New IW And type star discovered by astronomers

A team of Chinese astronomers conducted photometric observations of a dwarf nova known as Karachurin 12. They discovered that Karachurin 12 is an IW And type star. The discovery was detailed in a research paper published September 4 on the preprint server arXiv.

Cataclysmic variables (CVs) are binary star systems consisting of a primary white dwarf accreting matter from a normal companion star. Their luminosity increases irregularly and dramatically, then falls back to a quiescent state.

In CVs, mass transfer from the companion star often occurs via an accretion disk around the white dwarf, and in some cases, thermal instability of the disk triggers explosions called dwarf novae (DNe). This behavior is generally explained by the accretion disk instability model (DIM).

Z Camelopardalis (Z Cams) are a subtype of DNe particularly distinguished by their “shutdown” behavior during the decay phase of outbursts, where their brightness stabilizes at about 0.7 magnitudes below the peak level. The DIM explains the typical shutdown by describing the disk as being in a hot, stable state.

However, observations over the previous decade showed that some Z Cams, such as IW Andromedae (IW And for short), did not end with a return to quiescence, but instead culminated in an outburst, followed immediately by a decline and then a rapid return to quiescence. This unusual behavior was identified as the “abnormal arrest phenomenon,” and objects experiencing it were dubbed IW And-like systems and recognized as a subclass of Z Cams.

Now, a team of astronomers led by Qi-Bin Sun of Yunnan University in China reports the detection of such unusual behavior in Karachurin 12, a system classified in 2018 as a Z Cam-type DN. The discovery is based on photometric data from the All-Sky Automated Survey for Supernovae (ASAS-SN), the Zwicky Transient Facility (ZTF), and the Transiting Exoplanet Survey Satellite (TESS).

Observations have shown that Karachurin 12 is a negative supersun (NSH) system with a signal of accretion disk precession. Typically, NSH signals are signals with periods about 5% shorter than the orbital periods exhibited by inclined accretion disks in CVs.

The collected data revealed various cycle patterns in karachurin-12, with the NSH amplitude varying throughout the cycle. The IW And cycle period for karachurin-12 was measured to be 35.69 days, while the precession period of the accretion disk was estimated to be approximately 4.96 days.

The study also showed that the NSH amplitude of Karachurin 12 decreases with increasing explosions and increases with weakening of explosions. Astronomers assume that this could be related to changes in the radius of the accretion disk.

Overall, the authors of the study noted that the results obtained for Karachurin 12 indicate a potential link between the IW And phenomenon and a tilted disk. Therefore, they suggest that the tilted thermally unstable disk model effectively explains the IW And phenomenon in this system.

© 2024 Science X Network