Type Ia Supernova Luminosity Research Articles

Accreting carbon–oxygen white dwarfs at explosive C ignition

The conditions at which an accreting carbon-oxygen white dwarf (CO WD) ignites C explosively have been considered to be possibly responsible for the maximum luminosity of Type Ia supernovae (SNe Ia). However, the exact conditions for this explosion have been in controversy. Employing the latest powerful stellar evolution code, Modules for Experiments in Stellar Astrophysics, and the descriptions of the single-degenerate (SD) model for progenitors of SNe Ia, we studied the evolution of several Pop I CO WDs from the onset of mass accretion to the explosive C ignition, where the temperature increases sharply but the density keeps in constant at the maximum temperature point (T-max) of the accreting CO WD. The accreted material is CO-rich and we include two sets of calculations, i.e. one is for a simple accretion like in Lesaffre et al. (2006) while the other artificially adds an energy generation rate (1 x 10(5) erg g(-1) s(-1)) in the outermost 0.005 M-circle dot material during accretion to mimic the energy delivered inwards from H- and He-burning. Both simulations show that most CO WDs ignite C explosively (at the T-max) in the centre, with very similar properties such as WD masses (similar to 1.387 M-circle dot), central densities (similar to 2.63 x 10(9) g cm(-3)), central temperatures(similar to 10(9) K) and binding energies (similar to 5.23 x 10(50) erg). This means that most SNe Ia are ignited initially in the centre of CO WDs based on the SD model. However, the central density and WD mass have been influenced by the initial C/O ratio at the centre of CO WDs. A few initially very cold massive CO WDs ignite C at off-centre points but still in the deep interior of WDs. In these explosions, the offset distance to the centre, the WD mass and central density at the explosion clearly increase with the cooling age, while the inclusion of an extra energy source resists this increasing in part. The off-centre explosions can only occasionally happen in relatively old galaxies and could partly contribute to the diversity of SNe Ia.

Allan Sandage and the distance scale

AbstractAllan Sandage returned to the distance scale and the calibration of the Hubble constant again and again during his active life, experimenting with different distance indicators. In 1952 his proof of the high luminosity of Cepheids confirmed Baade's revision of the distance scale (H0 ~ 250 km s−1 Mpc−1). During the next 25 years, he lowered the value to 75 and 55. Upon the arrival of the Hubble Space Telescope, he observed Cepheids to calibrate the mean luminosity of nearby Type Ia supernovae (SNe Ia) which, used as standard candles, led to the cosmic value of H0 = 62.3 ± 1.3 ± 5.0 km s−1 Mpc−1. Eventually he turned to the tip of the red giant branch (TRGB) as a very powerful distance indicator. A compilation of 176 TRGB distances yielded a mean, very local value of H0 = 62.9 ± 1.6 km s−1 Mpc−1 and shed light on the streaming velocities in the Local Supercluster. Moreover, TRGB distances are now available for six SNe Ia; if their mean luminosity is applied to distant SNe Ia, one obtains H0 = 64.6 ± 1.6 ± 2.0 km s−1 Mpc−1. The weighted mean of the two independent large-scale calibrations yields H0 = 64.1 km s−1 Mpc−1 within 3.6%.

Conformal and affine Hamiltonian dynamics of general relativity

The Hamiltonian approach to the General Relativity is formulated as a joint nonlinear realization of conformal and affine symmetries by means of the Dirac scalar dilaton and the Maurer-Cartan forms. The dominance of the Casimir vacuum energy of physical fields provides a good description of the type Ia supernova luminosity distance--redshift relation. Introducing the uncertainty principle at the Planck's epoch within our model, we obtain the hierarchy of the Universe energy scales, which is supported by the observational data. We found that the invariance of the Maurer-Cartan forms with respect to the general coordinate transformation yields a single-component strong gravitational waves. The Hamiltonian dynamics of the model describes the effect of an intensive vacuum creation of gravitons and the minimal coupling scalar (Higgs) bosons in the Early Universe.

Model-independent reconstruction of the expansion history of the Universe from Type Ia supernovae

Based on the largest homogeneously reduced set of Type Ia supernova luminosity data currently available -- the Union2 sample -- we reconstruct the expansion history of the Universe in a model-independent approach. Our method tests the geometry of the Universe directly without reverting to any assumptions made on its energy content. This allows us to constrain Dark Energy models and non-standard cosmologies in a straightforward way. The applicability of the presented method is not restricted to testing cosmological models. It can be a valuable tool for pointing out systematic errors hidden in the supernova data and planning future Type Ia supernova cosmology campaigns.

