Short period variability in the globular cluster NGC 419 and the SMC field

TL;DR

This study identifies and analyzes delta Scuti variable stars in the globular cluster NGC 419 and the SMC field, revealing insights into cluster age, stellar populations, and distance measurements using time series observations.

Contribution

First detection of 54 delta Scuti stars in NGC 419 and the SMC field, providing new data on their distribution, properties, and implications for cluster age and distance.

Findings

Few delta Scuti stars at the MSTO suggest a younger cluster age.

Majority of delta Scuti stars are field stars in the SMC.

Distance estimates align with previous measurements.

Abstract

Delta Scuti ($\delta$ Sct) stars have been extensively studied in our Galaxy, but far less in extragalactic systems. Here we study the population of $\delta$ Sct variables in NGC 419, an intermediate-age globular cluster of the Small Magellanic Cloud (SMC), using $g,r,i$ Gemini-S/GMOS time series observations. Our goal is to study the role of such variables in the cluster extended main-sequence turnoff (MSTO). We report the discovery of 54 $\delta$ Sct stars and three eclipsing binaries in the NGC 419 field. We find only a handful of the $\delta$ Sct stars at the MSTO of NGC 419 while the majority is fainter, indicating that the cluster is younger ($\lesssim 1.2$ Gyr) than previously thought. Considering their radial distribution, we identify only six $\delta$ Sct stars as probable members of NGC 419 while the 48 remaining are likely $\delta$ Sct stars of the SMC field. Cluster $\delta$ Sct stars appear close to the red edge of the MSTO, supporting the idea that the extended MSTO has its origin in an age spread. The 48 field $\delta$ Sct stars represent the largest detection of $\delta$ Sct stars made in the SMC. The period distribution of these newly detected $\delta$ Sct stars ($0.04 \lesssim P \lesssim 0.15$ d) is similar to that detected in other systems. The amplitude distribution ($0.05 \lesssim \Delta r \lesssim 0.60$ mag) is likely biased because of the lack of low-amplitude stars. We finally use the $\delta$ Sct stars to calculate distances using different period-luminosity relations. The average distance moduli obtained are $18.76\pm0.14$ mag for NGC 419 and $18.86\pm0.11$ mag for the SMC field, which agree with previous measurements.