2,480 research outputs found
The progenitor mass of the Type IIP supernova SN 2004et from late-time spectral modeling
SN 2004et is one of the nearest and best-observed Type IIP supernovae, with a
progenitor detection as well as good photometric and spectroscopic
observational coverage well into the nebular phase. Based on nucleosynthesis
from stellar evolution/explosion models we apply spectral modeling to analyze
its 140-700 day evolution from ultraviolet to mid-infrared. We find a M_ZAMS=
15 Msun progenitor star (with an oxygen mass of 0.8 Msun) to satisfactorily
reproduce [O I] 6300, 6364 {\AA} and other emission lines of carbon, sodium,
magnesium, and silicon, while 12 Msun and 19 Msun models under- and overproduce
most of these lines, respectively. This result is in fair agreement with the
mass derived from the progenitor detection, but in disagreement with
hydrodynamical modeling of the early-time light curve. From modeling of the
mid-infrared iron-group emission lines, we determine the density of the
"Ni-bubble" to rho(t) = 7E-14*(t/100d)^-3 g cm^-3, corresponding to a filling
factor of f = 0.15 in the metal core region (V = 1800 km/s). We also confirm
that silicate dust, CO, and SiO emission are all present in the spectra.Comment: 21 pages, 15 figures. Accepted for publication in A&
Mapping High-velocity H-alpha and Lyman-alpha Emission from Supernova 1987A
We present new {\it Hubble Space Telescope} images of high-velocity
H- and Lyman- emission in the outer debris of SN~1987A. The
H- images are dominated by emission from hydrogen atoms crossing the
reverse shock. For the first time we observe emission from the reverse shock
surface well above and below the equatorial ring, suggesting a bipolar or
conical structure perpendicular to the ring plane. Using the H imaging,
we measure the mass flux of hydrogen atoms crossing the reverse shock front, in
the velocity intervals (7,500~~~~2,800 km s) and
(1,000~~~~7,500 km s), =
1.2~~10 M yr. We also present the first
Lyman- imaging of the whole remnant and new X-ray
observations. Comparing the spatial distribution of the Lyman- and
X-ray emission, we observe that the majority of the high-velocity
Lyman- emission originates interior to the equatorial ring. The
observed Lyman-/H- photon ratio, ~17, is significantly higher than the theoretically
predicted ratio of 5 for neutral atoms crossing the reverse shock
front. We attribute this excess to Lyman- emission produced by X-ray
heating of the outer debris. The spatial orientation of the Lyman- and
X-ray emission suggests that X-ray heating of the outer debris is the dominant
Lyman- production mechanism in SN 1987A at this phase in its evolution.Comment: 6 pages, 5 figures. ApJL - accepte
Evolution of the Reverse Shock Emission from SNR 1987A
We present new (2004 July) G750L and G140L Space Telescope Imaging
Spectrograph (STIS) data of the H-alpha and Ly-alpha emission from supernova
remnant (SNR) 1987A. With the aid of earlier data, from Oct 1997 to Oct 2002,
we track the local evolution of Ly-alpha emission and both the local and global
evolution of H-alpha emission. In addition to emission which we can clearly
attribute to the surface of the reverse shock, we also measure comparable
emission, in both H-alpha and Ly-alpha, which appears to emerge from supernova
debris interior to the surface. New observations taken through slits positioned
slightly eastward and westward of a central slit show a departure from
cylindrical symmetry in the H-alpha surface emission. Using a combination of
old and new observations, we construct a light curve of the total H-alpha flux,
F, from the reverse shock, which has increased by a factor ~ 4 over about 8
years. However, due to large systematic uncertainties, we are unable to discern
between the two limiting behaviours of the flux - F ~ t (self-similar
expansion) and F ~ t^5 (halting of the reverse shock). Such a determination is
relevant to the question of whether the reverse shock emission will vanish in
less than about 7 years (Smith et al. 2005). Future deep, low- or
moderate-resolution spectra are essential for accomplishing this task.Comment: 28 pages, 12 figures. Accepted by Ap
Supersolar Ni/Fe production in the Type IIP SN 2012ec
SN 2012ec is a Type IIP supernova (SN) with a progenitor detection and
comprehensive photospheric-phase observational coverage. Here, we present Very
Large Telescope and PESSTO observations of this SN in the nebular phase. We
model the nebular [O I] 6300, 6364 lines and find their strength to suggest a
progenitor main-sequence mass of 13-15 Msun. SN 2012ec is unique among
hydrogen-rich SNe in showing a distinct and unblended line of stable nickel [Ni
II] 7378. This line is produced by 58Ni, a nuclear burning ash whose abundance
is a sensitive tracer of explosive burning conditions. Using spectral synthesis
modelling, we use the relative strengths of [Ni II] 7378 and [Fe II] 7155 (the
progenitor of which is 56Ni) to derive a Ni/Fe production ratio of 0.20pm0.07
