In a study published in The Astrophysical Journal, Dr. DAI Zhibin from Yunnan Observatories of the Chinese Academy of Sciences and the collaborators reported progress on a candidate of cataclysmic variable star KZ Gemini. They identified the authentic coordinates of KZ Gemini, and achieved a complete analysis on the white dwarf accretion.

The current evolution theory of cataclysmic variables indicates that the orbital period gap is a forbidden area for the normal cataclysmic variables (i.e., accreting white dwarf). Hence, cataclysmic variables inside the gap are regarded as the abnormal targets. Since they are faint, few of the follow-up ground-based observations were done before.

In 2014, Kepler-II (K2) carried out a three month observation campaign on KZ Gemini, and detected the ellipsoidal modulation inconsistent with the expected irregular modulation.

Dr. DAI and the collaborators made the ground-based follow-up observations and re-identification on KZ Gemini, using several meter-class telescopies on Xinglong Observatory, Apache Point Observatory and Michigan-Dartmouth-MIT Observatory.

They found a significant deviation of coordinates in several public databases (SDSS, SIMBAD, Kepler, and AAVSO) and cataclysmic variable catalog. The wrong coordinates and identification confused the researchers, and therefore none of observation data has been published over half a century.

Cataclysmic variable star is a typical single-lined binary star, because the complex accretion progress and high luminosity ratio of two component stars overwhelm the spectra from the secondary star. The researchers then measured cross-correlation velocities of the secondary star and improved the orbital period to be the order of millisecond. This precision of period is almost two orders of magnitude higher than that derived from the K2 data.

With this period and multi-band light curves, the researchers derived a complete white dwarf accretion pattern and a set of high-resolution basic parameters, which will help future analysis on the secular evolution of accretion progress.