Gómez Maqueo Chew, Yadira Gómez Maqueo; Hebb, Leslie; Stempels, Henricus C.; Walter, Frederick M.; James, David J.; Feiden, Gregory A.; Petrucci, Romina P.; Lister, Tim A.; Baraffe, Isabelle; Brodheim, Max N.; Faedi, Francesca; Anderson, David R.; Street, Rachel A.; Hellier, Coel; Stassun, Keivan Guadalupe. (2025). Discovery of the pre-main-sequence eclipsing binary MML 48. Astronomy and Astrophysics, 702, A17. https://doi.org/10.1051/0004-6361/202555622
MML 48 is a newly discovered eclipsing binary star system—two stars that orbit each other and periodically pass in front of one another, causing dips in their combined brightness as seen from Earth. It is located in the Upper Centaurus Lupus region, part of the larger Scorpius–Centaurus association, and is estimated to be ~16 million years old. The system contains two young, low-mass stars with very different sizes and masses.
Using both space-based and ground-based telescopes, astronomers studied the system through time-series photometry (tracking changes in brightness) and spectroscopy (analyzing starlight to measure motion and composition). Because one star is much more massive and brighter than the other—with a mass ratio of ~0.21—the system was modeled as a single-lined spectroscopic and eclipsing binary, meaning only the brighter star’s spectrum can be clearly observed.
The stars orbit each other every ~2.017 days, measured with extremely high precision. The primary (larger) star has a mass of ~1.2 times that of the Sun, while the secondary (smaller) star has a mass of ~0.25 solar masses. Both stars are still contracting toward the main sequence and therefore have larger radii than mature stars of similar mass—~1.57 and ~0.59 times the Sun’s radius, respectively.
MML 48 is one of only five known eclipsing binary systems with low-mass, pre–main-sequence stars of intermediate age (~15–25 million years). It also has the most extreme mass ratio among them. Notably, the primary star is currently undergoing a “fusion bump,” a temporary increase in core energy due to the buildup of helium-3 (^3He) before it reaches equilibrium in the proton-proton (p–p) I fusion chain. This makes MML 48 A the first young star in an eclipsing system observed during this evolutionary stage.
Because of its age, well-measured properties, and unique evolutionary phase, MML 48 provides an important benchmark for understanding how low-mass stars develop, helping refine models of stellar evolution during periods of rapid change.
WASP time-series photometry of primary eclipses of MML 48 obtained in 2006–2014. The secondary eclipse is too shallow to see in this photometry, indicating the secondary is a very low-mass companion. These data were not used to derive the EB parameters since the light curves are contaminated by a nearby background star 15″ to the west (2MASS 14413595−4700280).