The Ups and Downs of Alpha Centauri

TL;DR

This study reports on the long-term coronal activity cycles of Alpha Centauri A and B using X-ray observations, revealing an 8.2-year cycle for B and a prolonged low state for A, comparable to solar activity patterns.

Contribution

The paper provides the first detailed long-term X-ray activity cycles for Alpha Centauri A and B, including a potential 19-year cycle for A, based on multi-year Chandra, XMM-Newton, and ROSAT data.

Findings

Alpha Centauri B has an 8.2-year X-ray activity cycle.

Alpha Centauri A was in a low activity state, similar to solar minima.

A possible 19-year cycle for Alpha Centauri A is suggested.

Abstract

The following is a progress report on the long-term coronal activity of Alpha Centauri A (HD128620: G2V) and B (HD128621: K1V). Since 2005, Chandra X-ray Observatory has carried out semiannual pointings on AB, mainly with the High Resolution Camera (HRC-I), but also on two occasions with the Low-Energy Transmission Grating Spectrometer (LETGS), fully resolving the close pair in all cases. During 2008-2013, Chandra captured the rise, peak, and initial decline of B's coronal luminosity. Together with previous high states documented by ROSAT and XMM-Newton, the long-term X-ray record suggests a period of 8.2+/-0.2 yr, compared to 11 yr for the Sun; with a minimum-to-peak contrast of 4.5, about half the typical solar cycle amplitude. Meanwhile, the A component has been mired in a Maunder-Minimum-like low state since 2005, initially recognized by XMM. But now, A finally appears to be climbing out of the extended lull. If interpreted simply as an over-long cycle, the period would be 19.1+/-0.7 yr, with a minimum-to-peak contrast of 3.4. The short X-ray cycle of B, and possibly long cycle of A, are not unusual compared with the diverse (albeit much lower amplitude) chromospheric variations recorded, for example, by the HK Project. Further, the deep low state of A also is not unusual, but instead is similar to the Sun during recent minima of the sunspot cycle.