arXiv subjects
Publications and source records attributed to R. Canal.
Vitamin-V is a 2023-2025 Horizon Europe project that aims to develop a complete RISC-V open-source software stack for cloud services with comparable performance to the cloud-dominant x86 counterpart and a powerful virtual execution environment for software development, validation, verification, and test that considers the relevant RISC-V ISA extensions for cloud deployment.
We have been searching for surviving companions of progenitors of Galactic Type-Ia supernovae, in particular SN 1572 and SN 1006. These companion stars are expected to show peculiarities: (i) to be probably more luminous than the Sun, (ii) to have high radial velocity and proper motion, (iii) to be possibly enriched in metals from the SNIa ejecta, and (iv) to be located at the distance of the SNIa remnant. We have been characterizing possible candidate stars using high-resolution spectroscopic data taken at 10m-Keck and 8.2m-VLT facilities. We have identified a very promising candidate companion (Tycho G) for SN 1572, but we have not found any candidate companion for SN 1006, suggesting that SN event occurred in 1006 could have been the result of the merging of two white dwarfs. Adding these results to the evidence from the other direct searches, the clear minority of cases (20\% or less) seem to disfavour the single-degenerate channel or that preferentially the single-degenerate escenario would involve main-sequence companions less massive than the Sun. Therefore, it appears to be very important to continue investigating these and other Galactic Type-Ia SNe such as the Johannes Kepler SN 1604.
With archival and new Hubble Space Telescope observations we have refined the space-velocity measurements of the stars in the central region of the remnant of Tycho's supernova (SN) 1572, one of the historical Galactic Type Ia supernova remnants (SNRs). We derived a proper motion for Tycho-G of (mu_RA_cos_dec;mu_dec)=(-2.63;-3.98)+/-(0.06;0.04)[formal errors]+/-(0.18;0.10)[expected errors] mas/yr. We also reconstruct the binary orbit that Tycho-G should have followed if it were the surviving companion of SN 1572. We redetermine the Ni abundance of this star and compare it with new abundance data from stars of the Galactic disk, finding that [Ni/Fe] is about 1.7 sigma above the Galactic trend. From the high velocity (v_b = -50+/-14 km/s) of Tycho-G perpendicular to the Galactic plane, its metallicity, and its Ni excess, we find the probability of its being a chance interloper to be P < 0.00037 at most. The projected rotational velocity of the star should be below current observational limits. The projected position of Tycho-G is, within the uncertainties, consistent with the centroid of the X-ray emission of Tycho's SNR; moreover, its brightness is generally consistent with the post-explosion evolution of the luminosity of a SN companion. Among the other 23 stars having V<22 mag and located within 42 arcsec from the X-ray centroid, only 4 are at distances compatible with that of the SNR, and none of them shows any peculiarity. Therefore, if even Tycho-G is not the surviving companion of SN 1572, the absence of other viable candidates does favor the merging of two white dwarfs as the producer of the SN.
Aims. We study the optical spectroscopic properties of Type Ia Supernova (SN Ia) 2004dt, focusing our attention on the early epochs. Methods. Observation triggered soon after the SN 2004dt discovery allowed us to obtain a spectrophotometric coverage from day -10 to almost one year (~353 days) after the B band maximum. Observations carried out on an almost daily basis allowed us a good sampling of the fast spectroscopic evolution of SN 2004dt in the early stages. To obtain this result, low-resolution, long-slit spectroscopy was obtained using a number of facilities. Results. This supernova, which in some absorption lines of its early spectra showed the highest degree of polarization ever measured in any SN Ia, has a complex velocity structure in the outer layers of its ejecta. Unburnt oxygen is present, moving at velocities as high as ~16,700 km/s, with some intermediate-mass elements (Mg, Si, Ca) moving equally fast. Modeling of the spectra based on standard density profiles of the ejecta fails to reproduce the observed features, whereas enhancing the density of outer layers significantly improves the fit. Our analysis indicates the presence of clumps of high-velocity, intermediate-mass elements in the outermost layers, which is also suggested by the spectropolarimetric data.
