Constraining the true nature of an exotic binary in the core of NGC 6624

Abstract

We report on the identification of the optical counterpart to Star1, the exotic object serendipitously discovered by Deutsch et al. in the core of the Galactic globular cluster NGC 6624. Star1 has been classified by Deutsch et al. as either a quiescent Cataclysmic Variable or a low-mass X-ray binary. Deutsch et al. proposed StarA as possible optical counterpart to this object. We used high-resolution images obtained with the Hubble Space Telescope to perform a variability analysis of the stars close to the nominal position of Star1. While no variability was detected for StarA, we found another star, here named COM_Star1, showing a clear sinusoidal light modulation with amplitude Δm_F435W~0.7 mag and orbital period of P_orb~98 min. The shape of the light curve is likely caused by strong irradiation by the primary heating one hemisphere of the companion, thus suggesting a quite hot primary.

Accepted for publication by ApJ Letters; 6 pages, 5 figures

References in corpus (6)

• Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars
• Dynamical age differences among coeval star clusters as revealed by blue stragglers
• Near-IR properties of 24 Globular Clusters in the Galactic Bulge
• Dynamical Formation of Close Binaries in Globular Clusters II: Cataclysmic Variables
• Measuring the accretion rate and kinetic luminosity functions of supermassive black holes
• A physical model for the flickering variability in cataclysmic variables

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