TY - JOUR
T1 - The outermost ejecta of type Ia supernovae
AU - Tanaka, Masaomi
AU - Mazzali, Paolo A.
AU - Benetti, Stefano
AU - Nomoto, Ken'ichi
AU - Elias-Rosa, Nancy
AU - Kotak, Rubina
AU - Pignata, Giuliano
AU - Stanishev, Vallery
AU - Hachinger, Stephan
N1 - Copyright:
Copyright 2015 Elsevier B.V., All rights reserved.
PY - 2008/4/10
Y1 - 2008/4/10
N2 - 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.
AB - 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.
KW - Line: profiles
KW - Radiative transfer
KW - Supernovae: general
KW - Supernovae: individual (SN 2001 el, SN 2002bo, SN 2002dj, SN 2002er, SN 2003cg, SN 2003du)
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U2 - 10.1086/528703
DO - 10.1086/528703
M3 - Article
AN - SCOPUS:42549161973
VL - 677
SP - 448
EP - 460
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
ER -