Variable stars in the globular cluster NGC 4372: An updated census from time-series photometry

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Abstract We present results from a time-series photometric survey of the metal-poor globular cluster NGC 4372. Within a ${24{^{\prime }_{.}}5}\times {24{^{\prime }_{.}}5}$ field of view, 23 new variable stars were identified, increasing the total number of variables in our observed field to 44. The sample comprises 21 short-period pulsators, 18 eclipsing binaries, two ellipsoidal variables, one RR Lyrae star, one long-period variable, and one semi-regular variable. Notably, an RR Lyrae variable was discovered on the horizontal branch, representing the first identification of its class in this cluster. Using Gaia DR3 proper motions together with photometric criteria, we evaluated cluster membership and classified the short-period pulsators as 18 cluster SX Phoenicis (SX Phe) stars and three field $\delta$ Scuti stars. From 14 fundamental-mode pulsators in the SX Phe sample, we derived the period–luminosity relation $\langle V\rangle = -3.942(\pm 0.304)\log P + 12.858(\pm 0.402)$, with a 1$\sigma$ scatter of 0.087 mag. A multi-frequency analysis of these pulsators revealed three double-radial mode pulsators (V11, V35, and V40) with period ratios typical of SX Phe stars. Among the eclipsing systems, three exhibit Algol-type light curves, whereas the remainder exhibit W UMa-type variability. For the W UMa binaries, Rucinski’s $M_V(\log P,\, \mathrm{color})$ calibrations together with Gaia DR3 proper motions suggest that V4, V5, V12, and V27 are consistent with cluster membership. V2 is classified as a Mira variable, exhibiting large-amplitude variability ($\Delta V \approx 3.28$ mag) with a tentative period of $P \sim 337$ d, as inferred from Gaia DR3 epoch photometry transformed to the Johnson V band. However, its position on the color–magnitude diagram and its proper motion imply that it is likely a field object. Our results provide an updated census and membership evaluation of variables in NGC 4372.

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