Two SMC Symbiotic Stars Undergoing Steady Hydrogen Burning
Two SMC Symbiotic Stars Undergoing Steady Hydrogen Burning
复制标题
两颗 SMC 共生星正在进行稳定的氢燃烧
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
E. Tepedelenlioglu
中科院分区：
文献类型：
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作者：
M. Orio;A. Zezas;U. Munari;A. Siviero;E. Tepedelenlioglu
小麦哲伦星云（SMC）中的两颗共生星Lin 358和SMC 3已经成为超软X射线源（SSS）超过10年。我们适合大气和星云模型，以他们的X射线，光学和紫外光谱在不同的时代。X射线光谱非常柔和，似乎是由白色矮星的大气层发出的，而不是像其他共生体那样由星云发出的。我们发现，SMC 3的白色矮星，两个来源中最热的，在1993-1994年，2003年和2006年有一个近似恒定的有效温度Teff约为500，000 K，在12年内没有下降的迹象。该系统在2003年3月的热光度比3年后低一个数量级以上;然而，观测时间与以前在ROSAT和光学观测中发现的白色矮星的日偏食一致。在SMC 3中，红巨星风必须是不对称的或非常密集的，因为源周围星云的填充因子不高于0.1。Lin 358中的致密天体自1993年以来一直处于Teff ≥ 180，000 K，并且有一些适度增加的证据。这两个天体的大气拟合都是在log g = 9的情况下得到的，这对于质量大于1.18 M的白色矮星是合适的。在过去的50年里，尽管对SMC进行了持续的光学监测，但没有记录到这些系统的新星样爆发，也没有迹象表明白色矮星在热核闪光后会冷却。因此，我们认为，在这两个系统中，氢在WD上的壳层中稳定燃烧，燃烧速率为10-7 M/年，足以抑制Ia型超新星祖先所需的新星型质量损失。
Two symbiotic stars in the Small Magellanic Cloud (SMC), Lin 358 and SMC 3, have been supersoft X-ray sources (SSSs) for more than 10 years. We fit atmospheric and nebular models to their X-ray, optical, and UV spectra obtained at different epochs. The X-ray spectra are extremely soft and appear to be emitted by the white dwarf atmosphere, not by the nebula, as in some other symbiotics. We find that the white dwarf of SMC 3, the hottest of the two sources, had an approximately constant effective temperature Teff ≃ 500,000 K in 1993-1994, 2003, and 2006, without indications of a decrease in 12 years. The bolometric luminosity of this system in 2003 March was more than an order of magnitude lower than 3 years later; however, the time of the observation is consistent with a partial eclipse of the white dwarf, previously found in ROSAT and optical observations. The red giant wind must be asymmetric or very clumpy in SMC 3, because the filling factor of the nebula around the source is not higher than 0.1. The compact object in Lin 358 has been at Teff ≥ 180,000 K since 1993, and there is some evidence of a moderate increase. Atmospheric fits for both objects are obtained with log g = 9, which is appropriate for white dwarf masses >1.18 M☉. No nova-like outbursts of these systems have been recorded in the last 50 years, despite continuous optical monitoring of the SMC, and there are no indications of cooling of the white dwarf, expected after a thermonuclear flash. We suggest therefore that in both systems hydrogen is burning steadily in a shell on the WD at the rate ≃10-7 M☉ yr-1, sufficiently high to inhibit nova-type mass loss as required for Type Ia supernovae progenitors.