607 research outputs found
Limits on stable iron in TypeIa supernovae from NIR spectroscopy
We obtained optical and near-infrared spectra of TypeIa supernovae
(SNeIa) at epochs ranging from 224 to 496 days after the explosion. The
spectra show emission lines from forbidden transitions of singly ionised iron
and cobalt atoms. We used non-local thermodynamic equilibrium (NLTE) modelling
of the first and second ionisation stages of iron, nickel, and cobalt to fit
the spectra using a sampling algorithm allowing us to probe a broad parameter
space. We derive velocity shifts, line widths, and abundance ratios for iron
and cobalt. The measured line widths and velocity shifts of the singly ionised
ions suggest a shared emitting region. Our data are fully compatible with
radioactive Ni decay as the origin for cobalt and iron. We compare the
measured abundance ratios of iron and cobalt to theoretical predictions of
various SNIa explosion models. These models include, in addition to
Ni, different amounts of Ni and stable Fe. We can
exclude models that produced only Fe or only Ni in addition to
Ni. If we consider a model that has Ni, Ni, and
Fe then our data imply that these ratios are Fe / Ni
and Ni / Ni .Comment: 10 pages, 7 figures, Accepted for publication in A&
A massive star origin for an unusual helium-rich supernova in an elliptical galaxy
The unusual helium-rich (type Ib) supernova SN 2005E is distinguished from
any supernova hitherto observed by its faint and rapidly fading light curve,
prominent calcium lines in late-phase spectra and lack of any mark of recent
star formation near the supernova location. These properties are claimed to be
explained by a helium detonation in a thin surface layer of an accreting white
dwarf (Perets et al. 2010). Here we report on observations of SN 2005cz
appeared in an elliptical galaxy, whose observed properties resemble those of
SN 2005E in that it is helium-rich and unusually faint, fades rapidly, shows
much weaker oxygen emission lines than those of calcium in the well-evolved
spectrum. We argue that these properties are best explained by a core-collapse
supernova at the low-mass end () of the range of massive stars
that explode (Smartt 2009). Such a low mass progenitor had lost its
hydrogen-rich envelope through binary interaction, having very thin oxygen-rich
and silicon-rich layers above the collapsing core, thus ejecting a very small
amount of radioactive Ni and oxygen. Although the host galaxy NGC 4589
is an elliptical, some studies have revealed evidence of recent star-formation
activity (Zhang et al. 2008), consistent with the core-collapse scenario.Comment: Accepted by Nature (24 March 2010), 32 pages including Supplementary
Informatio
Nebular spectroscopy of SN 2014J: Detection of stable nickel in near infrared spectra
We present near infrared (NIR) spectroscopy of the nearby supernova 2014J
obtained 450 d after explosion. We detect the [Ni II] 1.939 m line
in the spectra indicating the presence of stable Ni in the ejecta. The
stable nickel is not centrally concentrated but rather distributed as the iron.
The spectra are dominated by forbidden [Fe II] and [Co II] lines. We use lines,
in the NIR spectra, arising from the same upper energy levels to place
constraints on the extinction from host galaxy dust. We find that that our data
are in agreement with the high and low found in earlier studies
from data near maximum light. Using a Ni mass prior from near maximum
light -ray observations, we find 0.05 M of stable nickel
to be present in the ejecta. We find that the iron group features are
redshifted from the host galaxy rest frame by 600 km s.Comment: 6 pages, 4 figures, submitted to A&
Deflagrations in hybrid CONe white dwarfs: a route to explain the faint Type Iax supernova 2008ha
Stellar evolution models predict the existence of hybrid white dwarfs (WDs)
with a carbon-oxygen core surrounded by an oxygen-neon mantle. Being born with
masses ~1.1 Msun, hybrid WDs in a binary system may easily approach the
Chandrasekhar mass (MCh) by accretion and give rise to a thermonuclear
explosion. Here, we investigate an off-centre deflagration in a near-MCh hybrid
WD under the assumption that nuclear burning only occurs in carbon-rich
material. Performing hydrodynamics simulations of the explosion and detailed
nucleosynthesis post-processing calculations, we find that only 0.014 Msun of
material is ejected while the remainder of the mass stays bound. The ejecta
consist predominantly of iron-group elements, O, C, Si and S. We also calculate
synthetic observables for our model and find reasonable agreement with the
faint Type Iax SN 2008ha. This shows for the first time that deflagrations in
near-MCh WDs can in principle explain the observed diversity of Type Iax
supernovae. Leaving behind a near-MCh bound remnant opens the possibility for
recurrent explosions or a subsequent accretion-induced collapse in faint Type
Iax SNe, if further accretion episodes occur. From binary population synthesis
calculations, we find the rate of hybrid WDs approaching MCh to be on the order
of 1 percent of the Galactic SN Ia rate.Comment: 9 pages, 7 figures, 2 tables, accepted for publication in MNRA
Large Interstellar Polarisation Survey. LIPS I: FORS2 spectropolarimetry in the Southern Hemisphere
Polarimetric studies of light transmitted through interstellar clouds may
give constraints on the properties of the interstellar dust grains.
