A dwarf nova in the globular cluster M13

Abstract

Dwarf novae in globular clusters seem to be rare with only 13 detections in the 157 known Galactic globular clusters. We report the identification of a new dwarf nova in M13, the 14th dwarf nova identified in a globular cluster to date. Using the 2m Faulkes Telescope North, we conducted a search for stars in M13 that show variability over a year (2005-2006) on timescales of days and months. This led to the detection of one dwarf nova showing several outbursts. A Chandra X-ray source is coincident with this dwarf nova and shows both a spectrum and variability consistent with that expected from a dwarf nova, thus supporting the identification. We searched for a counterpart in Hubble Space Telescope ACS/WFC archived images and found at least 11 candidates, of which we could characterize only the 7 brightest, including one with a 3 sigma H-alpha excess and a faint blue star. The detection of one dwarf nova when more could have been expected likely indicates that our knowledge of the global Galactic population of cataclysmic variables is too limited. The proportion of dwarf novae may be lower than found in catalogs, or they may have a much smaller duty cycle in general as proposed by some population synthesis models and recent observations in the field.

Accepted for publication in ApJ, 12 pages, 12 figures, 5 tables (v2 contains corrections of the proofs)

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• Mass/Radius Constraints on the Quiescent Neutron Star in M13 Using Hydrogen and Helium Atmospheres
• A Census of X-ray Millisecond Pulsars in Globular Clusters
• X-ray Binaries in the Ultrahigh Encounter Rate Globular Cluster NGC 6388
• MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters -- III. Cataclysmic variables -- Implications of model assumptions
• Spectroscopic Follow-up of X-ray Sources in the ChaMPlane Survey: Identification of a New Cataclysmic Variable
• Chandra and HST Studies of Six Millisecond Pulsars in the Globular Cluster M13
• Astrometric Membership Tests for the Zinn-Newell-Gibson "UV-Bright" Stars in Galactic Globular Clusters
• Near-ultraviolet detections of four dwarf nova candidates in the globular cluster 47 Tucanae
• CV1 in the globular cluster M 22: confirming its nature through X-ray observations and optical spectroscopy
• On the use of variability time-scales as an early classifier of radio transients and variables
• Reevaluating the Origin of Detectable Cataclysmic Variables in Globular Clusters: Testing the Importance of Dynamics
• $\beta$-SGP: Scaled Gradient Projection with $\beta$-divergence for astronomical image restoration