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RR Lyrae Variables in M32 and the Disk of M31

Fiorentino, Giuliana and Monachesi, Antonela and Trager, Scott C. and Lauer, Tod R. and Saha, Abhijit and Mighell, Kenneth J. and Freedman, Wendy and Dressler, Alan and Grillmair, Carl and Tolstoy, Eline (2010) RR Lyrae Variables in M32 and the Disk of M31. Astrophysical Journal, 708 (1). pp. 817-833. ISSN 0004-637X.

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We observed two fields near M32 with the Advanced Camera for Surveys/High Resolution Channel (ACS/HRC) on board the Hubble Space Telescope. The main field, F1, is 1.'8 from the center of M32; the second field, F2, constrains the M31 background, and is 5.'4 distant. Each field was observed for 16 orbits in each of the F435W (narrow B) and F555W (narrow V) filters. The duration of the observations allowed RR Lyrae stars to be detected. A population of RR Lyrae stars determined to belong to M32 would prove the existence of an ancient population in that galaxy, a subject of some debate. We detected 17 RR Lyrae variables in F1 and 14 in F2. A 1σ upper limit of 6 RR Lyrae variables belonging to M32 is inferred from these two fields alone. Use of our two ACS/WFC parallel fields provides better constraints on the M31 background, however, and implies that 7^(+4)_(–3) (68% confidence interval) RR Lyrae variables in F1 belong to M32. We have therefore found evidence for an ancient population in M32. It seems to be nearly indistinguishable from the ancient population of M31. The RR Lyrae stars in the F1 and F2 fields have indistinguishable mean V-band magnitudes, mean periods, distributions in the Bailey diagram, and ratios of RRc to RR_(total) types. However, the color distributions in the two fields are different, with a population of red RRab variables in F1 not seen in F2. We suggest that these might be identified with the detected M32 RR Lyrae population, but the small number of stars rules out a definitive claim.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle
Saha, Abhijit0000-0002-6839-4881
Freedman, Wendy0000-0003-3431-9135
Grillmair, Carl0000-0003-4072-169X
Additional Information:© 2010 American Astronomical Society. Received 2009 September 29; accepted 2009 November 13; published 2009 December 15. Support for program GO-10572 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. We really thank E. Bernard, M. Monelli, R. Contreras Ramos, G. Clementini, and M. Irwin for interesting suggestions and comments about this work and A. Sarajedini, L. Koopmans, and S. Vegetti for helpful discussions. Facility: HST (ACS).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASANAS 5-26555
Subject Keywords:galaxies: elliptical and lenticular, cD; galaxies: individual (M32, M31); Local Group; stars: Population II; stars: variables: other
Issue or Number:1
Record Number:CaltechAUTHORS:20100128-135830061
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Official Citation:RR Lyrae Variables in M32 and the Disk of M31 Giuliana Fiorentino, Antonela Monachesi, Scott C. Trager, Tod R. Lauer, Abhijit Saha, Kenneth J. Mighell, Wendy Freedman, Alan Dressler, Carl Grillmair, and Eline Tolstoy 2010 ApJ 708 817-833 doi: 10.1088/0004-637X/708/1/817
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17343
Deposited By: Tony Diaz
Deposited On:01 Feb 2010 02:11
Last Modified:17 Nov 2019 06:11

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