New approaches to SNe Ia progenitors

Although Type Ia supernovae (SNe Ia) are a major tool in cosmology and play a key role in the chemical evolution of galaxies, the nature of their progenitor systems (apart from the fact that they must contain at least one white dwarf, that explodes) remains largely unknown. In the last decade, considerable efforts have been made, both observationally and theoretically, to solve this problem. Observations have, however, revealed a previously unsuspected variety of events, ranging from very underluminous outbursts to clearly overluminous ones, and spanning a range well outside the peak luminosity--decline rate of the light curve relationship, used to make calibrated candles of the SNe Ia. On the theoretical side, new explosion scenarios, such as violent mergings of pairs of white dwarfs, have been explored. We review those recent developments, emphasizing the new observational findings, but also trying to tie them to the different scenarios and explosion mechanisms proposed thus far.Comment: 63 pages, 9 figures, final version to appear as an invited review in New Astronomy Review

¿Es el Universo procesual? ¿Es su realidad estructural? Consideraciones metafísicas

Presentamos una discusión sobre las filosofías del devenir, del proceso y su ontología y reflexionamos sobre el lugar que una filosofía del cosmos tendría en ellas. ¿Es el Universo una estructura, un proceso? Si es proceso, ¿es determinista, como se sostiene desde el punto de vista de la teoría del universo bloque? Hacemos un repaso de ciertas corrientes incluyendo la del último Zubiri, y su dinamismo estructural bien informado desde la cosmología  de su tiempo. Traemos a colación esta vertiente estructuralista en el debate filosófico del siglo XXI

The Hubble constant from 56^{56}Co-powered Nebular Candles

Type Ia supernovae (SNe Ia), produced by the thermonuclear explosion of white dwarf (WD) stars, are used here to derive extragalactic distances and an estimate of the Hubble constant from their emission signatures at late phases ({\it Nebular SNe Ia Method}, NSM). The method, first developed in Ruiz--Lapuente \& Lucy (1992), makes use here of an improved modeling of the forbidden line emission at late phases. Hydrodynamic models of the explosion of WDs of different masses, both sub--Chandrasekhar and Chandrasekhar, provide the basis for comparison with the observations. It is shown that it is possible to probe the overall density structure of the ejecta and the mass of the exploding WD by the effect that the electron density profile has in shaping the forbidden line emission of the iron ions, and that a robust diagnostic of the mass of the exploding WD can be obtained. Cosmic distance scale can thus be related to basic diagnostics of excitation of iron lines. Once the most adequate model is selected, comparison of the predicted line emission at these phases with the observed spectra gives an internal estimate of both the reddening and the distance to the SNe Ia. The results presented here favor denser models than those corresponding to sub--Chandrasekhar explosions. From a sample of seven SNe Ia in Leo, Virgo, Fornax and beyond, a value of the Hubble constant $H_{0} = 68 \ \pm 6\ (stat) \pm 7\ (syst)\ km\ s^{-1}\ Mpc^{-1}$ is derived. The depth of the Virgo cluster is found to be large, ranging from 13 to 23 Mpc at least. If NGC 4526 traces well the core of the Virgo Cluster, then the latter is located at $16\pm 2 \ Mpc$. The galaxy NGC 3267 in Leo appears to be located at 9.8 $\pm$ 1.5 Mpc.Comment: 17 pages, including 2 figures. uuencoded, gzipped ps file. Submitted to the ApJ (Letters

A multianalytical approach to identifying the white marbles used in Roman imperial sculptures from Tarraco (Hispania)

A selection of the most outstanding white marble sculptures from Tarraco has been archaeometrically studied to know more about the marble sources and their respective artistic workshops. All are imperial portraits of the 2nd century AD (Trajan, Hadrian, Lucius Verus and Marcus Aurelius) and a thoracata bust assigned to Hadrian, found on display at the National Archaeological Museum of Tarragona (MNAT). The well-established multimethod approach, combining petrography, cathodoluminescence, C and O isotopes and Sr and Mn trace element composition, has revealed the use of different very fine- to fine-grained marbles of the highest quality exploited in classical times. In contrast to what was thought until now, in which all the pieces had been assigned to Luni-Carrara, this present study identifies the use of two varieties of the recently discovered site of Göktepe near Aphrodisias and Paros-lychnites marbles, being Carrara, in minority. This study confirms the importance of strontium concentration and the contribution of cathodoluminescence to distinguish Göktepe from Carrara marble, while carbon and oxygen isotopes were crucial for the identification of Cycladic marble. Finally, in line with recent published interdisciplinary studies, the marble provenance forces us to rethink the discourse on the use of marble, its sculptural workshops and its distribution in this temporal context

