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School of Physical, Environmental and Mathematical Sciences |
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Research Interests:
Current Research Projects
Before planets – the mineralogy and chemistry of pre-planetary disks (Dr Chris Wright & Assoc. Prof. Warrick Lawson)
Planets form within the circumstellar disks around young stars. Samples of the solid material comprising our own primitive disk are found in meteorites and interplanetary dust particles. Using the powerful technique of astronomical mid-infrared spectropolarimetry, supplemented by conventional spectroscopy, we are ascertaining the composition of the material existing within the disks around young stars. Further, we are imaging these disks in mm-wave molecular and dust continuum emission to constrain their chemistry and rotational dynamics, as well as look for evidence of pebble-sized particles. By studying a range of disk ages we can determine how the composition evolves with time, and what physical processes affect it, in order to better understand how our own solar system formed.
Interstellar medium (Dr Robert Smith, Dr Chris Wright, Dr Garry Robinson with Dr Steve Charnley, Dr Steve Rogers, Dr Yvonne Pendleton & Dr Harold Butner)
We are studying the formation, evolution and composition of the dust component of the interstellar medium, in particular the molecular ices found in cold, dense molecular clouds. Techniques employed are (i) observational; collecting infrared spectra of astronomical ices at both ground-based and space borne telescopes, (ii) theoretical; modeling the transmission, absorption and scattering properties of dust grains with different ice coatings and modeling different ways of incorporating the ices into the grains, and (iii) laboratory; infrared Fourier transform spectroscopy of analogs of astronomical ices and ice mixtures allows comparison with astronomical spectra.
Star formation (Dr Robert Smith, Assoc. Prof. Warrick Lawson & Dr Chris Wright)
The earliest stages of star formation, young stellar objects (YSO's) are characterized by a protostellar core, surrounded by an envelope which feeds the core, most likely via an accretion disk. This stage is often accompanied by large scale energetic outflows of matter from the core/disk. The envelope is normally so dense that only infrared or radio observations are able to penetrate it sufficiently to investigate the core. We are currently studying one such YSO, GGD30, by means of optical spectroscopy and imaging, infrared spectroscopy and imaging and radio interferometric and single dish observations.
Recent Achievements
• Detection of only the second instance of crystalline silicate band in polarisation toward an extremely young star (first case published in 1988). This hints that dust processing in the near vicinity of young stars (e.g. pre-planetary disks) may begin earlier than hitherto thought.
• Monitoring of the 18.5 GHz (16 mm) emission from a nearby young star shows a constant flux level, strengthening the assertion that at least some, if not all, of the emission arises from large pebble-sized bodies. Detections of the star at 8 and 4 GHz should allow decomposition of the relative contributions of emission mechanisms. A second, even younger, star has now also been observed with similar characteristics at 18.5 GHz.
• Wright consulted with Gemini-North members on the spectropolarimetric mode of the Michelle mid-infrared instrument. In March 2006 he reduced the first data and wrote a detailed report on the instrument performance, with recommendations for improvement.
• Wright accepted an invitation to participate in and draft the science case for the spectropolarimetric mode of an instrument proposal made to the UK Particle Physics and Astronomy Research Council (PPARC).
• Wright accepted an invitation to lead the science case for a polarimetry capability for a mid-IR instrument (MIDIR) on an Extremely Large Telescope (ELT) to be built by ESO next decade. A first draft of the science case was circulated amongst the international consortium participants in December 2007.
• First ever resolved image at 1.8 cm of the disk around HD100546. We found the disk to be about 50 Astronomical Units (1 AU = the Earth-Sun distance) in diameter, and its detection at such a long wavelength is indicative of cm-sized bodies (“pebbles”) orbiting the star. These could be from the growth of smaller grains or collisional destruction of larger asteroid- or comet-sized bodies.
• First interferometric detection of molecular gas toward HD100546. The solid component (i.e. dust) of the disk is well studied (see above) but detection of a gaseous component has been elusive. Such a detection (or upper limit) is important because as the dust grows to form larger bodies we expect the gas to deplete as it condenses onto the grains or is dissociated by ultra-violet radiation from the star. It had been thought that this process might already be complete in HD100546, but our new observation proves otherwise. The double-peaked nature of the spectral line profile suggests that the gas is in Keplerian rotation around the star at a radius of about 250 AU. This observation (and that described below) demonstrates that a gaseous disk does still co-exist with a highly processed dust disk around this star.
