2011A&A...525A.116G -
Astronomy and Astrophysics, volume 525A, 116-116 (2011/1-1)
The tight correlation of CCH and c-C3H2 in diffuse and translucent clouds.
GERIN M., KAZMIERCZAK M., JASTRZEBSKA M., FALGARONE E., HILY-BLANT P., GODARD B. and DE LUCA M.
Abstract (from CDS):
Using the IRAM 30m telescope we observed molecular absorption lines from CCH and c-C
3H
2 produced by diffuse and translucent clouds along the lines of sight towards massive star forming regions. The same sources are surveyed with Herschel/HIFI as part of the PRISMAS guaranteed time program, for molecular absorption lines due to hydrides and carbon clusters. The background sources are massive star-forming regions (G34.3+0.1, G10.62-0.39, W51, W49N) and Sgr A
*. The line profiles of the CCH and c-C
3H
2 are strikingly similar for all lines of sight, showing that the ratio of the opacities of the probed transitions, (J
Ka
,Kc
=2
1,2-1
0,1) for c-C
3H
2 and (J=1-0, F=5/2-3/2) for CCH, is nearly constant along all lines of sight, at τ
CCH∼1.8xτ
c–C3
H2
. As a consequence, the ratio of the column densities of CCH and c-C
3H
2 is nearly constant and similar to the value derived earlier for diffuse clouds detected along lines of sight towards extragalactic continuum sources, N(CCH)=(28±1.4) N(c-C
3H
2) (Lucas & Liszt,
2000A&A...358.1069L). PDR models are able to reproduce the observed CCH column densities for the range of physical conditions appropriate for the absorbing matter (n=100-3000cm
–3; A
V=1-5mag) but can neither fit the observed c-C
3H
2 column densities nor the tight correlation between CCH and c-C
3H
2.
Abstract Copyright:
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Journal keyword(s):
ISM: clouds - ISM: molecules
Simbad objects:
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