M75, a globular cluster with a trimodal horizontal branch. I. Color-magnitude diagram

Catelan, M.; Borissova, J.; Ferraro, FR; Corwin, TM; SMITH, HA; Kurtev, R

Abstract

Deep UBVI photometry for a large field covering the distant globular cluster M75 (NGC 6864) is presented. We confirm a previous suggestion that M75 possesses a bimodal horizontal branch (HB) bearing striking resemblance to the well-known case of NGC 1851. In addition, we detect a third, smaller grouping of stars on the M75 blue tail, separated from the bulk of the blue HB stars by a gap spanning about 0.5 mag in V. Such a group of stars may correspond to the upper part of a very extended, though thinly populated, blue tail. Thus M75 appears to have a trimodal HB. The presence of the "Grundahl jump" is verified using the broadband U filter. We explore the color-magnitude diagram of M75 with the purpose of deriving the cluster's fundamental parameters and find a metallicity of [Fe/H] = -1.03 ± 0.17 dex and -1.24 ± 0.21 in the Carretta & Gratton and Zinn & West scales, respectively. We discuss earlier suggestions that the cluster has an anomalously low ratio of bright red giants to HB stars. A differential age analysis with respect to NGC 1851 suggests that the two clusters are essentially coeval.

Más información

Título según WOS: M75, a globular cluster with a trimodal horizontal branch. I. Color-magnitude diagram
Título según SCOPUS: M75, a globular cluster with a trimodal horizontal branch. I. Color-magnitude diagram
Título de la Revista: ASTRONOMICAL JOURNAL
Volumen: 124
Número: 1
Editorial: IOP PUBLISHING LTD
Fecha de publicación: 2002
Página de inicio: 364
Página final: 378
Idioma: English
URL: http://stacks.iop.org/1538-3881/124/i=1/a=364
DOI:

10.1086/340804

Notas: ISI, SCOPUS