(by mass), which is a factor 3.4pm1.2 times the solar value. High production of
stable nickel is confirmed by a strong [Ni II] 1.939 micron line. This is the
third reported case of a core-collapse supernova producing a Ni/Fe ratio far
above the solar value, which has implications for core-collapse explosion
theory and galactic chemical evolution models.Comment: Published versio
Spatially dense 3D facial heritability and modules of co-heritability in a father-offspring design
Introduction: The human face is a complex trait displaying a strong genetic component as illustrated by various studies on facial heritability. Most of these start from sparse descriptions of facial shape using a limited set of landmarks. Subsequently, facial features are preselected as univariate measurements or principal components and the heritability is estimated for each of these features separately. However, none of these studies investigated multivariate facial features, nor the co-heritability between different facial features. Here we report a spatially dense multivariate analysis of facial heritability and co-heritability starting from data from fathers and their children available within ALSPAC. Additionally, we provide an elaborate overview of related craniofacial heritability studies. Methods: In total, 3D facial images of 762 father-offspring pairs were retained after quality control. An anthropometric mask was applied to these images to establish spatially dense quasi-landmark configurations. Partial least squares regression was performed and the (co-)heritability for all quasi-landmarks (∼7160) was computed as twice the regression coefficient. Subsequently, these were used as input to a hierarchical facial segmentation, resulting in the definition of facial modules that are internally integrated through the biological mechanisms of inheritance. Finally, multivariate heritability estimates were obtained for each of the resulting modules. Results: Nearly all modular estimates reached statistical significance under 1,000,000 permutations and after multiple testing correction (p ≤ 1.3889 × 10-3), displaying low to high heritability scores. Particular facial areas showing the greatest heritability were similar for both sons and daughters. However, higher estimates were obtained in the former. These areas included the global face, upper facial part (encompassing the nasion, zygomas and forehead) and nose, with values reaching 82% in boys and 72% in girls. The lower parts of the face only showed low to moderate levels of heritability. Conclusion: In this work, we refrain from reducing facial variation to a series of individual measurements and analyze the heritability and co-heritability from spatially dense landmark configurations at multiple levels of organization. Finally, a multivariate estimation of heritability for global-to-local facial segments is reported. Knowledge of the genetic determination of facial shape is useful in the identification of genetic variants that underlie normal-range facial variation
Single-nanowire, low-bandgap hot carrier solar cells with tunable open-circuit voltage
Compared to traditional pn-junction photovoltaics, hot carrier solar cells
offer potentially higher efficiency by extracting work from the kinetic energy
of photogenerated "hot carriers" before they cool to the lattice temperature.
Hot carrier solar cells have been demonstrated in high-bandgap ferroelectric
insulators and GaAs/AlGaAs heterostructures, but so far not in low-bandgap
materials, where the potential efficiency gain is highest. Recently, a high
open-circuit voltage was demonstrated in an illuminated wurtzite InAs nanowire
with a low bandgap of 0.39 eV, and was interpreted in terms of a
photothermoelectric effect. Here, we point out that this device is a hot
carrier solar cell and discuss its performance in those terms. In the
demonstrated devices, InP heterostructures are used as energy filters in order
to thermoelectrically harvest the energy of hot electrons photogenerated in
InAs absorber segments. The obtained photovoltage depends on the
heterostructure design of the energy filter and is therefore tunable. By using
a high-resistance, thermionic barrier an open-circuit voltage is obtained that
is in excess of the Shockley-Queisser limit. These results provide
generalizable insight into how to realize high voltage hot carrier solar cells
in low-bandgap materials, and therefore are a step towards the demonstration of
higher efficiency hot carrier solar cells
Defining the genetic susceptibility to cervical neoplasia - a genome-wide association study
