Five Decades of Chromospheric Activity in 59 Sun-like Stars and New Maunder Minimum Candidate HD 166620

TL;DR

This study compiles and analyzes five decades of chromospheric activity data for 59 Sun-like stars, identifying activity cycles and a potential Maunder minimum candidate, thereby enhancing understanding of stellar magnetic activity over long timescales.

Contribution

It provides the longest contiguous activity time series for Sun-like stars, identifies stellar activity cycles, and introduces a candidate for a Maunder minimum state.

Findings

29 stars show periodic activity cycles.

Best-fit periods for these cycles are determined.

HD 166620 is identified as a Maunder minimum candidate.

Abstract

We present five decades of chromospheric activity measurements in 59 Sun-like stars as time series. These include and extend the 35 yr of stellar chromospheric activity observations by the Mount Wilson Survey (1966--2001), and continued observations at Keck by the California Planet Search (1996--). The Mount Wilson Survey was studied closely in 1995, and revealed periodic activity cycles similar to the Sun's 11 yr cycle. The California Planet Search provides more than five decades of measurements, significantly improving our understanding of these stars' activity behavior. We have curated the activity measurements in order to create contiguous time series, and have classified the stellar sample according to a predetermined system. We have analyzed 29 stars with periodic cycles using the Lomb-Scargle periodogram, and present best-fit sinusoids to their activity time series. We report the best-fit periods for each cycling star, along with stellar parameters (T$_{eff}$, log(g), v$sin(i)$, etc.) for the entire sample. As a first application of these data, we offer a possible Maunder minimum candidate, HD 166620.