13 research outputs found
Radiative transfer and type Ia supernovae spectra analysis in the context of supernovae factory.
We showed the spectrum formation in SNeIa around maximum light to be a multi-layered process involving regions from 5000 km per s to 20000 km per s, interacting not only through scattering but also through pure emission. This new understanding allowed us to introduce a new spectral indicators we called RSiSu, which can be used to measure SNeIa blue magnitudes with a precision comparable to the stretch factor. This makes it possible to independently constraint the evolutionary effect on SNeIa that are of crucial importance for high z surveys.We used the multi-purpose radiative transfer code phoenix, developed by P. Hauschildt, F. Allard and E. Baron to produce a grid of synthetic spectra sampling dates from 10 to 25 days after explosion and bolometric magnitudes from -18.0 to -19.7. We also developed an adaptive grid scheme in order to stabilize phoenix convergence.This co-supervised dissertation was conducted in collaboration between The University of Oklahoma City (USA) and University Claude Bernard of Lyon (France). It addresses the radiative transfer issue in type Ia supernovae expanding envelopes, in the context of the SupernovaFactory
Quantitative Spectroscopy of Supernovae for Dark Energy Studies
Detailed quantitative spectroscopy of Type Ia supernovae (SNe~Ia) provides
crucial information needed to minimize systematic effects in both ongoing SNe
Ia observational programs such as the Nearby Supernova Factory, ESSENCE, and
the SuperNova Legacy Survey (SNLS) and in proposed JDEM missions such as SNAP,
JEDI, and DESTINY.
Quantitative spectroscopy is mandatory to quantify and understand the
observational strategy of comparing ``like versus like''. It allows us to
explore evolutionary effects, from variations in progenitor metallicity to
variations in progenitor age, to variations in dust with cosmological epoch. It
also allows us to interpret and quantify the effects of asphericity, as well as
different amounts of mixing in the thermonuclear explosion.Comment: White paper submitted to the Dark Energy Task Force, 13 pages, 5
figure
Multi-layered Spectral Formation in SNe Ia Around Maximum Light
We use the radiative transfer code PHOENIX to study the line formation of the
wavelength region 5000-7000 Angstroms. This is the region where the SNe Ia
defining Si II feature occurs. This region is important since the ratio of the
two nearby silicon lines has been shown to correlate with the absolute blue
magnitude. We use a grid of LTE synthetic spectral models to investigate the
formation of line features in the spectra of SNe Ia. By isolating the main
contributors to the spectral formation we show that the ions that drive the
spectral ratio are Fe III, Fe II, Si II, and S II. While the first two strongly
dominate the flux transfer, the latter two form in the same physical region
inside of the supernova. We also show that the naive blackbody that one would
derive from a fit to the observed spectrum is far different than the true
underlying continuum.Comment: 35 pages, 15 figures, ApJ (2008) 684 in pres
Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models
We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D
hydro models: the very highly parameterized deflagration model W7, and two
delayed detonation models. We find that overall both models do about equally
well at fitting well observed SNe Ia near to maximum light. However, the Si II
6150 feature of W7 is systematically too fast, whereas for the delayed
detonation models it is also somewhat too fast, but significantly better than
that of W7. We find that a parameterized mixed model does the best job of
reproducing the Si II 6150 line near maximum light and we study the differences
in the models that lead to better fits to normal SNe Ia. We discuss what is
required of a hydro model to fit the spectra of observed SNe Ia near maximum
light.Comment: 29 pages, 14 figures, ApJ, in pres
Type Ia Supernova Spectral Line Ratios as Luminosity Indicators
Type Ia supernovae have played a crucial role in the discovery of the dark
energy, via the measurement of their light curves and the determination of the
peak brightness via fitting templates to the observed lightcurve shape. Two
spectroscopic indicators are also known to be well correlated with peak
luminosity. Since the spectroscopic luminosity indicators are obtained directly
from observed spectra, they will have different systematic errors than do
measurements using photometry. Additionally, these spectroscopic indicators may
be useful for studies of effects of evolution or age of the SNe Ia progenitor
population. We present several new variants of such spectroscopic indicators
which are easy to automate and which minimize the effects of noise. We show
that these spectroscopic indicators can be measured by proposed JDEM missions
such as SNAP and JEDI.Comment: 50 pages, 19 figures, 24 tables, submitted to Ap
Multi-layered Spectral Formation in SNe Ia Around Maximum Light
We use the radiative transfer code \phx\ to study the line formation of the wavelength region 5000-7000 Angstrom. This is the region where the SNe Ia defining Si II feature occurs. This region is important since the ratio of the two nearby silicon lines has been shown to correlate with the absolute blue magnitude. We use a grid of LTE synthetic spectral models to investigate the formation of line features in the spectra of SNe Ia. By isolating the main contributors to the spectral formation we show that the ions that drive the spectral ratio are FeIII, FeII, SiII and SII. While the first two strongly dominate the flux transfer, the latter two form in the same physical region inside of the supernova. We also show that the naive blackbody that one would derive from a fit to the observed spectrum is far different than the true underlying continuum