462 research outputs found
Applying the expanding photosphere and standardized candle methods to Type II-Plateau supernovae at cosmologically significant redshifts: the distance to SN 2013eq
Based on optical imaging and spectroscopy of the Type II-Plateau SN 2013eq,
we present a comparative study of commonly used distance determination methods
based on Type II supernovae. The occurrence of SN 2013eq in the Hubble flow (z
= 0.041 +/- 0.001) prompted us to investigate the implications of the
difference between "angular" and "luminosity" distances within the framework of
the expanding photosphere method (EPM) that relies upon a relation between flux
and angular size to yield a distance. Following a re-derivation of the basic
equations of the EPM for SNe at non-negligible redshifts, we conclude that the
EPM results in an angular distance. The observed flux should be converted into
the SN rest frame and the angular size, theta, has to be corrected by a factor
of (1+z)^2. Alternatively, the EPM angular distance can be converted to a
luminosity distance by implementing a modification of the angular size. For SN
2013eq, we find EPM luminosity distances of D_L = 151 +/- 18 Mpc and D_L = 164
+/- 20 Mpc by making use of different sets of dilution factors taken from the
literature. Application of the standardized candle method for Type II-P SNe
results in an independent luminosity distance estimate (D_L = 168 +/- 16 Mpc)
that is consistent with the EPM estimate.Comment: 12 pages, 4 figures, accepted by A&
Three-dimensional simulations of the interaction between Type Ia supernova ejecta and their main sequence companions
The identity of the progenitor systems of SNe Ia is still uncertain. In the
single-degenerate (SD) scenario, the interaction between the SN blast wave and
the outer layers of a main sequence (MS) companion star strips off H-rich
material which is then mixed into the ejecta. Strong contamination of the SN
ejecta with stripped material could lead to a conflict with observations of SNe
Ia. This constrains the SD progenitor model. In this work, our previous
simulations based on simplified progenitor donor stars have been updated by
adopting more realistic progenitor-system models that result from fully
detailed, state-of-the-art binary evolution calculations. We use Eggleton's
stellar evolution code including the optically thick accretion wind model and
the possibility of the effects of accretion disk instabilities to obtain
realistic models of companions for different progenitor systems. The impact of
the SN blast wave on these companion stars is followed in three-dimensional
hydrodynamic simulations employing the SPH code GADGET3. We find that the
stripped masses range from 0.11 to 0.18 M_sun. The kick velocity is between 51
and 105 km/s. We find that the stripped mass and kick velocity depend on the
ratio of the orbital separation to the radius of a companion. They can be
fitted by a power law for a given companion model. However, the structure of
the companion star is also important for the amount of stripped material. With
more realistic companion star models than in previous studies, our simulations
show that the H masses stripped from companions are inconsistent with the best
observational limits (< 0.01 M_sun) derived from nebular spectra. However, a
rigorous forward modeling based on impact simulations with radiation transfer
is required to reliably predict observable signatures of the stripped H and to
conclusively assess the viability of the considered SN Ia progenitor scenario.Comment: 14 pages, 13 figures, accepted for publication by A&
The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?
iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN
2002es, is the first SN Ia for which a strong UV flash was observed in the
early-time light curves. This has been interpreted as evidence for a
single-degenerate (SD) progenitor system where such a signal is expected from
interactions between the SN ejecta and the non-degenerate companion star. Here,
we compare synthetic observables of multi-dimensional state-of-the-art
explosion models for different progenitor scenarios to the light curves and
spectra of iPTF14atg. From our models, we have difficulties explaining the
spectral evolution of iPTF14atg within the SD progenitor channel. In contrast,
we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and
0.76 solar masses, respectively, provides an excellent match to the spectral
evolution of iPTF14atg from 10d before to several weeks after maximum light.
Our merger model does not naturally explain the initial UV flash of iPTF14atg.
We discuss several possibilities like interactions of the SN ejecta with the
circum-stellar medium and surface radioactivity from a He ignited merger that
may be able to account for the early UV emission in violent merger models.Comment: 12 pages, 7 figures, accepted for publication in MNRA
COMPATIBILITY OF ATMOSPHERIC (CO2)-C-14 MEASUREMENTS:COMPARING THE HEIDELBERG LOW-LEVEL COUNTING FACILITY TO INTERNATIONAL ACCELERATOR MASS SPECTROMETRY (AMS) LABORATORIES.
