RR LYRAE VARIABLES IN M33. II. OOSTERHOFF PROPERTIES AND RADIAL TRENDS

Journal Article · Sat Nov 20 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/724/1/799· OSTI ID:21471166

Yang, S-C; Sarajedini, Ata ^[1]; Holtzman, Jon A ^[2]

---

1. Department of Astronomy, University of Florida, P.O. Box 112055, Gainesville, FL 32611 (United States)
2. Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger St., Las Cruces, NM 88003 (United States)

We present the results of an extensive survey of RR Lyrae (RRL) stars in three fields along the major axis of the Triangulum Galaxy (M33). From images taken with the Advanced Camera for Surveys (ACS) Wide Field Channel on board the Hubble Space Telescope through two passbands (F606W and F814W), we have identified and characterized a total of 119 RRL variables (96 RRab (RR0) and 23 RRc (RR1)) in M33. Using the properties of 83 RRL stars (65 RRab and 18 RRc) in the innermost ACS field (hereafter DISK2), we find mean periods of (P{sub ab}) = 0.553 {+-} 0.008 (error1) {+-} 0.05 (error2) and (P{sub c}) = 0.325 {+-} 0.008 (error1) {+-} 0.05 (error2), where the 'error1' value represents the standard error of the mean and the 'error2' value is based on the error of an individual RRL period calculated from our synthetic light curve simulations. The distribution of RRab periods and the frequency of RRc stars (N{sub c} = n{sub c} /n{sub abc} = 0.22) strongly suggest that these RRLs follow the general characteristics of those in Oosterhoff type I Galactic globular clusters. The metallicities of 65 individual RRab stars are calculated from the period-amplitude-metallicity relationship, yielding a mean metallicity of ([Fe/H]) = -1.48 {+-} 0.05 dex, where the uncertainty is the standard error of the mean. The VI minimum-light colors of the RRab stars are used to calculate a mean line-of-sight reddening toward the DISK2 field of (E(V - I)) = 0.175. By adopting this line-of-sight reddening and using a relation between RRL luminosity and metallicity (M{sub V} = 0.23[Fe/H]+0.93), we estimate a mean distance modulus of ((m - M){sub 0}) = 24.52 {+-} 0.11 for M33, where the error is the quadratic sum of the uncertainties in the absolute and dereddened V magnitudes of the RRLs. The Oosterhoff I properties of the M33 field RRL stars agree well with those of RRL populations found in the M31 halo consistent with the past interaction history of these two galaxies.

• OSTI ID: 21471166
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 724; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
GALAXIES
LUMINOSITY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
SIMULATION
STARS
TELESCOPES