CCD PHOTOMETRY OF GRO JO422+32 DURING ACTIVITY AND QUIESCENCE

We present CCD photometry of the optical counterpart of the X-ray tran sient GRO J0422+32 obtained with the 1.2-m telescope at Haute-Provence on 79 nights from September 1992 through March 1994. During this inte rval the source underwent several outbursts. One double event of large amplitude (7 mag in V), lasting 250 days, coincided with the major X- ray outburst and its secondary maximum, and had an e-folding time thre e times longer than in X-rays, while two other outbursts were shorter- lived (1 month), lower amplitude (5.5 mag in V) events with subsequent smaller after-events. Our BVI data are consistent with a power-law en ergy distribution (f(lambda) similar to lambda(-alpha)) over the 4000- 9000 Angstrom range whose index alpha varies from 2.8 to 2.0 as the so urce spectrum changes from being disk-dominated to one where the compa nion becomes progressively visible, first in I, then in V. Adopting a visual absorption of A(v) = 1.25 mag, and assuming alpha = 2 during qu iescence, we derive for the companion a probable spectral type of M0V at similar to 2 kpc, with the disk contributing similar to 40% of the total light in V. Time analysis of the high state data for January, Fe bruary and December 1993 shows a dominant period of 5.1 hours. The amp litude and shape of this light curve are highly variable with several occurrences of nights with no detectable modulation. Analysis of low s tate data for February and March 1994 reveals an identical period but with an even more complex and changing light curve, and although the d isk contribution is still not negligeable in this state, part of the v ariability and complexity of the light curve may be due to the compani on star itself.