Cancelling out systematic uncertainties

We present a method to minimize, or even cancel out, the nuisance parameters affecting a measurement. Our approach is general and can be applied to any experiment or observation where systematic errors are a concern e.g. are larger than statistical errors. We compare it with the Bayesian technique used to deal with nuisance parameters: marginalization, and show how the method compares and improves by avoiding biases. We illustrate the method with several examples taken from the astrophysics and cosmology world: baryonic acoustic oscillations (BAOs), cosmic clocks, Type Ia supernova (SNIa) luminosity distance, neutrino oscillations and dark matter detection. By applying the method we not only recover some known results but also find some interesting new ones. For BAO experiments we show how to combine radial and angular BAO measurements in order to completely eliminate the dependence on the sound horizon at radiation drag. In the case of exploiting SNIa as standard candles we show how the uncertainty in the luminosity distance by a second parameter modelled as a metallicity dependence can be eliminated or greatly reduced. When using cosmic clocks to measure the expansion rate of the universe, we demonstrate how a particular combination of observables nearly removes the metallicity dependence of the galaxy on determining differential ages, thus removing the age–metallicity degeneracy in stellar populations. We hope that these findings will be useful in future surveys to obtain robust constraints on the dark energy equation of state.

Effects of the explosion asymmetry and viewing angle on the Type Ia supernova colour and luminosity calibration★

Phenomenological relations exist between the peak luminosity and other observables of type Ia supernovae (SNe Ia) that allow one to standardize their peak luminosities. However, several issues are yet to be clarified: SNe Ia show colour variations after the standardization. Also, individual SNe Ia can show residuals in their standardized peak absolute magnitude at the level of ∼0.15 mag. In this paper, we explore how the colour and luminosity residual are related to the wavelength shift of nebular emission lines observed at ≳150 d after the maximum light. A sample of 11 SNe Ia which likely suffer from little host extinction indicates a correlation (3.3σ) between the peak B−V colour and the late-time emission-line shift. Furthermore, a nearly identical relation applies for a larger sample in which only three SNe with B−V≳ 0.2 mag are excluded. Following the interpretation that the late-time emission-line shift is a tracer of the viewing direction from which an off-centre explosion is observed, we suggest that the viewing direction is a dominant factor controlling the SN colour and that a large part of the colour variations is intrinsic, rather than due to the host extinction. We also investigate a relation between the peak luminosity residuals and the wavelength shift in nebular emission lines in a sample of 20 SNe. We thereby found a hint of a correlation (at ∼1.6σ level). The confirmation of this will require a future sample of SNe with more accurate distance estimates. Radiation transfer simulations for a toy explosion model where different viewing angles cause the late-time emission-line shift are presented, predicting a strong correlation between the colour and shift, and a weaker one for the luminosity residual.

Cosmic dynamics in $${F(R,\phi)}$$ gravity

In this paper we consider FRW cosmology in $F(R,\phi)$ gravity. It is shown that in particular cases the bouncing behavior may appears in the model whereas the equation of state (EoS) parameter may crosses the phantom divider. For the dynamical universe, quantitatively we also find parameters in the model which satisfies two independent tests:the model independent Cosmological Redshift Drift (CRD) test and the type Ia supernova luminosity distances.

Using spectral flux ratios to standardize SN Ia luminosities

We present a new method to standardize Type Ia supernova (SN Ia) luminosities to ~<0.13 magnitudes using flux ratios from a single flux-calibrated spectrum per SN. Using Nearby Supernova Factory spectrophotomery of 58 SNe Ia, we performed an unbiased search for flux ratios which correlate with SN Ia luminosity. After developing the method and selecting the best ratios from a training sample, we verified the results on a separate validation sample and with data from the literature. We identified multiple flux ratios whose correlations with luminosity are stronger than those of light curve shape and color, previously identified spectral feature ratios, or equivalent width measurements. In particular, the flux ratio R(642/443) = F(642 nm) / F(443 nm) has a correlation of 0.95 with SN Ia absolute magnitudes. Using this single ratio as a correction factor produces a Hubble diagram with a residual scatter standard deviation of 0.125 +- 0.011 mag, compared with 0.161 +- 0.015 mag when fit with the SALT2 light curve shape and color parameters x1 and c. The ratio R(642/443) is an effective correction factor for both extrinsic dust reddening and instrinsic variations such as those of SN 1991T-like and SN 1999aa-like SNe. When combined with broad-band color measurements, spectral flux ratios can standardize SN Ia magnitudes to ~0.12 mag. These are the first spectral metrics that improve over the standard normalization methods based upon light curve shape and color and they provide among the lowest scatter Hubble diagrams ever published.

