The Binary Pulsar PSR 1908+00 in NGC 6760

Abstract

We present orbital parameters of the 3.6 ms binary pulsar 1908 +00 in the globular cluster NGC 6760. The orbital period is 3.4 hr, and the mass function is 3 x 10^6 M_⊙ , implying a minimum companion mass of 0.018 M_⊙ . The companion is probably degenerate; and if it is hydrogen, it is close to overflowing its Roche lobe. The only other millisecond binary radio pulsar systems with orbital period < 10 hr and mass function below 10-3 M_⊙ are the eclipsing pulsar 1957+20 and 1744-24A, and the very low mass binary 0021-721. These pulsars are ablating their companions and may be the progenitors of isolated millisecond pulsars. PSR 1908+00 shows no evidence for long-duration eclipses as are seen in 1744-24A, but short-duration eclipses as in 1957 + 20 are not excluded.

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