Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aspc..332..415d&link_type=abstract
The Fate of the Most Massive Stars, ASP Conference Series, Vol. 332, Proceedings of the conference held 23-28 May, 2004 in Grand
Astronomy and Astrophysics
Astronomy
1
Scientific paper
The code CMFGEN (Hillier & Miller 1998) solves the radiative transfer equation in the co-moving frame subject to statistical and radiative equilibrium, assuming an expanding, spherically-symmetric, homogeneous and steady-state atmosphere, allowing for line-blanketing and clumping (Hillier, these proceedings). From its original version suited for hot stars, the code has been adjusted to treat relativistic effects, handle a Hubble velocity law and a power law density distribution of exponent n, with assumptions appropriate for supernovae photospheric evolution. In practice, supernovae spectroscopic modeling is complicated by the dominance of scattering, which affects both line and continuum formation. Due to the large expansion velocities, observed features in general result from the overlap of many distinct lines, while only few spectral regions show continuum photons. We obtain high quality fits to observations of SN1999em during the photospheric phase, covering the early epoch where hydrogen is fully ionized in the outflow until the hydrogen-recombination epoch which initiates the plateau phase. A single set of model parameters can reproduce the observed energy distribution in the optical and near-IR, or UV and optical, using a large density exponent of ca. 10. We find that emission features in the UV mostly arise from spectral regions occupied by fewer metal lines, Fe II being the dominant source of opacity at all times. We find that observed optical features of Fe II come from multiplets, overlapping with lines of Fe III, Si II, He I and H I, which may affect the profile measurements used for the inference of the photospheric velocity and the Expanding Photosphere method. Unlike for hot star winds, no clumping is needed to reproduce line profile shapes. Relativistic effects are found to be weak and only noticeable for the fastest observed velocities (usually for the first observations taken). Details of this work will be presented soon in a journal article.
Dessart Luc
Hillier Desmond John
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