This paper discusses the initial mass function, the oxygen yield and the helium abundance in irregular and blue compact galaxies.

We review the tracers of star formation in galaxies and show how they demonstrate the presence of bursts of star formation in various astrophysical contexts: large extragalactic HII regions in spiral and irregular galaxies and in blue compact galaxies, nuclei of some galaxies, extended star formation in other galaxies. We show that strong bursts seem to occur mainly in interacting galaxies. A few comments are made about the theory of such phenomena.

I would like to pick out a few items that I found particularly interesting. The choice probably reflects my ignorance, because many of these topics are no doubt more known to most of you. I am fairly sure that some of them are basic and important. We will start with the first session.

Observations by Hartwig, Wolf, Dunér and Bigourdan are used to show that SN 1885a reached MV(max) = −18.8 ± 0.5 on 17 or 18 August 1885. The lightcurve of S And is found to have declined more rapidly after maximum than that of any other well-observed supernova. The existence of S And and the relatively young age of the supernova remnant Sgr A East appear to indicate that the supernova frequencies near the nucleus of M31 and the Galactic centre are respectively ∽102 and ∽103 times higher than expected. It is spectulated that S And may belong to a population of supernovae (“type 0”) that only occur near the nuclei of giant galaxies. Beyond the Local Group such objects might perhaps have been missed because of their fast decline and close proximity to luminous nuclei.

A review of progress made by amateurs in visual searching for supernovae in other galaxies reveals twelve discoveries made so far. A comparison between photographic and visual search methods reveals that each type of method has certain advantages and disadvantages. There are three minor problems and three major problems confronting visual searching. The main problem is the poor availability of good Survey photographs of many galaxies to amateurs and the restricted range of galaxies covered by available charts.

There are a lot of records concerning ancient Guest Stars (AGS) in Chinese historical books. Two catalogues of ancient nova or supernova were compiled (Xi 1955, Xi and Bo 1965, 1966) that listed 90 probable nova or supernova observed between 14 BC and 17 AD. The identify of AD. 1054 Guest star with Crab Nebula proved that the historical records are valuable to astrophysics. Since the discovery of the Crab pulsar in 1967, much attention has been paid to the relation between AGS and supernova remnants (SNR). Eight pairs of identification were suggested by Clark and Stephenson (1977). The number of SNR identified is two few to compare with the expectation from the frequency of supernova. In fact a lot of SNR or AGS have not been identified. It seems necessary, important and possible to look for further identification.

The arm structure of supernova host galaxies has been studied in order to ascertain whether or not spiral density waves have an impact on supernovae frequencies. The ensembles of Type I and Type II supernova hosts were found to contain identical fractions of grand design spirals consistent with the representations in control samples chosen without regard to supernovae production. The results suggest that a density wave does not greatly enhance the massive star formation rate per unit luminosity of a galaxy. Instead, star formation in most galaxies may be dominated by stochastic processes.

This paper reviews some of the basic optical properties of supernovae (SNe), concentrating on the most interesting new observations. It is emphasized that SNe can be securely subdivided into the two well-known classes (Type I and Type II) only on the basis of their spectra, since the light curves alone can be misleading. Brief interpretations of the spectra and light curves are presented. Spectroscopic and photometric characteristics of “peculiar” Type I supernovae (SNe I-pec), which may be physically distinct from “normal” SNe I, are discussed. Finally, the complete optical spectrum of SN 1985f in NGC 4618 is illustrated, and comparisons are made with the spectra of SNe I and SNe II. No resemblance is found, suggesting that this object belongs to a truly new class (Type III) of SNe. There is, however, very recent evidence that the spectra of SNe I-pec obtained more than eight months past maximum brightness are strikingly similar to that of SN 1985f.

Type I supernovae can be modeled as the carbon deflagration of white dwarfs and Type II supernovae as the explosions of massive stars with hydrogen envelopes. The massive stars at the ends of their lives are expected to be red supergiants, which are observed to have slow, dense winds. The interaction of the supernova kinetic energy and radiation with the circumstellar gas gives rise to observational phenomena at a range of wavelengths. Additional phenomena, such as a scattered light echo, are predicted. While the light from a Type II supernova near maximum light is probably from energy deposited in the initial explosion, there is now good evidence that the radioactive decay of 56Co powers the emission at late times. It was been noted that the explosions of massive stars without hydrogen envelopes would be quite unlike normal Type II supernovae. There is now good evidence for such explosions – SN1985f and the class of peculiar Type I supernovae. It is suggested that these supernovae be called Type III with the spectroscopic definition of a) no H lines and b) broad [01] lines at late times. That not all very massive star explosions are of this type is indicated by SN1961v, which was probably a very massive explosion, but in which hydrogen was present.

The ionizing and heating effects of the radiation from the supernova on the circumstellar matter are discussed. In particular, it is shown how observations of UV absorption lines can give information about the ionization structure and radiative acceleration of the gas. In the second part, the physics of the late phases of supernovae is studied with special emphasis on the metal rich interiors of massive corecollapse supernovae. These results are then applied to SN 1985f.

