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.