Philipp Podsiadlowski

Abstract:

The discovery of an excess of light in the far-ultraviolet (UV) in 1969 in elliptical galaxies was a major surprise. While it is now clear that this UV excess (UV-upturn) is probably caused by an old population of helium-burning stars. Han et al (2002, 2003) proposed a binary model for the formation of hot subdwarfs (helium burning stars) and the model can reproduce the observations in our Galaxy. By applying the binary model to the study of evolutionary population synthesis, we have obtained an {\it a priori} model for the UV-upturn of elliptical galaxies. The model shows that the UV-upturn is most likely resulted from binary interactions and it is universal (not very much metallicity-dependant) in ellipticals. This has major implications for understanding the evolution of the UV-upturn and elliptical galaxies in general; contrary to previous postulates, it implies that the UV-upturn is not a sign of age, but could be a potentially powerful indicator for a recent minor burst of star-forming activity.

Abstract:

Supernova 1987A, the first naked-eye supernova observed since Kepler's supernova in 1604, defies a number of theoretical expectations. Its anomalies have long been attributed to a merger between two massive stars that occurred some 20,000 years before the explosion, but so far there has been no conclusive proof that this merger took place. Here, we present three-dimensional hydrodynamical simulations of the mass ejection associated with such a merger and the subsequent evolution of the ejecta, and we show that this accurately reproduces the properties of the triple-ring nebula surrounding the supernova.

Abstract:

Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these, we find that single-star models cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs.