We study a sample of 16 Type Ia supernovae (SNe Ia) having both spectroscopic and photometric observations within 2 $-$ 3 days after the first light. The early $B-V$ colors of such a sample tends to show a continuous distribution. For objects with normal ejecta velocity (NV), the C~II $\lambda$6580 feature is always visible in the early spectra while it is absent or very weak in the high-velocity (HV) counterpart. Moreover, the velocities of the detached high-velocity features (HVFs) of Ca~II NIR triplet (CaIR3) above the photosphere are found to be much higher in HV objects than in NV objects, with typical values exceeding 30,000 km~s$^{-1}$ at 2 $-$ 3 days. We further analyze the relation between %velocities of Si~II~$\lambda$6355 at maximum, $v_{\rm Si,max}$, the velocity shift of late-time [Fe~II] lines ($v_{\rm [Fe~II]}$) and host galaxy mass. We find that all HV objects have redshifted $v_{\rm [Fe~II]}$ while NV objects have both blue- and redshifted $v_{\rm [Fe~II]}$. It is interesting to point out that the objects with redshifted $v_{\rm [Fe~II]}$ are all located in massive galaxies, implying that HV and a portion of NV objects may have similar progenitor metallicities and explosion mechanisms. We propose that, with a geometric/projected effect, the He-detonation model may account for the similarity in birthplace environment and the differences seen in some SNe Ia, including $B-V$ colors, C~II feature, CaIR3 HVFs at early time and $v_{\rm [Fe~II]}$ in the nebular phase. Nevertheless, some features predicted by He-detonation simulation, such as the rapidly decreasing light curve, deviate from the observations, and some NV objects with blueshifted nebular $v_{\rm [Fe~II]}$ may involve other explosion mechanisms.

中文翻译：

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氦爆炸模型能否解释观测到的 Ia 型超新星的多样性？

我们研究了 16 颗 Ia 型超新星 (SNe Ia) 的样本，它们在第一次发光后的 2 $-$ 3 天内进行了光谱和光度观测。这种样本的早期 $BV$ 颜色倾向于显示连续分布。对于具有正常喷射速度 (NV) 的物体，C~II $\lambda$6580 特征在早期光谱中始终可见，而在高速 (HV) 对应物中则不存在或非常弱。此外，发现光球层上方 Ca~II NIR 三重峰 (CaIR3) 的分离高速特征 (HVFs) 在 HV 物体中的速度远高于 NV 物体，典型值超过 30,000 km~s$^ {-1}$ 2 $-$ 3 天。我们进一步分析了最大Si~II~$\lambda$6355 的%velocities, $v_{\rm Si,max}$, 后期[Fe~II] 线的速度偏移($v_{\rm [Fe~II]}$) 和宿主星系质量。我们发现所有 HV 天体都发生了红移 $v_{\rm [Fe~II]}$ 而 NV 天体同时发生了蓝移和红移 $v_{\rm [Fe~II]}$。有趣的是指出红移$v_{\rm [Fe~II]}$ 的天体都位于大质量星系中，这意味着HV 和部分NV 天体可能具有相似的前身金属丰度和爆炸机制。我们提出，通过几何/投影效应，He 爆炸模型可以解释出生地环境的相似性以及在某些 SNe Ia 中看到的差异，包括 $BV$ 颜色、C~II 特征、早期的 CaIR3 HVF 和$v_{\rm [Fe~II]}$ 在星云相中。然而，He-爆轰模拟预测的一些特征，如快速下降的光变曲线，与观察结果有偏差，