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Non-Radial Pulsations from RX J0105.1-7211

ATel #648; Paul C. Schmidtke and Anne P. Cowley (Arizona State Univ.)
on 2 Nov 2005; 18:57 UT
Credential Certification: Paul Schmidtke (Paul.Schmidtke@asu.edu)

Subjects: Optical, X-ray, Binary, Neutron Star, Pulsar

RX J0105.1-7211 (SXP3.34) is a Be/neutron-star binary in the Small Magellanic Cloud. It has one of the shortest pulsation periods among the many SMC Be/pulsar systems. The optical counterpart is #1506 from the emission-line catalogue of Meyssonnier & Azzopardi (1993, A&AS, 102, 451). In addition Coe et al. (2005, MNRAS, 356, 502) have shown that it has very strong H-alpha emission. They found a photometric period of 11.09 days, which they suggested was the orbital period, but found this to be inconsistent with the strength of the emission.

We have carried out an analysis of the MACHO data to much higher frequencies and find that there is an exceptionally prominent period at 1.099 days. The 11-day period is present, but it is a weaker alias of the 1.099-day period. A folded light curve shows sinusoidal variations with a full amplitude in R and V light of ~0.05 and 0.03 mag, respectively. The signal is stable in frequency, phasing, and amplitude over the 7.5 years of MACHO observations. We identify this periodicity with non-radial pulsations of the Be star.

In addition, the residuals from the 1.099-day period show a second, weaker period at 0.980 days, with an amplitude about one-third of the primary pulsation period. This appears to be a second pulsational mode. When the MACHO data are divided into 4 time segments, we find this secondary signal is strongest in the second segment and nearly disappears in the last segment.

We were unable to identify any photometric signature of the orbital period of this system.