Traditionally, broadband linear polarisation (BBLP) measurements have been
considered an important diagnostic tool for the study of the interstellar dust,
while comparatively less attention has been paid to spectropolarimetric
measurements. However, spectropolarimetry may offer stronger constraints than
BBLP, for example by revealing narrowband features, and by allowing us to
distinguish the contribution of dust from the contribution of interstellar gas.
Therefore, we have decided to carry out a Large Interstellar Polarisation
Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we
present the results obtained in the Southern Hemisphere with the FORS2
instrument of the ESO Very Large Telescope. Our spectra cover the wavelength
range 380--950\,nm at a spectral resolving power of about 880. We have produced
a publicly available catalogue of 127 linear polarisation spectra of 101
targets. We also provide the Serkowski-curve parameters, as well as the
wavelength gradient of the polarisation position angle for the interstellar
polarisation along 76 different lines of sight. In agreement with previous
literature, we found that the best-fit parameters of the Serkowski-curve are
not independent of each other. However, the relationships that we obtained are
not always consistent with what was found in previous studies.Comment: Accepted by A&A (replaced on 12 October 2017 simply to correct a
Metadata error
The Hubble Constant determined through an inverse distance ladder including quasar time delays and Type Ia supernovae
Context. The precise determination of the present-day expansion rate of the
Universe, expressed through the Hubble constant , is one of the most
pressing challenges in modern cosmology. Assuming flat CDM,
inference at high redshift using cosmic-microwave-background data from Planck
disagrees at the 4.4 level with measurements based on the local
distance ladder made up of parallaxes, Cepheids and Type Ia supernovae (SNe
Ia), often referred to as "Hubble tension". Independent,
cosmological-model-insensitive ways to infer are of critical importance.
Aims. We apply an inverse-distance-ladder approach, combining strong-lensing
time-delay-distance measurements with SN Ia data. By themselves, SNe Ia are
merely good relative distance indicators, but by anchoring them to strong
gravitational lenses one can obtain an measurement that is relatively
insensitive to other cosmological parameters. Methods. A cosmological parameter
estimate is performed for different cosmological background models, both for
strong-lensing data alone and for the combined lensing + SNe Ia data sets.
Results. The cosmological-model dependence of strong-lensing measurements
is significantly mitigated through the inverse distance ladder. In combination
with SN Ia data, the inferred consistently lies around 73-74 km s
Mpc, regardless of the assumed cosmological background model. Our
results agree nicely with those from the local distance ladder, but there is a
>2 tension with Planck results, and a ~1.5 discrepancy with
results from an inverse distance ladder including Planck, Baryon Acoustic
Oscillations and SNe Ia. Future strong-lensing distance measurements will
reduce the uncertainties in from our inverse distance ladder.Comment: 5 pages, 3 figures, A&A letters accepted versio
In vivo evaluation of pathogenicity and transmissibility of influenza A(H1N1)pdm09 hemagglutinin receptor binding domain 222 intrahost variants isolated from a single immunocompromised patient
AbstractThe influenza A(H1N1)pdm09 virus has circulated worldwide and continued to cause complicated infections and deaths. Reports have identified an increased prevalence of the hemagglutinin receptor binding domain D222G mutation in viruses isolated from individuals who have suffered such severe infections, but this association is still unclear. Virus isolated from a nasopharyngeal wash of a severely ill immunocompromised patient at the time of diagnosis contained the D222, but isolates collected later in his course from a bronchoalveolar lavage contained primarily the G222 mutation and was mixed with a minor population of D222. These clinical isolates were compared to a G222 plaque purified virus in the ferret model. The G222 predominant clinical isolate was the most pathogenic in ferrets and developed the most diversity at the 222 amino acid position during infection, suggesting that increased diversity and not a specific polymorphism at HA 222 may be important in predicting pathogenic potential
Three-dimensional simulations of gravitationally confined detonations compared to observations of SN 1991T
The gravitationally confined detonation (GCD) model has been proposed as a
possible explosion mechanism for Type Ia supernovae in the single-degenerate
evolution channel. Driven by buoyancy, a deflagration flame rises in a narrow
cone towards the surface. For the most part, the flow of the expanding ashes
remains radial, but upon reaching the outer, low-pressure layers of the white
dwarf, an additional lateral component develops. This makes the deflagration
ashes converge again at the opposite side, where the compression heats fuel and
a detonation may be launched. To test the GCD explosion model, we perform a 3D
simulation for a model with an ignition spot offset near the upper limit of
what is still justifiable, 200 km. This simulation meets our deliberately
optimistic detonation criteria and we initiate a detonation. The detonation
burns through the white dwarf and leads to its complete disruption. We
determine nucleosynthetic yields by post-processing 10^6 tracer particles with
a 384 nuclide reaction network and we present multi-band light curves and
time-dependent optical spectra. We find that our synthetic observables show a
prominent viewing-angle sensitivity in UV and blue bands, which is in tension
with observed SNe Ia. The strong dependence on viewing-angle is caused by the
asymmetric distribution of the deflagration ashes in the outer ejecta layers.
