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P.C. Schmidtke, A.P. Cowley (ASU)
Using MACHO and OGLE-II data, we are investigating the long-term optical light curves of Be-star companions to X-ray pulsars in the Magellanic Clouds. Here we present new results for two SMC X-ray pulsars: RXJ0049.1-7250 (P(pulse)=74.7 s) and XMMUJ005517.7-723853 (P(pulse)=701.6 s). RXJ0049.1-7250, identified with Star 1 of Stevens et al. (MNRAS, 309, 421, 1999), has a mean V~16.9. We find a strong periodicity at P=33.3 days, which is likely the orbital period, in good agreement with the relation between orbital and pulse periods first recognized by Corbet (A&A, 141, 91, 1984). The folded OGLE-II light curve shows an I amplitude of ~0.03 mag. In addition, we find quasi-periodic variations (QPV) of the type discussed by Schmidtke et al. (AJ, 127, 3388, 2004) with periods in the range of 2.39 - 2.40 days, changing slightly in different orbits. The MACHO light curve of XMMUJ005517.7-723853 (=RXJ0055.2-7238) clearly shows short-term variability around mean V~15.9. Analysis of the photometric data reveals a pronounced period at P=0.28 days, much shorter than expected for either an orbital or rotational period of the Be star. The folded light curve shows approximately sinusoidal variations with amplitudes V~0.03 and R~0.02 mag. We suggest that this short period may be due to non-radial pulsations of the type seen in some single Be stars (e.g. Balona & James, MNRAS, 332, 714, 2002). The data, with the 0.28-day variation removed, show a possible long-term period of ~413 days, but further analysis is needed to confirm it. The folded light curve using this long period shows ~0.01 mag outbursts in R, very similar to the behavior found in other Be/X-ray systems.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.