Fast rotating giant stars behind the Coma Berenices star cluster

DOI: 
10.1093/mnras/staa2093
Publication date: 
01/07/2020
Main author: 
Casal, Estefanía
IAA authors: 
Casal, Estefanía;Fernández, Matilde;Alfaro, Emilio J.;Casanova, Víctor;Tobaruela, Ángel
Authors: 
Casal, Estefanía;Fernández, Matilde;Alfaro, Emilio J.;Casanova, Víctor;Tobaruela, Ángel
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Pages: 
2562-2568
Abstract: 
In the frame of a study of the empirical isochrones of young stellar clusters, we have carried out BVI<SUB>c</SUB> Johnson-Cousins photometry of a sample of K and M stars of the Coma Berenices star cluster. All these stars have known rotational periods. Our main goal is to get a valuable reference on the colour-magnitude diagram, M<SUB>v</SUB> vs B - V, for stars with ages within 400-800 Myr. For this purpose, we obtained BVI<SUB>c</SUB> photometry with an average upper limit for the precision of about 0.025 mag and used parallaxes from the Gaia Data Release 2. We found that one third of our sample is located well above the cluster main-sequence and these stars are confirmed as background giants by their radial velocities in the Gaia Data Release 2. This misclassification shows that giants with short surface rotational periods can mimic main-sequence stars if they are located at the appropriate distance. We recommend caution when using rotational periods in order to determine cluster membership. Besides, the gyrochronology technique should only be used when the luminosity class of the stars is well known. Finally, our cleared sample supports an age of ∼600 Myr for Coma Berenices, rather than an age of ∼800 Myr.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2020MNRAS.497.2562C/abstract
ADS Bibcode: 
2020MNRAS.497.2562C
Keywords: 
Stars: low-mass;Galaxy: open clusters and associations: Coma Berenices;Stars: rotation