Emission of CO (J = 1-0 and 2-1) in CRL 2688 - Photochemistry, kinetic temperature, and molecular abundance

Details Emission of CO (J = 1-0 and 2-1) in CRL 2688 - Photochemistry, kinetic temperature, and molecular abundance Emission of CO (J = 1-0 and 2-1) in CRL 2688 - Photochemistry, kinetic temperature, and molecular abundance

Apr 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...230..431t&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 230, no. 2, April 1990, p. 431-439.

Astronomy and Astrophysics

Astrophysics

48

Carbon Monoxide, Emission Spectra, Molecular Excitation, Nebulae, Photochemical Reactions, Stellar Envelopes, Abundance, Radiative Transfer, Temperature Distribution, Radiation Transfer, Radio Lines: Molecular, Stars: Abundances, Stars: Circumstellar Matter

Scientific paper

We report results of high-resolution mapping of CRL 2688 in the CO, J = 1-0 and 2-1 transitions, by using the IRAM 30-m telescope. Our maps integrated over the line profiles for both transitions show no significant departure from spherical symmetry. This shape does not agree with earlier single line (J=1-0) observations of Heiligman et al. (1986), who have detected a central core oriented North-South, and of Kawabe et al. (1987) who have found an ellipsoidal structure but elongated East-West.
To interpret the observations, we use a radiative transfer model which includes consistently photochemistry of CO and thermal-balance between heating and cooling processes. CO is assumed to be photodissociated into C and ions C+ by ambient uv photons in the external layers. We calculate the radial intensity distributions for both j=1-0 and 2-1 lines in order to fit the observations. The best fit gives, for the distance of d=1 kpc, a relative dust-to-gas mass ratio of δ=0.1, a mass-loss rate of Mṡ = 1.7 10-4 Mṡsun yr-1, and a CO radial abundance (relative to H2) which decreases outwards from the inner value χ0 = 610-4. The present values for the mass-loss rate and CO abundance are not very different from earlier results for CRL 2688 found by Knapp and Morris (1985).

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