1,585 research outputs found
Absolute-Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae
The absolute visual magnitudes of three Type IIb, 11 Type Ib and 13 Type Ic
supernovae (collectively known as stripped-envelope supernovae) are studied by
collecting data on the apparent magnitude, distance, and interstellar
extinction of each event. Weighted and unweighted mean absolute magnitudes of
the combined sample as well as various subsets of the sample are reported. The
limited sample size and the considerable uncertainties, especially those
associated with extinction in the host galaxies, prevent firm conclusions
regarding differences between the absolute magnitudes of supernovae of Type Ib
and Ic, and regarding the existence of separate groups of overluminous and
normal-luminosity stripped-envelope supernovae. The spectroscopic
characteristics of the events of the sample are considered. Three of the four
overluminous events are known to have had unusual spectra. Most but not all of
the normal luminosity events had typical spectra. Light curves of
stripped-envelope supernovae are collected and compared. Because SN 1994I in
M51 was very well observed it often is regarded as the prototypical Type Ic
supernova, but it has the fastest light curve in the sample. Light curves are
modeled by means of a simple analytical technique that, combined with a
constraint on E/M from spectroscopy, yields internally consistent values of
ejected mass, kinetic energy, and nickel mass.Comment: 39 pages, 14 figures, 7 tables; Accepted to A
Comment on "Superconducting gap anisotropy vs. doping level in high-T_c cuprates" by C. Kendziora et al, PRL 77, 727 (1996)
In a recent paper Kendziora et al concluded that the superconducting gap in
overdoped Bi-2212 is isotropic. From data obtained from electronic Raman
scattering measurements, their conclusion was based on the observation that
pair breaking peaks occured at approximately the same frequency in different
scattering geometries and that the normalized scattering intensity at low
energies was strongly depleted. We discuss a different interpretation of the
raw data and present new data which is consistent with a strongly anisotropic
gap with nodes. The spectra can be successfully described by a model for Raman
scattering in a d_{x^{2}-y^{2}} superconductor with spin fluctuations and
impurity scattering included.Comment: 1 page revtex plus 1 postscript figur
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
An asymmetric explosion as the origin of spectral evolution diversity in type Ia supernovae
Type Ia Supernovae (SNe Ia) form an observationally uniform class of stellar
explosions, in that more luminous objects have smaller decline-rates. This
one-parameter behavior allows SNe Ia to be calibrated as cosmological `standard
candles', and led to the discovery of an accelerating Universe. Recent
investigations, however, have revealed that the true nature of SNe Ia is more
complicated. Theoretically, it has been suggested that the initial
thermonuclear sparks are ignited at an offset from the centre of the
white-dwarf (WD) progenitor, possibly as a result of convection before the
explosion. Observationally, the diversity seen in the spectral evolution of SNe
Ia beyond the luminosity decline-rate relation is an unresolved issue. Here we
report that the spectral diversity is a consequence of random directions from
which an asymmetric explosion is viewed. Our findings suggest that the spectral
evolution diversity is no longer a concern in using SNe Ia as cosmological
standard candles. Furthermore, this indicates that ignition at an offset from
the centre of is a generic feature of SNe Ia.Comment: To appear in Nature, 1st July 2010 issue. 36 pages including
supplementary materials. 4 figures, 3 supplementary figures, 1 supplementary
tabl
Type Ia Supernovae and Cosmology
I discuss the use of Type Ia supernovae (SNe Ia) for cosmological distance
determinations. Low-redshift SNe Ia (z < 0.1) demonstrate that the Hubble
expansion is linear with H_0 = 72 +/- 8 km/s/Mpc, and that the properties of
dust in other galaxies are generally similar to those of dust in the Milky Way.
The measured luminosity distances of SNe Ia as a function of redshift have
shown that the expansion of the Universe is currently accelerating, probably
due to the presence of repulsive dark energy such as Einstein's cosmological
constant (Lambda). From about 200 SNe Ia, we find that Omega_Lambda - 1.4
Omega_M = 0.35 +/- 0.14. Combining our data with other results, we find a best
fit for Omega_M and Omega_Lambda of 0.28 and 0.72, respectively. A number of
possible systematic effects (dust, supernova evolution) thus far do not seem to
eliminate the need for Omega_Lambda > 0. Recently, analyses of SNe Ia at z =
1.0-1.7 provide further support for current acceleration, and give tentative
evidence for an early epoch of deceleration. The dynamical age of the Universe
is estimated to be 13.1 +/- 1.5 Gyr. According to the most recent data sets,
the SN Ia rate at z > 1 is several times greater than that at low redshifts,
presumably because of higher star formation rates long ago. Moreover, the
typical delay time from progenitor star formation to SNIa explosion appears to
be substantial, ~3 Gyr. Current projects include the measurement of a few
hundred SNe Ia at z = 0.2-0.8 to more accurately determine the
equation-of-state parameter of the dark energy, w = P/(\rho c^2), whose value
is now constrained by SNe Ia to be in the range -1.48 < w < -0.72 at 95%
confidence.Comment: 39 pages, 17 figures, to be published in "White Dwarfs: Probes of
Galactic Structure and Cosmology" ed. E. M. Sion, H. L. Shipman, and S.
