I finished my PhD in 2004 and then left astronomy, first to work for the Home Office, and then to go travelling, but after almost three years away from astronomical research I decided I missed it, and returned to the fold with a post-doctoral position at UCL, where I was an undergraduate and a postgraduate.

Current research

Currently I work on two topics:

Supernovae

Studies of the very distant universe show that galaxies which are less than a billion years old contain significant amounts of dust. The question is, where did this dust come from? In the beginning, the universe was more or less just hydrogen and helium. Dust is produced by evolved stars - both by low-mass stars like the Sun which produce dust as they evolve into planetary nebulae, and also supernovae - the most massive stars which end their lives in colossal explosions, briefly shining more brightly than entire galaxies.

The dust in the very early universe must have come from supernovae, because low mass stars would not have reached the end of their lives by then - they take a few billion years to start producing a lot of dust. The problem is that the sums don’t seem to add up - recent supernovae in nearby galaxies don’t seem to have produced as much dust as you’d expect, given the amount in the distant galaxies.

So, what is going on? Is there really that much dust in the early universe? Are the supernovae producing a lot of dust that we are not seeing for some reason? I’m working on this problem using optical and infra-red spectra of nearby supernovae. With modern sensitive infra-red telescopes like the Spitzer Space Telescope, we can better understand the infrared emission from cosmic dust, and simultaneous IR and optical observations should shed some light on the supernova dust problem.

Planetary nebulae

The other part of my work concerns a different type of dying star - planetary nebulae are delicate shells of gas ejected by small-ish stars when they reach the end of their lives. Our Sun, in about 5 billion years time, will form a planetary nebula.

There are two ways of determining how much carbon, nitrogen, oxygen and other elements there is in the gases of a planetary nebula. Unfortunately, there is a considerable discrepancy between these two methods: one method gives you abundances at least a factor of two — and up to a factor of 100 or more in extreme cases — higher than the other.

Many theories have been proposed to resolve this discrepancy. Our work at UCL has found strong evidence that the solution lies in the existence of cold, metal-rich clumps within planetary nebulae. The question then to be answered is where did these knots come from? How do they survive within gas ten times as hot and much less dense, without dissipating rapidly? And why can’t we see them, even with very high resolution instruments like the Hubble Space Telescope? I’m working on these problems with particular emphasis on the very few planetary nebulae which do contain visible metal-rich clumps.

Publications

Peer-reviewed

A Planetary Nebula around Nova V458 Vulpeculae Undergoing Flash Ionization
  Wesson R, Barlow, M. J.; Corradi, R. L. M.; Drew, J. E.; Groot, P. J.; Knigge, C.; Steeghs, D.; Gaensicke, B. T.; Napiwotzki, R.; Rodriguez-Gil, P.; Zijlstra, A. A.; Bode, M. F.; Drake, J. J.; Frew, D. J.; Gonzalez-Solares, E. A.; Greimel, R.; Irwin, M. J.; Morales-Rueda, L.; Nelemans, G.; Parker, Q. A.; Sale, S. E.; Sokoloski, J. L.; Somero, A.; Uthas, H.; Walton, N. A.; Warner, B.; Watson, C. A.; Wright, N. J., 2008, ApJL, 688, 21

The hydrogen-deficient knot of the `born again’ planetary nebula Abell 58 (V605 Aql)
  Wesson R., Barlow M.J., Liu X-W., Storey P.J., Ercolano B., De Marco O., 2008, MNRAS, 383, 1639

The abundance discrepancy - recombination line versus forbidden line abundances for a northern sample of galactic planetary nebulae
  Wesson R., Liu, X-W., Barlow M.J., 2005, MNRAS, 362, 424

Observations and 3D photoionisation modelling of the Wolf-Rayet planetary nebula NGC1501
  Ercolano B., Wesson R., Zhang Y., Barlow M.J., de Marco O., Rauch T., Liu, X-W., 2004, MNRAS, 354, 558

Discovery of a WO star in the Crux-Scutum arm
  Drew J.E., Barlow M.J., Unruh Y.C., Parker Q.A., Wesson R., Pierce M.J., Masheder M.R.W., Philipps S., 2004, MNRAS, 351, 206

Electron Temperatures and Densities of Planetary Nebulae determined from the nebular hydrogen recombination spectrum and temperature and density variations
  Zhang Y., Liu X-W., Wesson R., Storey P.J., Danziger I.J., 2004, MNRAS, 351, 935

Physical Conditions in the Planetary Nebula NGC6543
  Wesson R., Liu X-W., 2004, MNRAS, 351, 1026

Physical Conditions in the Planetary Nebula Abell 30
  Wesson R., Liu X-W., Barlow M.J., 2003, MNRAS, 340, 253

Conference proceedings

The Formation of PAHs: A Case Study on Carbon-rich AGB Stars
  Caputo D.P., Speck A.K., Barlow M.J., Wesson R., Volk K., Clayton G.C., 2008, American Astronomical Society, AAS Meeting #212, #6.04 (poster)

A nova inside a planetary nebula
  Wesson R., the IPHAS consortium, 2008, National Astronomy Meeting, Belfast (talk)

The hydrogen-deficient knot of Abell 58
  Wesson R., Barlow M.J., Liu X-W., Storey P.J., Ercolano B., De Marco O., Asymmetric Planetary Nebulae IV, Los Cancajos, La Palma, Spain, 18-22 June 2007 (talk)

Observations and modelling of the hydrogen-deficient knot of Abell 58
  Wesson R., Barlow M.J., Liu X-W., Storey P.J., Ercolano B., De Marco O., Deep spectroscopy and modelling of emission line nebulae, Wo Fo Shan Zhuang, Beijing, P.R. China, 16-18 April 2007 (talk)

Probing Nebular Physical Conditions Using the Hydrogen Recombination Spectrum
   Zhang Y., Liu X-W., Wesson R., Storey P.J., Liu Y., Danziger I.J., 2006, in Planetary Nebulae Beyond the Milky Way, p. 183 (poster)

Physical Conditions and Abundances in NGC 6543
  Wesson R., Liu X-W., 2003, in Planetary Nebulae: Their Evolution and Role in the Universe, IAUS209, p. 379 (poster)

Physical Conditions and Abundances in Abell 30
  Wesson R., Liu X-W., Barlow M.J., 2003, in Planetary Nebulae: Their Evolution and Role in the Universe, IAUS209, p. 381 (poster)

Others

Supernova 2008S in NGC 6946
  Wesson R., Fabbri J.F., Barlow M.J., Meixner M., 2008, Central Bureau Electronic Telegrams, 1381, Edited by Green, D. W. E.