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 Transiting Exoplanet Survey Satellite 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 yr 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.
NSFNational Science Foundation (NSF) [AST-1812634]; NASANational Aeronautics & Space Administration (NASA) [NNX17AF27G, NNX16AB97G, 80NSSC20K0458, 80NSSC19K0374]; Visiting Fellowship at the Max Planck Institute for Solar System Research; NASA through the TESS Guest Investigator Program [80NSSC18K1584, 80NSSC18K1585, 80NSSC19K0379]; NASA through the Living With A Star Program [NNX16AB76G]; TESS GI Program [80NSSC18K1585, 80NSSC19K0385]; UK Space Agency; Danish National Research FoundationDanmarks Grundforskningsfond [DNRF106]; NCAR Advanced Study Program Postdoctoral FellowshipNational Science Foundation (NSF)NSF - Directorate for Geosciences (GEO); National Science FoundationNational Science Foundation (NSF); CNES PLATO grant; German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt) under PLATO Data Center [50OO1501]; European Research Council (ERC)European Research Council (ERC) [715947]; Programme de Physique Stellaire et Planetaire; Australian Research CouncilAustralian Research Council; Spanish Ministry of Economy and Competitiveness (MINECO) [SEV-2015-0548-17-2, BES-2017-082610]; State Research Agency (AEI) of the Spanish Ministry of Science, Innovation and Universities (MCIU); European Social Fund via the Lithuanian Science Council (LMTLT)Research Council of Lithuania (LMTLT) [09.3.3-LMT-K-712-01-0103]; ESA PRODEX program; Spanish Ministry with the Ramon y Cajal fellowship [RYC-2015-17697]; Scientific and Technological Research Council of TurkeyTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [TuBTAK:118F352]
T.S.M. acknowledges support from NSF grant AST-1812634, NASA grants NNX16AB97G and 80NSSC20K0458, and a Visiting Fellowship at the Max Planck Institute for Solar System Research. Computational time at the Texas Advanced Computing Center was provided through XSEDE allocation TG-AST090107. J.v.S. acknowledges support from NASA through the TESS Guest Investigator Program (80NSSC18K1584). S.B. acknowledges NASA grant 80NSSC19K0374. D.B. acknowledges support from NASA through the Living With A Star Program (NNX16AB76G) and from the TESS GI Program under awards 80NSSC18K1585 and 80NSSC19K0385. W.J.C., W.H.B. and M.B.N. acknowledge support from the UK Space Agency. Funding for the Stellar Astrophysics Centre is provided by the Danish National Research Foundation (grant agreement No.: DNRF106). R.E. was supported by the NCAR Advanced Study Program Postdoctoral Fellowship. the National Center for Atmospheric Research is sponsored by the National Science Foundation. R.A.G. and B.M. acknowledge support from the CNES PLATO grant. P.G. acknowledges funding from the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt) under PLATO Data Center grant 50OO1501. D.H. acknowledges support from NASA through the TESS Guest Investigator Program (80NSSC18K1585, 80NSSC19K0379). T.R. acknowledges support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 715947). T.A. acknowledges support from the Programme de Physique Stellaire et Planetaire. T.R.B. acknowledges support from the Australian Research Council. L.G.C. acknowledges support from grant FPI-SO from the Spanish Ministry of Economy and Competitiveness (MINECO) (research project SEV-2015-0548-17-2 and predoctoral contract BES-2017-082610). A.J. Acknowledges support from the State Research Agency (AEI) of the Spanish Ministry of Science, Innovation and Universities (MCIU). H.K. acknowledges support from the European Social Fund via the Lithuanian Science Council (LMTLT) grant No. 09.3.3-LMT-K-712-01-0103. M.N.L. acknowledges support from the ESA PRODEX program. S.M. acknowledges support from the Spanish Ministry with the Ramon y Cajal fellowship number RYC-2015-17697. Z.C.O., S.o. and M.Y. acknowledge support from the Scientific and Technological Research Council of Turkey (TuBTAK:118F352). A.R.G.S. acknowledges support from NASA grant NNX17AF27G. This work benefited from discussions within the international team "The Solar and Stellar Wind Connection: Heating processes and angular momentum loss" at the International Space Science Institute (ISSI).