Combining atmospheric ∂14CO2 data sets from different networks or laboratories requires secure knowledge on their compatibility. In the present study, we compare ∂14CO2 results from the Heidelberg low-level counting (LLC) laboratory to 12 international accelerator mass spectrometry (AMS) laboratories using distributed aliquots of five pure CO2 samples. The averaged result of the LLC laboratory has a measurement bias of –0.3±0.5‰ with respect to the consensus value of the AMS laboratories for the investigated atmospheric ∂14C range of 9.6 to 40.4‰. Thus, the LLC measurements on average are not significantly different from the AMS laboratories, and the most likely measurement bias is smaller than the World Meteorological Organization (WMO) interlaboratory compatibility goal for ∂14CO2 of 0.5‰. The number of intercomparison samples was, however, too small to determine whether the measurement biases of the individual AMS laboratories fulfilled the WMO goal
High-Temporal-Resolution Rock Slope Monitoring Using Terrestrial Structure-from-Motion Photogrammetry in an Application with Spatial Resolution Limitations
Research on high-temporal-resolution rock slope monitoring has tended to focus on scenarios where spatial resolution is also high. Accordingly, there is a lack of understanding of the implications for rock slope monitoring results in cases with high temporal resolution but low spatial resolution, which is the focus of this study. This study uses automatically captured photos taken at a daily frequency by five fixed-base cameras in conjunction with multi-epoch Structure-from-Motion (SfM) photogrammetric processing techniques to evaluate changes in a rock slope in Majes, Arequipa, Peru. The results of the monitoring campaign demonstrate that there are potential issues with the common notion that higher frequency change detection is always superior. For lower spatial resolutions or when only large changes are of concern, using a high-frequency monitoring method may cause small volume changes that eventually aggrade into larger areas of change to be missed, whereas most of the total volume change would be captured with lower-frequency monitoring intervals. In this study, daily change detection and volume calculation resulted in a cumulative rockfall volume of 4300 m3 over about 14 months, while change detection and volume calculation between dates at the start and end of the 14-month period resulted in a total rockfall volume of 12,300 m3. High-frequency monitoring is still the most accurate approach for evaluating slope evolution from a rockfall frequency and size distribution perspective, and it allows for the detection of short accelerations and pre-failure deformations, but longer-term comparison intervals may be required in cases where spatial resolution is low relative to temporal resolution to more accurately reflect the total volume change of a given rock slope over a long period of time
Theory of "ferrisuperconductivity" in
We construct a two component Ginzburg-Landau theory with coherent pair motion
and incoherent quasiparticles for the phase diagram of .
The two staggered superconducting states live at the Brillouin zone center and
the zone boundary, and coexist for temperatures at concentrations
. We predict below
appearance of a charge density wave (CDW) and Be-sublattice distortion. The
distortion explains the SR relaxation anomaly, and Th-impurity mediated
scattering of ultrasound to CDW fluctuations explains the attenuation peak.Comment: 4 pages, 4 eps figures, REVTe
The Impact of Type Ia Supernova Explosions on Helium Companions in the Chandrasekhar-mass Explosion Scenario
In the version of the single-degenerate scenario of Type Ia supernovae (SNe Ia) studied here, a carbon–oxygen
white dwarf explodes close to the Chandrasekhar limit after accreting material from a non-degenerate helium
(He) companion star. In the present study, we employ the Stellar GADGET code to perform three-dimensional
hydrodynamical simulations of the interaction of the SN Ia ejecta with the He companion star taking into account
its orbital motion and spin. It is found that only 2%–5% of the initial companion mass is stripped off from the outer
layers of He companion stars due to the supernova (SN) impact. The dependence of the unbound mass (or the kick
velocity) on the orbital separation can be fitted to a good approximation by a power law for a given companion
model. After the SN impact, the outer layers of a He donor star are significantly enriched with heavy elements from
the low-expansion-velocity tail of SN Ia ejecta. The total mass of accumulated SN-ejecta material on the companion