The final stages of the evolution of electron--degenerate ONe cores, resulting from carbon burning in ``heavy weight'' intermediate--mass stars ($8 M_{\sun}\la M \la 11 M_{\sun}$) and growing in mass, either from carbon burning in a shell or from accretion of matter in a close binary system, are examined in the light of their detailed chemical composition. In particular, we have modelled the evolution taking into account the abundances of the following minor nuclear species, which result from the previous evolutionary history: $^{12}$C, $^{23}$Na, $^{24}$Mg, and $^{25}$Mg. Both $^{23}$Na and $^{25}$Mg give rise to Urca processes, which are found to be unimportant for the final outcome of the evolution. $^{24}$Mg was formerly considered a major component of ONe cores (hence called ONeMg cores), but updated evolutionary calculations in this mass range have severely reduced its abundance. Nevertheless, we have parameterized it and we have found that the minimum amount of $^{24}$Mg required to produce NeO burning at moderate densities is $\sim 23%$, a value exceedingly high in the light of recent evolutionary models. Finally, we have determined that models with relatively small abundances of unburnt carbon ($X(^{12}$C)$\sim 0.015$) could be a channel to explosion at low to moderate density ($\sim 1\times 10^9$ g cm$^{-3}$). This is clearly below the current estimate for the explosion/collapse threshold and would have interesting consequences.
The central regions of the remnants of Galactic SNe Ia have been examined for the presence of companion stars of the exploded supernovae. We present the results of this survey for the historical SN 1572 and SN 1006. The spectra of the stars are modeled to obtain Teff, log g and the metallicity. Radial velocities are obtained with an accuracy of 5--10 km s$^{-1}$. Implications for the nature of the companion star in SNeIa follow.
The nature of the binary systems giving rise to Type Ia supernovae (SNeIa) remains an unsolved problem. In this {\it Letter} we calculate, from the statistics of initial conditions (masses and binary separations), the mass, luminosity, and velocity distributions of the possible binary companions (main-sequence star, subgiant, red giant) following the explosion of the white dwarf which gives rise to the SNeIa. Those companions could be detected from either their proper or their radial motions, by means of high-precision astrometric and radial-velocity measurements in young, nearby supernova remnants. Peculiar velocities typically ranging from 100 to 450 km s$^{-1}$ should be expected, which places proper-motion measurements within reach of HST instruments and makes radial-velocity ones feasible with 2.5-4m class telescopes from the ground. Detections would solve the long-standing problem of which kind of binaries do produce SNeIa and clear up the way to accurate physical modeling of the explosions.
The present cosmic rate of Type Ia supernovae (SNeIa) suggests that about 6% of all stars in binary systems with primaries in the initial mass range $3-9\ M\sun$ end up as SNeIa. If that is confirmed, the unavoidable conclusion is that SNeIa can only be explained by the single degenerate scenario. At most 1% of stars in binary systems in the above range end up as CO + CO WD pairs, with total mass equal to or larger than the Chandrasekhar mass. Given that the number of mergers from pairs of CO + He WDs that reach the Chandrasekhar mass is even lower, the conclusion strongly favors binaries containing just one CO WD as the progenitors of SNeIa, since the SNeIa production efficiency (relative to the instantaneous star formation rate) predicted for double degenerate (DD) pairs lies more than $3σ$ below the observational data, and the DD scenario can be rejected at more than 99% confidence level. Only if the SFR measurements from $z\sim 0.1$ to $z\sim 0.5$ are being underestimated by a factor of 6 while SNeIa rates are not, can we escape the above conclusion. We evaluate the numbers and characteristics of double WD systems with different chemical compositions (CO and He WDs) that should form and compare them with the observations, in order to check our predictions. Our conclusions appear robust after that test.
