oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Type Ia Supernovae: Non-standard Candles of the Universe  [PDF]
A. I. Bogomazov,A. V. Tutukov
Physics , 2011, DOI: 10.1134/S1063772911060023
Abstract: We analyze the influence of the evolution of light absorption by gray dust in the host galaxies of type Ia supernovae (SNe Ia) and the evolution of the mean combined mass of close-binary carbon-oxygen white dwarfs merging due to gravitational waves (SNe Ia precursors) on the interpretation of Hubble diagrams for SNe Ia. A significant increase in the mean SNe Ia energy due to the higher combined masses of merging dwarfs should be observable at redshifts z > 2. The observed relation between the distance moduli and redshifts of SNe Ia can be interpreted not only as evidence for accelerated expansion of the Universe, but also as indicating time variations of the gray-dust absorption of light from these supernovae in various types of host galaxies, observational selection effects, and the decrease in mean combined masses of merging degenerate dwarfs.
Could Edge-Lit Type Ia Supernovae be Standard Candles  [PDF]
Eniko Regos,Christopher A. Tout,Dayal Wickramasinghe,Jarrod R. Hurley,Onno R. Pols
Physics , 2001,
Abstract: The progenitors of Type Ia supernovae (SNe Ia) have not been identified. Though they are no longer fashionable we investigate the consequences if a significant number of SNe Ia were edge-lit detonations (ELDs) of carbon/oxygen white dwarfs that have accreted a critical mass of helium. Our best understanding of the Phillips relation between light curve speed and peak luminosity assigns both these phenomena to the amount of $^{56}$Ni produced. In ELDs there are two sites of $^{56}$Ni synthesis. If the peak luminosity is determined primarily by the C/O ratio in the core it is primarily a function of its progenitor's initial mass. If the light curve decay speed is determined by the total mass of iron group elements ejected this is a function of the total mass of the ELD at the time of explosion. In general these two masses are correlated and an empirical relation between peak luminosity and light curve shape can be expected. However when we perform population synthesis for progenitors of different metallicities we find a systematic shift in this relation that would make distant SNe Ia fainter than those nearby. The abundances of alpha-rich isotopes, such as $^{44}$Ca, in the solar system indicate that only about 40 per cent of SNe Ia are edge-lit so any systematic effect that could be present would be correspondingly diluted. If we examine only the small subset of ELDs that accrete from a naked helium star, rather than a He white dwarf, the systematic effect disappears.
Properties and alignment of interstellar dust grains toward Type Ia Supernovae with anomalous polarization curves  [PDF]
Thiem Hoang
Physics , 2015,
Abstract: Recent photometric and polarimetric observations of type Ia supernovae (SNe Ia) show unusually low total-to-selective extinction ratio ($R_{V}<2$) and wavelength of maximum polarization ($\lambda_{max}<0.4\mu m$) for several SNe Ia, which indicates peculiar properties of interstellar (IS) dust in the SN hosted galaxies and/or the presence of circumstellar (CS) dust. In this paper, we use inversion technique to infer best-fit grain size distribution and alignment function of interstellar grains along the lines of sight toward four SNe Ia with anomalous extinction and polarization data (SNe 1986G, 2006X, 2008fp, and 2014J). We find that to reproduce low values of $R_{V}$, a significant enhancement in the mass of small grains of radius $a< 0.1\mu m$ is required. For SN 2014J, a simultaneous fit to observed extinction and polarization data is unsuccessful if the entire data is attributed to IS dust (model 1), but a good fit is obtained when accounting for the contribution of CS dust (model 2). For SN 2008fp, our fitting results for model 1 show that, to reproduce an extreme value of $\lambda_{\max}\sim 0.15\mu m$, very small silicate grains must be aligned as efficiently as big grains. We suggest that tiny grains in the intervening molecular cloud can be aligned efficiently by radiative torques (RATs) from the SNe Ia. The resulting time dependence polarization from this RAT alignment model can be tested by observing at ultraviolet wavelengths. Our results are in favor of the existence of CS dust in SN 2014J, but its presence in SN 2008fp remains uncertain.
