A DECam View of the Diffuse Dwarf Galaxy Crater II: Variable Stars

Time series observations of a single dithered field centered 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...

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Bibliographic Details
Published in:arXiv.org 2019-11
Main Authors: Vivas, A Katherina, Walker, Alistair R, Martínez-Vázquez, Clara E, Monelli, Matteo, Bono, Giuseppe, Dorta, Antonio, Nidever, David L, Fiorentino, Giuliana, Gallart, Carme, Andreuzzi, Gloria, Braga, Vittorio F, Dall'Ora, Massimo, Olsen, Knut, Stetson, Peter B
Format: Article
Language:English
Subjects:
Cepheid variables
Color-magnitude diagram
Craters
Dark energy
Dwarf galaxies
Ellipticity
Galactic evolution
Galaxies
Galaxy distribution
Metallicity
Observatories
Population
Stars
Stars & galaxies
Time series
Variable stars
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Summary:Time series observations of a single dithered field centered 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 \((m-M)_0=20.333\pm 0.004\) (stat) \(\pm 0.07\) (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 \(153^\circ\). 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 color-magnitude diagram of Crater II, the anomalous Cepheids in this galaxy must have formed through a binary evolution channel of an old population.
ISSN:2331-8422
DOI:10.48550/arxiv.1912.00081