RR Lyrae variables in the Small Magellanic Cloud - II. The extended
  area: chemical and structural analysis
  We have performed the Fourier decomposition analysis of 8- and 13-year V-band
light curves of a carefully selected sample of 454 fundamental-mode RR Lyrae
variables (RRab type), detected in a 14 square degree area of the Small
Magellanic Cloud (SMC) and listed in the Optical Gravitational Lensing
Experiment, phase III, Catalogue of Variable Stars. The Fourier decomposition
parameters were used to derive metal abundances and distance moduli, following
the methodology described by Kapakos, Hatzidimitriou & Soszy\'nski. The average
metal abundance of the RRab stars on the new scale of Carretta et al. was found
to be <[Fe/H]C09> = -1.69pm0.41 dex (std, with a standard error of 0.02 dex). A
tentative metallicity gradient of -0.013pm0.007 dex/kpc was detected, with
increasing metal abundance towards the dynamical center of the SMC, but
selection effects are also discussed. The distance modulus of the SMC was
re-estimated and was found to be <\mu> = 19.13pm0.19 (std) in a distance scale
where the distance modulus of the Large Magellanic Cloud (LMC) is \mu_LMC =
18.52pm0.06(std). The average 1-sigma line-of-sight depth was found to be
sigma_int = 5.3pm0.4 kpc (std), while spatial variations of the depth were
detected. The SMC was found to be deeper in the north-eastern region, while
metal richer and metal poorer objects in the sample seem to belong to different
dynamical structures. The former have smaller scale height and may constitute a
thick disk, its width being 10.40pm0.02 kpc, and a bulge whose size (radius) is
estimated to be 2.09pm0.81 kpc. The latter seem to belong to a halo structure
with a maximum depth along the line of sight extending over 16 kpc in the SMC
central region and falling to 12 kpc in the outer regions.
