Physics
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20308a&link_type=abstract
Spitzer Proposal ID #20308
Physics
Scientific paper
We propose to obtain IRS spectra (SH and LH mode), and MIPS SED observations of a sample of carefully selected Herbig Ae/Be stars. The observed spectral energy distribution of Herbig stars can be split up in roughly two groups: group I contains the strong mid-IR (20-100 micron) emitters, while group II sources have much more moderate excesses at these wavelengths. State-of-the-art models of protoplanetary disks indicate that the observational difference between the groups reflects the disk's geometry: group I sources have flared and group II self-shadowed disks. Moreover, we have found evidence that there is a evolutionary connection between both groups suggesting that flared disks evolve into self-shadowed disks as grain growth makes the grains settle to the disk's midplane. Unfortunately, the observational record till now is strongly biased towards the, by definition brighter, group I sources. This hampers our understanding of the evolution of protoplanetary disks around these stars. We therefore propose both IRS and MIPS spectroscopic observations which cover the vital wavelength region which defines the group I/II membership. The MIPS and IRS spectra will provide a powerful tool, not only to study in detail the connection between disk geometry and mineralogy of individual sources, but also to study the disk evolution by confronting our findings with the evolutionary timescales of the central objects. Moreover, disks surrounding binary post-AGB stars show remarkable similarities with those around group II Herbig stars. This resemblance sets stringent restrictions on the chemical and geometrical timescales involved in disk evolution. The unbiased sample of Herbig Ae/Be group I and II sources and the comparison with post-AGB binary disks will provide an excellent laboratory to investigate the phenomena which govern the physical processes in circumstellar disks. The ultimate goal of this proposal is to gain insight in the evolution of the protoplanetarey disks surrounding Herbig Ae/Be stars.
Acke Bram
Boekel Roy van
Bouwman Jeroen
van den Ancker Mario
van Winckel Hans
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