Ib/c型超新星的星云发射线轮廓-探测喷出物的非球面性
Nebular emission-line profiles of Type Ib/c Supernovae - probing the ejecta asphericity
摘要：
为了定性评估剥离信封核心坍缩超新星的喷出物的几何形状，我们调查了98晚的39个对象的光谱，其中许多以前未发表。我们在所有光谱中对[O I] 6300，6364特征进行高斯拟合，其中6300高斯的位置，半高宽（FWHM）和强度作为自由参数，并且适当地添加6364高斯以解释[O I]特征的双重性质。在最佳拟合参数的基础上，将物体组织成形态学类别，我们得出结论，至少有一半的Ib/c型超新星必须是非球面的。双极喷气模型似乎并不普遍适用，因为我们发现太少对称双峰[O I]配置文件。在某些天体中，[O I]线呈现出各种移动的次级峰或肩，解释为高速喷射的物质团块，并可能伴随着中子星的反冲，以确保动量守恒。早于~ 200 d，[O I] 6300、6364线的质心发生了系统的蓝移。剩余的不透明度提供了最有说服力的解释这一现象，光子发射的背面的SN被散射或吸收的方式通过喷出物。一旦考虑到氧特征的双重态性质进行修改，Mg I] 4571在足够晚的阶段的分布通常类似于[O I] 6300、6364的分布，这表明来自其他谱线的污染可以忽略不计，并证实O和Mg在喷出物中的分布类似。
英文摘要：
In order to assess qualitatively the ejecta geometry of stripped-envelope core-collapse supernovae, we investigate 98 late-time spectra of 39 objects, many of them previously unpublished. We perform a Gauss-fitting of the [O I] 6300, 6364 feature in all spectra, with the position, full width at half maximum (FWHM) and intensity of the 6300 Gaussian as free parameters, and the 6364 Gaussian added appropriately to account for the doublet nature of the [O I] feature. On the basis of the best-fit parameters, the objects are organised into morphological classes, and we conclude that at least half of all Type Ib/c supernovae must be aspherical. Bipolar jet-models do not seem to be universally applicable, as we find too few symmetric double-peaked [O I] profiles. In some objects the [O I] line exhibits a variety of shifted secondary peaks or shoulders, interpreted as blobs of matter ejected at high velocity and possibly accompanied by neutron-star kicks to assure momentum conservation. At phases earlier than ~200d, a systematic blueshift of the [O I] 6300, 6364 line centroids can be discerned. Residual opacity provides the most convincing explanation of this phenomenon, photons emitted on the rear side of the SN being scattered or absorbed on their way through the ejecta. Once modified to account for the doublet nature of the oxygen feature, the profile of Mg I] 4571 at sufficiently late phases generally resembles that of [O I] 6300, 6364, suggesting negligible contamination from other lines and confirming that O and Mg are similarly distributed within the ejecta.
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