Wavelength Dependence of Activity-Induced Photometric Variations for Young Cool Stars in Hyades

TL;DR

This study examines how stellar activity-induced photometric variations in young cool stars in the Hyades cluster depend on wavelength, with implications for improving radial-velocity exoplanet detection in the near-infrared.

Contribution

It provides the first detailed analysis of wavelength-dependent stellar activity signals in young stars, constraining starspot properties and their impact on radial-velocity jitter.

Findings

Photometric variability amplitude varies with wavelength due to starspots.

Radial-velocity jitter is likely more suppressed in the NIR than in optical wavelengths.

Starspot size and temperature contrast are approximately 10% and 0.95, respectively.

Abstract

We investigate photometric variations due to stellar activity which induce systematic radial-velocity errors (so-called "jitter") for the four targets in the Hyades open cluster observed by the K2 mission (EPIC 210721261, EPIC 210923016, EPIC 247122957, and EPIC 247783757). Applying Gaussian process regressions to the K2 light curves and the near-infrared (NIR) light curves observed with the IRSF 1.4-m telescope, we derive the wavelength dependences of the photometric signals due to stellar activity. To estimate the temporal variations in the photometric variability amplitudes between the two observation periods of K2 and IRSF, separated by more than 2 years, we analyze a number of K2 targets in Hyades that have also been observed in Campaigns 4 and 13 and find a representative variation rate over 2 years of 38%pm71%. Taking this temporal variation into account, we constrain projected sizes and temperature contrast properties of the starspots in the stellar photosphere to be approximately 10% and 0.95, respectively. These starspot properties can induce relatively large differences in the variability amplitude over different observational passbands, and we find that radial-velocity jitter may be more suppressed in the NIR than previously expected. Our result supports profits of on-going exoplanet search projects that are attempting to detect or confirm young planets in open clusters via radial-velocity measurements in the NIR.