2010A&A...521L..23F


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.05CEST05:29:18

2010A&A...521L..23F - Astronomy and Astrophysics, volume 521, L23-23 (2010/10-1)

Herschel observations in the ultracompact HII region Mon R2. Water in dense photon-dominated regions (PDRs).

FUENTE A., BERNE O., CERNICHARO J., RIZZO J.R., GONZALEZ-GARCIA M., GOICOECHEA J.R., PILLERI P., OSSENKOPF V., GERIN M., GUESTEN R., AKYILMAZ M., BENZ A.O., BOULANGER F., BRUDERER S., DEDES C., FRANCE K., GARCIA-BURILLO S., HARRIS A., JOBLIN C., KLEIN T., KRAMER C., LE PETIT F., LORD S.D., MARTIN P.G., MARTIN-PINTADO J., MOOKERJEA B., NEUFELD D.A., OKADA Y., PETY J., PHILLIPS T.G., ROELLIG M., SIMON R., STUTZKI J., VAN DER TAK F., TEYSSIER D., USERO A., YORKE H., SCHUSTER K., MELCHIOR M., LORENZANI A., SZCZERBA R., FICH M., McCOEY C., PEARSON J. and DIELEMAN P.

Abstract (from CDS):

Monoceros R2, at a distance of 830pc, is the only ultracompact HII region (UC HII) where the photon-dominated region (PDR) between the ionized gas and the molecular cloud can be resolved with Herschel. Therefore, it is an excellent laboratory to study the chemistry in extreme PDRs (G0>105 in units of Habing field, n >106cm–3). Our ultimate goal is to probe the physical and chemical conditions in the PDR around the UC HII Mon R2. HIFI observations of the abundant compounds 13CO, C18O, o-H218O, HCO+, CS, CH, and NH have been used to derive the physical and chemical conditions in the PDR, in particular the water abundance. The modeling of the lines has been done with the Meudon PDR code and the non-local radiative transfer model described by Cernicharo et al. The 13CO, C18O, o-H218O, HCO+ and CS observations are well described assuming that the emission is coming from a dense (n=5x106cm–3, N(H2)>1022cm–2) layer of molecular gas around the HII region. Based on our o-H218O observations, we estimate an o-H2O abundance of ≃2x10–8. This is the average ortho-water abundance in the PDR. Additional H218O and/or water lines are required to derive the water abundance profile. A lower density envelope (n ∼105cm–3, N(H2)=2-5x1022cm–2) is responsible for the absorption in the NH 11->02 line. The emission of the CH ground state triplet is coming from both regions with a complex and self-absorbed profile in the main component. The radiative transfer modeling shows that the 13CO and HCO+ line profiles are consistent with an expansion of the molecular gas with a velocity law, ve=0.5x(r/Rout)–1km/s, although the expansion velocity is poorly constrained by the observations presented here. We determine an ortho-water abundance of ≃2x10–8 in Mon R2. Because shocks are unimportant in this region and our estimate is based on H218O observations that avoids opacity problems, this is probably the most accurate estimate of the water abundance in PDRs thus far.

Abstract Copyright:

Journal keyword(s): ISM: structure - ISM: kinematics and dynamics - ISM: molecules - HII regions - submillimeter: ISM

Simbad objects: 4

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Number of rows : 4

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME Orion Bright Bar reg 05 35 22.30 -05 24 33.0           ~ 716 0
2 NAME Mon R2 IRS 1 cor 06 07 46.20 -06 23 09.5           B0 60 0
3 NAME Mon R2 HII 06 07 46.6 -06 22 59           ~ 650 2
4 NAME Sgr B2 MoC 17 47 20.4 -28 23 07           ~ 1909 1

    Equat.    Gal    SGal    Ecl

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2020.07.05-05:29:18

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