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Issue A&A
Volume 423, Number 1, August III 2004
Page(s) 97 - 109
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20034494



A&A 423, 97-109 (2004)
DOI: 10.1051/0004-6361:20034494

Properties of RR Lyrae stars in the inner regions of the Large Magellanic Cloud

J.  Borissova1, D. Minniti1, M.  Rejkuba2, D. Alves3, K. H.  Cook4 and K. C.  Freeman5

1  Department of Astronomy, P. Universidad Católica, Av. Vicuña Mackenna 4860, Casilla 306, Santiago 22, Chile
    e-mail: [jborisso;dante]@astro.puc.cl
2  European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
    e-mail: mrejkuba@eso.org
3  Columbia University, Dept. of Astronomy, New York, USA
    e-mail: alves@astro.columbia.edu
4  Lawrence Livermore National Laboratory, Livermore, California, USA
    e-mail: kcook@llnl.org
5  Mount Stromlo Observatory, Canberra ACT, Australia
    e-mail: kcf@mso.anu.edu

(Received 11 October 2003 / Accepted 24 March 2004 )

Abstract
We present the radial velocities, metallicities and the K-band magnitudes of 74 RR Lyrae stars in the inner regions of the LMC. The intermediate resolution spectra and infrared images were obtained with FORS1 at the ESO VLT and with the SOFI infrared imager at the ESO NTT. The best 43 RR Lyrae with measured velocities yield an observed velocity dispersion of $\sigma=61\pm 7$ km s -1. We obtain a true LMC RR Lyrae velocity dispersion of $\sigma=53$ km s -1, which is higher than the velocity dispersion of any other LMC population previously measured. This is the first empirical evidence for a kinematically hot, metal-poor halo in the LMC as discussed in Minniti et al. (2003). Using Layden's (1994) modification of the $\Delta S$ method we measured the metallicity for 23 of our stars. The mean value is ${\rm [Fe/H]} =-1.46\pm0.09$ dex. The absolute magnitudes  MV and  MK of RR Lyrae stars are linear functions of metallicity. In the V band, our data agree with the Olech et al. (2003) relation, in the K band the slope is flatter. The average apparent V luminosity of 70 RR Lyrae stars is $\langle V\rangle = 19.45\pm0.04$ and the average  K luminosity of 37 RR Lyrae stars is $\langle K\rangle=18.20\pm0.06$. There is no obvious relation between apparent V magnitude and Log  P, while the RR Lyrae K band magnitudes show a well defined linear trend with Log  P. Using the Bono et al. (2003) and Bono et al. (2003) theoretical Near-Infrared Period-Luminosity-Metallicity relations we calculate the LMC distance modulus $\mu_{0} = 18.48\pm0.08$.


Key words: galaxies: Magellanic clouds -- stars: variables: RR Lyrae -- galaxies: formation

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© ESO 2004


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