Supernovae type Ia: non-standard candles of the Universe  [PDF]
A. I. Bogomazov,A. V. Tutukov
Physics , 2011,
Abstract: We analyze the influence of the evolution of light absorbtion by grey dust in SNe Ia host galaxies and the influence of the evolution of average total mass of coalescing double carbon-oxygen white dwarfs (progenitors of SNe Ia) under the influence of gravitational radiation on the interpretation of Hubble diagrams of SNe Ia. Significant increase in the average energy of SNe Ia due to increase in the total mass of merging dwarfs can be observed at red shift z> 2. The observed dependence of the distance modulus from the red shift in observations of SNe Ia can be explained not only by the assumption about accelerated expansion of the Universe, but also by the evolution of the absorbtion of light by grey dust in various types of host galaxies of SNe Ia, by the effects of observational selection and by the decrease in the average mass of coalescing degenerate dwarfs.
Near-infrared observations of type Ia supernovae: The best known standard candle for cosmology  [PDF]
R. L. Barone-Nugent,C. Lidman,J. S. B. Wyithe,J. Mould,D. A. Howell,I. M. Hook,M. Sullivan,P. E. Nugent,I. Arcavi,S. B. Cenko,J. Cooke,A. Gal-Yam,E. Y. Hsiao,M. M. Kasliwal,K. Maguire,E. Ofek,D. Poznanski,D. Xu
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21412.x
Abstract: We present an analysis of the Hubble diagram for 12 Type Ia supernovae (SNe Ia) observed in the near-infrared J and H bands. We select SNe exclusively from the redshift range 0.03 < z < 0.09 to reduce uncertainties coming from peculiar velocities while remaining in a cosmologically well-understood region. All of the SNe in our sample exhibit no spectral or B-band light-curve peculiarities and lie in the B-band stretch range of 0.8-1.15. Our results suggest that SNe Ia observed in the near-infrared (NIR) are the best known standard candles. We fit previously determined NIR light-curve templates to new high-precision data to derive peak magnitudes and to determine the scatter about the Hubble line. Photometry of the 12 SNe is presented in the natural system. Using a standard cosmology of (H_0, Omega_m, Lambda) = (70,0.27,0.73) we find a median J-band absolute magnitude of M_J = -18.39 with a scatter of 0.116 and a median H-band absolute magnitude of M_H = -18.36 with a scatter of 0.085. The scatter in the H band is the smallest yet measured. We search for correlations between residuals in the J- and H-band Hubble diagrams and SN properties, such as SN colour, B-band stretch and the projected distance from host-galaxy centre. The only significant correlation is between the J-band Hubble residual and the J-H pseudo-colour. We also examine how the scatter changes when fewer points in the near-infrared are used to constrain the light curve. With a single point in the H band taken anywhere from 10 days before to 15 days after B-band maximum light and a prior on the date of H-band maximum set from the date of B-band maximum, we find that we can measure distances to an accuracy of 6%. The precision of SNe Ia in the NIR provides new opportunities for precision measurements of both the expansion history of the universe and peculiar velocities of nearby galaxies.
Evolution of 3-9 Mo Stars for Z=0.001 - 0.03 and Metallicity Effects on Type Ia Supernovae  [PDF]
Hideyuki Umeda,Ken'ichi Nomoto,Hitoshi Yamaoka,Shinya Wanajo
Physics , 1998, DOI: 10.1086/306887
Abstract: Recent observations have revealed that Type Ia supernovae (SNe Ia) are not perfect standard candles but show some variations in their absolute magnitudes, light curve shapes, and spectra. The C/O ratio in the SNe Ia progenitors (C-O white dwarfs) may be related to this variation. In this work, we systematically investigate the effects of stellar mass (M) and metallicity (Z) on the C/O ratio and its distribution in the C-O white dwarfs by calculating stellar evolution from the main-sequence through the end of the second dredge-up for M=3-9 Mo and Z=0.001-0.03. We find that the total carbon mass fraction just before SN Ia explosion varies in the range 0.36 -- 0.5. We also calculate the metallicity dependence of the main-sequence-mass range of the SN Ia progenitor white dwarfs. Our results show that the maximum main-sequence mass to form C-O white dwarfs decreases significantly toward lower metallicity, and the number of SN Ia progenitors may be underestimated if metallicity effectis neglected. We discuss the implications of these results on the variation of SNe Ia, determination of cosmological parameters, luminosity function of white dwarfs, and the galactic chemical evolution.
