Evaluating Gyrochronology on the Zeroagemainsequence: Rotation Periods in the Southern Open Cluster Blanco 1 from the KELTSouth Survey
Abstract
We report periods for 33 members of Blanco 1 as measured from Kilodegree Extremely Little TelescopeSouth light curves, the first reported rotation periods for this benchmark zeroagemainsequence open cluster. The distribution of these stars spans from lateA or earlyF dwarfs to midK with periods ranging from less than a day to ~8 days. The rotation period distribution has a morphology similar to the coeval Pleiades cluster, suggesting the universal nature of stellar rotation distributions. Employing two different gyrochronology methods, we find an age of 146^{+13}_{14} Myr for the cluster. Using the same techniques, we infer an age of 134^{+9}_{10} Myr for the Pleiades measured from existing literature rotation periods. These rotationderived ages agree with independently determined cluster ages based on the lithium depletion boundary technique. Additionally, we evaluate different gyrochronology models and quantify levels of agreement between the models and the Blanco 1/Pleiades rotation period distributions, including incorporating the rotation distributions of clusters at ages up to 1.1 Gyr. We find the Skumanichlike spindown rate sufficiently describes the rotation evolution of stars hotter than the Sun; however, we find cooler stars rotating faster than predicted by a Skumanich law, suggesting a mass dependence in the efficiency of stellar angular momentum loss rate. Finally, we compare the Blanco 1 and Pleiades rotation period distributions to available nonlinear angular momentum evolution models. We find they require a significant mass dependence on the initial rotation rate of solartype stars to reproduce the observed range of rotation periods at a given stellar mass and are furthermore unable to predict the observed overdensity of stars along the upper envelope of the clusters' rotation distributions.
 Publication:

The Astrophysical Journal
 Pub Date:
 February 2014
 DOI:
 10.1088/0004637X/782/1/29
 arXiv:
 arXiv:1312.3946
 Bibcode:
 2014ApJ...782...29C
 Keywords:

 open clusters and associations: general;
 open clusters and associations: individual: Blanco 1;
 stars: evolution;
 stars: fundamental parameters;
 stars: rotation;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 19 pages,14 figures, 3 tables  Accepted for publication in ApJ