229 research outputs found
Early light curves for Type Ia supernova explosion models
Upcoming high-cadence transient survey programmes will produce a wealth of
observational data for Type Ia supernovae. These data sets will contain
numerous events detected very early in their evolution, shortly after
explosion. Here, we present synthetic light curves, calculated with the
radiation hydrodynamical approach Stella for a number of different explosion
models, specifically focusing on these first few days after explosion. We show
that overall the early light curve evolution is similar for most of the
investigated models. Characteristic imprints are induced by radioactive
material located close to the surface. However, these are very similar to the
signatures expected from ejecta-CSM or ejecta-companion interaction. Apart from
the pure deflagration explosion models, none of our synthetic light curves
exhibit the commonly assumed power-law rise. We demonstrate that this can lead
to substantial errors in the determination of the time of explosion. In
summary, we illustrate with our calculations that even with very early data an
identification of specific explosion scenarios is challenging, if only
photometric observations are available.Comment: 15 pages, 14 figures, 3 tables, accepted for publication in MNRA
EinfluĂ unterschiedlicher Anbauarten â mineralisch, organisch, biologisch-dynamisch â auf Kartoffeln: Inhaltsstoffe, Sensorik, Festigkeitskennwerte und bildschaffende Methoden
GrundsÀtzlich sprachen die Kartoffeln der Sorte ŽGranolaŽ sehr schwach auf die eingesetzten Versuchsfaktoren an, sodaà die Unterschiede selten statistisch abgesichert werden konnten.
Bei denjenigen Inhaltsstoffen, die deutlicher auf den Anbaufaktor DĂŒngermenge ansprachen, reagierten die Knollen der mineralisch gedĂŒngten Varianten eindeutig stĂ€rker (Abnahme der Trockenmasse, der Saccharose-, StĂ€rke- und Clorid-Gehalte, Zunahme der Glukose-, Fruktose-, Fluorid- und Asche-Gehalte) als die Vergleichsvarianten. Ein Grund hierfĂŒr könnte die schnellere VerfĂŒgbarkeit des mineralischen DĂŒngers gewesen sein.
Die biologisch-dynamisch gedĂŒngten Knollen zeigten nur bei drei Parametern dieselbe Reaktion auf die Intensivierung der DĂŒngung wie die organisch gedĂŒngten auf (Zunahme der Chlorid- und Asche-Gehalte, gleichbleibende Fluorid-Gehalte). Bei vier Merkmalen reagierten die biologisch-dynamischen Knollen ĂŒberhaupt nicht oder sehr gering, wogegen die organisch gedĂŒngten Kartoffeln eine Abnahme im Trockenmasse- und Saccharosegehalt bzw. keine gerichteten Tendenzen in den Glukose- und Fruktosegehalten aufwiesen.
Die Festigkeitskennwerte der mineralisch gedĂŒngten Kartoffeln wurde, im Vergleich zu den beiden anderen Varianten, schwĂ€cher bewertet. Die sensorischen Untersuchungen ergaben keine Bevorzugung einzelner Varianten, jedoch, besonders bei der minera-lischen Variante, eine tendenzielle Abnahme der sensorischen QualitĂ€t mit zunehmender DĂŒngung. Die Ergebnisse der Untersuchungen zur âVitalqualitĂ€tâ mit Hilfe bildschaf-fender Methoden bestĂ€tigte die prinzipielle Eignung dieser Methode fĂŒr ergĂ€nzende QualitĂ€tsuntersuchungen.
Eine abschlieĂende Beurteilung der QualitĂ€t der unterschiedlichen Anbauvarianten wird erst in Verbindung der bisherigen Daten mit noch zur Analyse anstehenden Parametern (Nitrat, AminosĂ€uren, AscorbinsĂ€ure, Kalium) möglich sein. Des weiteren wird in laufenden Sortenversuchen geprĂŒft, ob andere Sorten stĂ€rker auf die verschiedenen Versuchsfaktoren reagieren
Quantitative spectral analysis of the sdB star HD 188112: a helium-core white dwarf progenitor
HD 188112 is a bright (V = 10.2 mag) hot subdwarf B (sdB) star with a mass
too low to ignite core helium burning and is therefore considered as a
pre-extremely low mass (ELM) white dwarf (WD). ELM WDs (M 0.3 Msun) are
He-core objects produced by the evolution of compact binary systems. We present
in this paper a detailed abundance analysis of HD 188112 based on
high-resolution Hubble Space Telescope (HST) near and far-ultraviolet
spectroscopy. We also constrain the mass of the star's companion. We use hybrid
non-LTE model atmospheres to fit the observed spectral lines and derive the
abundances of more than a dozen elements as well as the rotational broadening
of metallic lines. We confirm the previous binary system parameters by
combining radial velocities measured in our UV spectra with the already
published ones. The system has a period of 0.60658584 days and a WD companion
with M 0.70 Msun. By assuming a tidally locked rotation, combined with
the projected rotational velocity (v sin i = 7.9 0.3 km s) we
constrain the companion mass to be between 0.9 and 1.3 Msun. We further discuss
the future evolution of the system as a potential progenitor of a
(underluminous) type Ia supernova. We measure abundances for Mg, Al, Si, P, S,
Ca, Ti, Cr, Mn, Fe, Ni, and Zn, as well as for the trans-iron elements Ga, Sn,
and Pb. In addition, we derive upper limits for the C, N, O elements and find
HD 188112 to be strongly depleted in carbon. We find evidence of non-LTE
effects on the line strength of some ionic species such as Si II and Ni II. The
metallic abundances indicate that the star is metal-poor, with an abundance
pattern most likely produced by diffusion effects.Comment: Accepted for publication in A&
Quality Comparison of Mineral, Organic and Biodynamic Cultivation of Potatoes: Contents, Strength Criteria, Sensory Investigations and Picture-Creating Methods
Nutritional quality of food can be characterized by the content of beneficial and harmful substances. For todayâs consumers the most important criteria for buying potatoes are taste, quality and shelf-life.
