A Stellar Activity F-statistic for Exoplanet Surveys (SAFE)

TL;DR

The paper introduces the SAFE indicator, a new stellar activity metric with higher detection power, capable of identifying stellar activity signals and aiding in distinguishing them from planetary signals in exoplanet surveys.

Contribution

The paper presents the SAFE indicator, a novel and more powerful stellar activity detection method validated through simulations and real star observations, improving exoplanet detection accuracy.

Findings

SAFE outperforms traditional indicators in simulations.

SAFE correlates with active region coverage on stars.

SAFE detects activity in high-variability stars and occasionally in low-variability stars.

Abstract

In the search for planets orbiting distant stars the presence of stellar activity in the atmospheres of observed stars can obscure the radial velocity signal used to detect such planets. Furthermore, this stellar activity contamination is set by the star itself and cannot simply be avoided with better instrumentation. Various stellar activity indicators have been developed that may correlate with this contamination. We introduce a new stellar activity indicator called the Stellar Activity F-statistic for Exoplanet surveys (SAFE) that has higher statistical power (i.e., probability of detecting a true stellar activity signal) than many traditional stellar activity indicators in a simulation study of an active region on a Sun-like star with moderate to high signal-to-noise. Also through simulation, the SAFE is demonstrated to be associated with the projected area on the visible side of the star covered by active regions. We also demonstrate that the SAFE detects statistically significant stellar activity in most of the spectra for HD 22049, a star known to have high stellar variability. Additionally, the SAFE is calculated for recent observations of the three low-variability stars HD 34411, HD 10700, and HD 3651, the latter of which is known to have a planetary companion. As expected, the SAFE for these three only occasionally detects activity. Furthermore, initial exploration appears to indicate that the SAFE may be useful for disentangling stellar activity signals from planet-induced Doppler shifts.