High-Velocity Features: A Ubiquitous Property of Type Ia Supernovae
Date
2005
Authors
Mazzali, Paolo A
Benetti, Stefano
Altavilla, G
Blanc, G
Cappellaro, Enrico
Elias-Rosa (Elias de la Rosa), Nancy
Garavini, Gabriele
Goobar, Ariel
Hartunian, A
Kotak, R
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IOP Publishing
Abstract
Evidence of high-velocity features (HVFs) such as those seen in the near-maximum spectra of some Type la supernovae (SNe Ia; e.g., SN 2000cx) has been searched for in the available SN Ia spectra observed earlier than 1 week before B maximum. Recent observational efforts have doubled the number of SNe Ia with very early spectra. Remarkably, all SNe Ia with early data (seven in our Research Training Network sample and 10 from other programs) show signs of such features, to a greater or lesser degree, in Ca II IR and some also in the Si II λ6355 line. HVFs may be interpreted as abundance or density enhancements. Abundance enhancements would imply an outer region dominated by Si and Ca. Density enhancements may result from the sweeping up of circumstellar material (CSM) by the highest velocity SN ejecta. In this scenario, the high incidence of HVFs suggests that a thick disk and/or a high-density companion wind surrounds the exploding white dwarf, as may be the case in single degenerate systems. Large-scale angular fluctuations in the radial density and abundance distribution may also be responsible: this could originate in the explosion and would suggest a deflagration as the more likely explosion mechanism. CSM interaction and surface fluctuations may coexist, possibly leaving different signatures on the spectrum. In some SNe, the HVFs are narrowly confined in velocity, suggesting the ejection of blobs of burned material.
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Keywords
Keywords: Supernovae: general
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Source
Astrophysical Journal, The
Type
Journal article
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2037-12-31
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