Kavli Affiliate: George R. Ricker
| First 5 Authors: Travis S. Metcalfe, Klaus G. Strassmeier, Ilya V. Ilyin, Derek Buzasi, Oleg Kochukhov
| Summary:
The consistently low activity level of the old solar analog 51 Peg not only
facilitated the discovery of the first hot Jupiter, but also led to the
suggestion that the star could be experiencing a magnetic grand minimum.
However, the 50 year time series showing minimal chromospheric variability
could also be associated with the onset of weakened magnetic braking (WMB),
where sufficiently slow rotation disrupts cycling activity and the production
of large-scale magnetic fields by the stellar dynamo, thereby shrinking the
Alfven radius and inhibiting the efficient loss of angular momentum to
magnetized stellar winds. In this Letter, we evaluate the magnetic evolutionary
state of 51 Peg by estimating its wind braking torque. We use new
spectropolarimetric measurements from the Large Binocular Telescope to
reconstruct the large-scale magnetic morphology, we reanalyze archival X-ray
measurements to estimate the mass-loss rate, and we detect solar-like
oscillations in photometry from the Transiting Exoplanet Survey Satellite,
yielding precise stellar properties from asteroseismology. Our estimate of the
wind braking torque for 51 Peg clearly places it in the WMB regime, driven by
changes in the mass-loss rate and the magnetic field strength and morphology
that substantially exceed theoretical expectations. Although our revised
stellar properties have minimal consequences for the characterization of the
exoplanet, they have interesting implications for the current space weather
environment of the system.
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