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An international team of astronomers reports the discovery of a new pre-main-sequence eclipsing binary system. The newfound binary, designated MML 48, consists of two young low-mass stars. The finding will be published in the upcoming issue of the Astronomy & Astrophysics journal.

Stellar systems showing regular light variations due to one of the stars passing directly in front of its companion are known as eclipsing binaries (EBs). In these systems, the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. EBs can provide direct accurate measurement of the mass, radius and effective temperature of stars; therefore, they are essential for testing and calibrating theoretical stellar-evolution models.

Astronomers are especially interested in finding new young EBs. This is due to the fact that such binaries constrain pre-main-sequence (PMS) stellar evolution models in the regime when the temperatures, luminosities, and radii of stars are changing rapidly as they settle onto the main sequence (MS).

Now, a group of astronomers led by Yilen Gómez Maqueo Chew of the National Autonomous University of Mexico (UNAM), reports the discovery of one such young EB. Using various spacecraft and ground-based observatories, they detected a new system of this type in the Upper Centaurus Lupus (UCL) region.

"In this paper, we present the discovery and preliminary analysis of the pre-main-sequence eclipsing binary MML 48, which is a member of Upper Centaurus Lupus (UCL) in the Scorpius-Centaurus association," the researchers wrote.

The observations found that MML 48 is an eclipsing binary system where the two eclipsing stars are still on the pre-main sequence. The age of the system is estimated to be about 16 million years old.

According to the study, the primary star MML 48 A has a radius of about 1.57 solar radii and a mass of 1.2 solar masses. When it comes to the secondary star MML 48 B, it is much smaller and less massive—it has a radius of approximately 0.59 solar radii, while its mass is around 0.25 solar masses. The orbital period of the system was measured to be 2.02 days.

The astronomers noted that the observations caught MML 48 A at the so-called "fusion bump"—an overproduction of energy in the core due to the buildup of the stable isotope of helium (³He). This is the first time that a young star in an eclipsing system has been observed during its fusion bump.

Summing up the results, the authors of the paper concluded that MML 48 joins the short list of intermediate-age EBs composed of stars that are still in the pre-main sequence. Therefore, MML 48 can be used to constrain stellar evolution during a time when such stars are quickly evolving and arriving onto the main sequence.