Sd. Doty et Cm. Leung, GAS TEMPERATURE DISTRIBUTION IN THE IRC+10216 CIRCUMSTELLAR ENVELOPE, Monthly Notices of the Royal Astronomical Society, 286(4), 1997, pp. 1003-1011
We construct a simple model for the emission-line profiles of CO from
the circumstellar envelope (CSE) of the carbon-rich star IRC +10216. U
sing the Sobolev approximation, and a given gas temperature distributi
on (gTD) we construct simulated observations of this source. We find t
hat the 'canonical' gTD [T(r)proportional to r(-0.7)] cannot reproduce
the observations. Guided by a strong correlation between telescope be
amsize and peak intensity, we vary the gTD to fit the observations, an
d find that the data are best reproduced by T(r) proportional to r(-1)
. This power law is consistent with CO line radiation being the domina
nt coolant in the CSE. Differences between this and other results may
be the result of a previous lack of high-resolution observations, the
use of older CO collisional rates, or reduced mass-loss rate. Although
an assumed source distance of 150 pc gives the best fit to the data,
we cannot rule out the possibility of a larger source distance (e.g. 3
00 pc).