Research investigated eclipsing binary V608 Cassiopeiae

Using the Sobaeksan Optical Astronomy Observatory (SOAO), Korean astronomers have performed photometric observations of a W UMa-type eclipsing binary known as V608 Cassiopeiae. Results of the observational campaign, published January 20 on the arXiv pre-print server, shed more light on the nature of this peculiar system.

In general, W UMa-type binaries are eclipsing binaries with a short orbital period (below one day) and continuous light variation during a cycle. They are composed of two dwarf stars with similar temperature and luminosity, sharing a common envelope of material and are thus in contact with one another. Therefore, they are often dubbed "contact binaries."

V608 Cassiopeiae (or V608 Cas for short) was discovered in 1976 as a variable star with an orbital period of approximately 0.47 days and an amplitude of about 1.0 mag. Further observations of V608 Cas revealed that its light curve showcases typical light variation of a W UMa-type binary with eclipse depths of about 0.55 mag, and the orbital period of this system was calculated to be 0.38 days. Astronomers also found that the binary exhibits continuous increase of the orbital period at a rate of nearly 0.001 minutes per year.

To get more insights into the properties of V608 Cas, Jang-Ho Park and Jae Woo Lee of Korea Astronomy and Space Science Institute conducted photometric observations of this object using a 61-cm reflector at SOAO.

"The aim of this study is to present the physical properties of V608 Cas through our new binary modeling, and to examine the characteristics of the orbital period change newly discovered through continuous monitoring of the times of minima," the astronomers wrote in the paper.

SOAO observations found that V608 Cas is an overcontact binary in a shallow contact of about 26 percent, with a temperature difference of 155 K. The primary star has a radius of 1.15 solar radii, mass of 0.88 solar masses, and a luminosity at a level of 0.88 solar luminosities. When it comes to the secondary star, these parameters are estimated to be: 0.7, 0.29 and 0.37, respectively.

The study revealed that the orbital period of V608 Cas through a combination of an upward parabola and two periodic variations, with period lengths of 16 and 26.3 years, and semi-amplitudes of 0.0341 and 0.0305 days, respectively. The continuous increase of the system's orbital period was calculated to be approximately 0.0005 minutes per year. The astronomers assume that this change may be caused by the mass transfer of about 1.51×10⁻⁷ solar masses per year from the companion to the primary star.

Trying to explain the observed two periodic variations in the orbital period of V608 Cas, the researchers suggested that they may be a pair of the so-called light-traveling time (LTT) effects due to the presence of two circumbinary objects around the binary. They noted that if these two hypothetical objects are main sequence stars, their minimum masses should be around 2.2 and 1.27 solar masses.