期刊
ASTROPHYSICAL JOURNAL
卷 904, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.3847/1538-4357/abbf58
关键词
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资金
- National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship [AST-1602662]
- National Aeronautics and Space Administration [NNX16AE64G, GO 7035]
- NSF [AST-1701468, AST-1255419]
- European Research Council under the European Union's Horizon 2020 research and innovation program [682393]
- NASA Heliophysics LWS [NNX16AB79G]
- Dunlap Fellowship at the Dunlap Institute for Astronomy Astrophysics
- University of Toronto
- Danish National Research Foundation [DNRF106]
- Pennsylvania State University
- Eberly College of Science
- NASA Science Mission directorate
- NASA [NAS5-26555]
- NASA Office of Space Science [NNX09AF08G]
- National Science Foundation [AST-0906060, AST-0960343, AST-1207891]
- Mt. Cuba Astronomical Foundation
Recent measurements of rotation periods (P-rot) in the benchmark open clusters Praesepe (670Myr), NGC.6811 (1Gyr), and NGC.752 (1.4Gyr) 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 P-rot 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 P-rot data for the approximately coeval cluster NGC.6819 (30 stars with M-star > 0.85 M-circle dot), our new measurements more than double the number of approximate to 2.5.Gyr benchmark rotators and extend this sample down to approximate to 0.55.M-circle dot. 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 M-circle dot 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.
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