Mu Centauri. Credit: Palomar Observatory/STScI/WikiSky
510 light years away, Mu Centauri is a very interesting dwarf nova, a close binary star system in which white dwarf accretes matter from its companion. Although little is know about Mu Centauri, we could observe temporal variations of its brightness and its flickering on a relatively low level. It was also found that this system’s light curve contains odd consistent modulations on 2 different periods.
Bruch used 0.6-m Zeiss and the 0.6-m Boller & Chivens telescopes of Observatorio do Pico dos Dias in Brazil. Photometric observations of its light curves were conducted on 6 nights in Feb, May, Jun 2015. The brightness of Mu Centauri was measured as magnitude difference with respect to several comparison stars in the field. There was a clear modulation of about 4 hrs. This points out to ellipsoidal variations of the secondary star which should contribute a significant part of the light in this long period dwarf nova.
The star’s flickering was found to be on a comparatively low level compared to most cataclysmic variables, what can be explained by the strong contribution of the secondary star to the total light. Mu Centauri experiences this phenomenon as flickering is a distinctive feature of cataclysmic variable stars. The study reveals the orbital period to be ~0.34 days and the 2nd period to be ~0.18 days. “Apart from the dominating orbital period which is due to ellipsoidal variations of the secondary star, variability on a second period, slightly longer than a half of orbital period, was detected. There is no obvious simple relation between second period and orbital period,” the paper reads.
The nature of these variations is unclear. One possible explanation is Mu Centauri could be an intermediate polar. The modulation may be due to the variable aspect of a magnetically confined accretion region on the surface of a white dwarf rotating with second period. However, the evidence collected so far to support this hypothesis is very weak.
2 important parameters of the system was derived. The orbital inclination should lie from 50 to 65 degrees. The temp of the secondary star was 5,000 K, similar to secondary star temperatures in other cataclysmic variables with similar orbital periods. Other crucial system parameters, eg mass ratio, could not be constrained due to strong parameter correlations.
The research is another significant step towards better understanding cataclysmic variable stars like Mu Centauri. http://phys.org/news/2016-01-mysterious-cataclysmic-variable-star-mu.htmljCp http://arxiv.org/abs/1601.05722
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