337 research outputs found
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
The Rise Times of High and Low Redshift Type Ia Supernovae are Consistent
We present a self-consistent comparison of the rise times for low- and
high-redshift Type Ia supernovae. Following previous studies, the early light
curve is modeled using a t-squared law, which is then mated with a modified
Leibundgut template light curve. The best-fit t-squared law is determined for
ensemble samples of low- and high-redshift supernovae by fitting simultaneously
for all light curve parameters for all supernovae in each sample. Our method
fully accounts for the non-negligible covariance amongst the light curve
fitting parameters, which previous analyses have neglected. Contrary to Riess
et al. (1999), we find fair to good agreement between the rise times of the
low- and high-redshift Type Ia supernovae. The uncertainty in the rise time of
the high-redshift Type Ia supernovae is presently quite large (roughly +/- 1.2
days statistical), making any search for evidence of evolution based on a
comparison of rise times premature. Furthermore, systematic effects on rise
time determinations from the high-redshift observations, due to the form of the
late-time light curve and the manner in which the light curves of these
supernovae were sampled, can bias the high-redshift rise time determinations by
up to +3.6/-1.9 days under extreme situations. The peak brightnesses - used for
cosmology - do not suffer any significant bias, nor any significant increase in
uncertainty.Comment: 18 pages, 4 figures, Accepted for publication in the Astronomical
Journal. Also available at http://www.lbl.gov/~nugent/papers.html Typos were
corrected and a few sentences were added for improved clarit
On the Spectroscopic Diversity of Type Ia Supernovae
A comparison of the ratio of the depths of two absorption features in the
spectra of TypeIa supernovae (SNe Ia) near the time of maximum brightness with
the blueshift of the deep red Si II absorption feature 10 days after maximum
shows that the spectroscopic diversity of SNe Ia is multi-dimensional. There is
a substantial range of blueshifts at a given value of the depth ratio. We also
find that the spectra of a sample of SNe Ia obtained a week before maximum
brightness can be arranged in a ``blueshift sequence'' that mimics the time
evolution of the pre-maximum-light spectra of an individual SN Ia, the well
observed SN 1994D. Within the context of current SN Ia explosion models, we
suggest that some of the SNe Ia in our sample were delayed-detonations while
others were plain deflagrations.Comment: accepted for publication in ApJ
Abundances and density structure of the inner circumstellar ring around SN 1987A
We present optical spectroscopic data of the inner circumstellar ring around
SN 1987A from the Anglo-Australian Telescope (AAT) and the Very Large Telescope
(VLT) between ~1400 and ~5000 days post-explosion. We also assembled the
available optical and near-infrared line fluxes from the literature between
~300 and ~2000 days. These line light curves were fitted with a photoionization
model to determine the density structure and the elemental abundances for the
inner ring. We found densities ranging from 1x10^3 to 3x10^4 atoms cm^-3 and a
total mass of the ionized gas of ~0.058 Msun within the inner ring. Abundances
inferred from the optical and near-infrared data were also complemented with
estimates of Lundqvist & Fransson (1996) based on ultraviolet lines. This way
we found an He/H-ratio (by number of atoms) of 0.17+-0.06 which is roughly 30%
lower than previously estimated and twice the solar and the Large Magellanic
Cloud (LMC) value. We found an N/O-ratio of 1.5+-0.7, and the total
(C+N+O)/(H+He) abundance about 1.6 times its LMC value or roughly 0.6 times the
most recent solar value. An iron abundance of 0.20+-0.11 times solar was found
which is within the range of the estimates for the LMC. We also present late
time (~5000 - 7500 days) line light curves of [O III], [Ne III], [Ne IV], [Ar
III], [Ar IV], and [Fe VII] from observations with the VLT. We compared these
with model fluxes and found that an additional 10^2 atoms cm^-3 component was
required to explain the data of the highest ionization lines. Such low density
gas is expected in the H II-region interior to the inner ring which likely
extends also to larger radii at higher latitudes (out of the ring plane). At
epochs later than ~5000 days our models underproduce the emission of most of
