Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 441, Issue 1, Pages 671-680Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stu610
Keywords
supernovae: general
Categories
Funding
- Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina) [GS-2008B-Q-56]
- ESO telescopes at the La Silla Paranal Observatory [076.A-0156, 078.D-0048, 080.A-0516, 082.A-0526]
- CONICYT through FONDECYT [3110142]
- Millennium Center for Supernova Science [P10-064-F]
- European Community [PIRG04-GA-2008-239184]
- Agence Nationale de la Recherche [ANR-2011-Blanc-SIMI-5-6-007-01]
- National Science Foundation [AST0306969, AST0607438, AST1008343]
- Millennium Institute of Astrophysics (MAS) of the Iniciativa Cientifica Milenio del Ministerio Economia, Fomento y Turismo de Chile [IC120009]
- 'Millennium Center for Supernova Science' of the Iniciativa Cientifica Milenio del Ministerio Economia, Fomento y Turismo de Chile [P10-064-F]
- Danish Agency for Science and Technology and Innovation through a Sapere Aude Level 2 grant
- National Aeronautics
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1008343] Funding Source: National Science Foundation
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In classical P-Cygni profiles, theory predicts emission to peak at zero rest velocity. However, supernova spectra exhibit emission that is generally blueshifted. While this characteristic has been reported in many SNe, it is rarely discussed in any detail. Here, we present an analysis of H alpha emission peaks using a data set of 95 Type II supernovae, quantifying their strength and time evolution. Using a post-explosion time of 30 d, we observe a systematic blueshift of H alpha emission, with a mean value of -2000 km s(-1). This offset is greatest at early times but vanishes as supernovae become nebular. Simulations of Dessart et al. match the observed behaviour, reproducing both its strength and evolution in time. Such blueshifts are a fundamental feature of supernova spectra as they are intimately tied to the density distribution of ejecta, which falls more rapidly than in stellar winds. This steeper density structure causes line emission/absorption to be much more confined; it also exacerbates the occultation of the receding part of the ejecta, biasing line emission to the blue for a distant observer. We conclude that blueshifted emission-peak offsets of several thousand km s(-1) are a generic property of observations, confirmed by models, of photospheric-phase Type II supernovae.
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