CO (J = 1-0 and 2-1) mapping of IRC + 10216 - A hot core model for the gas kinetic temperature distribution and the mass-loss rate

Details CO (J = 1-0 and 2-1) mapping of IRC + 10216 - A hot core model for the gas kinetic temperature distribution and the mass-loss rate CO (J = 1-0 and 2-1) mapping of IRC + 10216 - A hot core model for the gas kinetic temperature distribution and the mass-loss rate

Sep 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991a%26a...249..435t&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 249, no. 2, Sept. 1991, p. 435-442.

Astronomy and Astrophysics

Astrophysics

56

Carbon Monoxide, Gas Temperature, Kinetics, Stellar Cores, Stellar Mass Ejection, Momentum Transfer, Radiative Transfer, Stellar Models, Stellar Temperature, Temperature Distribution, Radiation Transfer, Radio Lines: Molecular, Stars: Abundances, Stars: Mass Loss, Stars: Gas Kinetic Temperature Distribution

Scientific paper

We report simultaneous high spatial resolution mapping of the inner region of the IRC+10216 envelope in the CO, J = 1-0 and 2-1, transitions using the IRAM 30m telescope.
Our results (radial distributions of line intensities and line profiles) together with up-to-date CO data (J = 1-0 to 6-5 line intensities) are used to derive the physical parameters of the circumstellar envelope. Our two-shell model assumes variations of the mass-loss rate, M˙, and of the fitting parameter, Q' = Qδ2/3, over the past, where Q is the dust-to-gas momentum transfer efficiency, and δ, the dust-to-gas mass ratio (=1 for typical interstellar gas). We performed the radiative transfer and the thermal balance calculations consistently. This modelling improves over (i) Kwan and Linke's (KL), which used fewer observed constraints (only lower spatial resolution CO, J = 1-0 and 2-1 line data), (ii) subsequent analyses which applied, with an arbitrary scaling factor, the gas kinetic temperature distribution derived by KL, (iii) and Huggins, Olofsson, and Johansson's, which did not constrain high-J line intensities.
With a distance of d = 200 pc, we derive: for the hot core of angular radius θ ≤ 4.2" M˙1 = 2.5 10-5 Msun yr-1, Q'1 = 8 10-2; and for the extended outer region, θ ≥ 4.2", M˙2 = 4 10-5 Msun yr-1, Q'2 = 0.6 10-2. If Q were constant, the values of Q' would imply a drastic diminution of the dust-to-gas mass ratio from the inner to the outer parts of the envelope. Our kinetic temperature distribution, Tk(θ), is ˜45% lower than Kwan and Linke's for the outer region, but 5-10 times higher for the inner core. For other currently adopted values of d (≤ 400 pc), Tk(θ) remains almost unchanged in the outer envelope, as the stellar luminosity L varies as d2, and M˙2 as d. However, the scaling with d does not apply for the hot core where the determination of Tk(θ) and M˙1 requires simultaneous radiative transfer and thermal balance calculations.

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