The First Ultraviolet Studies of the Optical Candidate for the X-Ray Source 1118-61

Abstract

The X-ray pulsator, 1118-61, discovered in 1975 by the Ariel-5 satellite, has been observed for the first time at UV wavelengths using IUE. Its UV spectrum clearly identifies the optical counterpart as a Be star similar to that seen in other X-ray pulsators. From the 2200 Å absorption feature a distance estimate of ∼ 4 kpc is obtained and the carbon-IV profile reveals the mass loss rate from the primary. The discrepancy seen in other similar systems between the optical/UV mass loss rate and that needed to power the X-ray source is also observed in this source. Possible models are reviewed.