Explosive Activity of the Padova-Asiago Supernova Group

Supernovae (SNe) are instrumental to many topics of modern Astrophysics. They are fundamental probes of stellar evolution theories and allow to link different kinds of explosion mechanisms to stars of different masses. The material ejected during the explosion, at velocities exceeding 10000 km/s, in many cases reach gas previously expelled at lower velocities thus uncovering the latest stages of the evolution of the progenitor, and(or) of the companion star. The SN ejecta are enriched in heavy chemical elements, e.g. oxygen, calcium, nitrogen and iron, which are the result of both thermonuclear burnings during the life of the star and of explosive nucleosynthesis. SNe are, therefore, key actors in the chemical evolution of galaxies. Core-collapse SNe, the endpoints of the evolution of massive stars, leave behind compact remnants, neutron stars or black holes, while thermonuclear explosions yield type Ia SNe which, thanks to their relatively homogeneous behaviour, are successfully used as distance indicators up to cosmological distances. The discovery that our Universe is expanding with a positive acceleration, probably because of an undefined Dark Energy, is mainly based on SNe at high-redshift. Finally, a number of nearby long GRBs have been recently associated to a subclass of core collapse SNe, the high-energy type Ic, thus establishing a link between these two classes of cosmic explosions. The activity of our team develops in this general context with a number of projects, both observational and theoretical, aimed at understanding the physics of the phenomena and unveil the nature of the progenitor systems.

Core Collapse Supernovae (click here for more details)

pastorello fig1

Figure 3:  The transients UGC4904-V1 and SN2006jc (from Pastorello et al 2007)

Core collapse SNe span a huge range in luminosities, explosion energies, ejecta masses. Using detailed observations and modelling we are collecting individual case studies that are used to sort out a coherent general scenario for massive star evolution and explosion. To achieve this aim we have developed a semi-analytic tool (Zampieri et al 2003, MNRAS 338, 711) in order to study the explosion mechanism(s) and the progenitors characteristics (in particular its main sequence mass) from a statistical point of view. The main input parameters are the supernova luminosity, the photospheric expansion velocities, the effective temperature while in output we obtain the explosion energy, the ejected 56Ni mass, and the mass of the ejecta. The application of the code has shown an overall continuity in the physical parameters of type II SNe from the lowest energy explosions (e.g. SN 1997D) to the brightest objects (e.g. SN 1983K), a clear indication of the existence of a single explosion mechanism. Several gaps in the distributions of energies and masses still exist which we are planning to fill by means of dedicated observational programs.
We are also concentrating our efforts on the studies of the most interesting objects in the core collapse zoo. A recent example is SN 2006jc, possibly the first example of the rare explosion of extremely massive stars and the first SN ever for which a pre-SN burst has been recorded (Pastorello et al. 2007, Nature 447, 829). We are also studying the type Ic SNe, contact point between Supernovae and GRBs.
Energetic SNeIc seem also to be the central engines that sustain a few very luminous SN IIn which have been discovered recently. The huge luminosity has been related to the shock of the SN ejecta with dense massive shells of material ejected by the SN progenitor shortly before explosion (Agnoletto et al. 2009, ApJ 691,1348)

Evolution of Supernova rates with z (click here for more details)

SN rates provide unique information on the initial mass function of stars over an extended mass range and are therefore fundamental tools for understanding the formation and chemical evolution of galaxies. The advent of Wide Field Imagers on large telescopes has allowed measurement of SN rates at high redshifts and of the evolution of the star formation history over a large fraction of the age of the Universe. The rate of type II+Ib/c SNe, in particular, measures the death rate of young, massive stars via core-collapse and, because of the short time-scale of the progenitor evolution, directly reflects the on-going star formation rate (SFR) in a given environment. On the contrary, the rate of type Ia SNe, whose precursors span a wide range of lifetimes, reflects the whole star formation history. Most of the available determinations of SN rates at high-z are based on the material of SN searches focused on the search of SNIa for determining the geometry of the Universe. At the end of a pilot program, especially designed to determine the rates of all SN types, we have obtained estimates of both core collapse and SNIa rates. In particular, we have been able to demonstrated that "only" 3 billions years ago the star formation rate was 3 times higher than in the present Universe (Cappellaro et al. 2005 , Botticella et al 2008). On the other hand, the evolution of the rate of SNIa with redshift seems to suggest that after a single episode of star formation SNIa may occur with a wide range of ages, starting from 100 millions up to 10 billions years afterwards. In this field, we have now started two new observational projects namely a deep SN search with LBC at the LBT, which is intended to measure the rate evolution at very high redshift (0.5<z<1.3), and a infrared SN search in Starburst galaxies using HAWK-I at the VLT, which is aimed to verify the link between SFR and SN rate and get a better handle on the extinction bias.

People: I. Agnoletto, S. Benetti, F. Bufano, E. Cappellaro, L. Greggio, P. Mazzali, H. Navasardyan, L. Zampieri

Collaboration: M. Turatto (INAF OA Catania), R. Barbon (Padova Univ.), E. Pian (INAF OA Trieste); M. Della Valle, F. Mannucci (INAF OA Arcetri); O. Straniero, M. Dolci, G. Valentini, E. di Carlo (INAF OA Teramo); M. Limongi, A. Tornambe' (INAF OA Roma); V. Lorenzi (TNG); F. Patat, S. Valenti (ESO); M.T. Botticella, A. Pastorello, S. Smartt (Queen's Univ. Belfast); M. Riello (Cambridge Univ.); Elias-Rosa, W. Hillebrandt, S. Taubenberger (MPA-Garching); P. Milne (Steward Obs. Arizona); K. Nomoto (Tokio Univ. - Japan); D. Branch, E. Baron (Oklahoma Univ.-USA); V. Stanishev (Stocholm Univ. - Sweden); A. Gal-Yam (Caltec - USA); S. Perlmutter (Berkeley Univ. - USA)

 Publications: see text

Link: SN group homepage


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