X-Ray, UV, and Optical Observations of Proxima Centauri's Stellar Cycle

TL;DR

This study combines multi-wavelength observations over a decade to confirm an 8-year stellar cycle in Proxima Centauri across X-ray, UV, and optical bands, revealing anti-correlated activity patterns and potential coronal mass ejections.

Contribution

It provides the first comprehensive multi-band analysis confirming a consistent 8-year stellar cycle in Proxima Centauri with detailed modeling and new observational data.

Findings

Confirmed 8-year stellar cycle across X-ray, UV, and optical bands.

UV and X-ray intensities are anti-correlated with optical brightness.

Possible indications of two coronal mass ejections.

Abstract

Proxima Cen (GJ 551; dM5.5e) is one of only about a dozen fully convective stars known to have a stellar cycle, and the only one to have long-term X-ray monitoring. A previous analysis found that X-ray and mid-UV observations, particularly two epochs of data from Swift, were consistent with a well sampled 7 yr optical cycle seen in ASAS data, but not convincing by themselves. The present work incorporates several years of new ASAS-SN optical data and an additional five years of Swift XRT and UVOT observations, with Swift observations now spanning 2009 to 2021 and optical coverage from late 2000. X-ray observations by XMM-Newton and Chandra are also included. Analysis of the combined data, which includes modeling and adjustments for stellar contamination in the optical and UV, now reveals clear cyclic behavior in all three wavebands with a period of 8.0 yr. We also show that UV and X-ray intensities are anti-correlated with optical brightness variations caused by the cycle and by rotational modulation, discuss possible indications of two coronal mass ejections, and provide updated results for the previous finding of a simple correlation between X-ray cycle amplitude and Rossby number over a wide range of stellar types and ages.