Abstract:

We have performed the Fourier decomposition analysis of 11-yr V-band light curves of a carefully selected sample of 100 RR Lyrae variables, detected in the central regions of the Small Magellanic Cloud (SMC), with the Optical Gravitational Lensing Experiment, phases II and III. The sample consisted of 84 fundamental mode pulsators (RRab stars) and 16 first-overtone pulsators (RRc stars). The Fourier decomposition parameters were used to derive metal abundances and distance moduli for these RR Lyrae variables. The average metal abundance of the RRab stars on the new scale of Carretta et al. is found to be <[Fe/H]_C09>=-1.62 ± 0.41 dex (std, with a standard error of 0.05 dex). The distance modulus of the SMC was found to be <μ>= 18.90 ± 0.18 (std) from the RRab population in a distance scale where the distance modulus of the Large Magellanic Cloud (LMC) is μ_LMC= 18.52 ± 0.06 (std). The 1σ line-of-sight depth for the RRab stars was found to be σ_int= 4.13 ± 0.27 kpc, in good agreement with that estimated from red clump stars and eclipsing binaries. There is a clear indication that the metal-poorer and metal-richer objects in the sample may belong to different dynamical structures. The metal-rich stars have smaller scaleheight and could be part of a disc-like structure, while the more metal poor objects could be part of a much thicker structure, such as an inner halo or a bulge component.

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