Why in news?
Astronomers from the Aryabhatta Research Institute of Observational Sciences (ARIES) in Nainital and the Physical Research Laboratory (PRL) in Ahmedabad announced new findings on 6 January 2026 after studying four W Ursae Majoris (W UMa) stars. Using the Devasthal Fast Optical Telescope in Uttarakhand and data from NASA’s Transiting Exoplanet Survey Satellite (TESS), the team produced detailed light curves showing subtle variations in brightness. These observations provide insights into how close binary stars exchange mass and evolve.
Background
W UMa stars are a class of contact binary stars in which two low‑mass stars orbit so closely that they share a common outer envelope. Typically of spectral types F, G or K, these binaries complete an orbit in less than a day and exhibit continuous fluctuations in brightness rather than discrete eclipses. They are subdivided into A‑type systems, where the hotter star is more massive, and W‑type systems, where the cooler star is more massive. Because both components have filled their Roche lobes, they share material through a common envelope. Studying these systems helps astronomers refine mass–radius relations and understand stellar evolution.
What the study found
- Detailed light curves: The researchers obtained high precision photometric data that show how the brightness of the four binaries changes over time. Irregularities in the curves pointed to star spots – cooler regions on the stellar surface caused by magnetic activity – rotating in and out of view.
- Mass transfer and orbital changes: The light curves and period analyses indicate that mass is flowing from one star to the other, leading to slight changes in orbital periods. Such observations offer clues about how contact binaries evolve into more exotic systems.
- Emission lines: Spectroscopic observations detected prominent H‑α and H‑β emission lines, suggesting strong chromospheric activity and magnetic fields in these stars.
Significance
- Improved models: The data will help refine theoretical models of how stars of different masses interact when they share a common envelope, influencing predictions for the evolution of close binaries.
- Exoplanet studies: Accurate mass–radius relations for low‑mass stars are essential for determining the properties of planets orbiting them. Contact binaries provide natural laboratories for testing these relations.
- Role of Indian observatories: The study highlights the capabilities of India’s ground‑based telescopes and the importance of combining them with space‑based data.
Sources: PIB
