Sarajedini, Ata and Mancone, Conor L. and Lauer, Tod R. and Dressler, Alan and Freedman, Wendy and Trager, S. C. and Grillmair, Carl and Mighell, Kenneth J. (2009) RR Lyrae Variables in Two Fields in the Spheroid of M31. Astronomical Journal, 138 (1). pp. 184-195. ISSN 0004-6256 http://resolver.caltech.edu/CaltechAUTHORS:20090818-150135114
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We present Hubble Space Telescope observations taken with the Advanced Camera for Surveys Wide Field Channel of two fields near M32—between 4 and 6 kpc from the center of M31. The data cover a time baseline sufficient for the identification and characterization of 681 RR Lyrae variables of which 555 are ab-type and 126 are c-type. The mean magnitude of these stars is <V> = 25.29 ± 0.05, where the uncertainty combines both the random and systematic errors. The location of the stars in the Bailey diagram and the ratio of c-type RR Lyraes to all types are both closer to RR Lyraes in Oosterhoff type I globular clusters in the Milky Way as compared with Oosterhoff II clusters. The mean periods of the ab-type and c-type RR Lyraes are <P_(ab)> = 0.557 ± 0.003 and <P_c> = 0.327 ± 0.003, respectively, where the uncertainties in each case represent the standard error of the mean. When the periods and amplitudes of the ab-type RR Lyraes in our sample are interpreted in terms of metallicity, we find the metallicity distribution function to be indistinguishable from a Gaussian with a peak at <[Fe/H]> = –1.50 ± 0.02, where the quoted uncertainty is the standard error of the mean. Using a relation between RR Lyrae luminosity and metallicity along with a reddening of E(B – V) = 0.08 ± 0.03, we find a distance modulus of (m – M)_0 = 24.46 ± 0.11 for M31. We examine the radial metallicity gradient in the environs of M31 using published values for the bulge and halo of M31 as well as the abundances of its dwarf spheroidal companions and globular clusters. In this context, we conclude that the RR Lyraes in our two fields are more likely to be halo objects rather than associated with the bulge or disk of M31, in spite of the fact that they are located at 4-6 kpc in projected distance from the center.
|Additional Information:||© 2009 The American Astronomical Society. Received 2008 October 21; accepted 2009 April 25; published 2009 June 1. We are grateful to Andy Layden, Nathan De Lee, and Karen Kinemuchi for useful conversations as this manuscript was being written. A.S. is grateful for support from NASA through grant AR-11277.01-A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS5- 26555. The National Optical Astronomy Observatory is operated by AURA, Inc., under cooperative agreement with the National Science Foundation.|
|Subject Keywords:||galaxies: individual (M31); galaxies: spiral; galaxies: stellar content; stars: variables: other|
|Official Citation:||RR Lyrae Variables in Two Fields in the Spheroid of M31 Ata Sarajedini, Conor L. Mancone, Tod R. Lauer, Alan Dressler, Wendy Freedman, S. C. Trager, Carl Grillmair, and Kenneth J. Mighell 2009 The Astronomical Journal 138 184-195 doi: 10.1088/0004-6256/138/1/184.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||08 Sep 2009 21:20|
|Last Modified:||26 Dec 2012 11:13|
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