I am no longer teaching at the University of Bonn. However, there is potential to supervise part III projects. Please email me for details!
I am available to supervise projects on a wide variety of subjects, ranging from stellar population studies to detailed stellar evolution. In particular, if you are interested in the following subjects please contact me:
Chemical abundances in single- and binary-stars, particularly at low metallicity
Mass-transfer and orbital evolution in binary stars
Quantiative studies of large numbers of massive stars: comparing models to the new Tarantula VLT FLAMES survey
Explaining spin rates in massive stars
Mixing in stars: rotation, magnetic fields, chemical gradients
Globular clusters and the multiple-population problem
Galactic chemical evolution
Stellar explosion progenitor studies, in particular the progenitors of gamma-ray bursts and type Ib/c supernovae
Masters Project: Blue Stragglers in the Period Gap
Blue Straggler stars are bluer (hotter) and more luminous than they should be for their age. There are two main channels for making these stars: 1) mergers, which might be common in dense stellar environments, e.g. globular clusters; 2) Mass transfer in binary stars. Stars that evolve through this second channel should remain as binary stars during their blue straggler phase of evolution, and indeed many blue stragglers are seen in binaries. We can model the mass transfer by means of computer simulations, e.g. Geller, Hurley and Mathieu (2013, AJ 145,8), but the predicted post-mass transfer period distribution disagrees with that observed. While blue stragglers are observed to have periods in the range 100 to 1000 days, none are predicted in the models. One might say these are just a few stars, but the same discrepancy is seen in e.g. the Barium stars, see Izzard, Dermine and Church 2010. Something is clearly wrong with our mass transfer algorithm! However, the latest results of Abate et al. 2011 - which use hybrid wind-Roche lobe overflow mass transfer - may explain these intermediate period stars. This project will use our binary-star population synthesis code binary_c to test whether Wind-RLOF can solve either the Barium-star intermediate period problem, or the similar problem seen in blue straggler systems.
Masters Project: "Off-grid" AGB stars
Asymptotic giant branch stars make most of the carbon, nitrogen and much of the heavy metal content of the Universe. Stars with masses between 1.5 and 3.0 solar masses make primarily carbon, while those between 3.0 and 8.0 solar masses are hot enough to burn carbon, via the CNO cycle, into nitrogen.
AGB stars are too big to survive in close binary systems. They are so large that they will often overflow material onto a companion star, with which they may merge. If the companion itself is evolved, e.g. it is a white dwarf, then the white dwarf can merge with the AGB star to form a new star with an anomalously large core mass - an "off grid" AGB star. The aim of this project is to determine whether these "off grid" AGB stars exhibit the same nucleosynthesis as normal AGB stars: how much carbon do they dredge up? What range of core and envelope masses lead to dredge up and CNO cycling of the envelope? To do this, a detailed stellar evolutionary code (with the help of Richard Stancliffe) will be used to modify single AGB stars such that they have increased core masses. They will then be evolved to determine surface abundances and ejected yields. The results will be implemented in our binary-star population synthesis code binary_c, which should lead to a publication.