Nucleosynthesis, the late stages of stellar evolution, chemical and dynamical evolution of late-type galaxies

Among the topics studied by this program, we have selected here a subset including studies of the energetic core-collapse SNe known as ‘Hypernovae’, an investigation of the Star Formation History in Late-Type Galaxies and the effect of both the SN explosions and the Star Formation Rate on the chemical and dynamical evolution of Late-Type Galaxies. In particular: The recent Type Ic SN 2002ap is spectroscopically a member of the group of Type Ic ‘Hypernovae’ including SN 1998bw/GRB980425, SN 1997ef, and SN1997dq. Analysis of the spectra and of the light curve of SN 2002ap suggest that it ejected less mass and exploded with a smaller kinetic energy than the other hypernovae, but yet the kinetic energy was significantly larger (4-10 times) than in normal core-collapse SNe. We discuss the implication of the energetics and progenitor mass of 2002ap in the context of the general properties of core-collapse SNe. The approach adopted to derive the Star Formation History (SFH) of Late-Type Dwarf Galaxies from the observational Color-Magnitude Diagram is described. We present the results of the SFH inferred in different regions of the Blue Compact Dwarf NGC 1705 through the comparison of synthetic Color-Magnitude Diagrams with HST optical and near infrared photometry. We find that NGC 1705 is not a young galaxy, but has started forming stars at least 5 Gyr ago. While the old population is spread throughout the entire galaxy, the young and intermediate stars are mostly located in the central regions. An interesting result is the presence of a strong burst started only 2 Myr ago and still active. The effect of different star formation regimes on the dynamical and chemical evolution of Blue Compact Dwarf galaxies is studied. A 2-D hydrocode, coupled with detailed chemical yields originating from SNeII, SNeIa and from intermediatemass stars, is used. This type of simulation is applied to a model of galaxy resem-