Merged Red-Giant Stars

红巨星是最大、最亮的恒星，产生许多常见的化学元素，如碳和氮。由于它们的体积很大，而且大多数恒星都在双星系统中，与伴星的相互作用非常可能。这种相互作用是通过共同包络演化进行的，形成了奇异的双星现象，如热核新星、超新星、中子星和黑洞双星，它们合并形成了最近检测到的引力波。不幸的是，共同包络演化是所有恒星演化阶段中最不确定的。对幸存下来的恒星的速率和性质的定量预测是出了名的不可靠。这个项目将扭转这一问题。许多双星系统没有在共同包络进化中幸存下来：相反，它们合并成了单一的、特殊的巨星--红散星。这些巨星的详细模型将被构建来预测恒星结构、自转和化学成分，然后与最新的观测结果进行比较，以了解这些神秘但极其重要的共同包络浮现。

Red giants are the biggest and brightest stars, and make many common chemical elements, like carbon and nitrogen.Because of their great size, and because most stars are in binary systems, interaction with a companion star is very likely.This proceeds through common-envelope evolution and forms exotic binary phenomena like thermonuclear novae, type-Iasupernovae and neutron-star and black-hole binaries which merge to make the recently-detected gravitational waves.Unfortunately, common-envelope evolution is the most uncertain of all stellar-evolution phases. Quantitative predictions ofrates and properties of stars that survive it are notoriously unreliable. This project will reverse the problem. Many binarysystems do not survive common-envelope evolution: instead they merge to form single, peculiar giants, the ?redstragglers?. Detailed models of these giants will be constructed to predict stellar-structure, rotation and chemistry, andthen be compared to the latest observations to understand the mysterious, but hugely important, common-envelopemergers.