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CHEMICAL EVOLUTION OF STAR-FORMING REGIONS

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      Abstract

      Recent advances in the understanding of the chemical processes that occur during all stages of the formation of stars, from the collapse of molecular clouds to the assemblage of icy planetesimals in protoplanetary accretion disks, are reviewed. Observational studies of the circumstellar material within 100–10,000 AU of the young star with (sub)millimeter single-dish telescopes, millimeter interferometers, and ground-based as well as space-borne infrared observatories have only become possible within the past few years. Results are compared with detailed chemical models that emphasize the coupling of gas-phase and grain-surface chemistry. Molecules that are particularly sensitive to different routes of formation and that may be useful in distinguishing between a variety of environments and histories are outlined. In the cold, low-density prestellar cores, radicals and long unsaturated carbon chains are enhanced. During the cold collapse phase, most species freeze out onto the grains in the high-density inner region. Once young stars ignite, their surroundings are heated through radiation and/or shocks, whereupon new chemical characteristics appear. Evaporation of ices drives a “hot core” chemistry rich in organic molecules, whereas shocks propagating through the dense envelope release both refractory and volatile grain material, resulting in prominent SiO, OH, and H2O emission. The role of future instrumentation in further developing these chemical and temporal diagnostics is discussed.

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            Author and article information

            Affiliations
            [1 ]Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands; e-mail:
            [2 ]Division of Geological and Planetary Sciences, California Institute of Technology, Mail Stop 150-21, Pasadena, California 91125; e-mail:
            Journal
            Annual Review of Astronomy and Astrophysics
            Annu. Rev. Astron. Astrophys.
            Annual Reviews
            0066-4146
            1545-4282
            September 1998
            September 1998
            : 36
            : 1
            : 317-368
            10.1146/annurev.astro.36.1.317
            © 1998

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