2017A&A...608A.133L


C.D.S. - SIMBAD4 rel 1.7 - 2020.09.23CEST22:48:40

2017A&A...608A.133L - Astronomy and Astrophysics, volume 608A, 133-133 (2017/12-1)

Gas and dust in the star-forming region ρ Oph A. II. The gas in the PDR and in the dense cores.

LARSSON B. and LISEAU R.

Abstract (from CDS):

Context. The evolution of interstellar clouds of gas and dust establishes the prerequisites for star formation. The pathway to the formation of stars can be studied in regions that have formed stars, but which at the same time also display the earliest phases of stellar evolution, i.e. pre-collapse/collapsing cores (Class -1), protostars (Class 0), and young stellar objects (Class I, II, III).
Aims. We investigate to what degree local physical and chemical conditions are related to the evolutionary status of various objects in star-forming media.
Methods. ρ Oph A displays the entire sequence of low-mass star formation in a small volume of space. Using spectrophotometric line maps of H2, H2O, NH3, N2H+, O2, O I, CO, and CS, we examine the distribution of the atomic and molecular gas in this dense molecular core. The physical parameters of these species are derived, as are their relative abundances in ρ Oph A. Using radiative transfer models, we examine the infall status of the cold dense cores from their resolved line profiles of the ground state lines of H2O and NH3, where for the latter no contamination from the VLA 1623 outflow is observed and line overlap of the hyperfine components is explicitly taken into account.
Results. The stratified structure of this photon dominated region (PDR), seen edge-on, is clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and O I are seen throughout the region around the exciting star S 1. At the interface to the molecular core 0.05 pc away, atomic hydrogen is rapidly converted into H2, whereas O I protrudes further into the molecular core. This provides oxygen atoms for the gas-phase formation of O2 in the core SM 1, where X(O2)∼5x10–8. There, the ratio of the O2 to H2O abundance [X(H2O)∼5x10–9] is significantly higher than unity. Away from the core, O2 experiences a dramatic decrease due to increasing H2O formation. Outside the molecular core ρ Oph A, on the far side as seen from S 1, the intense radiation from the 0.5 pc distant early B-type star HD 147889 destroys the molecules.
Conclusions. Towards the dark core SM 1, the observed abundance ratio X(O2)/X(H2O)>1, which suggests that this object is extremely young, which would explain why O2 is such an elusive molecule outside the solar system.

Abstract Copyright: © ESO, 2017

Journal keyword(s): ISM: individual objects: ρ Oph A - ISM: molecules - ISM: abundances - photon-dominated region (PDR) - stars: formation - ISM: general - ISM: general

VizieR on-line data: <Available at CDS (J/A+A/608/A133): list.dat fits/*>

Simbad objects: 21

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Number of rows : 21

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 Ori A MoC 05 38 -07.1           ~ 2691 0
2 HD 147888 ** 16 25 24.2937199705 -23 27 36.816821785 6.71 7.05 6.74     B3/4V 194 0
3 HD 147889 pr* 16 25 24.3162969787 -24 27 56.570239619 8.56 8.73 7.90     B2III/IV 435 1
4 HD 147932 Ro* 16 25 35.0836168833 -23 24 18.788751256 7.24 7.59 7.27     B5V 104 0
5 * rho Oph A * 16 25 35.1182364594 -23 26 49.827436721 4.3 5.22 5.05     B2/3V 391 0
6 GSS 30 Y*O 16 26 21.38160 -24 23 04.0524           ~ 200 1
7 VSSG 12 Y*O 16 26 22.38552 -24 22 52.9464           ~ 52 0
8 NAME VLA 1623-243 Y*O 16 26 26.42 -24 24 30.0           ~ 375 0
9 NAME rho Oph A SM 1N cor 16 26 27.12 -24 23 34.8           ~ 43 0
10 NAME rho Oph A SM 1 cor 16 26 27.60 -24 23 55.0           ~ 59 0
11 NAME rho Oph A SM 2 cor 16 26 30.4 -24 24 31           ~ 31 0
12 VSSG 27 Y*O 16 26 30.46896 -24 22 57.1440           M 57 1
13 [DAM2004] Oph A-N6 cor 16 26 31.6 -24 24 52           ~ 16 0
14 GSS 35 TT* 16 26 34.1750440278 -24 23 28.331873112     16.53 14.75 12.51 B3 216 1
15 NAME rho Oph E MoC 16 27 02.0 -24 38 31           ~ 56 0
16 NAME rho Oph Cloud B1 PoC 16 27 10.5 -24 29 30           ~ 51 1
17 NAME rho Oph B2 Cloud PoC 16 27 27.9 -24 26 29           ~ 75 1
18 NAME rho Oph F MoC 16 27 37.3 -24 42 28           ~ 58 0
19 NAME Ophiuchus Molecular Cloud SFR 16 28 06 -24 32.5           ~ 3056 0
20 NAME Oph Cloud Complex DNe 16 30 -24.3           ~ 63 1
21 NAME M 17 SW SFR 18 20 23.1 -16 11 43           ~ 250 0

    Equat.    Gal    SGal    Ecl

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2020.09.23-22:48:40

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