Funding: MAB was funded by a National Health and Medical Research Council (Australia) Senior Principal Research Fellowship. Support was also received from the Australian Cancer Research Foundation. JL holds a Tier 1 Canada Research Chair in Human Genome Epidemiology. The Seattle study was supported by the following grants: NIH, National Cancer Institute grants P01CA042792 and R01CA112512. Cervical Health Study (from which the NSW component was obtained) was funded by NHMRC Grant 387701, and CCNSW core grant. The Montreal study was funded by the Canadian Institutes of Health Research (grant MOP-42532) and sample processing was funded by the Reseau FRQS SIDA-MI. The Swedish Research Council, the Swedish Foundation for Strategic Research, the ALF/LUA research grant in Gothenburg and Umeå, the Lundberg Foundation, the Torsten and Ragnar Soderberg’s Foundation, the Novo Nordisk Foundation, and the European Commission grant HEALTH-F2-2008-201865-GEFOS, BBMRI.se, the Swedish Society of Medicine, the KempeFoundation (JCK-1021), the Medical Faculty of Umeå University, the County Council of Vasterbotten (Spjutspetsanslag VLL:159:33-2007). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscriptPeer reviewedPublisher PDFPublisher PD
Six NSCL/P loci show associations with normal-range craniofacial variation
Objectives: Orofacial clefting is one of the most prevalent craniofacial malformations. Previous research has demonstrated that unaffected relatives of patients with non-syndromic cleft lip with/without cleft palate (NSCL/P) show distinctive facial features, which can be an expression of underlying NSCL/P susceptibility genes. These results support the hypothesis that genes involved in the occurrence of a cleft also play a role in normal craniofacial development. In this study, we investigated the influence of genetic variants associated with NSCL/P on normal-range variation in facial shape. Methods: A literature review of genome wide association studies (GWAS) investigating the genetic etiology of NSCL/P was performed, resulting in a list of 75 single nucleotide polymorphisms (SNPs) located in 38 genetic loci. Genotype data were available for 65 of these selected SNPs in three datasets with a combined sample size of 7,418 participants of European ancestry, whose 3D facial images were also available. The effect of each SNP was tested using a multivariate canonical correlation analysis (CCA) against 63 hierarchically-constructed facial segments in each of the three datasets and meta-analyzed. This allowed for the investigation of associations between SNPs known to be involved in NSCL/P and normal-range facial shape variations in a global-to-local perspective, without preselecting specific facial shape features or characteristics. Results: Six NSCL/P SNPs showed significant associations with variation in normal-range facial morphology. rs6740960 showed significant effects in the chin area (p = 3.71 × 10−28). This SNP lies in a non-coding area. Another SNP, rs227731 near the NOG gene, showed a significant effect in the philtrum area (p = 1.96 × 10−16). Three SNPs showed significant effects on the shape of the nose. rs742071 (p = 8.71 × 10−14), rs34246903 (p = 6.87 × 10−12), and rs10512248 (p = 8.4 × 10−9). Respectively, these SNPs are annotated to PAX7, MSX1, and PTCH1. Finally, rs7590268, an intron variant of THADA, showed an effect in the shape of the supraorbital ridge (p = 3.84 × 10−7). Conclusions: This study provides additional evidence NSCL/P-associated genetic variants influence normal-range craniofacial morphology, with significant effects observed for the chin, the nose, the supraorbital ridges and the philtrum area
HST-COS Observations of Hydrogen, Helium, Carbon and Nitrogen Emission from the SN 1987A Reverse Shock
We present the most sensitive ultraviolet observations of Supernova 1987A to
date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins
Spectrograph shows many narrow (dv \sim 300 km/s) emission lines from the
circumstellar ring, broad (dv \sim 10 -- 20 x 10^3 km/s) emission lines from
the reverse shock, and ultraviolet continuum emission. The high signal-to-noise
(> 40 per resolution element) broad LyA emission is excited by soft X-ray and
EUV heating of mostly neutral gas in the circumstellar ring and outer supernova
debris. The ultraviolet continuum at \lambda > 1350A can be explained by HI
2-photon emission from the same region. We confirm our earlier, tentative
detection of NV \lambda 1240 emission from the reverse shock and we present the
first detections of broad HeII \lambda1640, CIV \lambda1550, and NIV]
\lambda1486 emission lines from the reverse shock. The helium abundance in the
high-velocity material is He/H = 0.14 +/- 0.06. The NV/H-alpha line ratio
requires partial ion-electron equilibration (T_{e}/T_{p} \approx 0.14 - 0.35).
We find that the N/C abundance ratio in the gas crossing the reverse shock is
significantly higher than that in the circumstellar ring, a result that may be
attributed to chemical stratification in the outer envelope of the supernova
progenitor. The N/C abundance ratio may have been stratified prior to the ring
expulsion, or this result may indicate continued CNO processing in the
progenitor subsequent to the expulsion of the circumstellar ring.Comment: 12 pages, 8 figures. ApJ - accepte
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