普遍存在的H-α偏振线轮廓：Post-AGB、Herbig Ae/Be和其他恒星类型中的吸收分光偏振效应和时间变化
Ubiquitous H-alpha polarized line profiles: absorptive spectropolarimetric effects and temporal variability in Post-AGB, Herbig Ae/Be and other stellar types
摘要：
我们在这里表明，吸收H-α偏振线轮廓以前看到许多赫比格Ae/Be（HAeBe）的明星是一个几乎无处不在的功能，其他类型的嵌入式或遮蔽的恒星。这种特征性的1%线性偏振变化跨越了H-α线的吸收部分，在后AGB恒星以及RV-Tau，Delta-Scuti和其他类型的恒星中都可以看到。这些恒星中的每一个都显示出被星际氢气遮蔽的证据，并且偏振效应是在吸收分量中，与光学泵浦模型一致。我们提出了ESPaDOnS光谱偏振观测9后AGB和RV-Tau类型，除了许多多时代的HiVIS观测这些目标。我们发现在8/9颗恒星的H-α线上有显着的偏振变化，偏振幅度为0.5%至3%以上（5/6 Post-AGB和3/3 RV-Tau）。在所有这些，但其中之一，偏振变化是由线轮廓的吸收分量占主导地位。没有证据表明显示恒星脉动的暗星的子类（后AGB星的RV-Tau和赫比格Ae/Be星的Delta-Scuti）与主类有显着的分光偏振差异。从HiVIS和ESPaDOnS的数据中可以明显看出，这里介绍的几颗恒星：89 Her，AC Her，SS Lep，MWC 120，AB Aurigae和HD 144668。的形态和时间的变化是可比的赫比格Ae/Be和Be型恒星现有的大样本。由于后AGB恒星的星周气体是非常不同的Be星，我们讨论这些意见的背景下，他们不同的环境。
英文摘要：
We show here that the absorptive H-alpha polarized line profile previously seen in many Herbig Ae/Be (HAeBe) stars is a nearly ubiquitous feature of other types of embedded or obscured stars. This characteristic 1% linear polarization variation across the absorptive part of the H-alpha line is seen in Post-AGB stars as well as RV-Tau, Delta-Scuti, and other types. Each of these stars shows evidence of obscuration by intervening circumstellar hydrogen gas and the polarization effect is in the absorptive component, consistent with an optical pumping model. We present ESPaDOnS spectropolarimetric observations of 9 post-AGB and RV-Tau types in addition to many multi-epoch HiVIS observations of these targets. We find significant polarization changes across the H-alpha line in 8/9 stars with polarization amplitudes of 0.5% to over 3% (5/6 Post-AGB and 3/3 RV-Tau). In all but one of these, the polarization change is dominated by the absorptive component of the line profile. There is no evidence that subclasses of obscured stars showing stellar pulsations (RV-Tau for Post-AGB stars and Delta-Scuti for Herbig Ae/Be stars) show significant spectropolarimetric differences from the main class. Significant temporal variability is evident from both HiVIS and ESPaDOnS data for several stars presented here: 89 Her, AC Her, SS Lep, MWC 120, AB Aurigae and HD144668. The morphologies and temporal variability are comparable to existing large samples of Herbig Ae/Be and Be type stars. Since Post-AGB stars have circumstellar gas that is very different from Be stars, we discuss these observations in the context of their differing environments.
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