Pulsating Variable Stars in the Coma Berenices dwarf spheroidal galaxy

TL;DR

This study presents the first analysis of variable stars in the Coma Berenices dwarf galaxy, revealing RR Lyrae stars that help determine its distance and characteristics, indicating an Oosterhoff type-II classification.

Contribution

First identification and analysis of variable stars in the Coma Berenices dwarf galaxy, providing new insights into its stellar population and distance.

Findings

Two RR Lyrae stars identified, including an RRab with a long period.

Distance to the galaxy estimated at approximately 42 kpc.

RRab star's properties suggest Oosterhoff type-II classification.

Abstract

We present B, V, I time-series photometry of the Coma Berenices dwarf spheroidal galaxy, a faint Milky Way satellite, recently discovered by the Sloan Digital Sky Survey. We have obtained V, B-V and V, V-I color-magnitude diagrams that reach V~23.0-23.2 mag showing the galaxy turnoff at V~21.7 mag, and have performed the first study of the variable star population of this new Milky Way companion. Two RR Lyrae stars (a fundamental-mode -RRab- and a first overtone -RRc- pulsator) and a short period variable with period P=0.12468 days were identified in the galaxy. The RRab star has a rather long period of P_ab=0.66971 days and is about 0.2 mag brighter than the RRc variable and other non-variable stars on the galaxy horizontal branch. In the period-amplitude diagram the RRab variable falls closer to the loci of Oosterhoff type-II systems and evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. The average apparent magnitude of the galaxy horizontal branch, <V_HB>=18.64+-0.04 mag, leads to a distance modulus for the Coma dSph mu_0=18.13+-0.08 mag, corresponding to a distance d=42^{+2}_{-1} kpc, by adopting a reddening E(B-V) = 0.045 +- 0.015 mag and a metallicity [Fe/H]=-2.53 +- 0.05 dex.