PopRatio: A program to calculate atomic level populations in astrophysicalplasmas

We describe a Fortran 90 program to calculate population ratios of atomic l evels. The program solves the equations of statistical equilibrium consider ing all possible bound-bound processes: spontaneous, collisional or radiati on induced (the later either directly or by fluorescence), There is no limi t on the number of levels or in the number of processes that may be taken i nto account. The program may find a wide range of applicability in astronom ical problems, such as interpreting fine-structure absorption lines or coll isionally excited emission lines (such as coronal emission lines) in the sp ectra of several objects, and also in calculating the cooling rates due to collisional excitation. (C) 2001 Elsevier Science B.V. All rights reserved.