Spectral characterization and differential rotation study of active CoRoT stars

TL;DR

This study analyzes the rotational variability of young, active stars observed by CoRoT, revealing that differential rotation and starspot evolution cause complex light curve patterns, with spectral analysis confirming their stellar properties and low ages.

Contribution

It provides the first detailed spectral and rotational analysis of a sample of CoRoT stars exhibiting beating patterns, linking photometric variability to differential rotation and stellar age.

Findings

Light curves are consistent with rotational modulation by starspots.

Differential rotation explains the beating patterns in the light curves.

Spectral analysis confirms the stars are young, dwarf stars of spectral types F to mid-K.

Abstract

The CoRoT space telescope observed nearly 160 000 light curves. Among the most outstanding is that of the young, active planet host star CoRoT-2A. In addition to deep planetary transits, the light curve of CoRoT-2A shows strong rotational variability and a superimposed beating pattern. To study the stars that produce such an intriguing pattern of photometric variability, we identified a sample of eight stars with rotation periods between 0.8 and 11 days and photometric variability amplitudes of up to 7.5 %, showing a similar CoRoT light curve. We also obtained high-resolution follow-up spectroscopy with TNG/SARG and carried out a spectral analysis with SME and MOOG. We find that the color dependence of the light curves is consistent with rotational modulation due to starspots and that latitudinal differential rotation provides a viable explanation for the light curves, although starspot evolution is also expected to play an important role. Our MOOG and SME spectral analyses provide consistent results, showing that the targets are dwarf stars with spectral types between F and mid-K. Detectable Li i absorption in four of the targets confirms a low age of 100-400 Myr also deduced from gyrochronology. Our study indicates that the photometric beating phenomenon is likely attributable to differential rotation in fast-rotating stars with outer convection zones.