Does the Oosterhoff Dichotomy Exist in The Andromeda Galaxy? I. The case of G11
Abstract
We present the first evidence that Oosterhoff type II globular clusters exist in the Andromeda galaxy (M31). On the basis of time-series photometry of the moderately metal-poor ([Fe/H]\sim -1.6 dex) M31 globular cluster G11, obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope, we detected and derived periods for 14 RR Lyrae stars, of which five are found to lie inside the cluster tidal radius. They include three fundamental-mode (RRab) and two first-overtone (RRc) pulsators, with average periods <Pab> = 0.70 d, and <Pc> = 0.40 d, respectively. These mean periods and the position of the cluster variable stars in the period-amplitude and period-metallicity diagrams, all suggest that G11 is likely to be an Oosterhoff type II globular cluster. This appears to be in agreement with the general behavior of Milky Way globular clusters with similar metallicity and horizontal branch morphology.
Keywords
Cite
@article{arxiv.1301.4100,
title = {Does the Oosterhoff Dichotomy Exist in The Andromeda Galaxy? I. The case of G11},
author = {Rodrigo Contreras Ramos and Gisella Clementini and Luciana Federici and Giuliana Fiorentino and Carla Cacciari and Marcio Catelan and Horace A. Smith and Flavio Fusi Pecci and Marcella Marconi and Barton J. Pritzl and Karen Kinemuchi},
journal= {arXiv preprint arXiv:1301.4100},
year = {2015}
}
Comments
23 pages, 14 figures, 4 tables. Fig. 10 (right panel) replaced. ApJ in press