2000ApJ...529..428V

We report on Keck and Hubble Space Telescope optical observations of the eclipsing binary pulsar system PSR B1718-19, in the direction of the globular cluster NGC 6342. These reveal a faint star (m_F702W=25.21±0.07; Vega system) within the pulsar's 0".5 radius positional error circle. This may be the companion. If it is a main-sequence star in the cluster, it has radius R_C≃0.3 R_☉, temperature T_eff≃3600 K, and mass M_C≃0.3 M_☉. In many formation models, however, the pulsar (spun-up by accretion or newly formed) and its companion are initially in an eccentric orbit. If so, for tidal circularization to have produced the present-day highly circular orbit, a large stellar radius is required, i.e., the star must be bloated. Using constraints on the radius and temperature from the Roche and Hayashi limits, we infer from our observations that R_C≲0.44 R_☉ and T_eff≳3300 K. Even for the largest radii, the required efficiency of tidal dissipation is larger than expected for some prescriptions.