Abstract
ABSTRACT We present simultaneous high-resolution optical spectroscopy and X-ray data of theX-ray binary system GRMus (XB1254–690), obtained over a full range of orbitalphases. The X-ray observations are used to re-establish the orbital ephemeris for thissource. The optical data includes the first spectroscopic detection of the donor starin this system, through the use of the Doppler Tomography technique on the Bowenfluorescence blend (∼4630-4650 ˚A). In combination with an estimate for the orbitalparameters of the compact object using the wings of the Heii λ4686 emission line,dynamical mass constraints of 1.20 6 M X /M⊙ 6 2.64 for the neutron star and 0.456 M 2 /M⊙ 6 0.85 for the companion are derived.Key words: binaries: close - stars: binaries: individual: GRMus, XB1254–690 -binaries: spectroscopic - X-rays: binaries. 1 INTRODUCTIONXB1254–690 is a persistently bright, low-mass X-ray binary(LMXB). It was identified with a faint blue star (GRMus,V = 19.1), which exhibited the Bowen blend of NIII andCIII in emission (Griffiths et al. 1978). The object producedType 1 X-ray bursts (Mason et al. 1980; Courvoisier et al.1986), indicating the presence of a neutron star as the com-pact object. Dips of up to 95% of the 1–10 keV flux, witha recurrence period of P
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