Stellar Activity Cycles Grow Longer and Weaker Before Disappearing

Abstract

In 2007, Erika Bohm-Vitense published a provocative figure suggesting that the solar rotation period and activity cycle made the Sun an outlier compared to the trends observed for stars in the Mount Wilson HK survey. A decade later, after the discovery of weakened magnetic braking (WMB), an evolutionary scenario was proposed that could account for the properties of the Sun if activity cycles grow longer and weaker in the WMB regime. Recent observations of the gradual onset of WMB suggest that the efficiency of the global stellar dynamo declines by at least two orders of magnitude as the stellar Rossby number approaches a critical point slightly above the solar value. A new sample of activity cycle data from the California Legacy Survey suggests that the Sun is not an outlier, and unambiguously confirms that activity cycles grow longer and weaker on stellar evolutionary timescales.

Published in RNAAS, arXiv version includes data behind Fig.1 in an appendix and csv file

References in corpus (8)

• Weakened magnetic braking as the origin of anomalously rapid rotation in old field stars
• The Mount Wilson Observatory S-index of the Sun
• The Solar Twin Planet Search: The age - chromospheric activity relation
• Forward Modeling of the Kepler Stellar Rotation Period Distribution: Interpreting Periods from Mixed and Biased Stellar Populations
• Magnetic Evolution and the Disappearance of Sun-like Activity Cycles
• Understanding solar cycle variability
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• Weakened Magnetic Braking Signals the Collapse of the Global Stellar Dynamo