Opacity tells us how much a star’s material blocks light and heat from moving through it.
The final orbit means the orbit of the two stars in binary after mass transfer is over and the donor star has become a helium white dwarf.
Two objects orbiting each other—like a star and a planet, or two stars—each body has a region around it where its gravity is dominant. This region is called its Roche lobe. If gas reaches beyond the Roche lobe, the other object’s gravity can pull it away.
The study concludes that the relationship between a helium white dwarf’s mass and the final orbital period of its binary system depends strongly on low-temperature opacity in stellar models. It also depends on metallicity, angular momentum loss and how mass transfer happens.
The Freedman opacity is used here which consider molecular effects but not grain condensates. According to this, the predicted white dwarfs end up forming at slightly smaller radii during their red-giant phase, leading to shorter orbital periods.
Source: https://arxiv.org/html/2511.20147v1
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