Astronomy and Astrophysics – Astrophysics
Scientific paper
1999-08-31
Astroph. J., 529, 428 (2000)
Astronomy and Astrophysics
Astrophysics
10 pages, 2 figures, aas4pp2.sty. Accepted for publication in ApJ
Scientific paper
10.1086/308240
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 ($m_{\rm F702W}=25.21\pm0.07$; Vega system) within the pulsar's 0\farcs5 radius positional error circle. This may be the companion. If it is a main-sequence star in the cluster, it has radius $\rcomp\simeq0.3 \rsun$, temperature $\teff\simeq3600 $K, and mass $\mcomp\simeq0.3 \msun$. 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 $\rcomp\simlt0.44 \rsun$ and $\teff\simgt3300 $K. Even for the largest radii, the required efficiency of tidal dissipation is larger than expected for some prescriptions.
Buren Dave Van
Kaspi Victoria M.
Klemola Arnold R.
Kulkarni Sanjeev R.
Lyne Andrew G.
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