Verifying the Cosmological Utility of Type Ia Supernovae: Implications of a Dispersion in the Ultraviolet Spectra
R. S. Ellis, M. Sullivan, P. E. Nugent, D. A. Howell, A. Gal-Yam, P. Astier, D. Balam, C. Balland, S. Basa, R. G. Carlberg, A. Conley, D. Fouchez, J. Guy, D. Ha… 展开作者
R. S. Ellis, M. Sullivan, P. E. Nugent, D. A. Howell, A. Gal-Yam, P. Astier, D. Balam, C. Balland, S. Basa, R. G. Carlberg, A. Conley, D. Fouchez, J. Guy, D. Hardin, I. Hook, R. Pain, K. Perrett, C. J. Pritchet, N. Regnault
We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe Ia) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40% of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high quality local spectra. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes [ABRIDGED].
Circumstellar Na I and Ca II lines in type IIP supernovae and SN 1998S
研究了在光球期IIP型超新星光谱中探测到Na I D $_{1,2}$和Ca II H，K的星周吸收线的可能性。模拟表明，在中等风密度的IIP型超新星中不会看到Na I双重态的星周线，例如，SN 1999em的特征，而具有天鹅座P分布的相当明显的Ca II线应该是可检测的。一个类似的模型被用来描述在SN 1998S中看到的Na I和Ca II拱星线，类型IIL，风很密。我们表明，在这颗超新星的线强度再现，如果一个假设的紫外线过剩，这主要是由于在冲击波中的超新星辐射的康普顿化。
