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Monash Astro Seminars
3pm, Tuesday 25 August 2009; Maths, Rm. 345
Sarah Maddison
"Resolving structure in the HD100546 disk - signatures of planet building?"
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Several lines of evidence demonstrate the existence of a circumstellar disk around the enigmatic Herbig Be star HD100546. Structure within the disk, such as an inner cavity and spiral pattern, as well as similar mineralogy of the dust grains to those seen in our own solar system, further suggest that the growth to planets may be well underway. To learn more about the processes occurring in this disk we have conducted a multifrequency observing program with the Australia Telescope Compact Array (ATCA). From spatially resolved and temporally stable emission, we find that the flux at 3, 7 and 16 mm is dominated by thermal emission from dust grains up to several tens of centimetre in size. The data suggests that the larger grains are concentrated in the inner region of the disk, suggesting vertical settling and radial migration of the largest grains. At all mm wavelengths the peak emission is centred on or near the HD100546 stellar position, but we do resolve structure, especially at 3 mm where we detect a discrete clump about an arcsecond to the south-west, and a second clump about 2.5 arcsec to the north. The nature of these clumps is unknown, but could feasibly represent the location of massive secondary bodies in the disk. Subarcsecond 3 mm observations also find a depletion of dust at the centre of the disk, consistent with IR observations. The longer wavelength cm emission is dominated by free-free processes, likely a stellar wind which we have resolved to be elongated orthogonal to the disk major axis with a mass loss rate of ~1e-8 Msun/yr. We also present HCO+ J=1-0 line data which demonstrates the presence of dense molecular gas still exists in the disk. The line profile is double-peaked, are is the APEX CO J=3-2 profile. If interpreted as Keplerian rotation, the gas disk is about ~300 AU, much larger than the ~100AU emission from the dusty disk. We suggest that HD100546 is indeed in the process of forming planets, and may be younger than previously thought.
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Please email all enquiries to daniel.price@sci.monash.edu.au or rosemary.mardling@sci.monash.edu.au
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