A DECam view of the diffuse dwarf galaxy Crater II - Variable stars
Abstract
Time series observations of a single dithered field centred on the diffuse dwarf satellite galaxy Crater II were obtained with the Dark Energy Camera (DECam) at the 4m Blanco Telescope at Cerro Tololo Inter-American Observatory, Chile, uniformly covering up to two half-light radii. Analysis of the g and I time series results in the identification and characterization of 130 periodic variable stars, including 98 RR Lyrae stars, 7 anomalous Cepheids, and 1 SX Phoenicis star belonging to the Crater II population, and 24 foreground variables of different types. Using the large number of ab-type RR Lyrae stars present in the galaxy, we obtained a distance modulus to Crater II of (m - M)0 = 20.333 ± 0.004 (stat) ±0.07 (sys). The distribution of the RR Lyrae stars suggests an elliptical shape for Crater II, with an ellipticity of 0.24 and a position angle of 153°. From the RR Lyrae stars, we infer a small metallicity dispersion for the old population of Crater II of only 0.17 dex. There are hints that the most metal-poor stars in that narrow distribution have a wider distribution across the galaxy, while the slightly more metal-rich part of the population is more centrally concentrated. Given the features in the colour-magnitude diagram of Crater II, the anomalous Cepheids in this galaxy must have formed through a binary evolution channel of an old population.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2020
- DOI:
- 10.1093/mnras/stz3393
- arXiv:
- arXiv:1912.00081
- Bibcode:
- 2020MNRAS.492.1061V
- Keywords:
-
- stars: variables: general;
- stars: variables: RR Lyrae;
- galaxies: dwarf;
- galaxies: individual: (Crater II);
- Local Group;
- galaxies: stellar content;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted for publication in MNRAS