Magnetic activity cycles in solar-like stars: The cross-correlation technique of p-mode frequency shifts

TL;DR

This paper develops and validates a cross-correlation technique to measure magnetic activity-induced p-mode frequency shifts in solar-like stars, providing precise error estimates and revealing magnetic cycles in multiple stars.

Contribution

It introduces a validated cross-correlation method with error estimation for detecting stellar magnetic activity cycles from p-mode frequency shifts.

Findings

Confirmed magnetic cycle in HD 49933.

Detected magnetic variations in KIC 3733735.

KIC 7940546 appears magnetically quiet.

Abstract

Aims. We aim studying the use of cross-correlation techniques to infer the frequency shifts induced by changing magnetic fields in the p-mode frequencies and provide precise estimation of the error bars. Methods. This technique and the calculation of the associated errors is first tested and validated on the Sun where the p-mode magnetic behaviour is very well known. These validation tests are performed on 6000-day time series of Sun-as-a-star observations delivered by the SoHO spacecraft. Errors of the frequency shifts are quantified through Monte Carlo simulations. The same methodology is then applied to three solar-like oscillating stars: HD 49933, observed by CoRoT, as well as KIC 3733735 and KIC 7940546 observed by Kepler. Results. We first demonstrate the reliability of the error bars computed with the Monte Carlo simulations using the Sun. From the three analyzed stars we confirm the presence of a magnetic activity cycle with this methodology in HD 49933 and we unveil seismic signature of on going magnetic variations in KIC 3733735. Finally, the third star, KIC 7940546, seems to be in a quiet regime.