The OSCROX stellar oscillaton code

This paper describes the OSCROX stellar oscillation code for the calculation of the adiabatic oscillations of low degree l of a spherical star. There are two principal versions: one in Lagrangian variables (oscroxL), the second in Eulerian variables (oscroxE). The Lagrangian code does not require values of the Brunt Vaisala frequency or equivalently the density gradient. For l = 1 the oscillation equations have both an exact integral and an exact partial wave solution, and codes oscroxL1 and oscroxE1 incorporate these exact solutions. The difference in the frequencies obtained with the various codes gives some estimate of the uncertainty in the results due both to limited accuracy of hydrostatic support of the stellar model, and the limited accuracy of the integration of the oscillation equations. We compare the results of the different methods by calculating the frequencies in the range 20-2500 mu Hz of a model of a 1.5 M(circle dot) main-sequence star (ModelJC) kindly provided by J. Christensen-Dalsgaard for the purposes of cross comparison of codes, a modified version of this model (ModelJCA) with improved hydrostatic support, and of a highly accurate n=3 polytropic model of a star with the same mass and radius. For the polytropic model the frequencies as calculated by all codes agree to within 0.001 mu Hz, whereas for the 1.5 M(circle dot) main sequence model the frequency differences reach a maximum of 0.04 mu Hz, due primarily to the limited accuracy of hydrostatic support in the model; this is reduced to 0.01 mu Hz for ModelJCA.