these lines as expected due to the contribution from the interaction of the
supernova ejecta with the ring.Comment: 17 pages, 8 figures, accepted for publication in Ap
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
Plasma lipid species at type 1 diabetes onset predict residual beta-cell function after 6 months
INTRODUCTION: The identification of metabolomic dysregulation appears promising for the prediction of type 1 diabetes and may also reveal metabolic pathways leading to beta-cell destruction. Recent studies indicate that regulation of multiple phospholipids precede the presence of autoantigens in the development of type 1 diabetes. OBJECTIVES: We hypothesize that lipid biomarkers in plasma from children with recent onset type 1 diabetes will reflect their remaining beta-cell function and predict future changes in beta-cell function. METHODS: We performed targeted lipidomic profiling by electrospray ionization tandem mass spectrometry to acquire comparative measures of 354 lipid species covering 25 lipid classes and subclasses in plasma samples from 123 patients < 17 years of age followed prospectively at 1, 3, 6 and 12 months after diagnosis. Lipidomic profiles were analysed using liner regression to investigate the relationship between plasma lipids and meal stimulated C-peptide levels at each time point. P-values were corrected for multiple comparisons by the method of Benjamini and Hochberg. RESULTS: Linear regression analysis showed that the relative levels of cholesteryl ester, diacylglycerol and triacylglycerol at 1 month were associated to the change in c-peptide levels from 1 to 6 months (corrected p-values of 4.06E-03, 1.72E-02 and 1.72E02, respectively). Medium chain saturated and monounsaturated fatty acids were the major constituents of the di- and triacylglycerol species suggesting a link with increased lipogenesis. CONCLUSION: These observations support the hypothesis of lipid disturbances as explanatory factors for residual beta-cell function in children with new onset type 1 diabetes
Exosomes containing HIV protein Nef reorganize lipid rafts potentiating inflammatory response in bystander cells.
HIV infection has a profound effect on "bystander" cells causing metabolic co-morbidities. This may be mediated by exosomes secreted by HIV-infected cells and containing viral factors. Here we show that exosomes containing HIV-1 protein Nef (exNef) are rapidly taken up by macrophages releasing Nef into the cell interior. This caused down-regulation of ABCA1, reduction of cholesterol efflux and sharp elevation of the abundance of lipid rafts through reduced activation of small GTPase Cdc42 and decreased actin polymerization. Changes in rafts led to re-localization of TLR4 and TREM-1 to rafts, phosphorylation of ERK1/2, activation of NLRP3 inflammasome, and increased secretion of pro-inflammatory cytokines. The effects of exNef on lipid rafts and on inflammation were reversed by overexpression of a constitutively active mutant of Cdc42. Similar effects were observed in macrophages treated with exosomes produced by HIV-infected cells or isolated from plasma of HIV-infected subjects, but not with exosomes from cells and subjects infected with ΔNef-HIV or uninfected subjects. Mice injected with exNef exhibited monocytosis, reduced ABCA1 in macrophages, increased raft abundance in monocytes and augmented inflammation. Thus, Nef-containing exosomes potentiated pro-inflammatory response by inducing changes in cholesterol metabolism and reorganizing lipid rafts. These mechanisms may contribute to HIV-associated metabolic co-morbidities
K-corrections and Extinction Corrections for Type Ia Supernovae
The measurement of the cosmological parameters from Type Ia supernovae hinges
on our ability to compare nearby and distant supernovae accurately. Here we
present an advance on a method for performing generalized K-corrections for
Type Ia supernovae which allows us to compare these objects from the UV to
near-IR over the redshift range 0<z<2. We discuss the errors currently
associated with this method and how future data can improve upon it
significantly. We also examine the effects of reddening on the K-corrections
and the light curves of Type Ia supernovae. Finally, we provide a few examples
of how these techniques affect our current understanding of a sample of both
nearby and distant supernovae.Comment: Accepted for the August issue of PASP. 39 pages, 15 figure
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