# Near-IR period-luminosity relations for pulsating stars in $\omega$ Centauri (NGC 5139)

## TL;DR

This study derives near-infrared period-luminosity relations for pulsating stars in $ ext{omega}$ Centauri using extensive light curves, including the first IR PL relations for SX Phoenicis stars, and refines the cluster's distance estimate.

## Contribution

It provides the first near-IR PL relations for fundamental-mode SX Phoenicis stars and updates the distance to $ ext{omega}$ Centauri using these relations.

## Key findings

- First IR PL relations for SX Phoenicis stars.
- Updated distance modulus of 13.708 mag for the cluster.
- Heliocentric distance of 5.52 kpc derived.

## Abstract

$\omega$ Centauri (NGC 5139) hosts hundreds of pulsating variable stars of different types, thus representing a treasure trove for studies of their corresponding period-luminosity (PL) relations. Our goal in this study is to obtain the PL relations for RR Lyrae, and SX Phoenicis stars in the field of the cluster, based on high-quality, well-sampled light curves in the near-infrared (IR). $\omega$ Centauri was observed using VIRCAM mounted on VISTA. A total of 42 epochs in $J$ and 100 epochs in $K_{\rm S}$ were obtained, spanning 352 days. Point-spread function photometry was performed using DoPhot and DAOPHOT in the outer and inner regions of the cluster, respectively. Based on the comprehensive catalogue of near-IR light curves thus secured, PL relations were obtained for the different types of pulsators in the cluster, both in the $J$ and $K_{\rm S}$ bands. This includes the first PL relations in the near-IR for fundamental-mode SX Phoenicis stars. The near-IR magnitudes and periods of Type II Cepheids and RR Lyrae stars were used to derive an updated true distance modulus to the cluster, with a resulting value of $(m-M)_0 = 13.708 \pm 0.035 \pm 0.10$ mag, where the error bars correspond to the adopted statistical and systematic errors, respectively. Adding the errors in quadrature, this is equivalent to a heliocentric distance of $5.52\pm 0.27$ kpc.