When Do Stalled Stars Resume Spinning Down? Advancing Gyrochronology with Ruprecht 147

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DOI

  • Jason Lee Curtis, Columbia University, American Museum of Natural History
  • ,
  • Marcel A. Aguëros, Columbia University
  • ,
  • Sean P. Matt, University of Exeter
  • ,
  • Kevin R. Covey, Western Washington University
  • ,
  • Stephanie T. Douglas, Harvard University
  • ,
  • Ruth Angus, Columbia University, American Museum of Natural History, Simons Foundation
  • ,
  • Steven H. Saar, Harvard University
  • ,
  • Ann Marie Cody, Bay Area Environmental Research Institute
  • ,
  • Andrew Vanderburg, Harvard University, University of Texas at Austin
  • ,
  • Nicholas M. Law, University of North Carolina
  • ,
  • Adam L. Kraus, University of Texas at Austin
  • ,
  • David W. Latham, Harvard University
  • ,
  • Christoph Baranec, University of Hawaii at Hilo
  • ,
  • Reed Riddle, California Institute of Technology
  • ,
  • Carl Ziegler, University of Toronto
  • ,
  • Mikkel N. Lund
  • Guillermo Torres, Harvard University
  • ,
  • Soren Meibom, Harvard University
  • ,
  • Victor Silva Aguirre
  • Jason T. Wright, Pennsylvania State University

Recent measurements of rotation periods () in the benchmark open clusters Praesepe (670 Myr), NGC 6811 (1 Gyr), and NGC 752 (1.4 Gyr) demonstrate that, after converging onto a tight sequence of slowly rotating stars in mass-period space, stars temporarily stop spinning down. These data also show that the duration of this epoch of stalled spin-down increases toward lower masses. To determine when stalled stars resume spinning down, we use data from the K2 mission and the Palomar Transient Factory to measure for 58 dwarf members of the 2.7 Gyr old cluster Ruprecht 147, 39 of which satisfy our criteria designed to remove short-period or near-equal-mass binaries. Combined with the Kepler data for the approximately coeval cluster NGC 6819 (30 stars with M ∗ > 0.85, our new measurements more than double the number of ≈2.5 Gyr benchmark rotators and extend this sample down to ≈0.55. The slowly rotating sequence for this joint sample appears relatively flat (22 ± 2 days) compared to sequences for younger clusters. This sequence also intersects the Kepler intermediate-period gap, demonstrating that this gap was not created by a lull in star formation. We calculate the time at which stars resume spinning down and find that 0.55 stars remain stalled for at least 1.3 Gyr. To accurately age-date low-mass stars in the field, gyrochronology formulae must be modified to account for this stalling timescale. Empirically tuning a core-envelope coupling model with open cluster data can account for most of the apparent stalling effect. However, alternative explanations, e.g., a temporary reduction in the magnetic braking torque, cannot yet be ruled out.

OriginalsprogEngelsk
Artikelnummer140
TidsskriftAstrophysical Journal
Vol/bind904
Nummer2
Antal sider40
ISSN0004-637X
DOI
StatusUdgivet - dec. 2020

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