During the first half of main-sequence lifetimes, the evolution of rotation and magnetic activity in solar-type stars appears to be strongly coupled. Recent observations suggest that rotation rates evolve much more slowly beyond middle-age, while stellar activity continues to decline. We aim to characterize this mid-life transition by combining archival stellar activity data from the Mount Wilson Observatory with asteroseismology from the Transiting Exoplanet Survey Satellite (TESS). For two stars on opposite sides of the transition (88 Leo and ρ CrB), we independently assess the mean activity levels and rotation periods previously reported in the literature. For the less active star (ρ CrB), we detect solar-like oscillations from TESS photometry, and we obtain precise stellar properties from asteroseismic modeling. We derive updated X-ray luminosities for both stars to estimate their mass-loss rates, and we use previously published constraints on magnetic morphology to model the evolutionary change in magnetic braking torque. We then attempt to match the observations with rotational evolution models, assuming either standard spin-down or weakened magnetic braking. We conclude that the asteroseismic age of ρ CrB is consistent with the expected evolution of its mean activity level, and that weakened braking models can more readily explain its relativelymore »
The Evolution of Rotation and Magnetic Activity in 94 Aqr Aa from Asteroseismology with TESS
Most previous efforts to calibrate how rotation and magnetic activity
depend on stellar age and mass have relied on observations of clusters,
where isochrones from stellar evolution models are used to determine the
properties of the ensemble. Asteroseismology employs similar models to
measure the properties of an individual star by matching its normal modes
of oscillation, yielding the stellar age and mass with high precision. We
use 27 days of photometry from the {\it Transiting Exoplanet Survey
Satellite} (TESS) to characterize solar-like oscillations in the G8
subgiant of the 94~Aqr triple system. The resulting stellar properties,
when combined with a reanalysis of 35 years of activity measurements from
the Mount Wilson HK project, allow us to probe the evolution of rotation
and magnetic activity in the system. The asteroseismic age of the
subgiant agrees with a stellar isochrone fit, but the rotation period is
much shorter than expected from standard models of angular momentum
evolution. We conclude that weakened magnetic braking may be needed to
reproduce the stellar properties, and that evolved subgiants in the
hydrogen shell-burning phase can reinvigorate large-scale dynamo action
and briefly sustain magnetic activity cycles before ascending the red
giant branch.
- Authors:
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Award ID(s):
- 1812634
- Publication Date:
- NSF-PAR ID:
- 10175082
- Journal Name:
- The Astrophysical journal
- ISSN:
- 2471-4259
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Publisher's Version of Record
- https://doi.org/10.3847/1538-4357/aba963
