On the Evolution of the Cosmic Supernova Rates

Ongoing searches for supernovae (SNe) at cosmological distances have recently started to provide a link between SN Ia statistics and galaxy evolution. We use recent estimates of the global history of star formation to compute the theoretical Type Ia and Type II SN rates as a function of cosmic time from the present epoch to high redshifts. We show that accurate measurements of the frequency of SN events in the range 0<z<1 will be valuable probes of the nature of Type Ia progenitors and the evolution of the stellar birthrate in the universe. The Next Generation Space Telescope should detect of order 20 Type II SNe per 4'x 4' field per year in the interval 1<z<4.Comment: LaTeX, 19 pages, 3 figures, to be published in the MNRA

On Core Collapse Supernovae in Normal and in Seyfert Galaxies

This paper estimates the relative frequency of different types of core-collapse supernovae, in terms of the ratio f between the number of type Ib--Ic and of type II supernovae. We estimate f independently for all normal and Seyfert galaxies whose radial velocity is <=14000 km/s, and which had at least one supernova event recorded in the Asiago catalogue from January 1986 to August 2000. We find that the ratio f is approx. 0.23+/-0.05 in normal galaxies. This value is consistent with constant star formation rate and with a Salpeter Initial Mass Function and average binary rate approx. 50 %. On the contrary, Seyfert galaxies exceed the ratio f in normal galaxies by a factor approx. 4 at a confidence level >= 2 sigma. A caveat is that the numbers for Seyferts are still small (6 type Ib-Ic and 6 type II supernovae discovered as yet). Assumed real, this excess of type Ib and Ic with respect to type II supernovae, may indicate a burst of star formation of young age (<= 20 Myr), a high incidence of binary systems in the inner regions (r <= 0.4 R25) of Seyfert galaxies, or a top-loaded mass function.Comment: Accepted for Publication in MNRA

A Radial Velocity Survey for LMC Microlensed Sources

We propose a radial velocity survey with the aim to resolve the current dispute on the LMC lensing: in the pro-macho hypothesis the lenses are halo white dwarfs or machos in general; in the pro-star hypothesis both the lenses and the sources are stars in various observed or hypothesized structures of the Magellanic Clouds and the Galaxy. Star-star lensing should prefer sources at the backside or behind the LMC disc because lensing is most efficient if the source is located a few kpc behind a dense screen of stars, here the thin disc of the LMC. This signature of self-lensing can be looked for by a radial velocity survey since kinematics of the stars at the back can be markedly different from that of the majority of stars in the cold, rapidly rotating disc of the LMC. Detailed simulations of effect together with optimal strategies of carrying out the proposed survey are reported here. Assuming that the existing 30 or so alerted stars in the LMC are truely microlensed stars, their kinematics can test the two lensing scenarios; the confidence level varies with the still very uncertain structure of the LMC. Spectroscopy of the existing sample and future events requires about two or three good-seeing nights per year at a 4m-8m class southern telescope, either during the amplification phase or long after.Comment: minor changes of text, ApJ accepte

Unemployment, Cost and Availability of Accommodation and Wage Changes in Ontario

Au cours des dix dernières années, plusieurs travaux aux États-Unis, en Grande-Bretagne et au Canada ont étudié les relations entre les changements dans les salaires et certaines variables explicatives telles le chômage et les variations des prix et bénéfices des sociétés. Le texte introduit deux autres variables explicatives : le co*t et la disponibilité du logement Les changements de salaire seraient négativement reliés au taux de chômage et à la disponibilité du logement et directement reliés au coût du logement.Les données du taux de chômage sont les enregistrements mensuels de chômeurs aux centres de main-d'oeuvre du Canada exprimés en pourcentage de la force ouvrière locale. Le coût et la disponibilité du logement sont groupés en une seule variable en multipliant les coûts du logement par un facteur variant inversement avec la disponibilité du logement. L'étude utilise les données de vingt-huit villes ontariennes et se limite à la période de juillet-décembre 1968, la seule où les données du chômage sont disponibles.Si on exclut la ville de St. Thomas qui connut au cours de la période une variation anormale des salaires à la suite d'une implantation d'une usine d'assemblage d'automobiles, le taux de chômage et la variable coût et disponibilité du logement expliquent avec une régression multiple linéaire, 48% de la variance des augmentations de salaires dans les villes de l'Ontario. Les pentes des deux variables sont significatives à un niveau de 99%. Une régression logarithmique linéaire donne sensiblement les mêmes résultats pour l'ensemble des vingt-huit villes.The purpose of this paper is to determine whether there are consistent and significant relationships between wages changes, unemployment and cost and availability of accommodation in urban areas in Ontario

Turbulent mixing of two immiscible fluids

International audienc

Prospects for multi-messenger extended emission from core-collapse supernovae in the Local Universe

Multi-messenger emissions from SN1987A and GW170817/GRB170817A suggest a Universe rife with multi-messenger transients associated with black holes and neutron stars. For LIGO-Virgo, soon to be joined by KAGRA, these observations promise unprecedented opportunities to probe the central engines of core-collapse supernovae (CC-SNe) and gamma-ray bursts. Compared to neutron stars, central engines powered by black hole-disk or torus systems may be of particular interest to multi-messenger observations by the relatively large energy reservoir $E_J$ of angular momentum, up to 29\% of total mass in the Kerr metric. These central engines are expected from relatively massive stellar progenitors and compact binary coalescence involving a neutron star. We review prospects of multi-messenger emission by catalytic conversion of $E_J$ by a non-axisymmetric disk or torus. Observational support for this radiation process is found in a recent identification of ${\cal E}\simeq (3.5\pm1)\%M_\odot c^2$ in Extended Emission to GW170817 at a significance of 4.2\,$\sigma$ concurrent with GRB170817A. A prospect on similar emissions from nearby CC-SNe justifies the need for all-sky blind searches of long duration bursts by heterogeneous computing.Comment: 96 pages, 20 figure