arXiv 1104.42022011-04-21astro-ph.SR

快速旋转的低重力亚矮星B星EC 22081 - 1916--一个共同包层合并事件的遗迹

The fast rotating, low gravity subdwarf B star EC 22081-1916 - Remnant of a common envelope merger event

S. Geier, L. Classen, U. Heber

备注：: 16 pages, 4 figures, ApJL, accepted
DOI：: 10.1088/2041-8205/733/1/L13

摘要：

热亚矮星B星（sDBs）是演化的核心燃烧氦的恒星，具有非常薄的氢包层。为了形成sdB，在红巨星分支的尖端，祖先必须失去几乎所有的氢包层。在双星系统中，向伴星的质量转移提供了它们形成所需的非凡质量损失。然而，显然也存在单一的sdB，几十年来它们的形成并不清楚。氦白矮星的合并导致核心氦燃烧的点火，或者氦核心和低质量恒星在共同包层阶段的合并已经被提出。在这里，我们报告发现EC 22081 - 1916作为一个快速旋转，低重力的单一sdB恒星。它的大气参数表明，氢包层必须异常厚，这与He-WD合并的情况不同，但与低质量的普通包层合并一致，可能是具有红巨星核心的亚恒星物体。

英文摘要：

Hot subdwarf B stars (sdBs) are evolved core helium-burning stars with very thin hydrogen envelopes. In order to form an sdB, the progenitor has to lose almost all of its hydrogen envelope right at the tip of the red giant branch. In binary systems, mass transfer to the companion provides the extraordinary mass loss required for their formation. However, apparently single sdBs exist as well and their formation is unclear since decades. The merger of helium white dwarfs leading to an ignition of core helium-burning or the merger of a helium core and a low mass star during the common envelope phase have been proposed. Here we report the discovery of EC 22081-1916 as a fast rotating, single sdB star of low gravity. Its atmospheric parameters indicate, that the hydrogen envelope must be unusually thick, which is at variance with the He-WD merger scenario, but consistent with a common envelope merger of a low-mass, possibly substellar object with a red-giant core.

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