New SX Phe variables in the globular cluster NGC 288

TL;DR

This study reports the discovery of two new SX Phoenicis variable stars in the globular cluster NGC 288, refines period estimates for known variables, and derives a Period-Luminosity relation useful for distance measurements.

Contribution

The paper introduces two newly identified SX Phe variables in NGC 288 and refines their period estimates, enhancing the understanding of variable star populations in this cluster.

Findings

Discovered two new SX Phe variables in NGC 288.

Derived the Period-Luminosity relation for SX Phe stars in the cluster.

Estimated cluster parameters: metallicity, reddening, and distance modulus.

Abstract

We report the discovery of two new variable stars in the metal-poor globular cluster NGC 288, found by means of time-series CCD photometry. We classified the new variables as SX Phoenicis due to their characteristic fundamental mode periods (1.02 +- 0.01 and 0.69 +- 0.01 hours), and refine the period estimates for other six known variables. SX Phe stars are known to follow a well-defined Period-Luminosity (P-L) relation and, thus, can be used for determining distances; they are more numerous than RR Lyraes in NGC~288. We obtain the P-L relation for the fundamental mode M_V = (-2.59 +- 0.18) log P_0(d) + (-0.34 +- 0.24) and for the first-overtone mode M_V = (-2.59 +- 0.18) log P_1(d) + (0.50 +- 0.25). Multi-chromatic isochrone fits to our UBV color-magnitude diagrams, based on the Dartmouth Stellar Evolution Database, provide <[Fe/H]> = -1.3 +- 0.1, E(B-V) = 0.02 +- 0.01 and absolute distance modulus (m-M)0 = 14.72 +- 0.01 for NGC 288.