B[e]超巨星LHA 120-S 73周围的非均匀分子环
Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73
摘要：
我们的目标是提高我们的知识的结构和动力学的拱星盘的LMC B[e]超巨星LHA 120-S 73。高分辨率的光学和近红外光谱数据，分别在16年和7年的时间。光谱覆盖了来自[CaII]和[OI]的诊断发射线，以及CO带。这些特征在距离恒星不同的距离上跟踪圆盘。我们分析了运动学的个别发射区，通过模拟其发射轮廓。还获得了低分辨率的中红外光谱，这提供了有关尘埃盘组成的信息。所有的诊断发射功能显示双峰线轮廓，我们解释为由于开普勒旋转。我们发现LHA 120-S 73被至少四个具有交替密度的物质环（或具有强烈非单调径向密度分布的圆盘）包围。此外，我们发现分子环必须有间隙或至少有强的密度不均匀性，或者换句话说，一个团簇结构。中红外光谱显示了富氧和富碳颗粒物质的特征，这表明它是一个寿命长、稳定的尘埃盘。我们无法证实先前报道的恒星自转速度的高值。HeI 5876 A的谱线轮廓在宽度和形状上都有很大的变化，与非径向脉动恒星相似。因此，要正确地确定恒星的真实自转速度是不可能的。多个稳定的、密度交替的星团环的存在让人想起行星周围的环结构。虽然目前没有足够的观测证据，但提出一个（或多个）小天体或行星围绕LHA 120-S 73旋转并稳定环系统的假设是很有吸引力的，类似于行星系统中的牧羊人卫星。
英文摘要：
We aim to improve our knowledge on the structure and dynamics of the circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution optical and near-IR spectroscopic data were obtained over a period of 16 and 7 years, respectively. The spectra cover the diagnostic emission lines from [CaII] and [OI], as well as the CO bands. These features trace the disk at different distances from the star. We analyzed the kinematics of the individual emission regions by modeling their emission profiles. A low-resolution mid-infrared spectrum was obtained as well, which provides information on the composition of the dusty disk. All diagnostic emission features display double-peaked line profiles, which we interpret as due to Keplerian rotation. We find that LHA 120-S 73 is surrounded by at least four individual rings of material with alternating densities (or by a disk with strongly non-monotonic radial density distribution). Moreover, we find that the molecular ring must have gaps or at least strong density inhomogeneities, or in other words, a clumpy structure. The mid-infrared spectrum displays features of oxygen- and carbon-rich grain species, which indicates a long-lived, stable dusty disk. We cannot confirm the previously reported high value for the stellar rotation velocity. The line profile of HeI 5876 A is strongly variable in both width and shape and resembles of those seen in non-radially pulsating stars. A proper determination of the real underlying stellar rotation velocity is hence not possible. The existence of multiple stable and clumpy rings of alternating density recalls ring structures around planets. Although there is currently insufficient observational evidence, it is tempting to propose a scenario with one (or more) minor bodies or planets revolving around LHA 120-S 73 and stabilizing the ring system, in analogy to the shepherd moons in planetary systems.
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