In order to provide accurate fluxes of supernovae Type II as needed for the application of the Baade-Wesselink method we have constructed spherical model photospheres for these objects under the assumption that hydrogen and helium are in statistical equilibrium. Although the densities are very low it is found that NLTE effects on the continuum radiation are small, because the temperature stratification is sufficiently flat and the strong scattering makes the radiation field rather local.

Present stellar evolution codes predict that stars with He-core masses above approximately 2 M⊙, corresponding to main sequence masses of at least 8 M⊙ burn carbon non-violently. After hydrostatic core carbon burning all those stars contain O-Ne-Mg cores but their further evolution is strongly dependent on the stellar entropy and thus on the main sequence and the core mass. If the He-core mass is below 3 M⊙ the O-Ne-Mg core grows due to carbon-burning in a shell and the crucial question is, whether or not it grows beyond the critical mass for Neignition (≅1.37 M⊙). Stars with He-cores less massive than about 2.4 M⊙ will never ignite Ne, but due to electron-captures, mainly on Ne and Mg, their cores will contract until O-burning begins. Since the matter of the O-Ne-Mg core is weakly degenerate O-burning propagates as a (subsonic) deflagration front and incinerates a certain fraction of the core into a nuclear statistical equilibrium (NSE) composition of iron-group elements (Nomoto, 1984). If, on the other hand, the mass of the O-Ne-Mg core is slightly larger than 1.37 M⊙ Ne and O burn in a shell from about 0.6 M⊙ to 1.4 M⊙, but again the outcome is a NSE-composition (Wilson et al., 1985). In both cases the core-mass finally exceeds the Chandrasekhar limit because electron captures on free protons and heavy nuclei lower the electron concentration and consequently also the effective Chandrasekhar mass. The cores, therefore, continue to contract and finally collapse to neutron star densities with iron-core masses between 0.7 and 1.4 M⊙.

We discuss effects of angular momentum on gravitational collapse and the fate of rapidly rotating stellar cores just before the gravitational collapse. It is found that Stellar cores become dynamically unstable against the modes of P0 and/or P2± 2 before the central densities become higher than the neutron drip density(˜ 4.3×1011 g/cm3). this suggests that fission occurs at pre-supernova stage or in the collapsing stage. In order to make clear whether these dynamical instabilities induce supernova explosion or not, three dimensional hydrodynamic computation would be necessary.

The reduction of the ratio between specific angular momentum and mass (a/m) due to gravitational radiation has been investigated for a model of collapsing rotating stellar core in a post-newtonian scheme. Results show that if the initial value of the ratio is significantly greater than one, it tends towards one and if the initial ratio is nearly one, no sharp reduction happens as the core collapses to the neutron star or black hole size.

Effects of the phase transitions of superdense matter on supernova explosions are investigated with the aid of an idealized model of phase transition. It is found that in the case of strong phase transitions explosions become weaker, while in the case of weak phase transitions explosions become stronger, but the increment of the ejectecd energy is less than 20 percent and is not large as suggested by Migdal et al.

A brief review of the observations of X-ray emission from supernova remnants is presented including the results from the Einstein, EXOSAT and TENMA satellites. The status of the interpretation of the spectra and images is highlighted and the need for broad band, spectrally resolved imaging measurements is emphasized.

I review the presently existing four partly independent methods of determining extragalactic distances through supernova investigations and conclude that, although each of these methods has its difficulties, application of all of them on the same class of objects provides the opportunity of obtaining unique redundancy in determinations of extragalactic distances and Hubble’s constant.

The nearby IrrII galaxy M82 (3C 231, NGC3034) is known to have a complex, very elongated radio brightness distribution in the central region of the galaxy (e.g., Kronberg and Wilkinson 1975). Because of the galaxy’s proximity (distance ~ 3.3 Mpc; Tammann and Sandage 1968), the brightness distribution can be investigated in considerable detail. Recently Unger et al. (1984) and Kronberg, Biermann, and Schwab (1985; see also Kronberg 1986) distinguished about 20 compact components in the central region, most of them unresolved with an upper limit on their angular sizes of ~ 150 mas corresponding to an upper limit on their linear sizes of ~ 2 pc. About half of the components were observed at more than one frequency and at several epochs and were found typically to have steep spectra between 5 and 15 GHz and (Kronberg and Sramek 1985) slowly decreasing flux densities.

An entire population of radio supernova and SNR candidates has been discovered and monitored in the region near M82’s nucleus. VLA maps at a resolution of 150 milliarcseconds have thus far detected the order of 100 discrete radio sources in the inner 600 pc nuclear region. None is optically identified due to obscuration, but the brightest sources have radio luminosities and variability behaviour which are comparable to some identified radio SN in other nearby galaxies.