V0332+53

N. E. White, J. Davelaar, A. N. Parmar and L. Stella, European Space Agency; and M. van der Klis, Astronomical Institute, University of Amsterdam, report that the EXOSAT observations of the second recent outburst of V0332+53 gave a pulse period of 4.37532 +/- 0.0004 s on 1983 Dec. 24. The period therefore did not continue to decrease at the high rate reported during the first outburst (IAUC 3902). However, a similarly high rate of decrease was again present during the second outburst, suggesting that the period variations are due to orbital motion. The flux again decayed over the following week. A third series of observations during 1984 Jan. 19-24 again found the source to be in outburst at a level of 0.04 Crab with the pulse period increasing. Preliminary solutions yield an orbital period P = 34.2 +/- 1.5 days, periastron passage T = 1984 Jan. 20 +/- 4, a sin i = 55(+150)(-10) light seconds, e = 0.35 (+0.25)(-0.10). The outbursts are approximately centered on T.