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 \simeq 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 & Soszyński .
The average metal abundance of the RRab stars on the new scale of Carretta et al .
was found to be \langle [ Fe / H ] _ { C 09 } \rangle = -1.69 \pm 0.41 dex ( std , with a standard error of 0.02 dex ) .
A tentative metallicity gradient of -0.013 \pm 0.007 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 \langle \mu \rangle = 19.13 \pm 0.19 ( std ) in a distance scale where the distance modulus of the Large Magellanic Cloud ( LMC ) is \mu _ { LMC } = 18.52 \pm 0.06 ( std ) .
The average 1 \sigma line-of-sight depth was found to be \sigma _ { int } = 5.3 \pm 0.4 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 10.40 \pm 0.02 kpc , and a bulge whose size ( radius ) is estimated to be 2.09 \pm 0.81 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 \sim 12 kpc in the outer regions .