407 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
The dusty type IIn Supernova 1998S
The type IIn SN 1998S is one of the most remarkable core-collapse supernovae
ever observed. It underwent a complex interaction with a substantial
circumstellar medium, resulting in radiation at wavelengths from radio to
X-rays. IR and optical observations have revealed a wide variety of broad and
narrow emission lines. Examination of the SN/CSM interaction and of the ejecta
spectra has allowed us to deduce that the supernova probably arose from a
massive, RSG progenitor having a large (>3200 AU radius), dusty circumstellar
disk. SN 1998S also developed one of the strongest, most persistent infrared
excesses ever seen in a supernova. IR/optical monitoring of SN 1998S has been
carried out to nearly 1200 days post-explosion. This includes coverage to
wavelengths as long as 4.7 microns, making SN 1998S only the second supernova
(after SN 1987A) to be observed in this spectral region. Fading of the central
and redshifted components of the late-time H I and He I line profiles suggests
strongly that dust condensed in the ejecta. However, it is less clear whether
the strong late-time IR emission arose from this dust, or from an IR echo in
the dusty CSM. One interesting possibility is that dust condensed in the cool
dense shell between the outer and reverse shocks, thus simultaneously producing
both the line obscuration and the IR emission.Comment: 9 pages. {Invited talk given at ESO/MPA/MPE Workshop "From Twilight
to Highlight: The Physics of Supernovae", Garching, Germany, 29-31 July 2002.
To appear in the Proceedings, eds. W. Hillebrandt & B. Leibundgut (pub.
Springer-Verlag series ``ESO Astrophysics Symposia'
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
Lipidomic and metabolomic characterization of a genetically modified mouse model of the early stages of human type 1 diabetes pathogenesis
The early mechanisms regulating progression towards beta cell failure in type 1 diabetes (T1D) are poorly understood, but it is generally acknowledged that genetic and environmental components are involved. The metabolomic phenotype is sensitive to minor variations in both, and accordingly reflects changes that may lead to the development of T1D. We used two different extraction methods in combination with both liquid- and gas chromatographic techniques coupled to mass spectrometry to profile the metabolites in a transgenic non-diabetes prone C57BL/6 mouse expressing CD154 under the control of the rat insulin promoter (RIP) crossed into the immuno-deficient recombination-activating gene (RAG) knockout (−/−) C57BL/6 mouse, resembling the early stages of human T1D. We hypothesized that alterations in the metabolomic phenotype would characterize the early pathogenesis of T1D, thus metabolomic profiling could provide new insight to the development of T1D. Comparison of the metabolome of the RIP CD154 × RAG(−/−) mice to RAG(−/−) mice and C57BL/6 mice revealed alterations of >100 different lipids and metabolites in serum. Low lysophosphatidylcholine levels, accumulation of ceramides as well as methionine deficits were detected in the pre-type 1 diabetic mice. Additionally higher lysophosphatidylinositol levels and low phosphatidylglycerol levels where novel findings in the pre-type 1 diabetic mice. These observations suggest that metabolomic disturbances precede the onset of T1D. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-015-0889-1) contains supplementary material, which is available to authorized users
Spitzer measurements of atomic and molecular abundances in the Type IIP SN 2005af
We present results based on Spitzer Space Telescope mid-infrared (3.6-30
micron) observations of the nearby IIP supernova 2005af. We report the first
ever detection of the SiO molecule in a Type IIP supernova. Together with the
detection of the CO fundamental, this is an exciting finding as it may signal
the onset of dust condensation in the ejecta. From a wealth of fine-structure
lines we provide abundance estimates for stable Ni, Ar, and Ne which, via
spectral synthesis, may be used to constrain nucleosynthesis models.Comment: ApJ Letters (accepted
Disruption of beta cell acetyl-CoA carboxylase-1 in mice impairs insulin secretion and beta cell mass
Aims/hypothesis: Pancreatic beta cells secrete insulin to maintain glucose homeostasis, and beta cell failure is a hallmark of type 2 diabetes. Glucose triggers insulin secretion in beta cells via oxidative mitochondrial pathways. However, it also feeds mitochondrial anaplerotic pathways, driving citrate export and cytosolic malonyl-CoA production by the acetyl-CoA carboxylase 1 (ACC1) enzyme. This pathway has been proposed as an alternative glucose-sensing mechanism, supported mainly by in vitro data. Here, we sought to address the role of the beta cell ACC1-coupled pathway in insulin secretion and glucose homeostasis in vivo. Methods: Acaca, encoding ACC1 (the principal ACC isoform in islets), was deleted in beta cells of mice using the Cre/loxP system. Acaca floxed mice were crossed with Ins2cre mice (βACC1KO; life-long beta cell gene deletion) or Pdx1creER mice (tmx-βACC1KO; inducible gene deletion in adult beta cells). Beta cell function was assessed using in vivo metabolic physiology and ex vivo islet experiments. Beta cell mass was analysed using histological techniques. Results: βACC1KO and tmx-βACC1KO mice were glucose intolerant and had defective insulin secretion in vivo. Isolated islet studies identified impaired insulin secretion from beta cells, independent of changes in the abundance of neutral lipids previously implicated as amplification signals. Pancreatic morphometry unexpectedly revealed reduced beta cell size in βACC1KO mice but not in tmx-βACC1KO mice, with decreased levels of proteins involved in the mechanistic target of rapamycin kinase (mTOR)-dependent protein translation pathway underpinning this effect. Conclusions/interpretation: Our study demonstrates that the beta cell ACC1-coupled pathway is critical for insulin secretion in vivo and ex vivo and that it is indispensable for glucose homeostasis. We further reveal a role for ACC1 in controlling beta cell growth prior to adulthood.</p
- …