As part of the effort of astronomers to look for objects with large drops in flux, scientists have discovered a new peculiar binary system during the ongoing All-Sky Automated Survey for Supernovae (ASAS-SN). reported that astronomers from the Ohio State University (OSU) and colleagues found two chromospherically active variable stars in an eclipsing binary system with a highly eccentric orbit.

 Two Chromospherically Active Variable Stars Detected in Highly Eccentric, Eclipsing Binary System
(Photo: Wikimedia Commons)
This artist’s impression shows an eclipsing binary star system. As the two stars orbit each other, they pass in front of one another, and their combined brightness, seen from a distance, decreases. By studying how the light changes, and other properties of the system, astronomers can measure the distances to eclipsing binaries very accurately.

Highly Eccentric Eclipsing Binary J1921

Dubbed as ASASSN-V J192114.84+624950.8, a team of astronomers led by Zachary S. Way from OSU reports that this is a highly eccentric, eclipsing binary system has a rotational variation.

In the study, titled "Discovery of a Highly Eccentric, Chromospherically Active Binary: ASASSN-V J192114.84+624950.8" published in, researchers found that ASASSN-V J192114.84+624950.8 (J1921 for short) contains two chromospherically active, rotational variable stars in an eclipsing and highly eccentric orbit.

According to the Bulletin of the AAS, the team detected the variability of the J1921 and used the Transiting Exoplanet Survey Satellite (TESS) of NASA to conduct photometric observations, which led them to their discovery.

"As part of an All-Sky Automated Survey for SuperNovae search for sources with large flux decrements, we discovered a transient where the quiescent, stellar source, ASASSN-V J192114.84+624950.8, rapidly decreased in flux by ∼ 55% (∼ 0.9 mag) in the g-band. The TESS light curve revealed that the source is a highly eccentric, eclipsing binary," researchers wrote in the paper.

Moreover, they said that the eclipsing binary system has an eccentricity of about 0.79 and an 18.46-day orbit. It is located about 1,027 light-years away from Earth, and its eclipses span only 2% of the total phase.

The primary start of the system is assumed to be a late G or early K type of dwarf star with a radius of 0.9 solar radii and 29% less massive than the Sun. Meanwhile, the secondary star has a radius of 0.64 solar radii and is estimated to be 0.55 solar mass.

Astronomers concluded that discovering the peculiar properties of J1921 opens doors for interesting targets for future research focused on testing theoretical models of different types of stars.

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What is Eclipsing Binary?

According to an article in Australia Telescope National Facility, binary stars are classified based on the method used in detecting them. One of which depends upon the photometric measurement by measuring the change in the magnitude of the star.

A binary system in which the orbital plane lies edge-on when viewed on Earth so that its component stars eclipse one another is called eclipsing binaries. Algol (β Perseus) or also known as Demon star due to its changing brightness, was the first eclipsing binary system discovered.

For a system to be called an eclipsing binary, a light curve must be obtained. They are often displayed as "folded," where the phase is displayed rather than a time and date unit on the horizontal axis. These light curves are characterized by periodic dips in brightness when one of the components is eclipsed by the other.

The primary eclipse is the result of a greater drop in brightness than the secondary eclipse. Analysis shows that the light curve allows astronomers to determine the eclipsing binary's eccentricity, orientation, and inclination of the orbit. That is how OSU astronomers determined J1921's eccentricity and measured the radii of the two variable stars.

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