Analysis of the MOST light curve of the heavily spotted K2IV component of the single-line spectroscopic binary II Pegasi

TL;DR

This study analyzes continuous photometric data of II Pegasi, revealing star spots and flares, and suggests differential rotation of the primary star better explains the observed brightness variations.

Contribution

It provides detailed analysis of spot activity and flares on II Pegasi, and introduces a differential rotation model fitting the light curve more accurately than solid-body rotation.

Findings

Flares prefer phases with the most spotted hemisphere.

No primary minimum detected from secondary transits.

Differential rotation model fits the data better.

Abstract

Continuous photometric observations of the visible component of the single-line, K2IV spectroscopic binary II Peg carried out by the MOST satellite during 31 consecutive days in 2008 have been analyzed. On top of spot-induced brightness modulation, eleven flares were detected of three distinct types characterized by different values of rise, decay and duration times. The flares showed a preference for occurrence at rotation phases when the most spotted hemisphere is directed to the observer, confirming previous similar reports. An attempt to detect a grazing primary minimum caused by the secondary component transiting in front of the visible star gave a negative result. The brightness variability caused by spots has been interpreted within a cold spot model. An assumption of differential rotation of the primary component gave a better fit to the light curve than a solid-body rotation model.