Evidence of active regions in the donor of the Algol-type binary V393 Scorpii and test for the dynamo model of its long cycle

TL;DR

This study detects active regions on the donor star in the Algol-type binary V393 Scorpii, supporting a dynamo model explaining its long photometric cycle through increased stellar magnetic activity during mass transfer phases.

Contribution

It provides observational evidence of active regions on the donor star, validating the dynamo model for the long cycle in Double Periodic Variables.

Findings

Active metallic emission lines indicate stellar activity.

Emission strength varies with the system's high and low states.

Supports the dynamo model predicting increased magnetic activity during mass transfer.

Abstract

V393 Scorpii is a member of the subclass of Algols dubbed Double Periodic Variables (DPVs). These are semidetached binaries with B-type primaries showing a long-photometric cycle lasting in average 33 times the orbital period. We describe the behavior of unreported metallic emission lines in the cool stellar component of this system. The emissions can be single or double for a same line and sometimes show velocity shifts regarding the velocity of the center of mass of the star. In addition, these lines are stronger during the high state. This behavior suggests the presence of active regions in the surface of the rapidly rotating A7 donor covering a fraction of the visible hemisphere, which have larger emissivity during the high state. Our finding supports the recently proposed dynamo model for the long cycle of DPVs proposed by Schleicher & Mennickent. The model predicts an increase of the dynamo number of the donor during epochs of mass transfer in this system, and a theoretical long/orbital period ratio very close to the observed one at the present system age.