Finally, we perform a comparison of our model to SN 1991T. The overall
flux-level of the model is slightly too low and the model predicts pre-maximum
light spectral features due to Ca, S, and Si that are too strong. Furthermore,
the model chemical abundance stratification qualitatively disagrees with recent
abundance tomography results in two key areas: our model lacks low velocity
stable Fe and instead has copious amounts of high-velocity 56Ni and stable Fe.
We therefore do not find good agreement of the model with SN 1991T.Comment: 11 pages, accepted for publication in Astronomy & Astrophysic
Modelling the Type Ic SN 2004aw: a moderately energetic explosion of a massive C plus O star without a GRB
An analysis of the Type Ic supernova (SN) 2004aw is performed by means of models of the photospheric and nebular spectra and of the bolometric light curve. SN 2004aw is shown not to be âbroad-linedâ, contrary to previous claims, but rather a âfast-linedâ SN Ic. The spectral resemblance to the narrow-lined Type Ic SN 1994I, combined with the strong nebular [OâI] emission and the broad light curve, points to a moderately energetic explosion of a massive C+O star. The ejected 56Ni mass is â0.20 Mâ. The ejecta mass as constrained by the models is âŒ3â5 Mâ, while the kinetic energy is estimated as EK âŒ3â6 Ă 1051 erg. The ratio EK/Mâ, the specific energy that influences the shape of the spectrum, is therefore â1. The corresponding zero-age main-sequence mass of the progenitor star may have been âŒ23â28 Mâ. Tests show that a flatter outer density structure may have caused a broad-lined spectrum at epochs before those observed without affecting the later epochs when data are available, implying that our estimate of EK is a lower limit. SN 2004aw may have been powered by either a collapsar or a magnetar, both of which have been proposed for gamma-ray burst SNe. Evidence for this is seen in the innermost layers, which appear to be highly aspherical as suggested by the nebular line profiles. However, any engine was not extremely powerful, as the outer ejecta are more consistent with a spherical explosion and no gamma-ray burst was detected in coincidence with SN 2004aw
Optical quantification of intracellular mass density and cell mechanics in 3D mechanical confinement
Biophysical properties of cells such as intracellular mass density and cell mechanics are known to be involved in a wide range of homeostatic functions and pathological alterations. An optical readout that can be used to quantify such properties is the refractive index (RI) distribution. It has been recently reported that the nucleus, initially presumed to be the organelle with the highest dry mass density (Ï) within the cell, has in fact a lower RI and Ï than its surrounding cytoplasm. These studies have either been conducted in suspended cells, or cells adhered on 2D substrates, neither of which reflects the situation in vivo where cells are surrounded by the extracellular matrix (ECM). To better approximate the 3D situation, we encapsulated cells in 3D covalently-crosslinked alginate hydrogels with varying stiffness, and imaged the 3D RI distribution of cells, using a combined optical diffraction tomography (ODT)-epifluorescence microscope. Unexpectedly, the nuclei of cells in 3D displayed a higher Ï than the cytoplasm, in contrast to 2D cultures. Using a Brillouin-epifluorescence microscope we subsequently showed that in addition to higher Ï, the nuclei also had a higher longitudinal modulus (M) and viscosity (η) compared to the cytoplasm. Furthermore, increasing the stiffness of the hydrogel resulted in higher M for both the nuclei and cytoplasm of cells in stiff 3D alginate compared to cells in compliant 3D alginate. The ability to quantify intracellular biophysical properties with non-invasive techniques will improve our understanding of biological processes such as dormancy, apoptosis, cell growth or stem cell differentiation. <br
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