surface reaches about 10−3 M for different companion models. This enrichment with heavy elements provides
a potential way to observationally identify the surviving companion star in SN remnants. Finally, by artificially
adjusting the explosion energy of the W7 explosion model, we find that the total accumulation of SN ejecta on the
companion surface is also dependent on the explosion energy with a power-law relation to a good approximation
The Earliest Near-infrared Time-series Spectroscopy of a Type Ia Supernova
We present ten medium-resolution, high signal-to-noise ratio near-infrared
(NIR) spectra of SN 2011fe from SpeX on the NASA Infrared Telescope Facility
(IRTF) and Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North, obtained
as part of the Carnegie Supernova Project. This data set constitutes the
earliest time-series NIR spectroscopy of a Type Ia supernova (SN Ia), with the
first spectrum obtained at 2.58 days past the explosion and covering -14.6 to
+17.3 days relative to B-band maximum. C I {\lambda}1.0693 {\mu}m is detected
in SN 2011fe with increasing strength up to maximum light. The delay in the
onset of the NIR C I line demonstrates its potential to be an effective tracer
of unprocessed material. For the first time in a SN Ia, the early rapid decline
of the Mg II {\lambda}1.0927 {\mu}m velocity was observed, and the subsequent
velocity is remarkably constant. The Mg II velocity during this constant phase
locates the inner edge of carbon burning and probes the conditions under which
the transition from deflagration to detonation occurs. We show that the Mg II
velocity does not correlate with the optical light-curve decline rate
{\Delta}m15. The prominent break at ~1.5 {\mu}m is the main source of concern
for NIR k-correction calculations. We demonstrate here that the feature has a
uniform time evolution among SNe Ia, with the flux ratio across the break
strongly correlated with {\Delta}m15. The predictability of the strength and
the onset of this feature suggests that the associated k-correction
uncertainties can be minimized with improved spectral templates.Comment: 14 pages, 13 figures, accepted for publication in Ap
Superconductivity and Antiferromagnetism: Hybridization Impurities in a Two-Band Spin-Gapped Electron System
We present the exact solution of a one-dimensional model of a spin-gapped
correlated electron system with hybridization impurities exhibiting both
magnetic and mixed-valence properties. The host supports superconducting
fluctuations, with a spin gap. The localized electrons create a band of
antiferromagnetic spin excitations inside the gap for concentrations x of the
impurities below some critical value x_c. When x = x_c the spin gap closes and
a ferrimagnetic phase appears. This is the first example of an exactly solvable
model with coexisting superconducting and antiferromagnetic fluctuations which
in addition supports a quantum phase transition to a (compensated)
ferrimagnetic phase. We discuss the possible relevance of our results for
experimental systems, in particular the U-based heavy-fermion materials.Comment: 4 page
Punctuated Shutdown of Atlantic Meridional Overturning Circulation during Greenland Stadial 1.
The Greenland Stadial 1 (GS-1; ~12.9 to 11.65 kyr cal BP) was a period of North Atlantic cooling, thought to have been initiated by North America fresh water runoff that caused a sustained reduction of North Atlantic Meridional Overturning Circulation (AMOC), resulting in an antiphase temperature response between the hemispheres (the 'bipolar seesaw'). Here we exploit sub-fossil New Zealand kauri trees to report the first securely dated, decadally-resolved atmospheric radiocarbon ((14)C) record spanning GS-1. By precisely aligning Southern and Northern Hemisphere tree-ring (14)C records with marine (14)C sequences we document two relatively short periods of AMOC collapse during the stadial, at ~12,920-12,640 cal BP and 12,050-11,900 cal BP. In addition, our data show that the interhemispheric atmospheric (14)C offset was close to zero prior to GS-1, before reaching 'near-modern' values at ~12,660 cal BP, consistent with synchronous recovery of overturning in both hemispheres and increased Southern Ocean ventilation. Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but probably due to an equatorward migration of the Polar Front, reducing the advection of southwesterly air masses to high latitudes. Our findings suggest opposing hemispheric temperature trends were driven by atmospheric teleconnections, rather than AMOC changes
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