Merging in the common envelope and the origin of early R-type stars
Merging in the common envelope and the origin of early R-type stars
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DOI：
10.1051/0004-6361/201014046
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发表时间：
2010-11
影响因子：
6.5
通讯作者：
L. Piersanti;R. Cabezón;O. Zamora;I. Domínguez;D. García-Senz;C. Abia;O. Straniero
中科院分区：
文献类型：
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作者：
L. Piersanti;R. Cabezón;O. Zamora;I. Domínguez;D. García-Senz;C. Abia;O. Straniero
上下文双星系统在红巨星分支或赫兹弹簧间隙阶段经历一个或两个共同的包络事件，可以产生一个单一的星星，沿着沿着Hayashi轨道演化，作为最终的结果。即使这些物体预计在自然界中非常常见，但仍然缺少对其演化和物理特性的适当描述。此外，这种情况（红巨星合并的情况）已被调用作为早期R星的祖先系统，通过假设作为核心合并的结果而发展的物理条件可以产生混合到在He闪光期间合成的新鲜碳的对流包层中。目标。我们详细分析了红巨星合并的情况下，以验证如果由此产生的星星开发的物理条件，适合挖掘的C-丰富的材料从核心到信封。方法.我们对合并的恒星进行了3D模拟，以检查他在形成自我维持的圆盘时是否有效地燃烧。因此，我们做了1D计算的吸积阶段合并后发生的和以下的演变，直到解决静态氦燃烧的中心。我们采用了不同的假设，从磁盘的核心转移的角动量的量和角动量输运。结果有效的氦燃烧不会发生在合并过程中，因为一个非常高的温度（T > 10 - 8 K）在磁盘/氦芯界面开发只有几分钟。我们的计算表明，吸积过程是决定合并对象的最终属性的主导参数。特别是，由吸积物质传递的热能决定了整个新生核心的加热，从而防止了高度简并的物理条件的发展。与标准RGB星相比，这种情况决定了氦燃烧的开始，氦闪光更温和且更靠近中心。旋转和不同的角动量输运效率起着次要的作用，通过确定的确切位置的第一个He闪光。在计算模型中，没有一个是在He核心中形成的物质混合到对流包络中，因为在He闪光期间和之后总是活跃的H燃烧壳层充当了屏障。结论.在红巨星合并的情况下，适合于特殊的He闪光和富含C的物质的物理条件从未发生过。我们的研究结果反对这样一种进化情景可能代表早期R星的祖先系统的可能性。
Context. Binary systems experiencing one or two common envelope episodes during the red giant branch or the Hertzsprung gap phases can produce a single star, evolving along the Hayashi track, as a final outcome. Even if these objects are expected to be very common in nature, a proper description of their evolution and physical properties is still missing. Moreover, this scenario (red giant merging scenario) has been invoked as the progenitor systems of early-R stars, by assuming that the physical conditions developed as a consequence of the cores merging could produce the mixing into the convective envelope of fresh carbon that was synthesized during the He-flash. Aims. We analyze in detail the red giant merging scenario to verify if the resulting star develops the physical conditions suitable for a dredge-up of C-enriched material from the core to the envelope. Methods. We performed 3D simulations of the merging stars, to check whether He is burnt efficiently during the formation of a self-sustained disk. We therefore did 1D computations of the accretion phase occurring after the merging and of the following evolution up to the settling of quiescent He-burning in the center. We adopted different assumptions on the amount of angular momentum transferred from the disk to the core and on the angular momentum transport. Results. Efficient He-burning does not occur during the merging, because a very high temperature (T > 10 8 K) at the disk/He-core interface develops only for a few minutes. Our computations show that the accretion process is the leading parameter in determining the final properties of the merged object. In particular, the thermal energy delivered by the accreted matter determines the heating of the whole newborn core, thus preventing the developing of highly degenerate physical conditions. This occurrence determines the onset of the He-burning with an He-flash milder and closer to the center, as compared to standard RGB stars. Rotation and different angular momentum transport efficiency plays a secondary role by determining the exact location of the first He-flash. In none of the computed models is material formed in the He-core mixed into the convective envelope, because the H-burning shell, which always active during the He-flashes and later on, acts as a barrier. Conclusions. In the red giant merging scenario, the physical conditions suitable for both a peculiar He-flash and the dredging-up of C-enriched material never occur. Our results speak against the possibility that such an evolutionary scenario could represent the progenitor system of early R-stars.