Chemical and structural analysis of the Large Magellanic Cloud using the fundamental mode RR Lyrae stars

We present a careful and detailed light-curve analysis of publicly available I-band data on fundamental mode RR Lyrae (RRab) stars of the Large Magellanic Cloud (LMC) obtained by the Optical Gravitational Lensing Experiment phase-III project. Using the Fourier parameters of 13 095 RRab stars, metallicities and absolute magnitudes of individual stars are obtained. The representation of stars on the P-φ _{31}^V plane shows the existence of three significant metallicity groups with mean metallicities as -1.20 ± 0.12, -1.57 ± 0.10 and -1.89 ± 0.09 dex. The corresponding absolute magnitudes of these three groups are obtained as 0.70 ± 0.08, 0.59 ± 0.06 and 0.49 ± 0.08 mag, respectively. Distribution of these three groups as a function of vertical |z| distance indicates that the formation of the LMC disc predates the formation of the inner halo. Issue of the existence of a metallicity gradient as a function of galactocentric distances has also been addressed. Approximating the structure of the LMC disc as a triaxial ellipsoid, the inclination angle (i) relative to the plane of the sky and the position angle of the line of nodes (θ_lon) were estimated as 24.20° and 176.01°, respectively. The axes ratios and the eccentricity were also determined using the principal axis transformation method.