a st ro - p h / 98 08 32 3 v 1 2 8 A ug 1 99 8 Period derivative of the M 15 X - ray Binary AC 211 / X 2127 + 119
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چکیده
We have combined Rossi X-ray Timing Explorer observations of X2127+119, the low-mass X-ray binary in the globular cluster M15, with archival X-ray lightcurves to study the stability of the 17.1 hr orbital period. We find that the data cannot be fit by the Ilovaisky et al. (1993) ephemeris, and requires either a 7σ change to the period or a period derivative ˙ P /P ∼ 9 × 10 −7 yr −1. Given its remarkably low L X /L opt such a ˙ P lends support to models that require super-Eddington mass transfer in a q ∼ 1 binary.
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