Query : 2015A&A...578A.124N

2015A&A...578A.124N - Astronomy and Astrophysics, volume 578A, 124-124 (2015/6-1)

C2H observations toward the Orion Bar.


Abstract (from CDS):

The ethynyl radical (C2H) is one of the first radicals to be detected in the interstellar medium. Its higher rotational transitions have recently become available with the Herschel Space Observatory. We aim to constrain the physical parameters of the C2H emitting gas toward the Orion Bar. We analyze the C2H line intensities measured toward the Orion Bar CO+ Peak and Herschel/HIFI maps of C2H, CH, and HCO+ and a NANTEN map of [CI]. We interpret the observed C2H emission using the combination of Herschel/HIFI and NANTEN data with radiative transfer and PDR models. Five rotational transitions of C2H (from N=6-5 up to N=10-9) have been detected in the HIFI frequency range toward the CO+ peak of the Orion Bar. Based on the five detected C2H transitions, a single component rotational diagram analysis gives a rotation temperature of ∼64K and a beam-averaged C2H column density of 4x1013cm–2. The rotational diagram is also consistent with a two-component fit, resulting in rotation temperatures of 43±0.2K and 123±21K and in beam-averaged column densities of ∼8.3x1013cm–2 and ∼2.3x1013cm–2 for the three lower-N and for the three higher-N transitions, respectively. The measured five rotational transitions cannot be explained by any single parameter model. According to a non-LTE model, most of the C2H column density produces the lower-N C2H transitions and traces a warm (Tkin∼100-150K) and dense (n(H2)∼105-106cm–3) gas. A small fraction of the C2H column density is required to reproduce the intensity of the highest-N transitions (N=9-8 and N=10-9) originating in a high-density (n(H2)∼5x106cm–3) hot (Tkin∼400K) gas. The total beam-averaged C2H column density in the model is 1014cm–2. A comparison of the spatial distribution of C2H to those of CH, HCO+, and [CI] shows the best correlation with CH. Both the non-LTE radiative transfer model and a simple PDR model representing the Orion Bar with a plane-parallel slab of gas and dust suggest that C2H cannot be described by a single pressure component, unlike the reactive ion CH+, which was previously analyzed toward the Orion Bar CO+ peak. The physical parameters traced by the higher rotational transitions (N=6-5, ..., 10-9) of C2H may be consistent with the edges of dense clumps exposed to UV radiation near the ionization front of the Orion Bar.

Abstract Copyright:

Journal keyword(s): stars: formation - ISM: molecules

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NAME OMC1 Ridge reg 05 35 13.4 -05 23 07           ~ 127 0
2 NAME Ori Trapezium OpC 05 35 16.5 -05 23 14           ~ 1598 1
3 NAME Orion Bright Bar reg 05 35 22.30 -05 24 33.0           ~ 841 0
4 NAME Orion Molecular Cloud MoC 05 56 -01.8           ~ 1065 1
5 NAME Mon R2 HII 06 07 47.58 -06 22 42.6           ~ 727 2
6 [MBS2007c] CygX-N44 Rad 20 39 01.01 +42 22 50.2           ~ 396 0
7 NGC 7023 RNe 21 01 36.9 +68 09 48           ~ 693 0
8 NGC 7027 PN 21 07 01.571952 +42 14 10.47120   10.358 8.831 10.157   ~ 2437 1

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