On April 15, The Astrophysical Journal published an observational study on a candidate of cataclysmic variable star KZ Gemini. Dr. DAI Zhibin from Yunnan Observatories of Chinese Academy of Sciences and his coauthors, not only identify the authentic coordinates of KZ Gemini, but also achieve 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 3-month observation campaign on KZ Gemini, and detected the ellipsoidal modulation inconsistent with the expected irregular modulation.

Dr. DAI and his cooperators 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 researchers and resulted that none of observation data is 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. Researchers 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, researchers successfully 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.

Contact:
DAI Zhibin, YNAO, CAS
Zhibin_dai@ynao.ac.cn

The white dwarf accretion pattern (Image by DAI Zhibin)