Periodic UV modulation of X1850-087: a double degenerate binary in the globular cluster NGC 6712?
van Paradijs, J.; Charles, P. A.; Naylor, T.; Koch-Miramond, L.; Auriere, M.; Homer, L.
United Kingdom, Netherlands, France
Abstract
We report the discovery with the Hubble Space Telescope (HST) of a short-period (20.6 min) UV modulation in X1850-087, the luminous X-ray source in the globular cluster NGC 6712. The low-amplitude modulation (0.044+/-0.007 mag) is not detected in archival X-ray observations with EXOSAT. We compare the properties of X1850-087 with the 11-min binary X1820-303 and identify the modulation as the orbital period, which requires the mass-losing companion to be degenerate and of low mass (0.04 M_solar).