Characterising the stellar differential rotation based on largest-spot statistics from ground-based photometry

TL;DR

This study models the spot distribution and differential rotation of two active Solar-type stars using ground-based photometry, revealing non-monotonic rotation in V889 Her and rigid rotation in LQ Hya, challenging the universality of solar differential rotation.

Contribution

It introduces a statistical approach to analyze stellar spot distributions and differential rotation from ground-based photometry, providing new insights into stellar rotation profiles.

Findings

V889 Her exhibits non-monotonic differential rotation with a maximum at 37-40° latitude.

LQ Hya rotates nearly as a rigid body, with little differential rotation.

Results support the idea that solar differential rotation is not universal among solar-type stars.

Abstract

Stellar spot distribution has consequences on the observable periodic signals in long-time baseline ground-based photometry. We model the statistics of the dominating spots of two young and active Solar-type stars, V889 Her and LQ Hya, in order to obtain information on the underlying spot distribution, rotation of the star, as well as the orientation of the stellar axis of spin. By calculating estimates for spot-induced periodicities in independent subsets of photometric data, we obtain statistics based on the dominating spots in each subset, giving rise to largest-spot statistics accounting for stellar geometry and rotation, including differential rotation. Our simple statistical models are able to reproduce the observed distribution of photometric signals rather well. This also enables us to estimate the dependence of angular velocity of the spots as a function of latitude. Our results indicate that V889 Her has a non-monotonic differential rotation curve with a maximum angular velocity between latitudes of 37-40 deg and lower angular velocity at the pole than the equator. Our results for LQ Hya indicate that the star rotates much like a rigid body. Furthermore, the results imply that the monotonic Solar differential rotation curve may not be a universal model for other solar-type stars. The non-monotonicity of the differential rotation of V889 Her is commonly produced in magnetohydrodynamic simulations, which indicates that our results are realistic from a theoretical perspective.