On the origin of sub-subgiant stars. I. Demographics

Par Conseil national de recherches du Canada

DOI	Trouver le DOI : https://doi.org/10.3847/1538-4357/aa6af3
Auteur	Rechercher : Geller, Aaron M.; Rechercher : Leiner, Emily M.; Rechercher : Bellini, Andrea; Rechercher : Gleisinger, Robert; Rechercher : Haggard, Daryl; Rechercher : Kamann, Sebastian; Rechercher : Leigh, Nathan W. C.; Rechercher : Mathieu, Robert D.; Rechercher : Sills, Alison; Rechercher : Watkins, Laura L.; Rechercher : Zurek, David
Format	Texte, Article
Sujet	binaries: close; blue stragglers; globular clusters: general; open clusters and associations: general; stars: evolution; stars: variables: general
Résumé	Sub-subgiants are stars that are observed to be redder than normal main-sequence stars and fainter than normal subgiant (and giant) stars in an optical color–magnitude diagram (CMD). The red straggler stars, which lie redward of the red giant branch, may be related and are often grouped together with the sub-subgiants in the literature. These stars defy our standard theory of single-star evolution and are important tests for binary evolution and stellar collision models. In total, we identify 65 sub-subgiants (SSG) and red stragglers (RS) in 16 open and globular star clusters from the literature; 50 of these, including 43 sub-subgiants, pass our strict membership selection criteria (though the remaining sources may also be cluster members). In addition to their unique location on the CMD, we find that at least 58% (25/43) of sub-subgiants in this sample are X-ray sources with typical 0.5–2.5 keV luminosities of order 1030–1031 erg s−1. Their X-ray luminosities and optical–to–X-ray flux ratios are similar to those of RS CVn active binaries. At least 65% (28/43) of the sub-subgiants in our sample are variables, 21 of which are known to be radial-velocity binaries. Typical variability periods are lesssim ≲15 days. At least 33% (14/43) of the sub-subgiants are Hα emitters. These observational demographics provide strong evidence that binarity is important for sub-subgiant formation. Finally, we find that the number of sub-subgiants per unit mass increases toward lower-mass clusters, such that the open clusters in our sample have the highest specific frequencies of sub-subgiants.
Date de publication	2017-05-08
Maison d’édition	IOP Publishing
Dans	The Astrophysical Journal 840, nº 2 : 66–.
Langue	anglais
Publications évaluées par des pairs	Oui
Publication du CNRC	Cette publication n’est pas du CNRC Ce sont des publications qui ont été rédigées par un auteur du CNRC, mais avant que celui-ci soit employé du CNRC.
Numéro NPARC	23003237
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Identificateur de l’enregistrement	5663d047-cec8-42c7-9349-eba9c5fc2fd3
Enregistrement créé	2018-05-08
Enregistrement modifié	2020-03-16

Date de modification :: 2024-06-29