The OGLE-III Catalog of Variable Stars

X. Enigmatic Class of Double Periodic Variables in the Large Magellanic Cloud

The tenth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) describes so-called Double Periodic Variables (DPVs) in the Large Magellanic Cloud (LMC). The characteristic feature of these stars is the presence of two periods with ratio around 33.

Period-period relation for LMC DPV

The shorter period is typically a few days long and is caused by the orbital motion of the semi-detached binary system. The origin of the longer period is not known, though previous studies suggest circumbinary matter is involved in the process causing this long cycle. The main argument placing the source of the long cycle outside the binary was the fact that no influence of orbital variability on long cycle was observed. The relation between orbital and long periods is shown above for all 125 DPVs from our catalog. The dotted line in the figure above show median relation between both periods. Vertical line represents positions of OGLE-LMC-DPV-065 during last 18 years. Its rate of period change is so rapid that, if remains constant, will cause long period to be 0 around the year 2040.

LMC DPV with extraordinary behaviour

The figure above shows the light curve of OGLE-LMC-DPV-097. Same symbols correspond to the same epochs of observations. It is seen that primary eclipses are deeper during long cycle minimum. Other intriguing fact is disappearing of secondary minimum when the star is fainter than the mean brightness of the long cycle.

For each object the multi-epoch V- and I-band photometry collected over 8 or 13 years of observations and finding charts together with basic parameters of variability are available to the astronomical community from the OGLE Internet archive.

PLEASE cite the following paper when using the data or referring to these OGLE results:

Poleski et al., 2010, Acta Astron., 60, 179 (arXiv:1009.5376)

Any comments about the data and the form of their presentation are welcome as they can improve the future releases of catalogs of variable stars detected by the OGLE collaboration. Send your messages to this address.