早期赫比格Be星PDS 27和PDS 37的光谱学和线性分光偏振
Spectroscopy and Linear Spectropolarimetry of the early Herbig Be Stars PDS 27 and PDS 37
摘要：
经过充分研究的早期型前主序星的数量非常有限，从观测的角度阻碍了对大质量恒星形成的研究。在这里，我们提出的VLT/FORS 2分光偏振和VLT/X-射手光谱观测的两个最近公认的候选赫比格恒星，PDS 27和PDS 37的结果。通过谱线分析和光度测量，我们发现这两个天体都是热的，其温度为17500 $\pm$ 3500~K，半径为17.0 $\pm$ 4.0和25.8 $\pm$ 5.0~ ${\rm R}_\odot$，质量为15.3 PDS 27和PDS 37的$_{\odot}$分别为21.1（+5.4，-4.4）和21.1（+11.0，-5.3）~M $_{\odot}$。这表明这两个天体在演化过程中非常年轻，可能会成为O型恒星。它们的年轻是由于它们的高增长率，即$10^{-3}$/年。在两个物体中检测到H $α$的吸收分量上的线性偏振的变化。这种变化表明，在几个恒星半径的尺度上，靠近恒星的星周环境具有扁平的结构，我们将其确定为内部吸积盘。在这两个天体的许多线条上都可以看到强烈的变化，这进一步表明了活跃的星周环境。
英文摘要：
The number of well-studied early-type pre-main-sequence objects is very limited, hampering the study of massive star formation from an observational point of view. Here, we present the results of VLT/FORS2 spectropolarimetric and VLT/X-shooter spectroscopic observations of two recently recognised candidate Herbig Be stars, PDS 27 and PDS 37. Through analysis of spectral lines and photometry, we find that these two objects are hot, 17500 $\pm$ 3500~K, have large radii, 17.0 $\pm$ 4.0 and 25.8 $\pm$ 5.0~${\rm R}_\odot$, and are very massive, 15.3 (+5.4, -4.4) and 21.1 (+11.0, -5.3)~M$_{\odot}$ for PDS 27 and PDS 37, respectively. This suggests that these two objects are very young in their evolution and may become O-type stars. Their youth is supported by their high accretion rates of the order of $10^{-3}$--$10^{-4.5}~{\rm M}_\odot$/yr. A change in linear polarisation across the absorption component of H$α$ is detected in both objects. This change indicates that the circumstellar environment close to the star, at scales of several stellar radii, has a flattened structure, which we identify as an inner accretion disk. Strong variability is seen in both objects in many lines as further indication of an active circumstellar environment.
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