SN 2005cg: Explosion Physics and Circumstellar Interaction of a Normal Type Ia Supernova in a Low-Luminosity Host
SN 2005cg: Explosion Physics and Circumstellar Interaction of a Normal Type Ia Supernova in a Low-Luminosity Host
复制标题
DOI：
10.1086/498014
复制
发表时间：
2005-09
期刊：
影响因子：
--
通讯作者：
R. Quimby;P. Hoeflich;S. Kannappan;E. Rykoff;W. Rujopakarn;C. Akerlof;C. Gerardy;J. C. W. U. O. Texas;U. Michigan;I. College
中科院分区：
文献类型：
--
作者：
R. Quimby;P. Hoeflich;S. Kannappan;E. Rykoff;W. Rujopakarn;C. Akerlof;C. Gerardy;J. C. W. U. O. Texas;U. Michigan;I. College
给出了ROTSE-IIIc发现的“常亮”Ia型超新星2005cg的光谱演化、光曲线和相应的解释。宿主是一个低光度(MR=-16.75)的蓝色星系，具有强烈的活动恒星形成迹象，其环境类似于SNE Ia在高红移时的预期环境。用高能电子对撞机获得的早期(t~-10天)光谱显示，在大约6100ä处有一个不对称的三角形的Si II吸收特征，在蓝移约24,000公里的S-1处有一个急剧的跃迁到连续谱。到最大值前4天，Si II吸收特征变得对称，边缘光滑弯曲。以前在其他超新星中也观察到了类似的SiII剖面演化，并通过一些爆炸模型进行了预测，但其意义尚未得到充分认识。尽管纯爆燃模型和延迟爆轰模型预测的光谱在最大光强附近相似，但它们预测的外层化学丰度定性不同，因此在最早的阶段给出了定性不同的光谱。在SN2005cg早期观测到的硅线需要高速燃烧产物的存在，而三角形很可能是在延时爆轰模型中硅丰度缓慢下降的扩展区域形成的。光谱显示出高速的Ca II红外特征，在速度空间上与Si II截止点重合。这支持了这样的解释，即当锡喷出物的外层扫过前驱系统内约5×10-3M☉的物质时，形成了CaII。我们将我们的结果与其他具有早期时间谱的“分支正常”的SNE Ia，即SN2003Du、1999ee和1994d进行了比较。尽管基于SiII吸收极小值的膨胀速度不同，但它们在23,000到25,000公里S-1之间都呈现出三角形的轮廓和速度截止，这与它们各自的高速CaII红外特征的多普勒频移相一致。然而，SN1990N类天体表现出明显不同的行为，这可能意味着独立的祖先亚类。
We present the spectral evolution, light curve, and corresponding interpretation for the "normal-bright" Type Ia supernova 2005cg discovered by ROTSE-IIIc. The host is a low-luminosity (Mr = -16.75) blue galaxy with strong indications of active star formation and an environment similar to that expected for SNe Ia at high redshifts. Early-time (t ~ -10 days) optical spectra obtained with the HET reveal an asymmetric, triangular-shaped Si II absorption feature at about 6100 Å with a sharp transition to the continuum at a blueshift of about 24,000 km s-1. By 4 days before maximum, the Si II absorption feature becomes symmetric with smoothly curved sides. Similar Si II profile evolution has previously been observed in other supernovae and is predicted by some explosion models, but its significance has not been fully recognized. Although the spectra predicted by pure deflagration and delayed detonation models are similar near maximum light, they predict qualitatively different chemical abundances in the outer layers and thus give qualitatively different spectra at the earliest phases. The Si line observed in SN 2005cg at early times requires the presence of burning products at high velocities, and the triangular shape is likely to be formed in an extended region of slowly declining Si abundance that characterizes delayed detonation models. The spectra show a high-velocity Ca II IR feature that coincides in velocity space with the Si II cutoff. This supports the interpretation that the Ca II is formed when the outer layers of the SN ejecta sweep up about 5 × 10-3 M☉ of material within the progenitor system. We compare our results with other "Branch-normal" SNe Ia with early-time spectra, namely, SN 2003du, 1999ee, and 1994D. Although the expansion velocities based on their Si II absorption minima differ, all show triangular-shaped profiles and velocity cutoffs between 23,000 and 25,000 km s-1, which are consistent with the Doppler shifts of their respective high-velocity Ca II IR features. SN 1990N-like objects, however, showed distinctly different behavior, which may suggest separate progenitor subclasses.