The VMC Survey -- XLII. Near-infrared period-luminosity relations for RR Lyrae stars and the structure of the Large Magellanic Cloud

TL;DR

This study analyzes nearly 29,000 RR Lyrae stars in the Large Magellanic Cloud using near-infrared and optical data to derive period-luminosity relations and map the galaxy's three-dimensional structure.

Contribution

It provides new near-infrared period-luminosity relations for RR Lyrae stars and detailed 3D structural parameters of the LMC based on a large sample.

Findings

The LMC's RR Lyrae distribution is ellipsoidal with specified axes.

The inclination of the LMC is approximately 22 degrees.

No significant metallicity gradient or substructures detected.

Abstract

We present results from an analysis of $\sim$ 29,000 RR Lyrae stars located in the Large Magellanic Cloud (LMC). For these objects, near-infrared time-series photometry from the VISTA survey of the Magellanic Clouds system (VMC) and optical data from the OGLE (Optical Gravitational Lensing Experiment) IV survey and the Gaia Data Release 2 catalogue of confirmed RR Lyrae stars were exploited. Using VMC and OGLE IV magnitudes we derived period-luminosity (PL), period-luminosity-metallicity (PLZ), period-Wesenheit (PW) and period-Wesenheit-metallicity (PWZ) relations in all available bands. More that ~7,000 RR Lyrae were discarded from the analysis because they appear to be overluminous with respect to the PL relations. The $PL_{K_{\mathrm{s}}}$ relation was used to derive individual distance to $\sim 22,000$ RR Lyrae stars, and study the three-dimensional structure of the LMC. The distribution of the LMC RR Lyrae stars is ellipsoidal with the three axis $S_1$=6.5 kpc, $S_2$=4.6 kpc and $S_3$=3.7 kpc, inclination i=$22\pm4^{\circ }$ relative to the plane of the sky and position angle of the line of nodes $\theta=167\pm7^{\circ }$ (measured from north to east). The north-eastern part of the ellipsoid is closer to us and no particular associated substructures are detected as well as any metallicity gradient.