Far-Ultraviolet Observation of the Globular Cluster NGC 6397

Abstract

We present an observational far-UV (FUV) and near-UV (NUV) study of the core region of the globular cluster NGC 6397. The observations were obtained with the Space Telescope Imaging Spectrograph (STIS, FUV), and the Wide Field Camera 3 (WFC3, NUV) on board the Hubble Space Telescope. Here, we focus on the UV bright stellar populations such as blue stragglers (BSs), white dwarfs (WDs) and cataclysmic variables (CVs). We present the first FUV-NUV color-magnitude diagram (CMD) for this cluster. To support our classification of the stellar populations, we compare our FUV-NUV CMD with optical data from the ACS Survey of Galactic Globular Clusters. The FUV-NUV CMD indicates 16 sources located in the WD area, and ten BSs within the 25"x 25" of the STIS FUV data. Eighteen Chandra X-ray sources are located within the FUV field of view. Thirteen of those have a NUV counterpart, of which nine sources also have a FUV counterpart. Out of those, five sources are previously suggested CVs, and indeed all five are located in the WD/CV region in our FUV-NUV CMD. Another CV only has a FUV but no NUV counterpart. We also detect a NUV (but no FUV) counterpart to the MSP located in the core of this cluster. The NUV lightcurves of the CVs and MSP show flickering behaviour typical of CVs. We found that the BSs and CVs are the most centrally concentrated population. This might be an effect of mass segregation or indicate the preferred birth place of BSs and CVs via dynamical interactions in the dense core region of GCs. HB stars are the least centrally concentrated population and absent in the innermost area of the core.

13 pages, MNRAS accepted

References in corpus (18)

• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• The White Dwarf Cooling Sequence of NGC6397
• Formation and evolution of compact binaries in globular clusters: I.Binaries with white dwarfs
• Dynamical Formation of Close Binaries in Globular Clusters II: Cataclysmic Variables
• Deep ACS Imaging in the Globular Cluster NGC 6397: The Cluster Color Magnitude Diagram and Luminosity Function
• The Physics of Crystallization from Globular Cluster White Dwarf Stars in NGC 6397
• Stellar Exotica in 47 Tucanae
• Identification of Faint Chandra X-ray Sources in the Core-Collapsed Globular Cluster NGC 6397: Evidence for a Bimodal Cataclysmic Variable Population
• Monte Carlo Simulations of Star Clusters - VI. The globular cluster NGC 6397
• Chandra X-ray Sources in the Collapsed-Core Globular Cluster M30 (NGC 7099)
• Absolute motions of globular clusters. II. [HST astrometry and VLT radial velocities in NGC6397]
• A Chandra Look at the X-ray Faint Millisecond Pulsars in the Globular Cluster NGC 6752
• Upper limits on the central black hole masses of 47Tuc and NGC6397
• Chandra X-Ray Observatory Observations of the Globular Cluster M71
• The Space Motion of the Globular Cluster NGC 6397
• Combined Chandra, XMM-Newton and Hubble Space Telescope observations of the Galactic globular cluster NGC 2808
• Deep ACS Imaging in the Globular Cluster NGC6397: Dynamical Models
• Compact X-ray Binaries in and out of Core Collapsed Globulars

Cited by in corpus (6)

• A Deep Search for Faint Chandra X-ray Sources, Radio Sources, and Optical Counterparts in NGC 6752
• Identifications of Faint Chandra Sources in the Globular Cluster M3
• Isochrone fitting of Galactic globular clusters -- V. NGC6397 and NGC6809 (M55)
• Study of UV bright stellar populations in the globular cluster NGC 1261 using AstroSat
• Far-ultraviolet investigation into the galactic globular cluster M30 (NGC 7099): I. Photometry and radial distributions
• Reevaluating the Origin of Detectable Cataclysmic Variables in Globular Clusters: Testing the Importance of Dynamics