CSENV

• exponentially [exp(-tau)] for internal radiation

• with the Morris & Jura (1983) approximation of a pure spherical 1/r^2 absorber (neglecting scattering) [exp(-1.644 tau^0.86] for external radiation, but can alternatively be specified as exponential or taken from a file

Shielding of line-absorbing species (e.g. CO, H2) can be incorporated:

• for external radiation, the code applies the escape probability formalism times a continuum shielding factor (Morris & Jura 1983), the latter being made up of the contributions from dust, H2 blocking, and continuum, blocking from other species. The dependence of the shielding factor on optical depth is again taken from Morris & Jura's approximation of a pure spherical 1/r^2 absorber, but can alternatively be specified as exponential.
• for internal radiation, the code assumes exponential shielding of the continuum blockers (except from H2 lines)

The stellar and insterstellar radiation fields are respectively black-body and a good match to Draine's (1978) fit, by default, but can be altered.

The envelope is spherical by default, but can be made bipolar with an opening solid-angle that varies with radius. In the non-spherical case, no provision is made for photons penetrating the envelope from the sides.

The envelope is subject to a radial outflow (or wind), constant velocity by default, but the wind velocity can be made to vary with radius.

The temperature of the envelope is specified (and thus not computed self-consistently).

The data from all input files is fit to cubic splines (log X vs log radius, or log wavelength, except for species cross-sections which are fit to linear cubic splines and dust selective extinction). Internal wavelength integrations for photo-rates and mean cross-sections are obtained by cubic spline fit to the linear relations.

The code starts out at the base of the wind, and integrates outwards the (photo-)chemical orindary differential equations, using Gear's stiff method, along steps of log (radial distance), with much smaller internal steps of log (radial distance).

The integration is repeated in the case of shielding of interstellar radiation, so as to use the ith order estimate of the column density N(r) for the (i+1)th order photo-chemical integration. Convergence is based upon the absolute variations from one iteration to the next of the column densities of all continuum photo-absorbing species as well as the total column density.

• Glassgold, Mamon, Omont & Lucas, 1987, A&A 180, 183 Photochemistry and molecular ions in carbon-rich circumstellar envelopes

• Mamon, Glassgold & Omont, 1987, ApJ 323, 306 Photochemistry and molecular ions in oxygen-rich circumstellar envelopes

• Mamon, Glassgold & Huggins, 1988, ApJ 328, 797 The photodissociation of CO in circumstellar envelopes

• Glassgold, Mamon & Huggins, 1989, ApJ 336, L29 Molecule formation in fast neutral winds from protostars

• Glassgold, Mamon & Huggins, 1991, ApJ 373, 254 The formation of molecules in protostellar winds

• Cherchneff, Glassgold & Mamon, 1993, ApJ 410, 188 The formation of cyanopolyyne molecules in IRC + 10216