A complete census of $H\alpha$ emitters in NGC 6397

Abstract

We used a dataset of archival Hubble Space Telescope images obtained through the F555W, F814W and F656N filters, to perform a complete search for objects showing $H\alpha$ emission in the globular cluster NGC 6397. As photometric diagnostic, we used the $(V-H\alpha {)}_0$ color excess in the $(V-H\alpha {)}_0$-$(V-I{)}_0$ color-color diagram. In the analysed field of view, we identified 53 $H\alpha$ emitters. In particular, we confirmed the optical counterpart to 20 X-ray sources (7 cataclysmic variables, 2 millisecond pulsars and 11 active binaries) and identified 33 previously unknown sources, thus significantly enlarging the population of known active binaries in this cluster. We report the main characteristics for each class of objects. Photometric estimates of the equivalent width of the $H\alpha$ emission line, were derived from the $(V-H\alpha {)}_0$-excess and, for the first time, compared to the spectroscopic measurements obtained from the analysis of MUSE spectra. The very good agreement between the spectroscopic and photometric measures fully confirmed the reliability of the proposed approach to measure the $H\alpha$ emission. The search demonstrated the efficiency of this novel approach to pinpoint and measure $H\alpha$-emitters, thus offering a powerful tool to conduct complete census of objects whose formation and evolution can be strongly affected by dynamical interactions in star clusters.

Accepted for publication by ApJ; 14 pages, 8 Figures, 1 Table

References in corpus (9)

• The Dartmouth Stellar Evolution Database
• Dynamical age differences among coeval star clusters as revealed by blue stragglers
• Discovery of PSR J1227-4853: A transition from a low-mass X-ray binary to a redback millisecond pulsar
• Formation and evolution of compact binaries in globular clusters: I.Binaries with white dwarfs
• Deep ACS Imaging in the Globular Cluster NGC 6397: The Cluster Color Magnitude Diagram and Luminosity Function
• Identification of Faint Chandra X-ray Sources in the Core-Collapsed Globular Cluster NGC 6397: Evidence for a Bimodal Cataclysmic Variable Population
• Radio timing and optical photometry of the black widow system PSR J1518+0204C in the globular cluster M5
• RXTE determination of the intermediate polar status of XSS J00564+4548, IGR J17195-4100, and XSS J12270-4859
• Radio Timing and Optical Photometry of the Black Widow System PSR J1953+1846A in the Globular Cluster M71

Cited by in corpus (5)

• The "dynamical clock": dating the internal dynamical evolution of star clusters with Blue Straggler Stars
• High-resolution extinction map in the direction of the strongly obscured bulge fossil fragment Liller 1
• Searching for exotic object companions in the dense core of NGC 362: a multi-wavelength and multi-epoch photometric analysis
• Exploration of faint X-ray and radio sources in the massive globular cluster M14: A UV-bright counterpart to Nova Ophiuchus 1938
• The ESO-VLT MIKiS survey reloaded: velocity dispersion profile and rotation curve of NGC 1904