Jeroen BOUWMAN : MPIA Heidelberg
Disc mineralogy as a diagnostic of grain growth
Herbig Ae (HAE) and T~Tauri (TTS) stars represent the final stage of pre-main-sequence evolution of low and intermediate-mass stars (~0.1 to 2 solar masses). As a consequence of the star formation process these stars are typically surrounded by a gas and dust disc and/or envelope. They are most likely the precursors of the young main sequence Vega-like objects. These latter systems are surrounded by circumstellar debris discs, possibly containing planetary bodies. The discs in HAE and TTS systems therefore most likely represent the environment in and from which the formation of planets occur. Infrared Spectroscopy provides an unparalleled tool to study the composition, i.e. the mineralogy of the dust in protoplanetary discs and the processes that play a role in its evolution.
In this review, recent IR spectroscopic observations by Spitzer and ground based observatories will be discussed. Infrared spectroscopy studies have revealed an incredible richness of solid state emission features characteristic for dust species such as amorphous silicates, crystalline silicates, iron oxide and sulfides, ices and Polycyclic Aromatic Hydrocarbon molecules. These emission features show systematic variations which can be correlated with the evolutionary processes of the circumstellar disc. To correctly interpret the rich IR spectroscopic data, comparisons to experimental and theoretical studies elucidating the processes (growth, evaporation, condensation, crystallisation, and large scale mixing) acting on dust in protoplanetary discs, are required. This review will, therefore, extensively discuss the interplay between observations and experiments/theory.
Finally, these recent observations provide a direct link to the fossil record of the TTS phase during the early stages in the evolution of the solar system preserved in solar-system objects like comets, meteorites, and interplanetary dust particles. Indeed, such comparisons are essential to correctly interpret the spectroscopic observations and to determine the evolution of the protoplanetary discs and the onset of planet formation.
Last modified: Sun Jul 9 17:29:39 2006