx-0.0022\pm0.0016$, and a coherent poleward spot migration with an average velocity of $220\pm10$ m s$^{-1}$. This result agrees with our recent findings from another study and could also be confirmed theoretically.