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A&A Supplement Ser., Vol. 124, August 1997, 205-253

Received February 28; accepted September 30, 1996

Physical and chemical variations within the W 3 star-forming region

II. The 345 GHz spectral line surveygif

F.P. Helmichtex2html_wrap3691 - E.F. van Dishoecktex2html_wrap3693

Send offprint request: E.F. van Dishoeck
Leiden Observatory, P.O.-Box 9513, 2300 RA Leiden, The Netherlands - SRON Laboratory Groningen, P.O.-Box 800, 9700 AV Groningen, The Netherlands


Results are presented of the 345 GHz spectral survey toward three sources in the W 3 Giant Molecular Cloud: W 3 IRS4, W 3 IRS5 and W 3(tex2html_wrap_inline3659). Nearly 90% of the atmospheric window between 334 and 365 GHz has been scanned using the James Clerk Maxwell Telescope (JCMTgif) down to a noise level of tex2html_wrap_inline3661 per resolution element. These observations are complemented by a large amount of data in the 230 GHz atmospheric window. From this data set physical conditions and beam-averaged column densities are derived for more than 14 chemically different species (over 24 different isotopes). The physical parameters derived in Paper I (Helmich et al. 1994) are confirmed by the analysis of the excitation of other species, although there is evidence that the silicon- and sulfur-bearing molecules exist in a somewhat denser and warmer environment. The densities are high, tex2html_wrap_inline3663, in the three sources and the kinetic temperatures for the bulk of the gas range from 55 K for IRS4 to 220 K for W 3(tex2html_wrap_inline3665). The chemical differences between the three sources are very striking: silicon- and sulfur-bearing molecules such as SiO and tex2html_wrap_inline3667 are prominent toward IRS5, whereas organic molecules like tex2html_wrap_inline3669, tex2html_wrap_inline3671 and tex2html_wrap_inline3673 are at least an order of magnitude more abundant toward W 3(tex2html_wrap_inline3675). Vibrationally excited molecules are also detected toward this source. Only simple molecules are found toward IRS4. The data provide constraints on the amount of deuterium fractionation and the ionization fraction in the observed regions as well. These chemical characteristics are discussed in the context of an evolutionary sequence, in which IRS5 is the youngest, W 3(tex2html_wrap_inline3677) somewhat older and IRS4, although still enigmatic, the oldest.

keywords: ISM: molecules -- ISM: clouds -- ISM: individual: W 3 IRS5, W 3 IRS4, W 3(tex2html_wrap_inline3679) -- surveys -- radio lines: ISM

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