Is there a standard measuring rod in the Universe?

Abstract The Caltech-Jodrell Bank very long baseline interferometry (VLBI) Surveys give detailed 5 GHz VLBI images of several hundred milliarcsecond (mas) radio sources, and the full width at half-maximum angular sizes of the corresponding compact cores. Using the latter, I have constructed an angular-diameter/redshift diagram comprising 271 objects, which shows clearly the expected features of such a diagram, without redshift binning. Cosmological parameters are derived which are compatible with existing consensus values, particularly when the VLBI data are combined with recent Baryon Acoustic Oscillations observations; the figures are presented as indications of what might be expected of larger samples of similar data. The importance of beaming and relativistic motion towards the observer is stressed; a model of the latter indicates that the emitting material is close to the observer's line of sight and moving with a velocity which brings it close to the observer's rest frame. With respect to linear size, these objects compare reasonably well in variance with the absolute luminosity of type Ia supernovae; the efficacy of the latter is improved by the brighter-slower and brighter-bluer correlations, and by the inverse-square law.

Gravitational Energy as Dark Energy: Concordance of Cosmological Tests

We provide preliminary quantitative evidence that a new solution to averaging the observed inhomogeneous structure of matter in the universe may lead to an observationally viable cosmology without exotic dark energy. We find parameters which simultaneously satisfy three independent tests: the match to the angular scale of the sound horizon detected in the cosmic microwave background anisotropy spectrum; the effective comoving baryon acoustic oscillation scale detected in galaxy clustering statistics; and Type Ia supernova luminosity distances. Independently of the supernova data, concordance is obtained for a value of the Hubble constant which agrees with the measurement of the Hubble Key team of Sandage and coworkers. Best-fit parameters include a global average Hubble constant -->H0 = 61.7−1.1+1.2 km s−1 Mpc−1, a present epoch void volume fraction of -->fv 0 = 0.76−0.09+0.12, and an age of the universe of -->14.7−0.5+0.7 billion years as measured by observers in galaxies. The mass ratio of nonbaryonic dark matter to baryonic matter is -->3.1−2.4+2.5, computed with a baryon-to-photon ratio that is in concordance with primordial lithium abundances.

The Hubble Constant: A Summary of theHubble Space TelescopeProgram for the Luminosity Calibration of Type Ia Supernovae by Means of Cepheids

This is the final summary paper of our 15 yr program using the Hubble Space Telescope (HST) to determine the Hubble constant from the Cepheid-calibrated luminosity of Type Ia supernovae. Several recent developments have made it necessary to put the summary on H0 on a broader basis than we originally thought (see the four papers cited in the text). The new Cepheid distances of the subset of 10 galaxies, which were hosts of normal SNe Ia, give weighted mean luminosities in B, V, and I at maximum light of -19.49, -19.46, and -19.22, respectively. These calibrate the adopted SNe Ia Hubble diagram from Paper III to give H0 = 62.3 ± 1.3(random) ± 5.0(systematic) in units of km s-1 Mpc-1. This is a global value because it uses the Hubble diagram between redshift limits of 3000 and 20,000 km s-1, beyond the effects of any local random and streaming motions. Local values of H0 between 4.4 and 30 Mpc from Cepheids, SNe Ia, 21 cm line widths, and the tip of the red giant branch (TRGB) all agree within 5% of our global value. This agreement of H0 on all scales from ~4 to 200 Mpc finds its most obvious explanation in the smoothing effect of vacuum energy on the otherwise lumpy gravitational field due to the nonuniform distribution of the local galaxies. The present value of H0 is consistent with physical methods relying on the time delay of gravitational lenses and the Sunyaev-Zeldovich effect, and it is not in contradiction with the CMB data. Our value of H0 is 14% smaller than the value of H0 found by Freedman et al. because our independent Cepheid distances to the six SNe Ia-calibrating galaxies used in that analysis average 0.35 mag larger than those used earlier.

Reflections on reflexions - II. Effects of light echoes on the luminosity and spectra of Type Ia supernovae

In this paper we present and discuss the effects of scattered light echoes (LE) on the luminosity and spectral appearance of Type Ia Supernovae (SNe). After introducing the basic concepts of LE spectral synthesis, by means of LE models and real observations we investigate the deviations from pure SN spectra, light and colour curves, the signatures that witness the presence of a LE and the possible inferences on the extinction law. The effects on the photometric parameters and spectral features are also discussed. In particular, for the case of circumstellar dust, LEs are found to introduce an apparent relation between the post-maximum decline rate and the absolute luminosity which is most likely going to affect the well known Pskowski-Phillips relation.

