Stellar cycle and evolution of polar spots in an M+WD binary
The Astrophysical Journal(2024)
Abstract
Stellar activity cycles reveal continuous relaxation and induction of
magnetic fields. The activity cycle is typically traced through the observation
of cyclic variations in total brightness or Ca H K emission flux of stars, as
well as cyclic variations of orbital periods of binary systems. In this work,
we report the identification of a semi-detached binary system (TIC 16320250)
consisting of a white dwarf (0.67 M_⊙) and an active M dwarf (0.56
M_⊙). The long-term multi-band optical light curves spanning twenty
years revealed three repeated patterns, suggestive of a possible activity cycle
of about ten years of the M dwarf. Light curve fitting indicates the repeated
variation is caused by the evolution, particularly the motion, of polar spots.
The significant Ca H K, Hα, ultra-violet, and X-ray emissions imply that
the M dwarf is one of the most magnetically active stars. We propose that in
the era of large time-domain photometric sky surveys (e.g., ASAS-SN, ZTF, LSST,
Sitian), long-term light curve modeling can be a valuable tool for tracing and
revealing stellar activity cycle, especially for stars in binary systems.
MoreTranslated text
Key words
Neutron stars,White dwarf stars,Binary stars,Stellar activity
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