Vennes (Kluwer: Dordrecht). Part of the Astrophysics and Space Science
Library Serie
A Search for Radio Emission from Supernovae With Ages from About One Week to More Than 80 Years
We report VLA radio observations of 29 SNe with ages ranging from 10 days to
about 90 years past explosion. These observations significantly contribute to
the existing data pool on such objects. Included are detections of known radio
SNe~1950B, 1957D, 1970G, 1983N, the suspected radio SN 1923A, and the possible
radio SN 1961V. None of the remaining 23 observations resulted in detections,
providing further evidence to support the observed trend that most SNe are not
detectable radio emitters. To investigate the apparent lack of radio emission
from the SNe reported here, we have followed standard practice and used
Chevalier's ``standard model'' to derive (upper limits to) the mass-loss rates
for the super nova progenitors. These upper limits to the fluxes are consistent
with a lack of circumstellar material needed to provide detectable radio
emission for SNe at these ages and distances. Comparison of the radio
luminosities of these supernovae as a function of age past explosion to other
well-observed radio SNe indicates that the Type II SNe upper limits are more
consistent with the extrapolated light curves of SN 1980K than of SN 1979C,
suggesting that SN 1980K may be a more typical radio emitter than SN 1979C. For
completeness, we have included an appendix where the results of analyses of the
non-SN radio sources are presented. Where possible, we make (tentative)
identifications of these sources using various methods.Comment: 42 pages, 9 fiugres, 5 tables; To appear in Ap
Constraints on Type Ib/c and GRB Progenitors
Although there is strong support for the collapsar engine as the power source
of long-duration gamma-ray bursts (GRBs), we still do not definitively know the
progenitor of these explosions. Here we review the current set of progenitor
scenarios for long-duration GRBs and the observational constraints on these
scenarios. Examining these, we find that single-star models cannot be the only
progenitor for long-duration GRBs. Several binary progenitors can match the
solid observational constraints and also have the potential to match the trends
we are currently seeing in the observations. Type Ib/c supernovae are also
likely to be produced primarily in binaries; we discuss the relationship
between the progenitors of these explosions and those of the long-duration
GRBs.Comment: 36 pages, 6 figure
WD + MS systems as the progenitor of SNe Ia
We show the initial and final parameter space for SNe Ia in a () plane and find that the positions of some famous
recurrent novae, as well as a supersoft X-ray source (SSS), RX J0513.9-6951,
are well explained by our model. The model can also explain the space velocity
and mass of Tycho G, which is now suggested to be the companion star of Tycho's
supernova. Our study indicates that the SSS, V Sge, might be the potential
progenitor of supernovae like SN 2002ic if the delayed dynamical-instability
model due to Han & Podsiadlowski (2006) is appropriate. Following the work of
Meng, Chen & Han (2009), we found that the SD model (WD + MS) with an optically
thick wind can explain the birth rate of supernovae like SN 2006X and reproduce
the distribution of the color excess of SNe Ia. The model also predicts that at
least 75% of all SNe Ia may show a polarization signal in their spectra.Comment: 6 pages, 2 figures, accepted for publication in Astrophysics & Space
Science (Proceeding of the 4th Meeting on Hot Subdwarf Stars and Related
Objects, edited by Zhanwen Han, Simon Jeffery & Philipp Podsiadlowski
Hypernovae and Other Black-Hole-Forming Supernovae
During the last few years, a number of exceptional core-collapse supernovae
(SNe) have been discovered. Their kinetic energy of the explosions are larger
by more than an order of magnitude than the typical values for this type of
SNe, so that these SNe have been called `Hypernovae'. We first describe how the
basic properties of hypernovae can be derived from observations and modeling.
These hypernovae seem to come from rather massive stars, thus forming black
holes. On the other hand, there are some examples of massive SNe with only a
small kinetic energy. We suggest that stars with non-rotating black holes are
likely to collapse "quietly" ejecting a small amount of heavy elements (Faint
supernovae). In contrast, stars with rotating black holes are likely to give
rise to very energetic supernovae (Hypernovae). We present distinct
nucleosynthesis features of these two types of "black-hole-forming" supernovae.
Hypernova nucleosynthesis is characterized by larger abundance ratios
(Zn,Co,V,Ti)/Fe and smaller (Mn,Cr)/Fe. Nucleosynthesis in Faint supernovae is
characterized by a large amount of fall-back. We show that the abundance
pattern of the most Fe deficient star, HE0107-5240, and other extremely
metal-poor carbon-rich stars are in good accord with those of
black-hole-forming supernovae, but not pair-instability supernovae. This
suggests that black-hole-forming supernovae made important contributions to the
early Galactic (and cosmic) chemical evolution.Comment: 49 pages, to be published in "Stellar Collapse" (Astrophysics and
Space Science; Kluwer) ed. C. L. Fryer (2003
Optical Spectroscopy of Supernova 1993J During Its First 2500 Days
We present 42 low-resolution spectra of Supernova (SN) 1993J, our complete
collection from the Lick and Keck Observatories, from day 3 after explosion to
day 2454, as well as one Keck high-dispersion spectrum from day 383. SN 1993J
began as an apparent SN II, albeit an unusual one. After a few weeks, a
dramatic transition took place, as prominent helium lines emerged in the
spectrum. SN 1993J had metamorphosed from a SN II to a SN IIb. Nebular spectra
of SN 1993J closely resemble those of SNe Ib and Ic, but with a persistent
H_alpha line. At very late times, the H_alpha emission line dominated the
spectrum, but with an unusual, box-like profile. This is interpreted as an
indication of circumstellar interaction.Comment: 19 pages plus 13 figures, AASTeX V5.0. One external table in AASTeX
V4.0, in landscape format. Accepted for publication in A
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