0.7. It is interesting to note that 5 and 0.8 are the average total mass and 1 Jeans masss in the Taurus Molcular Cloud complex (Goodwin et al. [@gww04]).

For the purpose of comparison with model calculations, we have used the 1.2 mm continuum data to estimate the density distribution under the assumption of spherical symmetry. This inevitably involves a rough approximation since the L1521F core clearly [*is not spherically symmetric*]{} (the aspect ratio in the 1.2mm continuum emission is 1.6, see Tab. \[gauss2d\]) and would be better approximated with an ellipsoid.

Nevertheless, we have followed the technique adopted by Tafalla et al. ([@taf02]) and fit our data with a model of the form: $$n_{\MOLH }(r) = \frac{n_{0}}{1 + \left( \frac{r}{r_0}
\right)^\alpha} ,$$ We thus circularly averaged the 1.2 mm data around the peak and used a $\chi^2$ routine to fit the dust profile using the above model integrated along the line of sight and convolved with a 10.5 gaussian. The result of the fitting procedure can be seen in Fig. \[dprof\] . The parameters that best fit our data are $n_{0}= 10^6$ cm$^{-3}$, $r_0 = 20$ (corresponding to 0.014 parsec or 2800 AU) and $\alpha = 2.0$.

CO freeze–out 