276 research outputs found
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
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
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
Maximum Brightness and Post-Maximum Decline of Light Curves of SN~Ia: A Comparison of Theory and Observations
We compare the observed correlations between the maximum brightness,
postmaximum decline rate and color at maximum light of Type Ia supernovae (SN
Ia) with model predictions.
The observations are based on a total of 40 SN Ia with 29 SN of the Calan
Tololo Supernova Search and 11 local SN which cover a range of 2 mag in the
absolute visual brightness.
The observed correlations are not tight, one dimensional relations.
Supernovae with the same postmaximum decline or the same color have a spread in
visual magnitude of about 0.7 mag. The dispersion in the color-magnitude
relation may result from uncertainties in the distance determinations or the
interstellar reddening within the host galaxy. The dispersion in the decline
rate-magnitude relation suggests that an intrinsic spread in the supernova
properties exists that cannot be accounted for by any single relation between
visual brightness and postmaximum decline.
Theoretical correlations are derived from a grid of models which encompasses
delayed detonations, pulsating delayed detonations, the merging scenario and
helium detonations.
We find that the observed correlations can be understood in terms of
explosions of Chandrasekhar mass white dwarfs.
Our models show an intrinsic spread in the relations of about 0.5 mag in the
maximum brightness and about 0.1 mag in the B-V color.
Our study provides strong evidence against the mechanism of helium detonation
for subluminous, red SN Ia.Comment: 7 pages, 3 figures, macros ''aaspp.sty'. LaTeX Style. Astrophysical
Journal Letters, submitted Jul. 1995, revised Aug. 1995, resubmitted Sep.
199
Properties of the ultraviolet flux of type Ia supernovae: an analysis with synthetic spectra of SN 2001ep and SN 2001eh
The spectral properties of type Ia supernovae in the ultraviolet (UV) are
investigated using the early-time spectra of SN 2001ep and SN 2001eh obtained
using the Hubble Space Telescope (HST). A series of spectral models is computed
with a Monte Carlo spectral synthesis code, and the dependence of the UV flux
on the elemental abundances and the density gradient in the outer layers of the
ejecta is tested. A large fraction of the UV flux is formed by reverse
fluorescence scattering of photons from red to blue wavelengths. This process,
combined with ionization shifts due to enhanced line blocking, can lead to a
stronger UV flux as the iron-group abundance in the outer layers is increased,
contrary to previous claims.Comment: 14 pages, 13 figures. Replaced with revised version accepted for
publication in MNRA
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
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