Western University Physics adn AstronomyWestern Science

Interstellar Gas and Dust

Supervisor: Dr. Jan Cami & Els Peeters

Project: Characterizing Cosmic Carbonaceous Material

Can extend to MSc?:  Yes

Project Description (Abstract):

Polycyclic Aromatic Hydrocarbon molecules (PAHs) are among the largest and most complex molecules known in space. They pervade the universe, and play a crucial role in many astrophysical and astrochemical processes that shape the environments of young and evolved stars, the interstellar medium and entire galaxies. They may well have played an important role in the evolution of prebiotic material from which biological systems evolved, and they are thus arguably the most important players in the cosmic organic inventory. 

PAHs are widespread in space, and are typically observed through their characteristic infrared emission bands that results from UV-pumped fluorescence. These bands are common to all PAHs, but astronomical observations reveal clear variations in the peak positions, band shapes and relative band strengths of these features that must be related to changes in the underlying PAH population. The precise nature of these changes as well as the processes that drive these changes are not well understood.

The aim of this project is to investigate in detail what drives the variations in the PAH characteristics in the well-known reflection nebula NGC 2023. You will use a technique called "Principal Component Analysis" (PCA) on the various PAH features to reveal how many parameters you need to explain all the observed variations. You will interpret your results in terms of local physical parameters (e.g temperature, density, strength of the radiation field, ...) and relate these to changes in the properties of the PAH population (e.g. changes in size, shape, charge and composition). These results will represent an important contribution towards the development of PAH diagnostic tools as well as to a better understanding of the cosmic carbonaceous inventory.

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Project: How to make buckyballs in Planetary Nebulae?

Can extend to MSc?:  Yes

Project Description (Abstract):

Planetary Nebulae (PNe) are beautiful astronomical objects that signal the death throes of low-mass stars like our Sun. These stars have ejected their outer envelopes in a previous evolutionary phase, and now their hot cores become gradually more exposed. The intense UV radiation from these cores ionizes the ejected gas and makes it glow.

In the last few years, we have detected the unmistakable spectral fingerprints of buckyballs in several PNe. Buckyballs (technically called buckminsterfullerene or C60) are large molecules made of carbon and shaped like a soccer ball; these are now the largest molecules known to exist in space. While the presence of these species in PNe is now well established, we do not understand how they are formed there, since none of the known mechanisms to make buckyballs is viable in the tenuous surroundings of evolved stars. How to form buckyballs in space is a key question that has important implications for our overall understanding of cosmic carbon chemistry.

In this project, you will contribute to figuring out the formation pathways to buckyballs in PNe by analyzing brand new observations of C60-rich PNe obtained with the Very Large Telescope (VLT) in Chile. These observations contain a large number of atomic emission lines whose strengths depend on the temperature, density and the strength of the ambient UV radiation field. You will use state of the art software to measure the properties of these lines and analyze them to map the temperature, density and radiation field in these PNe. In turn, this will reveal the conditions required to make buckyballs, and from this, we can reconstruct the C60 formation pathways.

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