The California Legacy Survey V. Chromospheric Activity Cycles in Main Sequence Stars

TL;DR

This study analyzes chromospheric activity cycles in 710 nearby stars over twenty years, providing insights into stellar magnetic behavior and aiding exoplanet detection by mitigating stellar activity effects.

Contribution

It presents the largest spectroscopic dataset of stellar activity cycles, establishing a detailed relationship between cycle periods and stellar temperature across a broad sample.

Findings

138 stars exhibit detectable activity cycles.

Cycle periods tightly constrained between specific activity levels.

S-values help mitigate stellar activity in exoplanet detection.

Abstract

We present optical spectroscopy of 710 solar neighborhood stars collected over twenty years to catalog chromospheric activity and search for stellar activity cycles. The California Legacy Survey stars are amenable to exoplanet detection using precise radial velocities, and we present their Ca II H and K time series as a proxy for stellar and chromospheric activity. Using the HIRES spectrometer at Keck Observatory, we measured stellar flux in the cores of the Ca II H and K lines to determine S-values on the Mt. Wilson scale and the log(R'HK) metric, which is comparable across a wide range of spectral types. From the 710 stars, with 52,372 observations, 285 stars are sufficiently sampled to search for stellar activity cycles with periods of 2-25 years, and 138 stars show stellar cycles of varying length and amplitude. S-values can be used to mitigate stellar activity in the detection and characterization of exoplanets. We use them to probe stellar dynamos and to place the Sun's magnetic activity into context among solar neighborhood stars. Using precise stellar parameters and time-averaged activity measurements, we find tightly constrained cycle periods as a function of stellar temperature between log(R'HK) of -4.7 and -4.9, a range of activity in which nearly every star has a periodic cycle. These observations present the largest sample of spectroscopically determined stellar activity cycles to date.