Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...324.1135w&link_type=abstract
Astronomy and Astrophysics, v.324, p.1135-1144
Astronomy and Astrophysics
Astrophysics
16
Ism: Clouds, Ism: Molecules, Radio Lines: Ism, Ism: Individual: Ngc 2023, S 140 (Sh 2-140)
Scientific paper
We have used the Effelsberg 100-m telescope to observe the C91α radio recombination line towards the photon-dominated regions associated with NGC 2023 and S 140. This has been supplemented with observations of the C^18^O (2-1) and (3-2) lines using the 3-m KOSMA telescope. We have analyzed the C91α observations using 1-dimensional homogeneous models in order to derive estimates of the density and ultraviolet radiation field. Towards both sources, our radio line data suggest densities of 10^5^cm^-3^ although we have evidence for a drop-off to a value of around 10^4^cm^-3^ at offsets of 0.4 pc from the exciting star in NGC 2023. The molecular line data towards NGC 2023 are also consistent with high densities (certainly above 10^4^ and probably of order 10^5^cm^-3^). We discuss the influence of clumping on these models and conclude that densities as high as 10^6^cm^-3^ are possible in both the molecular and carbon line emitting gas.
Natta Antonella
Tielens Alexander G. G. M.
Walmsley Charles Malcolm
Wyrowski Frank
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