RR Lyrae stars in the inner Large Magellanic Cloud: halo-like location with a disk-like distribution

Indian Institute of Astrophysics, Koramangala II Block, Bangalore - 34, India e-mail: purni@iiap.res.in

Received: 16 September 2005
Accepted: 24 November 2005

Abstract

Aims. The distribution of RR Lyrae stars (RRLS) in the inner Large Magellanic Cloud (LMC), and the structure of the halo of the LMC delineated by these stars are studied here. Methods.RRLS identified by the OGLE II survey are used to estimate their number density distribution in the bar region of the LMC. To find their location, I estimated the scale-height of their distribution in the LMC using extinction corrected average magnitudes of ab type stars. Results.The density is found to vary differently along and across the bar of the LMC, and the difference is found to be statistically significant. The density distribution is found to be elongated like the LMC bar and the position angle (PA) of the elongation is estimated to be 1125 ± 153. This value of PA is found to be same as the PA_maj of the bar, within the errors, estimated using red clump stars and giants. The ellipticity of their density distribution is estimated to be ~0.5, very similar to the ellipticity of the bar, estimated from giants. The above results show that majority of the population of RRLS in the central region of the LMC are found to have the signature of the bar. This result could mean that most of these stars are located in the disk, considering the bar as a disk feature. On the other hand, their scale-height was found to be 3.0 ± 0.9 kpc. This indicates that RRLS are located in the halo and not in the disk. Conclusions.Thus these stars in the inner LMC have halo-like location and a disk-like density distribution. I discuss some possible formation scenarios for this puzzling combination.