392 research outputs found
Jet-Induced Explosions of Core Collapse Supernovae
We numerically studied the explosion of a supernova caused by supersonic jets
present in its center. The jets are assumed to be generated by a
magneto-rotational mechanism when a stellar core collapses into a neutron star.
We simulated the process of the jet propagation through the star, jet
breakthrough, and the ejection of the supernova envelope by the lateral shocks
generated during jet propagation. The end result of the interaction is a highly
nonspherical supernova explosion with two high-velocity jets of material moving
in polar directions, and a slower moving, oblate, highly distorted ejecta
containing most of the supernova material. The jet-induced explosion is
entirely due to the action of the jets on the surrounding star and does not
depend on neutrino transport or re-acceleration of a stalled shock. The jet
mechanism can explain the observed high polarization of Type Ib,c and Type II
supernovae, pulsar kicks, very high velocity material observed in supernova
remnants, indications that radioactive material was carried to the
hydrogen-rich layers in SN1987A, and some others observations that are very
difficult or impossible to explain by the neutrino energy deposition mechanism.
The breakout of the jet from a compact, hydrogen- deficient core may account
for the gamma-ray bursts and radio outburst associated with SN1998bw/GRB980425.Comment: 14 pages, LaTeX, aaspp4.sty, epsf.sty, submitted to ApJ Let
Exploring the perceptions of cognitive and affective capabilities of four, real, physical robots with a decreasing degree of morphological human likeness.
Spectropolarimetry of the Type Ia SN 2007sr Two Months After Maximum Light
We present late time spectropolarimetric observations of SN 2007sr, obtained
with the VLT telescope at ESO Paranal Observatory when the object was 63 days
after maximum light. The late time spectrum displays strong line polarization
in the CaII absorption features. SN 2007sr adds to the case of some normal Type
Ia SNe that show high line polarization or repolarization at late times, a fact
that might be connected with the presence of high velocity features at early
times
Plasmonic gold helices for the visible range fabricated by oxygen plasma purification of electron beam induced deposits
Electron beam induced deposition (EBID) currently provides the only direct writing technique for truly three-dimensional nanostructures with geometrical features below 50 nm. Unfortunately, the depositions from metal-organic precursors suffer from a substantial carbon content. This hinders many applications, especially in plasmonics where the metallic nature of the geometric surfaces is mandatory. To overcome this problem a post-deposition treatment with oxygen plasma at room temperature was investigated for the purification of gold containing EBID structures. Upon plasma treatment, the structures experience a shrinkage in diameter of about 18 nm but entirely keep their initial shape. The proposed purification step results in a core-shell structure with the core consisting of mainly unaffected EBID material and a gold shell of about 20 nm in thickness. These purified structures are plasmonically active in the visible wavelength range as shown by dark field optical microscopy on helical nanostructures. Most notably, electromagnetic modeling of the corresponding scattering spectra verified that the thickness and quality of the resulting gold shell ensures an optical response equal to that of pure gold nanostructures
Polarimetry of the Type Ia Supernova SN 1996X
We present broad-band and spectropolarimetry of the Type Ia SN 1996X obtained
on April 14, 1996 (UT), and broad-band polarimetry of SN 1996X on May 22,1996,
when the supernova was about a week before and 4 weeks after optical maximum,
respectively. The Stokes parameters derived from the broad-band polarimetry are
consistent with zero polarization. The spectropolarimetry, however, shows broad
spectral features which are due intrinsically to an asymmetric SN atmosphere.
The spectral features in the flux spectrum and the polarization spectrum show
correlations in the wavelength range from 4900 AA up to 5500 AA. The degree of
this intrinsic component is low (<0.3 %). Theoretical polarization spectra have
been calculated. It is shown that the polarization spectra are governed by line
blending. Consequently, for similar geometrical distortions, the residual
polarization is smaller by about a factor of 2 to 3 compared to the less
blended Type II atmosphere, making it intrinsically harder to detect
asphericities in SNIa. Comparison with theoretical model polarization spectra
shows a resemblance to the observations. Taken literally, this implies an
asphericity of about 11 % in the chemical distribution in the region of partial
burning. This may not imperil the use of Type Ia supernovae as standard candles
for distance determination, but nontheless poses a source of uncertainty. SN
1996X is the first Type Ia supernova for which spectropolarimetry revealed a
polarized component intrinsic to the supernova and the first Type Ia with
spectropolarimetry well prior to optical maximum.Comment: 7 pages, 5 figures, macros 'aas2pp4.sty,psfig.tex'. LaTeX Style.
Astrophysical Journal Letters, submitted September 199
Early-time Spitzer observations of the type II-Plateau supernova, 2004dj
We present mid-infrared observations with the Spitzer Space Telescope of the
nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have
obtained the first mid-IR spectra of any supernova apart from SN 1987A. A
prominent [NiII] 6.64 micron line is observed, from which we deduce that the
mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red
wing of the CO-fundamental band. We relate our findings to possible progenitors
and favour an evolved star, most likely a red supergiant, with a probable
initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted
Theoretical Light Curves of Type II-P SNe and Applications to Cosmology
Based on an extensive grid of stellar models between 13 and 25 Mo and a wide
range of metallicities, we have studied the light curves of core collapse
supernovae, their application to cosmology and evolutionary effects with
redshift. The direct link between the hydro and radiation transport allows to
calculate monochromatic light curves.
With decreasing metallicity Z and increasing mass, progenitors tend to
explode as compact Blue Supergiants and produce sub-luminous supernovae that
are about 1.5 mag dimmer compared to "normal" SNe II with Red
Supergiant progenitors (RSGs). Progenitors with small masses tend to explode
as RSGs even at low Z. The consequences are obvious for probing the chemical
evolution, namely, a strong bias when using the statistics of core collapse
supernovae to probe the history of star formation.
Our study is limited in scope with respect to the explosion energies and the
production of radioactive Ni. Within the class of "extreme SNe II-P"
supernovae, the light curves are rather insensitive with respect to the
progenitor mass and explosion energy compared to analytic models which are
based on parameterized stellar structures. We expect a wider range of
brightness due to variations in Ni56 because radioactive energy is a main
source of luminosity.
However, the overall insensitivity of LCs may allow their use as
quasi-standard candles for distance determination.Comment: 14 pages, 16 figures, accepted for publication in MNRA
Optical polarimetric monitoring of the type II-plateau SN 2005af
Aims. Core-collapse supernovae may show significant polarization that implies
non-spherically symmetric explosions. We observed the type II-plateau SN 2005af
using optical polarimetry in order to verify whether any asphericity is present
in the supernova temporal evolution. Methods. We used the IAGPOL imaging
polarimeter to obtain optical linear polarization measurements in R (five
epochs) and V (one epoch) broadbands. Interstellar polarization was estimated
from the field stars in the CCD frames. The optical polarimetric monitoring
began around one month after the explosion and lasted ~30 days, between the
plateau and the early nebular phase. Results. The weighted mean observed
polarization in R band was [1.89 +/- 0.03]% at position angle (PA) 54 deg.
After foreground subtraction, the level of the average intrinsic polarization
for SN 2005af was ~0.5% with a slight enhancement during the plateau phase and
a decline at early nebular phase. A rotation in PA on a time scale of days was
also observed. The polarimetric evolution of SN 2005af in the observed epochs
is consistent with an overall asphericity of ~20% and an inclination of ~30
deg. Evidence for a more complex, evolving asphericity, possibly involving
clumps in the SN 2005af envelope, is found.Comment: 6 pages, 5 figures, to be published A&
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