Astronomy & Astrophysics Program, Mathematical Sciences Institute, ANU Suggested Topics Polarised Radiative Transfer The polarised radiative transfer equations consist of four coupled first order differential equations in the four Stokes parameters which describe the radiation field. In the general case, one is dealing with a set of coupled integro-differential equations, and their solution can only be carried out by numerical methods. In simpler cases, analytical solutions are possible. The student will be required to review the theory behind the polarised transfer equations, and to discuss methods of solution currently used in the literature Some numerical work will be required. Radial Velocity Survey And Non-LTE Line Profile Modelling Using state-of-the-art non-LTE model atmospheres from two different codes, the student will model non-LTE Balmer line cores, and determine rotational velocities in conjunction with stellar parameters of a sample of young white dwarf stars observed on 1999 October 3-11 and November 10-17 with the 74" telescope. The Project involves comparing different numerical schemes and testing those schemes with real data. Model Fitting to Astronomical Data Astronomers are often faced with the problem of constructing models for systems which are not fully constrained by observational data. Multi-parameter model fitting is therefore an important component of the modelling process. In binary star research, time-dependent spectroscopic observations reveal the motions of the gas giving rise to the radiation through Doppler shifts of spectral lines (Doppler Tomography). The data set is then inverted to construct geometrical and physical models for the system. Methods currently widely used for model fitting are the Maximum Entropy Method, and the Genetic Algorithm method. It is proposed that the student reviews these methods and tests them against accretion disc and magnetically confined accretion curtain and funnel models using simulated and real data. Compact Binary Stars About 50 percent of stars in our Galaxy occur in binary systems. The orbits of such systems evolve with time due to a variety of mechanisms involving mass and angular momentum loss. In extreme cases orbital evolution leads to the merger of the two stars, and such mergers may be detected as gamma ray bursts or supernova explosions. The student will be expected to review the theory of binary star evolution, as it presently stands, and to discuss attempts to link this theory to observations of gamma ray bursters. The project will have an analytical/numerical component where the student will be expected to solve the orbit evolution equation under simplifying assumptions. Some Astrophysics background may help, but it is not essential. Pre-Cataclysmic Binaries Echelle spectroscopy (here Hamilton echelle at the Lick Observatory 3m telescope) of short period evolved binaries is the key to understanding the origin of cataclymic variables. Various surveying techniques are used to identify white dwarfs with close late-type star companions and follow-up optical and far ultraviolet (with Hubble Space Telescope) spectroscopy allow detailed dynamical studies of the binaries. The work involves ground based optical observations as well archival research of NASA databases. Ultramassive White Dwarfs and the Origin of Type Ia Supernovae White dwarfs are at the center of some of the most spectacular cataclysms in our Galaxy. Novae involve explosive burning of a massive amount of hydrogen accreted from a companion onto a high-mass white dwarf, and, supernoave involve accretion onto a white dwarf near the chandrasekhar limit leading to its collapse. The general population of white dwarfs shows evidence of high-mass white dwarfs, some near the Chandrasekhar mass limit and some in close double white dwarf binaries. Optical and ultraviolet survey of white dwarfs are most useful in identifying candidates and spectroscopic studies will be conducted with MSSSO telescopes to study binary and stellar properties. The Formation and Detection of Black Holes Over the past five years, there has been a flood of new observational evidence which strongly supports the view that stellar mass black holes are common place in our Galaxy. Likewise, supermassive black holes may also occur in the centres of galaxies. It is proposed that the student presents a review of the theory of black hole formation, and a critical evaluation of the arguments used to deduce their existence in the universe. The project can be mainly mathematical so no detailed knowledge is required of astrophysics. Circulalrly polarised radiation in early proto-planetary systems and the homochirality of biomolecules The discovery of strong 17% circular polarisation in the IR in the Orion OMC-1 star forming region (Bailey et al. 1998, Science 281, 579) has provided a new impetus to the view that the homochirality of natural amino-acids seen in biological systems on Earth may have been triggered by asymmetric photolysis of biogenic amino acids in space through the action of circulalrly polarised radiation. The circular polarisation seen in OMC-1 has been attributed to scattering of linearly polarised light by dust grains that have been aligned by magnetic fields in the molecular cloud complex. There is no direct evidence that the high levels of CP observed in the IR will extend to the UV spectral region which is known to carry circular dichroism bands that may be responsible for the asymmetric photolysis, but this is expected to be the case. The scattering geometry required to make the proposed mechanism work is very special. The proto-planetary system will need to be shielded from the direct glare of the source of the unpolarised primary radiation that is being scattered by the dust cloud assumed to be an early type star. Given the clumpyness of the dusty environment of Orion, this is not implausible. However, the process needs to be modelled to estimate the fraction of proto-planetary systems that may be subjected to such a process. The student will be expected to review this field, and to use an existing code on dust extinction to construct such a model. The project will be supervised in collaboration with Dr Jeremy Bailey of the Anglo-Australian Observatory in Sydney. Honours Program Postgraduate Program Scholarships Back to Astronomy & Astrophysics contact: lilia@maths.anu.edu.au