Dust Grain Processing in Keplerian discs around Post-AGB Binaries


First Author:
Clio Gielen
Email: clio.gielen AT ster.kuleuven.be
Instituut voor Sterrenkunde, KULeuven, Belgium
Celestijnenlaan 200D
Leuven, 3001, Belgium
Coauthors:
Van Winckel, Hans, Instituut voor Sterrenkunde, KULeuven, Belgium
Waters, Rens, Instituut voor Sterrenkunde, KULeuven, Belgium
Min, Michiel, Sterrenkundig Instituut Anton Pannenkoek, Universiteit Amsterdam, The Netherlands
Dominik, Carsten, Sterrenkundig Instituut Anton Pannenkoek, Universiteit Amsterdam, The Netherlands
Deroo, Pieter, JPL, Los Angeles, USA
Matsuura, Mikako, Astrophysics Group, University College London, United Kingdom
Lloyd Evans, Tom, SUPA, School of Physics and Astronomy, University of St Andrews, United Kingdom

Abstract

Studies of circumstellar discs generally focus on proto-planetary discs around young stellar objects. In this contribution, however, we present our ongoing study of stable Keplerian discs around evolved objects. By combining a wide range in observational data and techniques, (optical photometry, interferometry, radial velocity monitoring and optical and infrared spectroscopy), we show that stable compact dusty discs are indeed commonly found, but likely only around post-AGB binaries. In this contribution we focus on our detailed mineralogy study, based on high quality Spitzer-IRS and TIMMI2 spectra. In all sampled stars, the dust is oxygen rich, with avariable, but very high degree of crystallinity. Features of the Mg-rich end members of olivine and pyroxene, namely forsterite and enstatite, dominate the dust spectra. Both cool and hot crystalline dust grains must be present to produce the observed dust emission features. Our 2D SED-modelling shows that the presence of acomponent of large grains is needed to account for the 850 micron flux. This grain growth, together with the high crystallinity, is evidence for efficient dust processing in these circumbinary discs. We end with a more detailed comparison between the dust processing around young stellar objects and around evolved binaries. Our study appears to indicate that the chemico-physical processes in the discs of evolved binaries are very similar to those governing in proto-planetary discs around young stellar objects.
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