NEW EVIDENCE FOR MASS LOSS FROM δ CEPHEI FROM H i 21 cm LINE OBSERVATIONS
NEW EVIDENCE FOR MASS LOSS FROM δ CEPHEI FROM H i 21 cm LINE OBSERVATIONS
复制标题
H i 21 cm 线观测中关于仙王座 δ 质量损失的新证据
DOI：
--
复制
发表时间：
2011
期刊：
影响因子：
--
通讯作者：
G. Bono
中科院分区：
文献类型：
--
作者：
L. D. Matthews;Massimo Marengo;N. R. Evans;G. Bono
最近发表的斯皮策太空望远镜对经典造父变星原型δ造父变星的观测显示，这颗恒星和它的热伙伴HD 213307周围有一个扩展的尘埃星云。在远红外波段，发射类似于与恒星空间运动方向一致的弓形激波，表明δ造父变星正在经历恒星风的质量损失。在这里，我们报告了用甚大阵列(VLA)进行的21厘米线观测，以寻找与这股风有关的中性原子氢。我们的VLA数据显示，围绕着∼造父变星位置的是一个空间上延伸的HI星云(δ13‘或1个PC)。该星云具有头部和尾部的形态，与恒星风和星际介质(ISM)之间的相互作用形成的恒星周围抛射物一致。我们直接测量星际原子氢的质量，尽管总的氢原子质量可能更大，这取决于被银河系污染隐藏在我们波段内的星际物质的比例，或者存在于太大而无法被VLA探测到的角度尺度上的星际物质。看起来大部分恒星周围的气体直接来自恒星，尽管它可能会被来自周围ISM的物质所增强。HI数据与流出速度为Vo=35.6±1.2 km S−1，质量损失率为Yr−1的恒星风一致。我们计算了包括不稳定带质量损失在内的理论演化轨迹，结果表明，在δ造父变星之前的造父变星寿命期间，维持这样的质量损失率，足以解决这颗恒星的脉动质量和演化质量之间的很大一部分差异。
Recently published Spitzer Space Telescope observations of the classical Cepheid archetype δ Cephei revealed an extended dusty nebula surrounding this star and its hot companion HD 213307. At far-infrared wavelengths, the emission resembles a bow shock aligned with the direction of space motion of the star, indicating that δ Cephei is undergoing mass loss through a stellar wind. Here we report H i 21 cm line observations with the Very Large Array (VLA) to search for neutral atomic hydrogen associated with this wind. Our VLA data reveal a spatially extended H i nebula (∼13′ or 1 pc across) surrounding the position of δ Cephei. The nebula has a head-tail morphology, consistent with circumstellar ejecta shaped by the interaction between a stellar wind and the interstellar medium (ISM). We directly measure a mass of circumstellar atomic hydrogen , although the total H i mass may be larger, depending on the fraction of circumstellar material that is hidden by Galactic contamination within our band or that is present on angular scales too large to be detected by the VLA. It appears that the bulk of the circumstellar gas has originated directly from the star, although it may be augmented by material swept from the surrounding ISM. The H i data are consistent with a stellar wind with an outflow velocity Vo = 35.6 ± 1.2 km s−1 and a mass-loss rate of yr−1. We have computed theoretical evolutionary tracks that include mass loss across the instability strip and show that a mass-loss rate of this magnitude, sustained over the preceding Cepheid lifetime of δ Cephei, could be sufficient to resolve a significant fraction of the discrepancy between the pulsation and evolutionary masses for this star.