• Our observing program on HD100546 provided two other ‘firsts' in 2007. We believe we made the first detection of a protoplanetary disk at 7 mm using the new receiver at the Australia Telescope Compact Array. This has filled in a ‘missing' data point in the so-called spectral energy distribution of the HD100546 system, and so allowed us to constrain the respective contributions of various emission mechanisms, and arrive at a better estimate of the pebble population. We were also the first Australian-led group to obtain data with the NANTEN2 submillimetre telescope on the Atacama altiplano in Chile , a facility of which UNSW is a consortium member. The data on carbon monoxide in the HD100546 disk will allow detailed study of the physics (e.g. temperature) and chemistry (e.g. abundances) in the HD100546 disk.
(Dr Chris Wright in collaboration with Dr Robert Smith)
• Detection of the 12 micron librational band of water ice toward an embedded young star. This confirms the only published detection of this band 20 years ago from a low signal-to-noise spectrum. Such an observation can only be made from a space telescope. The new data is of a much higher quality, but importantly includes separate spectra of the two components of the binary system. The presence of the band toward this source, but not others, suggests a unique chemistry.
- Dr Warrick Lawson, UNSW@ADFA
- Dr Robert Smith, UNSW@ADFA
- Dr Sarah Maddison, Swinburne University
- Prof. Michael Burton, UNSW
- Prof. Ewine van Dishoeck, Leiden University, The Netherlands
- Dr Dave Lommen, Leiden University, The Netherlands
- Dr Alistair Glasse, United Kingdom Astrophysical Technology Centre, Edinburgh
- Dr Ralf Siebenmorgen, European Southern Observatory, Germany
- Dr Michael Sterzik, European Southern Observatory, Chile
- Dr Bringfried Stecklum, Thuringer Landessternwarte, Tautenburg, Germany
- Dr David Wilner, Harvard Smithsonian Center for Astrophysics, USA
- Dr Tyler Bourke, Harvard Smithsonian Center for Astrophysics, USA
Recent Publications
Journal - refereed
Lommen, D., Wright, C.M., Maddison, S., Jorgensen, J., Bourke, T.L., Van Dishoeck, E.F., Hughes, A.O., Wilner, D.J., Burton, M.M. & van Langevelde, H., 2007, Investigating grain growth in disks around southern T Tauri stars at millimetre wavelengths, Astronomy & Astrophysics, 462(1), 211-220.
Smith, R.G. , Lawson, W.A. & Wright, C.M., 2007, A Herbig-Haro object associated with GGD30 and its exciting source, Monthly Notices of the Royal Astronomical Society, 375(1), 257-260.
Wright, C.M. , 2007, Mid-infrared polarisation and inferred magnetic field direction toward YSOs with outflow, Astrophysics & Space Science, 311(1-3), 47-55.
Maercker, M., Burton , M.G. & Wright, C.M., 2006, L-band (3.5 mu m) IR-excess in massive star formation - II. RCW 57/NGC 3576, Astronomy & Astrophysics, 450(1), 253-263.
Journal - non-refereed
Maddison, S., Lommen, D., Wright, C., Bourke, T., Burton, M., Hughes, A., Jorgensen, J., van Dishoeck, E., Wilner, D., & van Langevelde, H., 2006, Investigating grain growth in southern protoplanetary disks, ATNF News, Issue 59, June 2006.
Conference - refereed
Wright, C., Siebenniorgen, R., Stecklurn, B., Sterzik, B., Kaeufl, H., 2008, A mid-infrared polarization capability for the ELT - art. no. 701429, Ground-based and Airborne Instrumentation for Astronomy II, Proceedings of SPIE Vol. 7014, 1429 (13pp).
Conference - non-refereed
Maddison, S., Lommen D., Wright, C., Bourke, T., Jorgensen, J., van Dishoeck, E., Burton, M., Hughes, A. & Wilner, D., 2007, Observing grain growth in protoplanetary disks, poster at January 2007 209th AAS meeting, Bulletin of the American Astronomical Society, 38, p. 912, http://cdsads.u-strasbg.fr/abs/2006AAS...209.1010M
Wright, C.M., 2007, Spatially resolved mid-infrared spectroscopy of debris disks and embedded YSOs, Gemini Science Meeting, Foz do Iguacu Brazil, 11-13 June 2007, http://www.lna.br/~gsm2007/wright.html
Grants
C. M. Wright (CI, ARF, UNSW@ADFA), PI's Prof Ewine van Dishoeck (Leiden), Dr Alistair Glasse (UKATC), Dr RalfSiebenmorgen (ESO), DP0345227 - Before Planets: The mineralogy and chemistry of pre-planetary disks, ARC 2003-2007: $48,6605.
Service
• Completed 3 year tenure on the Australia Telescope Users Committee in June 2006.
• Co-Chair of the Scientific Organising Committee and member of the Local Organising Committee for the 2006 Annual Scientific Meeting of the Astronomical Society of Australia held in July 2006 at UNSW@ADFA.
• Judge for the best Poster prize at 2006 ASA.