We present a model for big bang nucleosynthesis which combines baryon inhomogeneities with the effects of the decays of massive particles (masses higher than a few GeV). Those particles, with half-lives longer than the standard nucleosynthesis epoch, give rise to both electromagnetic and hadron cascades which modify the abundances of the light nuclides resulting from the previous, inhomogeneous thermonuclear nucleosynthesis stage. We find a region in the parameter space of this composite model where there is agreement with currently inferred primordial abundances for values of $Ω_{b}h^{2}_{50}$ as high as 0.35 ($Ω_{b}$ being the baryon fraction of the closure density and $h_{50}$ the Hubble constant in units of 50 km/s/Mpc). Possible improvements of the model are pointed out.
We investigate the possibility of accounting for the currently inferred primordial abundances of D, 3He, 4He, and 7Li by big bang nucleosynthesis in the presence of baryon density inhomogeneities plus the effects of late-decaying massive particles (X), and we explore the allowed range of baryonic fraction of the closure density Omega_b in such context. We find that, depending on the parameters of this composite model (characteristic size and density contrast of the inhomogeneities; mass-density, lifetime, and effective baryon number in the decay of the X-particles), values as high as Ω_{b}h_{50}^{2}\simeq 0.25-0.35 could be compatible with the primordial abundances of the light nuclides. We include diffusion of neutrons and protons at all stages, and we consider the contribution of the X particles to the energy density, the entropy production by their decay, the possibility that the X-products could photodissociate the light nuclei produced during the previous stages of nucleosynthesis, and also the possibility that the decay products of the X-particles would include a substantial fraction of hadrons. Specific predictions for the primordial abundance of Be are made.
Determination of the rates at which supernovae of Type Ia (SNe Ia) occur in the early Universe can give signatures of the time spent by the binary progenitor systems to reach explosion and of the geometry of the Universe. Observations made within the Supernova Cosmology Project are already providing the first numbers. Here it is shown that, for any assumed SNe Ia progenitor, SNe Ia counts up to $m_{R}\simeq 23-26$ are useful tests of the SNe Ia progenitor systems and cosmological tracers of a possible non-zero value of the cosmological constant, $Λ$. The SNe Ia counts at high redshifts compare differently with those at lower redshifts depending on the cosmological model. Flat $Ω_Λ$--dominated universes would show a more significant increase of the SNe Ia counts at $z \sim 1$ than a flat, $Ω_{M} = 1$ universe. Here we consider three sorts of universes: a flat universe with $H_{0} = 65 km s^{-1} Mpc^{-1}$, $Ω_{M} = 1.0$, $Ω_Λ = 0.0$; an open universe with $H_{0} = 65 km s^{-1} Mpc^{-1}$, $Ω_{M} = 0.3$, $Ω_Λ = 0.0$; and a flat, $Λ$--dominated universe with $H_{0} = 65 km s^{-1} Mpc^{-1}$, $Ω_{M} = 0.3$, $Ω_Λ = 0.7$). On the other hand, the SNe Ia counts from one class of binary progenitors (double degenerate systems) should not increase steeply in the $z= 0$ to $z= 1$ range, contrary to what should be seen for other binary progenitors. A measurement of the SNe Ia counts up to $z \sim 1$ is within reach of ongoing SNe Ia searches at high redshifts.
The suggestion that roughly half the mass of the galactic halo might be in the form of white dwarfs, together with the limits on the infrared background light and on the initial metallicity of the galactic disk, would set strong constraints on the initial mass function (IMF) of the halo. Particular IMFs have been proposed to cut off both the numbers of low-mass stars contributing to the infrared background and of high-mass stars which contribute to the growth of metallicity when they promptly explode as gravitational-collapse (Type II and Type Ib/c) supernovae. Here we examine the further contribution to metallicity from the Type Ia (thermonuclear) supernovae which would later be produced from the halo white dwarf population. We find that, for most of the evolutionary scenarios for the Type Ia supernova progenitor systems proposed so far, the constraints on the white dwarf mass fraction in the halo from the predicted production of iron would be extremely severe. When the predicted iron excess is not so large, then the exceedingly high Type Ia supernova rate predicted for the present time would also exclude a major contribution of white dwarfs to the halo mass. The white dwarf contribution, in all cases, should be below 5-10%. Besides, for the IMFs considered, the duration of the halo burst should be shorter than 1 Gyr in order to avoid too large a spread in the iron abundances of Population II halo dwarfs, and the predicted halo $[O/Fe]$ ratio would be at odds with observations.
The current status of the problem of whether neutron stars can form, in close binary systems, by accretion-induced collapse (AIC) of white dwarfs is examined. We find that, in principle, both initially cold C+O white dwarfs in the high-mass tail of their mass distribution in binaries and O+Ne+Mg white dwarfs can produce neutron stars. Which fractions of neutron stars in different types of binaries (or descendants from binaries) might originate from this process remains uncertain.
A review of type Ia supernovae (SNe Ia) statistics as expected from the different scenarios and explosion models so far suggested is presented.
The occurrence and properties of Type Ia supernovae (SNe Ia) in single-degenerate binary systems (white dwarf [WD] + nondegenerate companion) is examined for galaxies of different types, and as a function of redshift. The rates and characteristics (peak luminosities, expansion velocities of the ejecta) expected from the explosion of mass-accreting WDs in symbiotic systems and "helium star cataclysmics" are found to be different from those arising in another class of candidate systems: cataclysmic-like (contact) systems (CLS), where a CO WD accretes hydrogen on a thermal time scale from a Roche-lobe filling main-sequence or subgiant companion. We derive the evolution of the SNe Ia rate and properties resulting from the thermonuclear explosion of sub-Chandrasekhar mass WDs in such systems when they detonate a helium layer accumulated from steady burning of hydrogen at the surface. A fraction of CLS are believed to form a subset of the observed luminous supersoft X-ray sources (SSS). Sub-Chandrasekhar explosions from CLS are disfavored in all types of galaxies at redshifts z > 1. On the other hand, CLS where the WD succeeds to grow to the Chandrasekhar mass are more likely found in spiral galaxies, and absent from early-type galaxies. SNe Ia statistics could (if the uncertainties still involved are reduced) help to discriminate among proposed SNe Ia scenarios. The range of variation of the characteristics of SNe Ia in the CLS scenario should be narrower than in symbiotics. The predicted correlation between peak luminosity and expansion velociy of the ejecta in SNe Ia coming from these systems is weak. For CLS, the distinction between the characteristics of SNe Ia respectively arising from sub-Chandrasekhar and from Chandrasekhar-mass explosions should be sharp, since all sub-Chandrasekhar
The dependence of the Type Ia supernova (SN Ia) rate on galaxy type is examined for three currently proposed scenarios: merging of a Chandrasekhar--mass CO white dwarf (WD) with a CO WD companion, explosion of a sub--Chandrasekhar mass CO WD induced by accretion of material from a He star companion, and explosion of a sub--Chandrasekhar CO WD in a symbiotic system. The variation of the SNe Ia rate and explosion characteristics with time is derived, and its correlation with parent population age and galaxy redshift is discussed. Among current scenarios, CO + He star systems should be absent from E galaxies. Explosion of CO WDs in symbiotic systems could account for the SNe Ia rate in these galaxies. The same might be true for the CO + CO WD scenario, depending on the value of the common envelope parameter. A testable prediction of the sub--Chandrasekhar WD model is that the average brightness and kinetic energy of the SN Ia events should increase with redshift for a given Hubble type. Also for this scenario, going along the Hubble sequence from E to Sc galaxies SNe Ia events should be brighter on average and should show larger mean velocities of the ejecta. The observational correlations strongly suggest that the characteristics of the SNe Ia explosion are linked to parent population age. The scenario in which WDs with masses below the Chandrasekhar mass explode appears the most promising one to explain the observed variation of the SN Ia rate with galaxy type together with the luminosity--expansion velocity trend.