Query : 2007A&A...464L..41P

2007A&A...464L..41P - Astronomy and Astrophysics, volume 464, L41-44 (2007/3-4)

Deuterium fractionation in the Horsehead edge.


Abstract (from CDS):

Deuterium fractionation is known to enhance the [DCO+]/[HCO+] abundance ratio over the D/H ∼10–5 elemental ratio in the cold and dense gas typically found in pre-stellar cores. We report the first detection and mapping of very bright DCO+ J=3-2 and J=2-1 lines (3 and 4K respectively) towards the Horsehead photodissociation region (PDR) observed with the IRAM-30m telescope. The DCO+ emission peaks close to the illuminated warm edge of the nebula (<50'' or ∼0.1pc away). Detailed nonlocal, non-LTE excitation and radiative transfer analyses have been used to determine the prevailing physical conditions and to estimate the DCO+ and H13CO+ abundances from their line intensities. A large [DCO+]/[HCO+] abundance ratio (≥0.02) is inferred at the DCO+ emission peak, a condensation shielded from the illuminating far-UV radiation field where the gas must be cold (10-20K) and dense (≥2x105cm–3). DCO+ is not detected in the warmer photodissociation front, implying a lower [DCO+]/[HCO+] ratio (<10–3). According to our gas phase chemical predictions, such a high deuterium fractionation of HCO+ can only be explained if the gas temperature is below 20K, in good agreement with DCO+ excitation calculations.

Abstract Copyright:

Journal keyword(s): ISM: clouds - ISM: molecules - ISM: individual objects: Horsehead nebula - radio lines: ISM

Simbad objects: 3

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Number of rows : 3
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 * sig Ori Y*O 05 38 44.7653828520 -02 36 00.283179888 2.54 3.58 3.79 3.87 4.11 O9.5V+B0.2V(n) 782 0
2 [WNB2006] B33-SMM1 smm 05 40 54.0 -02 27 32           ~ 5 0
3 NAME Horsehead Nebula DNe 05 40 59.0 -02 27 30           ~ 493 0

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