Unveiling stellar magnetic activity using CoRoT seismic observations

TL;DR

This paper investigates stellar magnetic activity cycles by analyzing CoRoT seismic data, revealing activity-related frequency shifts and amplitude modulations in stars similar to the Sun, and establishing a lower limit for the activity cycle period.

Contribution

It presents the first detection of magnetic activity cycles in stars other than the Sun using seismic observations from CoRoT, including a lower limit estimate for the cycle period.

Findings

Detected magnetic activity cycle in HD49933 with a period of at least 120 days.

Observed anticorrelation between mode amplitude and frequency shifts.

Confirmed star's activity status through Ca H and K line measurements.

Abstract

It is well known that in the Sun, the frequencies and amplitudes of acoustic modes vary throughout the solar cycle. Indeed, while the magnetic activity goes towards its maximum, the frequencies of the modes increase and their amplitudes decrease. We have analyzed data from the CoRoT mission on a few stars that exhibit solar-like oscillations. The study of HD49933 (observed during 60 days and 137 days spanning a total of 400 days) showed a modulation of the maximum amplitude per radial mode and the frequency shifts of the modes, showing magnetic activity in this rapidly rotating star. Moreover, both properties vary in an anticorrelated way and the data allowed us to establish a lower limit for the activity-cycle period of ~120 days. Measurements in Ca H and K lines confirmed that this star is in the "active stars" category. We will also discuss the results obtained for other targets such as HD181420 and HD49835 for which we have investigated a similar behavior.