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

II. The extended sample

¹ Departamento de Física y Meteorología, Facultad de Ciencias, Universidad de Valparaíso, Ave. Gran Bretaña 644, Playa Ancha, Casilla 53, Valparaíso, Chile e-mail: jura.borissova@uv.cl
² Department of Astronomy, P. Universidad Católica, Av. Vicuña Mackenna 4860, Casilla 306, Santiago 22, Chile e-mail: dante@astro.puc.cl
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany e-mail: mrejkuba@eso.org
⁴ 3549 Lynne Way, Sacramento, CA 95821-3722, USA e-mail: alvesdavid@ucdavis-alumni.com

Received: 31 August 2005
Accepted: 17 August 2006

Abstract

Context.All galaxies that have been adequately examined so far have shown an extended stellar halo.

Aims.To search for such a halo in the LMC we have obtained low-resolution spectra for 100 LMC RR Lyrae stars, of which 87 are in the field and 13 in the clusters NGC 1835 and NGC 2019.

Methods.We measured radial velocities for 87 LMC RR Lyrae stars, and metallicities for 78 RR Lyrae stars, nearly tripling the previous sample. These targets are located in 10 fields covering a wide range of distances, out to 2.5 degrees from the center of the LMC.

Results.Our main result is that the mean velocity dispersion for the LMC RR Lyrae stars is  km s^-1. This quantity does not appear to vary with distance from the LMC center. The metallicity shows a Gaussian distribution, with mean [Fe/H] = – dex, and dispersion  dex in the Harris metallicity scale, confirming that they represent a very homogeneous metal-poor population. There is no dependence between the kinematics and metallicity of the field RR Lyrae star population.

Conclusions.Using good quality low-resolution spectra from FORS1, FORS2 and GEMINI-GMOS we have found that field RR Lyrae stars in the LMC show a large velocity dispersion and that this indicate the presence of old and metal-poor stellar halo. All the evidence so far for the halo, however, is from the spectroscopy of the inner LMC regions, similar to the inner flattened halo in our Galaxy. Further study is necessary to confirm this important result.