Resolving subdwarf B stars in binaries by HST imaging
Resolving subdwarf B stars in binaries by HST imaging
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DOI：
10.1051/0004-6361:20020127
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发表时间：
2002-01
影响因子：
6.5
通讯作者：
U. Heber;S. Moehler;R. Napiwotzki;P. Thejll;E. M. G. U. O. Erlangen-Nuernberg;Danish Meteorogical Institute;S. Observatory
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文献类型：
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作者：
U. Heber;S. Moehler;R. Napiwotzki;P. Thejll;E. M. G. U. O. Erlangen-Nuernberg;Danish Meteorogical Institute;S. Observatory
亚光度B星的起源仍然是恒星演化中一个未解决的问题。单星以及接近的双星演化场景已经被调用，但到目前为止还没有取得什么成功。我们使用哈勃太空望远镜上的 WFPC2 行星相机对光谱双星候选体（19 个系统，包括一颗 sdB 恒星和晚型伴星）进行了一次小型调查，以测试这些场景。蒙特卡罗模拟表明，通过对 R 波段的程序恒星进行成像，大约三分之一的样本（6-7 颗星）应该在 0" 的极限角分辨率下被解析。如果它们像主序星（“单星演化”）那样具有线性分离，则应该无法解析。如果所有系统都是由接近的二元演化产生的，则没有一个应该是可解析的。此外，我们预计我们的样本中会存在三个三重系统。其中大多数（如果不是全部）应该是可解析的。在 6 个系统中解析了组件然而，只有在 TON 139 和 PG 1718+519 两个系统（分别为 0".32 和 0".24）中，解析分量的星等才符合光谱能量分布反卷积的预期。这两个恒星可能是物理双星，而在其他情况下，附近的恒星可能是偶然投影或第三分量。径向速度测量表明解析的系统 TON。 139 是一个三重系统，sdB 的一个紧密伴星对第二个解析系统 PG 1718+519 的径向速度信息没有可检测的贡献，假设它不是一个三重系统，那么它是我们样本中唯一的解析系统，因此，成功率将仅为 5%，这明显低于单星演化的预测。我们的结果进一步证明，紧密双星演化是 sdB 恒星演化的基础。
The origin of subluminous B stars is still an unsolved problem in stellar evolution. Single star as well as close binary evolution scenarios have been invoked but until now have met with little success. We have carried out a small survey of spectroscopic binary candidates (19 systems consisting of an sdB star and late type companion) with the Planetary Camera of the WFPC2 onboard Hubble Space Telescope to test these scenarios. Monte Carlo simulations indicate that by imaging the programme stars in the R-band about one third of the sample (6-7 stars) should be resolved at a limiting angular resolution of 0". 1 if they have linear separations like main sequence stars ("single star evolution"). None should be resolvable if all systems were produced by close binary evolution. In addition we expect three triple systems to be present in our sample. Most of these, if not all, should be resolvable. Components were resolved in 6 systems with separations between 0".2 and 4".5. However, only in the two systems TON 139 and PG 1718+519 (separations 0".32 and 0".24, respectively) do the magnitudes of the resolved components match the expectations from the deconvolution of the spectral energy distribution. These two stars could be physical binaries whereas in the other cases the nearby star may be a chance projection or a third component. Radial velocity measurements indicate that the resolved system TON 139 is a triple system, with the sdB having a close companion that does not contribute detectably to the integrated light of the system. Radial velocity information for the second resolved system, PG 1718+519, is insufficient. Assuming that it is not a triple system, it would be the only resolved system in our sample. Accordingly the success rate would be only 5% which is clearly below the prediction for single star evolution. We conclude that the distribution of separations of sdB binaries deviates strongly from that of normal stars. Our results add further evidence that close binary evolution is fundamental for the evolution of sdB stars.