Journal Article

Variable stars in the Cetus dwarf spheroidal galaxy: population gradients and connections with the star formation history*

M. Monelli, E. J. Bernard, C. Gallart, G. Fiorentino, I. Drozdovsky, A. Aparicio, G. Bono, S. Cassisi, E. D. Skillman and P. B. Stetson

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 422, issue 1, pages 89-105
Published in print May 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20539.x
Variable stars in the Cetus dwarf spheroidal galaxy: population gradients and connections with the star formation history*

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We investigate the variable star content of the isolated, Local Group, dwarf spheroidal (dSph) galaxy Cetus. Multi-epoch, wide-field images collected with the Very Large Telescope/Visible Multiobject Spectrograph camera allowed us to detect 638 variable stars (630 RR Lyrae stars and eight anomalous Cepheids), 475 of which are new detections. We present a full catalogue of periods, amplitudes and mean magnitudes. Motivated by the recent discovery that the pulsational properties of the RR Lyrae stars in the Tucana dSph revealed the presence of a metallicity gradient within the oldest (>rsim10 Gyr old) stellar populations, we investigated the possibility of an analogous effect in Cetus. We found that, despite the obvious radial gradient in the horizontal branch and red giant branch morphologies, both becoming bluer on average for increasing distance from the centre of Cetus, the properties of the RR Lyrae stars are homogeneous within the investigated area (out to r∼ 15 arcmin), with no significant evidence of a radial gradient. We discuss this in connection with the star formation history previously derived for the two galaxies. The observed differences between these two systems show that even systems this small show a variety of early evolutionary histories. These differences could be due to different merger or accretion histories.

Keywords: stars: variables: RR Lyrae; galaxies: individual: Cetus dSph; Local Group; galaxies: stellar content

Journal Article.  11739 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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