Short-period stellar activity cycles with Kepler photometry

TL;DR

This study analyzes short-period stellar activity cycles in fast-rotating stars using Kepler photometry, revealing a new activity branch linked to alpha-quenching effects that influence magnetic dynamo saturation.

Contribution

It introduces two non-spectral methods to measure stellar cycle periods and identifies a new activity branch connected to alpha-quenching in stellar dynamos.

Findings

Measured cycle periods in 462 stars up to 1000 days.

Discovered a new activity branch in the Saar-Brandenburg diagram.

Linked the branch formation to alpha-quenching effects.

Abstract

We study the short-periodic component of stellar activity with a cycle periods Pcyc up to 1000 days using the Kepler mission photometry of fast-rotating (rotational periods from 1 to 4 days) stars with spectra of M4V to F3V. Applying the originally developed two non-spectral methods, we measured the effective period of stellar cycles in 462 objects. The obtained results are in accordance with previous measurements by Vida et al. (2014), do not seem to result from a beating effect. The performed measurements of Pcyc cluster in a specific branch which covers the previously unstudied region in the Saar-Brandenburg (1999) diagram, and connects the branch of inactive stars with the area populated by super-active objects. It is shown that the formation of the discovered branch is due to the alpha-quenching effect, which saturates the magnetic dynamo and decreases the cycle periods with the increase of inverted Rossby number. This finding is important in the context of the discussion on catastrophic quenching and other heuristic approximations of the non-linear alpha-effect.