The VMC survey – XXVI. Structure of the Small Magellanic Cloud from RR Lyrae stars

Abstract

We present results from the analysis of 2997 fundamental mode RR Lyrae\nvariables located in the Small Magellanic Cloud (SMC). For these objects\nnear-infrared time-series photometry from the VISTA survey of the Magellanic\nClouds system (VMC) and visual light curves from the OGLE IV survey are\navailable. In this study the multi-epoch $K_{\\rm s}$-band VMC photometry was\nused for the first time to derive intensity-averaged magnitudes of the SMC RR\nLyrae stars. We determined individual distances to the RR Lyrae stars from the\nnear-infrared period-absolute magnitude-metallicity ($PM_{K_{\\rm s}}Z$)\nrelation, which has a number of advantages in comparison with the visual\nabsolute magnitude-metallicity ($M_{V}-{\\rm [Fe/H]}$) relation, such as a\nsmaller dependence of the luminosity on interstellar extinction, evolutionary\neffects and metallicity. The distances we have obtained were used to study the\nthree-dimensional structure of the SMC. The distribution of the SMC RR Lyrae\nstars is found to be ellipsoidal. The actual line-of-sight depth of the SMC is\nin the range from 1 to 10 kpc, with an average depth of 4.3 $\\pm$ 1.0 kpc. We\nfound that RR Lyrae stars in the eastern part of the SMC are affected by\ninteractions of the Magellanic Clouds. However, we do not see a clear\nbimodality in the distribution of RR Lyrae stars as observed for red clump (RC)\nstars.\n