Biodynamic preparations are used by about 20% of all organic farms in Germany. These preparations do not primarily serve to increase the yield but are said to support the production of high quality food, having balanced nutrient contents and improved shelf-life characteristics.
Since 1993 investigations have been carried out to evaluate the effect of mineral fertilization and organic manuring at varied intensities, combined with application of biodynamic preparations, on some of these parameters.
The potatoes of the variety ÂŽGranolaÂŽ responded rather slightly to the factors of the trial, hence statistical differences could be confirmed only in few cases. Tubers deriving from the mineral fertilized plots showed the strongest response to elevated fertilization (decrease in dry matter, sucrose, chloride content and density, and an increase in glucose, fructose, fluoride and ash content). Only in three parameters tubers from the biodynamic plots responded in the same way as the organic ones to elevated fertilization (increase in the chloride and ash contents, stagnating fluoride contents). In four parameters, no or only a weak response of the biodynamic tubers has been found, whereas organic potatoes showed decreasing dry matter and sucrose contents, but no distinctive tendency in the parameters glucose and fructose. The parameter strength criteria has been assessed as the weakest in mineral fertilized potatoes. The sensory investigations did not allow to differentiate between the three cropping systems but there was a tendency of worsening sensoric quality at increased fertilization, particularly in the tubers of the mineral plots. The results of the determination of vital quality following picture-creating methods confirmed the applicability of this assay for additional quality determinations.
A final assessment of the quality according to the different cropping systems cannot be made at this point of time. Therefore, further parameters (nitrate, potassium, amino acids, ascorbic acid) will be analyzed which might allow a final assessment in combination with the present data. Furthermore, current trials might reveal if other varieties respond stronger to the relevant factors
Strongly lensed SNe Ia in the era of LSST: observing cadence for lens discoveries and time-delay measurements
The upcoming Large Synoptic Survey Telescope (LSST) will detect many strongly
lensed Type Ia supernovae (LSNe Ia) for time-delay cosmography. This will
provide an independent and direct way for measuring the Hubble constant ,
which is necessary to address the current tension in between
the local distance ladder and the early Universe measurements. We present a
detailed analysis of different observing strategies for the LSST, and quantify
their impact on time-delay measurement between multiple images of LSNe Ia. For
this, we produced microlensed mock-LSST light curves for which we estimated the
time delay between different images. We find that using only LSST data for
time-delay cosmography is not ideal. Instead, we advocate using LSST as a
discovery machine for LSNe Ia, enabling time delay measurements from follow-up
observations from other instruments in order to increase the number of systems
by a factor of 2 to 16 depending on the observing strategy. Furthermore, we
find that LSST observing strategies, which provide a good sampling frequency
(the mean inter-night gap is around two days) and high cumulative season length
(ten seasons with a season length of around 170 days per season), are favored.
Rolling cadences subdivide the survey and focus on different parts in different
years; these observing strategies trade the number of seasons for better
sampling frequency. In our investigation, this leads to half the number of
systems in comparison to the best observing strategy. Therefore rolling
cadences are disfavored because the gain from the increased sampling frequency
cannot compensate for the shortened cumulative season length. We anticipate
that the sample of lensed SNe Ia from our preferred LSST cadence strategies
with rapid follow-up observations would yield an independent percent-level
constraint on .Comment: 25 pages, 22 figures; accepted for publication in A&
Quality dating: a well-defined protocol implemented at ETH for high-precision 14c-dates tested on late glacial wood
Advances in accelerator mass spectrometry have resulted in an unprecedented amount of new high-precision radiocarbon (14C) -dates, some of which will redefine the international 14C calibration curves (IntCal and SHCal). Often these datasets are unaccompanied by detailed quality insurances in place at the laboratory, questioning whether the 14C structure is real, a result of a laboratory variation or measurement-scatter. A handful of intercomparison studies attempt to elucidate laboratory offsets but may fail to identify measurement-scatter and are often financially constrained. Here we introduce a protocol, called Quality Dating, implemented at ETH-ZĂŒrich to ensure reproducible and accurate high-precision 14C-dates. The protocol highlights the importance of the continuous measurements and evaluation of blanks, standards, references and replicates. This protocol is tested on an absolutely dated German Late Glacial tree-ring chronology, part of which is intercompared with the Curt Engelhorn-Center for Archaeometry, Mannheim, Germany (CEZA). The combined dataset contains 170 highly resolved, highly precise 14C-dates that supplement three decadal dates spanning 280 cal. years in IntCal, and provides detailed 14C structure for this interval
Maki Parameter and Upper critical Field of the Heavy-Fermion Superconductor UBe13
We have performed low-temperature specific-heat measurements in magnetic
fields for a single crystal UBe13. It has been observed that our sample
exhibits a superconducting transition at an intermediate temperature between
previously reported values for two variant samples called H type and L type.
The specific heat C(T) of our sample shows a T^3 behavior in the temperature
range below 0.7 Tc, which is similar to the behavior of the H-type sample,
suggesting the existence of point nodes in the superconducting gap function. We
have obtained the upper-critical-field curves Hc2 for the [001], [110], and
[111] crystal axes, which show no anisotropy at least down to the lowest
measured temperature of 0.5 K. We have also derived the Maki parameter kappa2,
and it has been revealed that the kappa2 steeply decreases isotropically upon
cooling just below Tc. Paramagnetic effects and the symmetry of Cooper pairing
of UBe13 are discussed.Comment: 4 pages, 5 figure
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
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