The Carnegie RR Lyrae Program: Mid-infrared Period-Luminosity relations of RR Lyrae stars in Reticulum

TL;DR

This study establishes new mid-infrared period-luminosity relations for RR Lyrae stars in the Reticulum cluster, using space-based observations and parallaxes, to improve distance measurements within the Large Magellanic Cloud.

Contribution

The paper presents the first mid-infrared PL relations for RR Lyrae stars in Reticulum, calibrated with Gaia and HST parallaxes, enhancing distance estimation accuracy.

Findings

Distances using Gaia parallaxes are consistent and slightly smaller than HST-based distances.

Reticulum is approximately 3 kpc closer than the LMC barycenter.

New MIR PL relations improve RR Lyrae distance measurements.

Abstract

We analysed 30 RR Lyrae stars (RRLs) located in the Large Magellanic Cloud (LMC) globular cluster Reticulum that were observed in the 3.6 and 4.5 $\mu$m passbands with the Infrared Array Camera (IRAC) on board of the Spitzer Space Telescope. We derived new mid-infrared (MIR) period-luminosity PL relations. The zero points of the PL relations were estimated using the trigonometric parallaxes of five bright Milky Way (MW) RRLs measured with the Hubble Space Telescope (HST) and, as an alternative, we used the trigonometric parallaxes published in the first Gaia data release (DR1) which were obtained as part of the Tycho-Gaia Astrometric Solution (TGAS) and the parallaxes of the same stars released with the second Gaia data release (DR2). We determined the distance to Reticulum using our new MIR PL relations and found that distances calibrated on the TGAS and DR2 parallaxes are in a good agreement and, generally, smaller than distances based on the HST parallaxes, although they are still consistent within the respective errors. We conclude that Reticulum is located ~3 kpc closer to us than the barycentre of the LMC.