van Dishoeck, E. F. and Black, J. H. and Boogert, A. C. A. and Boonman, A. M. S. and Ehrenfreund, P. and Gerakines, P. A. and de Graauw, Th. and Helmich, F. P. and Keane, J. V. and Lahuis, F. and Schutte, W. A. and Tielens, A. G. G. M. and Whittet, D. C. B. and Wright, C. M. and van den Ancker, M. E. and Blake, G. A. and Creech-Eakman, M. and Waters, L. B. F. M. and Wesselius, P. R. (1999) ISO Spectroscopy of Young Stellar Objects. In: The Universe as Seen by ISO. ESA SP (427). European Space Agency , Noordwijk, Netherlands, pp. 437-448. ISBN 9789290927082 http://resolver.caltech.edu/CaltechAUTHORS:20121002-160505684
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Observations of gas-phase and solid-state species toward young stellar objects (YSOs) with the spectrometers on board the Infrared Space Observatory are reviewed. The excitation and abundances of the atoms and molecules are sensitive to the changing physical conditions during star-formation. In the cold outer envelopes around YSOs, interstellar ices contain a significant fraction of the heavy element abundances, in particular oxygen. Different ice phases can be distinguished, and evidence is found for heating and segregation of the ices in more evolved objects. The inner warm envelopes around YSOs are probed through absorption and emission of gas-phase molecules, including CO, CO_2, CH_4 and H_2O. An overview of the wealth of observations on gas-phase H_2O in star-forming regions is presented. Gas/solid ratios are determined, which provide information on the importance of gas-grain chemistry and high temperature gas-phase reactions. The line ratios of molecules such as H_2, CO and H_2O are powerful probes to constrain the physical parameters of the gas. Together with atomic and ionic lines such as [0 I] 63 µm, [S I] 25 µm and (Si II] 35 µm, they can also be used to distinguish between photon- and shock-heated gas. Finally, spectroscopic data on circumstellar disks around young stars are mentioned. The results are discussed in the context of the physical and chemical evolution of YSOs.
|Item Type:||Book Section|
|Additional Information:||© 1999 ESA Publications Division.|
|Subject Keywords:||molecules; ices; silicates; embedded YSOs; shocks; PDRs; circumstellar disks|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||02 Oct 2012 23:26|
|Last Modified:||27 Dec 2012 02:48|
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