The Hubble Diagram of the Calan/Tololo Type Ia Supernovae and the value of Ho  [PDF]
Mario Hamuy,M. M. Phillips,Nicholas B. Suntzeff,Robert A. Schommer,José Maza,R. Avilés
Physics , 1996, DOI: 10.1086/118191
Abstract: The Calan/Tololo supernova survey has discovered ~30 Type Ia supernovae out to z~0.1. Using BVI data for these objects and nearby SNe Ia, we have shown that there exists a significant dispersion in the intrinsic luminosities of these objects. We have devised a robust chisquare minimization technique simultaneously fitting the BVI light curves to parametrize the SN event as a function of (tb,m, m15(B)) where tb is the time of B maximum, m is the peak BVI magnitude corrected for luminosity variations, and m15(B) is a single parameter describing the whole light curve morphology. When properly corrected for m15(B), SNe Ia prove to be high precision distance indicators,yielding relative distances with errors 7-10%. The corrected peak magnitudes are used to construct BVI Hubble diagrams (HD), and with Cepheid distances recently measured with the HST to four nearby SNe Ia (37C, 72E, 81B, 90N) we derive a value of the Hubble constant of 63.1+/-3.4 (internal) km/s/Mpc. This value is ~10-15% larger than the value obtained by assuming that SNe Ia are perfect standard candles. As we have shown in Paper V, there is now strong evidence that galaxies with younger stellar population appear to host the slowest-declining, and therefore most luminous SNe Ia. Hence, the use of Pop I objects such as Cepheids to calibrate the zero point of the SNe Ia HD can easily bias the results toward luminous SNe Ia, unless the absolute magnitude-decline relation is taken into account.
Progenitors of Supernovae Type Ia  [PDF]
S. Toonen,G. Nelemans,M. Bours,S. Portegies Zwart,J. Claeys,N. Mennekens,A. Ruiter
Physics , 2013,
Abstract: Despite the significance of Type Ia supernovae (SNeIa) in many fields in astrophysics, SNeIa lack a theoretical explanation. The standard scenarios involve thermonuclear explosions of carbon/oxygen white dwarfs approaching the Chandrasekhar mass; either by accretion from a companion or by a merger of two white dwarfs. We investigate the contribution from both channels to the SNIa rate with the binary population synthesis (BPS) code SeBa in order to constrain binary processes such as the mass retention efficiency of WD accretion and common envelope evolution. We determine the theoretical rates and delay time distribution of SNIa progenitors and in particular study how assumptions affect the predicted rates.
Type Ia Supernovae: Their Origin and Possible Applications in Cosmology  [PDF]
Ken'ichi Nomoto,Koichi Iwamoto,Nobuhiro Kishimoto
Physics , 1997, DOI: 10.1126/science.276.5317.1378
Abstract: Spectroscopic and photometric evidence indicates that Type Ia supernovae (SNe Ia) are the thermonuclear explosions of accreting white dwarfs. However, the progenitor binary systems and hydrodynamical models for SNe Ia are still controversial. The relatively uniform light curves and spectral evolution of SNe Ia have led to their use as a standard candle for determining cosmological parameters, such as the Hubble constant, the density parameter, and the cosmological constant. Recent progress includes the calibration of the absolute maximum brightness of SNe Ia with the Hubble Space Telescope, the reduction of the dispersion in the Hubble diagram through the use of the relation between the light curve shape and the maximum brightness of SNe Ia, and the discovery of many SNe Ia with high red shifts.
The Cosmological Constant Constrained with Union2.1 Supernovae Type Ia Data. Derivation and evaluation of several FRW and Carmeli models presenting underwhelming support for the standard model  [PDF]
Ahmet M. ?zta?,Michael L. Smith
Physics , 2014, DOI: 10.1007/s10773-014-2061-5
Abstract: We derive several, detailed relationships in terms of the Friedmann, Robertson, Walker (FRW) generalization which describe the Universe during both the radiation and matter dominated epochs. We explicitly provide for the influence of radiation, rather than burying this term within the matter term. Several models allow the cosmological constant (CC) to vary with universe expansion in differing manners. We evaluate these and other popular models including the $\Lambda$CDM({standard model}), quintessence as presented by Vishwakarma, Equation of State (EoS) and the Carmeli model with data from the 580 Union2.1 supernovae type Ia collection, using several minimization routines and find models built about the CC, the $\Lambda$CDM models, fare no better than those without.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.