The Open UniversitySkip to content
 

Molecular and atomic fractionation effects in the NGC 1977 molecular cloud

Minchin, Nigel R. and White, Glenn J. (1995). Molecular and atomic fractionation effects in the NGC 1977 molecular cloud. Astronomy & Astrophysics, 302 L25-L28.

Full text available as:
[img]
Preview
PDF (Version of Record) - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader
Download (676Kb)
URL: http://cdsads.u-strasbg.fr/abs/1995A%26A...302L..2...
Google Scholar: Look up in Google Scholar

Abstract

The photon-dominated region (PDR) associated with the NGC 1977 molecular cloud has been observed at high resolution in the 13CO and C18O J=2→1 and the [CI] 3P1-3P0 lines. The N(13CO)/N(C18O) ratio has been plotted against visual extinction (Av) and fits a power law relation. The highest values, as expected, occur for observed positions with the lowest derived extinction, with N(13CO)/N(C18O) exceeding the terrestrial value (5.5) for Av≤60 magnitudes. In the outermost parts of the cloud (Av≤20 magnitudes) the N(13CO)/N(C18O) ratio is largest, up to 20. Comparison with similar observations of the S140 and Orion Bright Bar regions implies that higher incident UV field leads to increased fractionation effects. The N(CI)/N(CO) ratio has been plotted against visual extinction, as derived from N(C18O), for the range Av=20-100 magnitudes and also fits a power law relation. N(CI)/N(CO) increases with decreasing extinction from ~0.03-0.04 for Av ~100 mags. to ≥0.1 for Av ~20 mags., corresponding to positions near the edge of the HII region/molecular cloud interface. Comparison with identical observations of the S140 and Orion Bright Bar regions implies that, unlike N(13CO)/N(C18O), the behaviour of N(CI)/N(CO) is insensitive to incident UV field over this range of extinction.

Item Type: Journal Article
Copyright Holders: 1996 European Southern Observatory
ISSN: 1432-0746
Keywords: early-type stars; interstellar medium; HII regions; jets and outflows
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 32707
Depositing User: Glenn White
Date Deposited: 22 Mar 2012 16:54
Last Modified: 30 Oct 2014 19:51
URI: http://oro.open.ac.uk/id/eprint/32707
Share this page:

Actions (login may be required)

View Item
Report issue / request change

Policies | Disclaimer

© The Open University   + 44 (0)870 333 4340   general-enquiries@open.ac.uk