We introduce a new tool – ÆSOPUS : Accurate Equation of State and OPacity Utility Software – for computing the equation of state and 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 ~ { } \leq~ { } \log ( T ) ~ { } \leq~ { } 4.5 , and parameter R = ~ { } \rho / ( T / 10 ^ { 6 } { K } ) ^ { 3 } in the range -8 ~ { } \leq~ { } \log ( R ) ~ { } \leq~ { } 1 ) , and arbitrary chemical mixture .
The chemistry is presently solved for about 800 species , consisting of almost 300 atomic and 500 molecular species .
The gas opacities account for many continuum and discrete sources , including atomic opacities , molecular absorption bands , and collision-induced absorption .
Several tests made on ÆSOPUS 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 is to 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 to his/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 among various solar mixture compilations available in the literature ; ii ) varying CNO abundances , suitable for evolutionary models of red and asymptotic giant branch stars and massive stars in the Wolf-Rayet stages ; iii ) various degrees of enhancement in \alpha -elements , and C-N , O-Na , and Mg-Al abundance anti-correlations , necessary to properly describe the properties of stars in early-type galaxies and Galactic globular clusters ; iv ) zero-metal abundances appropriate for studies of gas opacity in primordial conditions .