11 research outputs found
Time-Dependent Spectropolarimetric Modeling of Interacting Core Collapse Supernovae
Explosive deaths of massive stars in core collapse supernovae are rare events that are only observed with any frequency at large intergalactic distances. This makes identification of progenitors difficult and massive star evolution a challenge to pin down. This dissertation addresses the question of how the properties of the circumstellar environment around supernovae can be used to identify progenitors via their mass loss history. Massive stars all lose mass through a variety of mechanisms that are characteristic of their mass, age, and binarity. This gives rise to a wide range of circumstellar environments which with supernovae may interact, producing multi-component emission lines with polarization profiles that are degenerately dependent on the properties of the medium and change over time. My dissertation approaches this problem computationally by modeling the polarized H-alpha emission lines for CSM with combinations of different morphologies and optical parameters.
My dissertation work fits these models against the polarized spectra of the Type IIn SNe 1997eg and 2010jl as a tool to diagnose their CSM properties and and constrain their mass loss histories. I find that both of these supernovae are preferentially fit by models with inclinations of close to 90 degrees and high shock luminosities. This suggests that an inclination effect may be a requirement in whether an interacting SNe presents observationally as a IIn
Spectropolarimetry of SN 2011dh in M51: geometric insights on a Type IIb supernova progenitor and explosion
We present seven epochs of spectropolarimetry of the Type IIb supernova (SN)
2011dh in M51, spanning 86 days of its evolution. The first epoch was obtained
9 days after the explosion, when the photosphere was still in the depleted
hydrogen layer of the stripped-envelope progenitor. Continuum polarization is
securely detected at the level of P~0.5% through day 14 and appears to diminish
by day 30, which is different from the prevailing trends suggested by studies
of other core-collapse SNe. Time-variable modulations in P and position angle
are detected across P-Cygni line features. H-alpha and HeI polarization peak
after 30 days and exhibit position angles roughly aligned with the earlier
continuum, while OI and CaII appear to be geometrically distinct. We discuss
several possibilities to explain the evolution of the continuum and line
polarization, including the potential effects of a tidally deformed progenitor
star, aspherical radioactive heating by fast-rising plumes of Ni-56 from the
core, oblique shock breakout, or scattering by circumstellar material. While
these possibilities are plausible and guided by theoretical expectations, they
are not unique solutions to the data. The construction of more detailed
hydrodynamic and radiative-transfer models that incorporate complex aspherical
geometries will be required to further elucidate the nature of the polarized
radiation from SN 2011dh and other Type IIb supernovae.Comment: Post-proof edit. Accepted to MNRAS 2015 Aug 1
Comparison of the Core-Collapse Evolution of Two Nearly Equal Mass Progenitors
We compare the core-collapse evolution of a pair of 15.8 stars with
significantly different internal structures, a consequence of bimodal
variability exhibited by massive stars during their late evolutionary stages.
The 15.78 and 15.79 progenitors have core masses of 1.47 and 1.78
and compactness parameters of 0.302 and 0.604. The core
collapse simulations are carried out in 2D to nearly 3 s post-bounce and show
substantial differences in the times of shock revival and explosion energies.
The 15.78 model explodes promptly at 120 ms post-bounce when a strong
density decrement at the Si--Si/O shell interface encounters the stalled shock.
The 15.79 model, which lacks the density decrement, takes 100 ms
longer to explode but ultimately produces a more powerful explosion. Larger
mass accretion rate of the 15.79 model during the first 0.8 s
post-bounce results in larger / luminosities and rms
energies. The / luminosities and rms energies arising
from the inner core are also larger in the 15.79 model throughout due
to the larger negative temperature gradient of this core due to greater
adiabatic compression. Larger luminosities and rms energies in the 15.79
model and a flatter and higher density heating region, result in more
energy deposition behind the shock and more ejected matter with higher
enthalpy. We find the ejected Ni mass of the 15.79 model is
more than double that of the 15.78 model. Most of the ejecta in both
models is moderately proton-rich, though counterintuitively the highest
electron fraction () ejecta in either model is in the less energetic
15.78 model while the lowest electron fraction () ejecta in
either model is in the 15.79 model.Comment: 24 pages; Submitted to Ap
SN2012ab: A Peculiar Type IIn Supernova with Aspherical Circumstellar Material
We present photometry, spectra, and spectropolarimetry of supernova (SN)
2012ab, mostly obtained over the course of days after discovery. SN
2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral
galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN
1998S, its spectral evolution does not. We see indications of CSM interaction
in the strong intermediate-width emission features, the high luminosity (peak
at absolute magnitude ), and the lack of broad absorption features in
the spectrum. The H emission undergoes a peculiar transition. At early
times it shows a broad blue emission wing out to km
and a truncated red wing. Then at late times (
100days) it shows a truncated blue wing and a very broad red emission wing
out to roughly km . This late-time broad red wing
probably arises in the reverse shock. Spectra also show an asymmetric
intermediate-width H component with stronger emission on the red side
at late times. The evolution of the asymmetric profiles requires a density
structure in the distant CSM that is highly aspherical. Our spectropolarimetric
data also suggest asphericity with a strong continuum polarization of % and depolarization in the H line, indicating asphericity in the
CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss
rate of for km extending back at least 75yr prior to the
SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest
that the progenitor was an eccentric binary system undergoing eruptive mass
loss.Comment: 18 pages, 12 figure
Analyse et modelisation stochastique d'un reseau local applique a la commande multiprocesseur et temps reel d'un robot mobile. Etude qualitative d'un delai aleatoire sur les asservissements
SIGLEINIST T 74327 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Health-status outcomes with invasive or conservative care in coronary disease
BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline