The present rate of Supernovae

We present and discuss the most recent determination of the rate of Supernovae in the local Universe. A comparison with other results shows a general agreement on the gross values but still significant differences on the values of the rates of various SN rates in different kinds of galaxies. The rate of SNe, used as a probe of Star Formation, confirms the young progenitor scenario for SNII+Ib/c. The increasing diversity of SNe reflects also in the SN yields which may affect the chemical evolution of the Galaxy but, because of the limited statistics, we cannot estimate the contributions of the new subtypes yet. It is also expected that in a few years observational determinations of the SN rates at various look-back times will be available.Comment: 9 pages, Latex, 1 figure, To appear in the proceedings of the conference "The Chemical Evolution of The Milky Way: Stars versus Clusters", eds. F. Matteucci and F. Giovannelli, Vulcano, Italy, September 20-24 199

Constraints on the Massive Supernova Progenitors

Generally accepted scheme distinguishes two main classes of supernovae (SNe): Ia resulting from the old stellar population (deflagration of a white dwarf in close binary systems), and SNe of type II and Ib/c whose ancestors are young massive stars (died in a core-collapse explosion). Concerning the latter, there are suggestions that the SNe II are connected to early B stars, and SNe Ib/c to isolated O or Wolf-Rayet (W-R) stars. However, little or no effort was made to further separate SNe Ib from Ic. We have used assumed SN rates for different SN types in spiral galaxies in an attempt to perform this task. If isolated progenitor hypothesis is correct, our analysis indicates that SNe Ib result from stars of main-sequence mass $23 \mathcal{M}_{\odot} \lesssim \mathcal{M} \lesssim 30 \mathcal{M}_{\odot}$, while the progenitors of SNe Ic are more massive stars with $\mathcal{M} \gtrsim 30 \mathcal{M}_{\odot}$. Alternatively, if the majority of SNe Ib/c appear in close binary systems (CBs) then they would result from the same progenitor population as most of the SNe II, i.e. early B stars with initial masses of order $\mathcal{M} \sim 10 \mathcal{M}_{\odot}$. Future observations of SNe at high-redshift ($z$) and their rate will provide us with unique information on SN progenitors and star-formation history of galaxies. At higher-$z$ (deeper in the cosmic past) we expect to see the lack of type Ia events, i.e. the dominance of core-collapse SNe. Better understanding of the stripped-envelope SNe (Ib/c), and their potential use as distance indicators at high-$z$, would therefore be of great practical importance.Comment: 11 pages, 2 figures, accepted for publication in IJMP

The Asiago Supernova Catalogue- 10 years after

Ten years after the publication of the previous release, we present a new edition of the Asiago Supernova Catalogue updated to December 31, 1998 and containing data for 1447 supernovae and their parent galaxies\footnote{Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html}. In addition to list the data for a large number of new SNe, we made an effort to search the literature for new information on past SNe as well. We also tried to update and homogenize the data for the parent galaxies. To allow a global view of the Catalogue, a few descriptive figures and a summary table is reported. The present Catalogue is intended as a large and modern database for statistical studies on the supernova phenomenon.Comment: 6 pages. To be published in A&A supplement. Enclosed as postscript files are the full lists in chronological (snean.ps) and R.A. (snear.ps) order (to be published only in electronic form.

Nonequilibrium Kinetics of One-Dimensional Bose Gases

We study cold dilute gases made of bosonic atoms, showing that in the mean-field one-dimensional regime they support stable out-of-equilibrium states. Starting from the 3D Boltzmann-Vlasov equation with contact interaction, we derive an effective 1D Landau-Vlasov equation under the condition of a strong transverse harmonic confinement. We investigate the existence of out-of-equilibrium states, obtaining stability criteria similar to those of classical plasmas.Comment: 16 pages, 6 figures, accepted for publication in Journal of Statistical Mechanics: Theory and Experimen

Revealing local failed supernovae with neutrino telescopes

We study the detectability of neutrino bursts from nearby direct black hole-forming collapses (failed supernovae) at Megaton detectors. Due to their high energetics, these bursts could be identified - by the time coincidence of N >= 2 or N >= 3 events within a ~ 1 s time window - from as far as ~ 4-5 Mpc away. This distance encloses several supernova-rich galaxies, so that failed supernova bursts could be detected at a rate of up to one per decade, comparable to the expected rate of the more common, but less energetic, neutron star-forming collapses. Thus, the detection of a failed supernova within the lifetime of a Mt detector is realistic. It might give the first evidence of direct black hole formation, with important implications on the physics of this phenomenon.Comment: LaTeX, 4 pages, 4 figures; minor changes to the text, results unchange

The 3-D ionization structure and evolution of NGC 7009 (Saturn Nebula)

Tomographic and 3-D analyses for extended, emission-line objects are applied to long-slit ESO NTT + EMMI high-resolution spectra of the intriguing planetary nebula NGC 7009, covered at twelve position angles. We derive the gas expansion law, the diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ionization model and the spatial recovery of the plasma structure and evolution. The Saturn Nebula (distance~1.4 kpc, age~6000 yr, ionized mass~0.18 Mo) consists of several interconnected components, characterized by different morphology, physical conditions, excitation and kinematics. The internal shell, the main shell, the streams and the ansae expand at V(exp)~4.0xR" km/s, the outer shell, the caps and the equatorial pseudo-ring at V(exp)~3.15xR" km/s, and the halo at V(exp)~10 km/s. We compare the radial distribution of the physical conditions and the line fluxes observed in the eight sub-systems with the theoretical profiles coming from the photo-ionization code CLOUDY, inferring that all the spectral characteristics of NGC 7009 are explainable in terms of photo-ionization by the central star, a hot (logT*~4.95) and luminous (log L*/Lo~3.70) 0.60--0.61 Mo post--AGB star in the hydrogen-shell nuclear burning phase. The 3--D shaping of the Saturn Nebula is discussed within an evolutionary scenario dominated by photo-ionization and supported by the fast stellar wind: it begins with the superwind ejection, passes through the neutral, transition phase (lasting ~ 3000 yr), the ionization start (occurred ~2000 yr ago), and the full ionization of the main shell (~1000 yr ago), at last reaching the present days: the whole nebula is optically thin to the UV stellar flux, except the caps and the ansae.Comment: accepted for pub. in A&A, 28 pages, 14 figures, full text with figures available at http://web.pd.astro.it/supern/ps/h4665.ps, movies on the 3D structure available at http://web.pd.astro.it/sabbadin

The Generation and Dissipation of Interstellar Turbulence - Results from Large Scale High Resolution Simulations

We study, by means of adaptive mesh refinement hydro- and magnetohydrodynamical simulations that cover a wide range of scales (from kpc to sub-parsec), the dimension of the most dissipative structures and the injection scale of the turbulent interstellar gas, which we find to be about 75 pc, in agreement with observations. This is however smaller than the average size of superbubbles, but consistent with significant density and pressure changes in the ISM, which leads to the break-up of bubbles locally and hence to injection of turbulence. The scalings of the structure functions are consistent with log-Poisson statistics of supersonic turbulence where energy is dissipated mainly through shocks. Our simulations are different from previous ones by other authors as (i) we do not assume an isothermal gas, but have temperature variations of several orders of magnitude and (ii) we have no artificial forcing of the fluid with some ad hoc Fourier spectrum, but drive turbulence by stellar explosions at the Galactic rate, self-regulated by density and temperature thresholds imposed on the ISM gas.Comment: Five pages and three figures. Accepted for publication in Astrophysical Journal (Letters