Determination of the Hubble Constant, the Intrinsic Scatter of Luminosities of Type Ia Supernovae, and Evidence for Nonstandard Dust in Other Galaxies

A sample of 109 type Ia supernovae (SNe Ia) with recession velocity < 30,000 km s^{-1}, is compiled from published SNe Ia light curves to explore the expansion rate of the local Universe. Based on the color parameter delta C_{12} and the decline rate delta m_{15}, we found that the average absorption to reddening ratio for SN Ia host galaxies to be R_{UBVI} = 4.37+/-0.25, 3.33+/-0.11, 2.30+/-0.11, 1.18+/-0.11, which are systematically lower than the standard values in the Milky Way. We investigated the correlations of the intrinsic luminosity with light curve decline rate, color index, and supernova environmental parameters. In particular, we found SNe Ia in E/S0 galaxies to be brighter close to the central region than those in the outer region, which may suggest a possible metallicity effect on SN luminosity. The dependence of SN luminosity on galactic environment disappears after corrections for the extinction and delta C_{12}. The Hubble diagrams constructed using 73 Hubble flow SNe Ia yield a 1-sigma scatter of <0.12 mag in BVI bands and ~0.16 mag in U band. The luminosity difference between normal SNe Ia and peculiar objects (including SN 1991bg-like and 1991T-like events) has now been reduced to within 0.15 mag via delta C_{12} correction. We use the same precepts to correct the nearby SNe Ia with Cepheid distances and found that the fully corrected absolute magnitudes of SNe Ia are: M_{B} = -19.33+/-0.06 mag, M_{V} = -19.27+/-0.05 mag. We deduced a value for the Hubble constant of H_{0} = 72 +/- 6 (total) km s^{-1} Mpc^{-1}.

Chemistry and Star Formation in the Host Galaxies of Type Ia Supernovae

We study the effect of environment on the properties of Type Ia supernovae by analyzing the integrated spectra of 57 local Type Ia supernova host galaxies. We deduce from the spectra the metallicity, current star formation rate, and star formation history of the host and compare these to the supernova decline rates. Additionally, we compare the host properties to the difference between the derived supernova distance and the distance determined from the best-fit Hubble law. From this we investigate possible uncorrected systematic effects inherent in the calibration of Type Ia supernova luminosities using light-curve fitting techniques. Our results indicate a statistically insignificant correlation in the direction of higher metallicity spiral galaxies hosting fainter Type Ia supernovae. However, we present qualitative evidence suggesting that progenitor age is more likely to be the source of variability in supernova peak luminosities than is metallicity. We do not find a correlation between the supernova decline rate and host galaxy absolute B magnitude, nor do we find evidence of a significant relationship between decline rate and current host galaxy star formation rate. A tenuous correlation is observed between the supernova Hubble residuals and host galaxy metallicities. Further host galaxy observations will be needed to refine the significance of this result. Finally, we characterize the environmental property distributions for Type Ia supernova host galaxies through a comparison with two larger, more general galaxy distributions using Kolmogorov-Smirnov tests. The results show the host galaxy metallicity distribution to be similar to the metallicity distributions of the galaxies of the NFGS and SDSS. Significant differences are observed between the SN Ia distributions of absolute B magnitude and star formation histories and the corresponding distributions of galaxies in the NFGS and SDSS. Among these is an abrupt upper limit observed in the distribution of star formation histories of the host galaxy sample, suggesting a Type Ia supernovae characteristic delay time lower limit of approximately 2.0 Gyr. Other distribution discrepancies are investigated and the effects on the supernova properties are discussed.

Spectropolarimetry with Extremely Large Telescopes

Spectropolarimetry has a broad spectrum of applications, for which there are mostly no substitute observing techniques. They range from the measurement of the strength and structure of magnetic fields via the detection of scattered light from sources obscured by high-density matter or lost in the glare of a nearby bright object to the possibility of individual corrections to the intrinsic luminosities of far-away Type Ia supernovae - and many more. First reconnaissance projects have succeeded with 10m-class telescopes. But the application and extension of the insights gained require substantially larger telescopes. An ELT would in particular enable studies of the formation of structure (AGNs, $\gamma$ -ray bursts) in early phases of the universe. At the large distances an ELT will reach, the spatial resolution of point sources, even though only at a very low level, will eventually beat any interferometer. Low cost, the possibility to exploit also not perfectly photometric nights, and the $D^4$ sensitivity of background-limited observations of point sources to telescope diameter are other strong assets.

