Molecular abundances and low-mass star formation. I: Si- and S-bearing species toward IRAS 16293-2422
Results from millimeter and submillimeter spectral line surveys of the protobinary source IRAS 16293-2422 are presented. Here we outline the abundances of silicon- and sulfur-containing species. A combination of rotation diagram and full statistical equilibrium/radiative transfer calculations is used to constrain the physical conditions toward IRAS 16293 and to construct its beam-averaged chemical composition over a 10-20" (1600-3200 AU) scale. The chemical complexity as judged by species such as SiO, OCS, and H_2S, is mtermedtate between that of dark molecular clouds such as Ll34N and hot molecular cloud cores such as Orion KL. From the richness of the spectra compared to other young stellar objects of similar luminosity, it is clear that molecular abundances do not scale simply with mass; rather, the chemistry is a strong function of evolutionary state, i.e., age.
© 1994 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1993 July 21; accepted 1993 December 22. The authors are grateful to John Black for discussions on the excitation of various molecules in this source. G. A. B. would like to acknowledge support from NASA (NAGW -2297), as well as the David and Lucille Packard and Alfred P. Sloan Foundations, while work on astrochemistry in Leiden is supported by a PIONIER grant from the Netherlands Organization for Scientific Research (NWO). L. G. M. would like to acknowledge support from NASA (NAGW-3066).
Published - 1994ApJ___428__680B.pdf