The outermost ejecta of type Ia supernovae

Masaomi Tanaka, Paolo A. Mazzali, Stefano Benetti, Ken'ichi Nomoto, Nancy Elias-Rosa, Rubina Kotak, Giuliano Pignata, Vallery Stanishev, Stephan Hachinger

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79 Citations (Scopus)


The properties of the highest velocity ejecta of normal Type Ia supernovae (SNe Ia) are studied via models of very early optical spectra of six SNe. At epochs earlier than 1 week before maximum, SNe with a rapidly evolving Si II λ6355 line velocity (HVG) have a larger photospheric velocity than SNe with a slowly evolving Si II λ6355 line velocity (LVG). Since the two groups have comparable luminosities, the temperature at the photosphere is higher in LVG SNe. This explains the different overall spectral appearance of HVG and LVG SNe. However, the variation of the Ca II and Si II absorptions at the highest velocities (v ≳ 20,000 km S-1) suggests that additional factors, such as asphericity or different abundances in the progenitor white dwarf, affect the outermost layers. The C II λ6578 line is marginally detected in three LVG SNe, suggesting that LVGs undergo less intense burning. The carbon mass fraction is small, only less than 0.01 near the photosphere, so that he mass of unburned C is only ≲0.01 M . Radioactive 56Ni and stable Fe are detected in both LVG and HVG SNe. Different Fe-group abundances in the outer layers may be one of the reasons for spectral diversity among SNe Ia at the earliest times. The diversity among SNe Ia at the earliest phases could also indicate an intrinsic dispersion in the LC width-luminosity relation.

Original languageEnglish
Pages (from-to)448-460
Number of pages13
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2008 Apr 10
Externally publishedYes


  • Line: profiles
  • Radiative transfer
  • Supernovae: general
  • Supernovae: individual (SN 2001 el, SN 2002bo, SN 2002dj, SN 2002er, SN 2003cg, SN 2003du)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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