Cosmic expansion history from SNe Ia data via information field theory -- the charm code

We present charm (cosmic history agnostic reconstruction method), a novel inference algorithm that reconstructs the cosmic expansion history as encoded in the Hubble parameter $H(z)$ from SNe Ia data. The novelty of the approach lies in the usage of information field theory, a statistical field theory that is very well suited for the construction of optimal signal recovery algorithms. The charm algorithm infers non-parametrically $s(a)=\ln(\rho(a)/\rho_{\mathrm{crit}0})$, the density evolution which determines $H(z)$, without assuming an analytical form of $\rho(a)$ but only its smoothness with the scale factor $a=(1+z)^{-1}$. The inference problem of recovering the signal $s(a)$ from the data is formulated in a fully Bayesian way. In detail, we have rewritten the signal as the sum of a background cosmology and a perturbation. This allows us to determine the maximum a posteriory estimate of the signal by an iterative Wiener filter method. Applying charm to the Union2.1 supernova compilation, we have recovered a cosmic expansion history that is fully compatible with the standard $\Lambda$CDM cosmological expansion history with parameter values consistent with the results of the Planck mission

Mithras in Tróia (Portugal): an art historical and archaeometric analysis of the roman marble bas-relief with the Banquet of the Gods Mithras and Helios

In the early 1930s, archaeologist Marques da Costa reported the finding of a fragmentary marble bas-relief depicting the banquet of the gods Mithras and Helios in Tróia, where a Roman industrial settlement producing fish-salting goods evolved since the 1st century CE. Tróia is located on a sandy peninsula on the left bank of the river Sado on the southwestern Atlantic coast of Portugal. Archaeometric analyses were carried out to determine the origin of the marble. A multi-method approach was applied to combine polarisedlight microscopy, cathodoluminescence, X-ray powder diffraction, and stable C and O isotope analysis in order to determine the marble features. After their checking with the available analytical data-base, they perfectly match with the most important regional marble, the Lusitanian Estremoz Anticline (Portugal). The article aims to present the art historical study of the mithraic bas-relief and to contribute to a better understanding of how the identification of the marble can clarify and support questions about the workshop that would have produced the piece

A new database of the quantitative cathodoluminescence of the main quarry marbles used in antiquity

Quantitative cathodoluminescence (CL) has rarely been applied for the archaeometric studies concerning marble provenance, despite its potential. This paper develops the method and provides a new database of the parameters obtained from the main marble quarries used in antiquity. With a total number of 473 marble samples from ten districts of the central and eastern Mediterranean, it is the first database on quantitative CL, with the additional advantage of being the same samples that have already characterized by other conventional techniques and that are available in the literature. Focused on the measurements of the intensity peaks at the UV and visible spectra, registered by a spectrometer coupled to a scanning electron microscope (CL-SEM), the representative values are plotted on different useful diagrams to be applied in the identification of marble provenance studies, as a complementary tool of other analyses

No surviving evolved companions to the progenitor of supernova SN 1006

Type Ia supernovae are thought to occur as a white dwarf made of carbon and oxygen accretes sufficient mass to trigger a thermonuclear explosion$^{1}$. The accretion could occur slowly from an unevolved (main-sequence) or evolved (subgiant or giant) star$^{2,3}$, that being dubbed the single-degenerate channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double- degenerate channel)$^{3,4}$. Obviously, a companion will survive the explosion only in the single-degenerate channel$^{5}$. Both channels might contribute to the production of type Ia supernovae$^{6,7}$ but their relative proportions still remain a fundamental puzzle in astronomy. Previous searches for remnant companions have revealed one possible case for SN 1572$^{8,9}$, though that has been criticized$^{10}$. More recently, observations have restricted surviving companions to be small, main-sequence stars$^{11,12,13}$, ruling out giant companions, though still allowing the single-degenerate channel. Here we report the result of a search for surviving companions to the progenitor of SN 1006$^{14}$. None of the stars within 4' of the apparent site of the explosion is associated with the supernova remnant, so we can firmly exclude all giant and subgiant companions to the progenitor. Combined with the previous results, less than 20 per cent of type Iae occur through the single degenerate channel.Comment: Published as a letter in Nature (2012 September 27