We present the results of our campaign of photometry of the X-ray nova GRO J0422 +32 in quiescence, the purpose of which was to confirm the proposed orbital period of ∼5.1 hr, and to search for the ellipsoidal variations which are a prerequisite for the mass determination of the primary. We find evidence for a weak ellipsoidal modulation corresponding to an orbital period of 5.1 hr, with a semi- amplitude of ∼0.03 mag the lowest known of any quiescent X-ray nova. With the assumption that the I-band contamination by the accretion disk is no greater than that observed in other quiescent X-ray novae, we estimate that the orbital inclination must be < 45°. Furthermore, a ZAMS secondary implies an upper limit on the distance of ∼2.2 kpc, and a quiescent accretion rate ∼3% that observed in A0620-00. The inclination estimate implies a mass of the compact object ≥3.4 Msun. ROSAT observations constrain the quiescent X-ray luminosity to be less than 2 x 10³² ergs s⁻¹ (for a distance of 2 kpc). We speculate that the low quiescent accretion rate through the disk, inferred from the optical observations, may well be related to the large outburst amplitude of GRO J0422+32.
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Callanan et al. (1996) studied this question.