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arXiv 0902.4279astro-ph.SR
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13颗爆发Be星的L带光谱

L-band spectra of 13 outbursting Be stars

R. E. Mennickent, B. Sabogal, A. Granada, L. Cidale

备注：
9 figures, to be published in PASP
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摘要：

我们提出了新的L-波段光谱的13个爆发的Be星获得ISAAC在ESO帕拉纳尔天文台。这些恒星可以分为三组，这取决于发射线的存在/不存在，以及Br $α$和Pf $γ$发射线相对于汉弗莱斯线从跃迁6- 14到系列结束的强度。这些组是具有不同光学深度的星周包层的代表。对于Br $α$和Pf $γ$谱线强于Humphreys谱线的组，Humphreys谱线衰减大致遵循光学薄条件下的门泽尔情况B。对于Br $α$、Pf $γ$和Humphreys发射线强度相当的恒星群，Humphreys在跃迁波长处从光学薄区向光学厚区递减，跃迁波长是每颗恒星的特征，但通常位于3.65- 3.75 $μ$ m左右（跃迁6- 19和6- 17）。高阶汉弗莱斯线探测光学薄的内部区域，即使在光学厚的信封。我们发现的证据更大的拓宽红外线发射线相比，光学线，可能反映较大的垂直速度场附近的恒星。上述群的存在原则上与de Wit等人（2006）提出的Be星爆发的描述一致，即光学厚盘在消散到星际介质之前膨胀并变得光学薄。时间分辨L波段光谱采样的爆发周期有望成为一个独特的工具，用于测试Be星盘演化。

英文摘要：

We present new L-band spectra of 13 outbursting Be stars obtained with ISAAC at the ESO Paranal observatory. These stars can be classified in three groups depending on the presence/absence of emission lines and the strength of Br$α$ and Pf$γ$ emission lines relative to those of Humphreys lines from transitions 6--14 to the end of the series. These groups are representative of circumstellar envelopes with different optical depths. For the group showing Br$α$ and Pf$γ$ lines stronger than Humphreys lines, the Humphreys decrement roughly follow the Menzel case-B for optically thin conditions. For the group showing comparable Br$α$, Pf$γ$ and Humphreys emission line strengths, the Humphreys decrements moves from an optically thin to an optically thick regime at a transition wavelength which is characteristic for each star, but typically is located around 3.65--3.75 $μ$m (transitions 6--19 and 6--17). Higher order Humphreys lines probe optically thin inner regions even in the optically thicker envelopes. We find evidence of larger broadening in the infrared emission lines compared with optical lines, probably reflecting larger vertical velocity fields near the star. The existence of the aforementioned groups is in principle consistent with the proposed description by de Wit et al. (2006) for Be star outbursts in terms of the ejection of an optically thick disk that expands and becomes optically thin before dissipation into the interstellar medium. Time resolved L-band spectroscopy sampling the outburst cycle promises to be an unique tool for testing Be star disk evolution.

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