VEGA/CHARA探测的奇特快速旋转恒星51 Oph
The peculiar fast-rotating star 51 Oph probed by VEGA/CHARA
摘要：
恒星自转是我们理解中等质量和大质量恒星的质量损失和演化的关键。它可以导致各向异性的质量损失的形式辐射风或排泄盘。我们希望在空间上解决的光球和气体环境的51 Oph，一个特殊的恒星与一个非常高的vsin（i）的267公里秒$^{-1}$和一个进化的状态，仍然没有解决。它被不同的作者分类为Herbig，$β$ Pic或经典Be星。我们使用的VEGA可见光束组合器安装在CHARA阵列，达到亚毫弧秒的分辨率。观察集中在H $α$发射线上。首次导出了51Oph光球的拉伸和压扁。我们发现长轴$θ_{\mathrm{eq}}$ =8.08 $\pm$ 0.70 $R_\odot$和短轴$θ_{\mathrm{pol}}$ =5.66 $\pm$ 0.23 $R_\odot$。如此高的光球层扭曲表明这颗恒星的旋转速度接近临界速度。最后，使用光谱干涉测量的H $ α$线，我们约束的拱星环境的几何形状和运动学，并表明，在5.2 $\pm$ 2R $_{*}$磁盘开普勒旋转的排放。从可见光的角度看，51 Oph具有经典Be星的所有特征：近临界自转和双峰H $α$线，产生于开普勒自转的气体盘中。然而，这并不能解释在中红外和毫米光谱中看到的尘埃的存在，51 Oph的演化状态仍然没有确定。
英文摘要：
Stellar rotation is a key in our understanding of both mass-loss and evolution of intermediate and massive stars. It can lead to anisotropic mass-loss in the form of radiative wind or an excretion disk. We wished to spatially resolve the photosphere and gaseous environment of 51 Oph, a peculiar star with a very high vsin(i) of 267km s$^{-1}$ and an evolutionary status that remains unsettled. It has been classified by different authors as a Herbig, a $β$ Pic, or a classical Be star. We used the VEGA visible beam combiner installed on the CHARA array that reaches a submilliarcsecond resolution. Observation were centered on the H$α$ emission line. We derived, for the first time, the extension and flattening of 51 Oph photosphere. We found a major axis of $θ_{\mathrm{eq}}$=8.08$\pm$0.70$R_\odot$ and a minor axis of $θ_{\mathrm{pol}}$=5.66$\pm$0.23$R_\odot$ . This high photosphere distortion shows that the star is rotating close to its critical velocity. Finally, using spectro-interferometric measurements in the H$ α$ line, we constrained the circumstellar environment geometry and kinematics and showed that the emission is produced in a 5.2$\pm$2R$_{*}$ disk in Keplerian rotation. From the visible point of view, 51 Oph presents all the features of a classical Be star: near critical-rotation and double-peaked H$α$ line in emission produced in a gaseous disk in Keplerian rotation. However, this does not explain the presence of dust as seen in the mid-infrared and millimeter spectra, and the evolutionary status of 51 Oph remains unsettled.
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