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MACHO Light Curve of IGR J05007-7047

ATEL # 2601; P.C. Schmidtke (Arizona State University), A.P. Cowley (Arizona State University)
on 8 May 2010; 0:02 UT
Password Certification: Paul Schmidtke (

Subjects: Optical, X-ray, Binaries, Neutron Stars

Masetti et al. (ATel #783) identified the optical counterpart for X-ray source IGR J05007-7047 with an LMC star showing H-alpha emission and other Balmer lines in absorption, which suggests it may be a Be star. Coe et al. (ATel #2597) have analyzed this star in the OGLE-III database. We find that it is also coincident with MACHO star 23.3300.10, whose longterm light curve shows dips ranging in depth from 0.1 to 0.5 mag every 600-800 days. At minimum light the color is blue (B-V~-0.15) consistent with a middle B star. As the source brightens the color becomes redder (B-V~+0.1), perhaps indicating a growing cool disk. After flattening the MACHO light curve to remove the longterm trends, the resulting periodogram shows a peak at ~28 days, consistent with the X-ray period of 30.77 days (La Parola et al., ATel #2594) and the OGLE-III period of 30.90 days (Coe et al., ATel #2597). The folded MACHO R data shows a sinusoidal light curve with a full amplitude of ~0.01 mag.

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