Spectroscopic Variations of the Be-Shell Star EW Lac in the V/R Variat ion Periods
Spectroscopic Variations of the Be-Shell Star EW Lac in the V/R Variat ion Periods
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Be-Shell星EW Lac在V/R变化周期的光谱变化
DOI：
10.1093/pasj/65.4.77
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发表时间：
2013
影响因子：
2.3
通讯作者：
T. Kogure
中科院分区：
文献类型：
--
作者：
M. Mon;M. Suzuki;Y. Moritani;T. Kogure
EW Lac在1976-1986年表现出明显的变化，在经历了一些准周期性的变化后，2007年左右又开始了类似的变化。对于第一变事例，我们分析了巴耳末系的发射线和壳层吸收线的光谱行为。H-H谱线的变化特征在于各发射谱线在时间滞后和相位持续时间上的不同变化方式。谱线轮廓参数（如峰值速度、发射谱线强度和峰间距）的变化与谱线轮廓参数的变化之间也存在弱相关性。我们分析了壳吸收线的较高成员的巴耳末系列关于他们的中心深度和径向速度。Hline的光学深度在2000 ~ 6000之间，其长期变化揭示了与变化不同的行为。结合发射线和壳层吸收线的分析，把这种变化看作波的传播现象，我们发现1976-1986年事件的这种变化是一种逆行结构，在该事件的后半期，盘内可能形成一种螺旋结构。物理参数之间的弱相关性表明圆盘在某个半径处被截断。结果表明，在事件的后半部分，恒星出现了显著的增亮，并伴随着发射线强度的显著下降。至于在2007年左右出现的变化，这看起来像是以前事件的重演，我们发现了一个不太发达的磁盘状态，没有明显的时间滞后。
EW Lac showed remarkablevariations in 1976–1986, and a similarvariation started again in around 2007, after some quasi-periodicvariations. For the firstvariation event, we analyzed the spectroscopic behaviors of emission lines and shell absorption lines of the Balmer series. Thevariations of the Hthrough Hlines are characterized by the different manner of variations of the individual emission line in time lag and in duration of thephases. Weak correlation is also notable between thevariations and other variations of the line-profile parameters, such as the peak velocities, emission-line intensities, and peak separations. We analyzed shell absorption lines for higher members of the Balmer series concerning their central depths and radial velocities. The optical depth of the Hline is in the range of 2000 to 6000, and its long-term variation discloses different behaviors as compared to thevariations. Combining the analyses of emission and shell absorption lines, and regarding thevariation as wave propagation phenomena, we find for the 1976–1986 event that thevariation is of retrograde structure, and that a spiral structure is likely formed inside the disk in the latter half of this event. The weak correlations among physical parameters are suggestive of the disk being truncated at some radius. It is noticed that remarkable stellar brightening occurred in the latter half of the event, accompanying a marked decrease of the emission-line intensities. As for avariation that appeared in around 2007, which looks like a recurrence of a previous event, we found a less developed state of the disk without an appreciable time lag.