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arXiv · 1411.6291

New SX Phe variables in the globular cluster NGC 288

E. Martinazzi·S. O. Kepler·J. E. S. Costa·A. Pieres·C. Bonatto·E. Bica·L. Fraga
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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.

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E. Martinazzi, S. O. Kepler, J. E. S. Costa, A. Pieres, C. Bonatto, E. Bica, L. Fraga. 2015-03-16. New SX Phe variables in the globular cluster NGC 288. https://doi.org/10.1093/mnras%2Fstu2472

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