DDSCAT.5a requires that these polarizable points be located on a cubic lattice. The DDA approximates the target by an array of polarizable points. The temperature of the envelope is specified (and thus not computed self-consistently).ĭDSCAT is a freely available software package which applies the "discrete dipole approximation" (DDA) to calculate scattering and absorption of electromagnetic waves by targets with arbitrary geometries and complex refractive index. 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. In the non-spherical case, no provision is made for photons penetrating the envelope from the sides. The envelope is spherical by default, but can be made bipolar with an opening solid-angle that varies with radius. Shielding of continuum-absorbing species by these species (self and mutual shielding), line-absorbing species, and dust varies with radial optical depth. The chemical species are shielded from the photons by circumstellar dust, by other species and by themselves (self-shielding). The photons originate from both the star and the external interstellar medium. wavelength, with appropriate thresholds, can be specified for each species, while for H2+ a photoabsorption cross-section is provided as a function of wavelength and temperature. Chemical reaction rates are specified with possible activation temperatures and additional power-law dependences. The chemical species interact with one another and can are subject to photo-processes (dissociation of molecules, radicals, and molecular ions as well as ionization of all species). Collisional ionization or excitation can be incorporated through the proper chemical channels. The chemical species can be atoms, molecules, ions, radicals, molecular ions, and/or their specific quantum states. CSENV is a code that computes the chemical abundances for a desired set of species as a function of radius in a stationary, non-clumpy, Circum Stellar ENVelope.
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