Low-temperature gas opacityIESOPUS: a versatile and quick computational tool

摘要

We introduce a new tool — AESOPUS: Accurate Equation of State and OPacity Utility Software — for computing the equation of stateand the Rosseland mean (RM) opacities of matter in the ideal gas phase. Results are given as a function of one pair of state variables,(i.e. temperature T in the range 3.2 log(T) 4.5, and parameter R p/(T/106 K)3 in the range —8 log(R) 1), and arbitrarychemical mixture. The chemistry is presently solved for about 800 species, consisting of almost 300 atomic and 500 molecularspecies. The gas opacities account for many continuum and discrete sources, including atomic opacities, molecular absorption bands,and collision-induced absorption. Several tests made on IESOPUS have proved that the new opacity tool is accurate in the results,flexible in the management of the input prescriptions, and agile in terms of computational time requirement. Purpose of this work isto greatly expand the public availability of Rosseland mean opacity data in the low-temperature regime. We set up a web-interface(http://stev. oapd. inaf. it/aesopus) which enables the user to compute and shortly retrieve RM opacity tables according tohis/her specific needs, allowing a full degree of freedom in specifying the chemical composition of the gas. As discussed in the paper,useful applications may regard, for instance, RM opacities of gas mixtures with i) scaled-solar abundances of metals, choosing amongvarious solar mixture compilations available in the literature; ii) varying CNO abundances, suitable for evolutionary models of redand asymptotic giant branch stars and massive stars in the Wolf-Rayet stages; iii) various degrees of enhancement in a-elements, andC-N, O-Na, and Mg-Al abundance anti-correlations, necessary to properly describe the properties of stars in early-type galaxies andGalactic globular clusters; iv) zero-metal abundances appropriate for studies of gas opacity in primordial conditions.