Double-edged sword: the influence of tidal interaction on stellar activity in binaries

TL;DR

This study investigates how tidal interactions in binary stars influence stellar activity, revealing both enhancement and suppression effects, and suggesting a complex, dual role of tidal forces in stellar magnetic activity.

Contribution

It provides the first evidence of potential super-saturation in chromospheric activity and explores the dual impact of tidal interactions on stellar magnetic phenomena.

Findings

Binary stars show enhanced activity compared to single stars in certain color ranges.

A possible decline in activity for close binaries suggests super-saturation or magnetic suppression.

Tidal interactions have a dual role, both increasing and decreasing stellar activity.

Abstract

Using the LAMOST DR7 low-resolution spectra, we carried out a systematic study of stellar chromospheric activity in both single and binary stars. We constructed a binary sample and a single-star sample, mainly using the binary belt and the main sequence in the Hertzsprung-Russell diagram, respectively. By comparing the $S$ indices between single and binary stars within each color bin, we found for K type stars, binaries exhibit enhanced activity compared to single stars, which could be attributed to the increase in spin rate caused by tidal synchronization or to the interactions of magnetic fields. Both single stars and binaries fall on a common sequence in the activity-period relation, indicating that chromospheric activities of binaries are dominated by the more active components. More intriguingly, in some color ranges, a slight decline of the $S$ index for smaller orbital period was observed for binary stars. Although the possibility of sample selection effects cannot be excluded, this may mark the first example of super-saturation (i.e., caused by reduced active regions) being detected in chromospheric activity, or provide evidence of the suppressing effect on the magnetic dynamo and stellar activities by strong tidal interaction in very close binaries. Our study suggests that tidal interaction acts as a double-edged sword in relation to stellar activities.