Bayesian model selection and isocurvature perturbations

Present cosmological data are well explained assuming purely adiabatic perturbations, but an admixture of isocurvature perturbations is also permitted. We use a Bayesian framework to compare the performance of cosmological models including isocurvature modes with the purely adiabatic case; this framework automatically and consistently penalizes models which use more parameters to fit the data. We compute the Bayesian evidence for fits to a data set comprised of WMAP and other microwave anisotropy data, the galaxy power spectrum from 2dFGRS and SDSS, and Type Ia supernovae luminosity distances. We find that Bayesian model selection favors the purely adiabatic models, but so far only at low significance.

Type Ia Supernovae and the Value of the Hubble Constant

The methodology involved in deriving the Hubble Constant via the calibration of the corrected peak luminosities of Type Ia supernovae (SNe) is reviewed. We first present a re-analysis of the Calán-Tololo (C-T) and Center for Astrophysics (CfA) Type Ia SN surveys. Bivariate linear least squares and quadratic boot-strapped fits in peak apparent magnitude and light curve shape are employed to correct this heterogeneous sample of peak apparent magnitudes, resulting in an homogeneous (and excellent) secondary distance indicator: the so-called corrected peak luminosity. We next provide an empirical calibration for this corrected luminosity, using Cepheid-based distances for seven nearby spiral galaxies host to Type Ia SNe. Included in this sample is the spectroscopically peculiar SN 1991T (in NGC 4527), whose corrected peak luminosity is shown to be indistinguishable from that of so-called “normal” SNe. A robust value of the Hubble Constant is derived and shown to be H0=73±2(r)±7(s)km s-1 Mpc-1.

The case against the progenitor's carbon-to-oxygen ratio as a source of peak luminosity variations in type Ia supernovae

One of the major challenges for theoretical modeling of type Ia supernova explosions is to explain the diversity of these events and the empirically established correlation between their peak luminosity and light curve shape. In the framework of the so-called Chandrasekhar mass models, the progenitor's carbon-to-oxygen ratio has been suggested as a principal source of peak luminosity variations due to a variation in the production of radioactive 56Ni during the explosion. We describe a mechanism resulting from an interplay between nucleosynthesis and turbulent flame evolution which counteracts such an effect. Based on three-dimensional simulations we argue that it is nearly balanced and only minor differences in the amount of synthesized 56Ni with varying carbon mass fraction in the progenitor can be expected. Therefore the progenitor's carbon-to-oxygen ratio is unlikely to account for the observed variations in type Ia supernova luminosity. We discuss possible effects on the calibration of cosmological measurements.

Supernova Cosmology and the Fine Structure Constant

We study the dependence of the peak luminosity of Type Ia supernovae on the fine structure constant α. We find that decreasing (increasing) α enhances (reduces) the luminosity. Future experiments like SNAP could determine the variation of α to a precision of 10−2.

On Variations in the Peak Luminosity of Type Ia Supernovae

We explore the idea that the observed variations in the peak luminosities of Type Ia supernovae (SNe Ia) originate in part from a scatter in metallicity of the main-sequence stars that become white dwarfs. Previous numerical studies have not self-consistently explored metallicities greater than solar. One-dimensional Chandrasekhar mass models of SNe Ia produce most of their 56Ni in a burn to nuclear statistical equilibrium between the mass shells 0.2 and 0.8 M?, for which the electron-to-nucleon ratio Ye is constant during the burn. We show analytically that under these conditions, charge and mass conservation constrain the mass of 56Ni produced to depend linearly on the original metallicity of the white dwarf progenitor. Detailed postprocessing of W7-like models confirms this linear dependence. The effect that we have identified is most evident at metallicities larger than solar and is in agreement with previous self-consistent calculations over the metallicity range common to both calculations. The observed scatter in the metallicity (-3 Z?) of the solar neighborhood is enough to induce a 25% variation in the mass of 56Ni ejected by SNe Ia. This is sufficient to vary the peak V-band brightness by |?MV| ? 0.2. This scatter in metallicity is present out to the limiting redshifts of current observations (z 1). Sedimentation of 22Ne can possibly amplify the variation in 56Ni mass to 50%. Further numerical studies can determine if other metallicity-induced effects, such as a change in the mass of the 56Ni-producing region, offset or enhance the variation that we identify.