Function tracks::renormalizeSurfaceAbundances

Function Documentation

inline void tracks::renormalizeSurfaceAbundances(std::array<double, static_cast<std::size_t>(FieldIdx::nTrackQty)> &props)

Rescale a star’s surface mass fractions so that they sum to at most 1.

Interpolating each surface mass fraction independently – which is how tracks and isochrones are evaluated, with a monotonicity- preserving but nonlinear scheme – does not preserve their sum: between two sample points across which X falls and Y rises (as when a massive star’s surface becomes hydrogen-poor), X + Y can exceed 1 even though every tabulated point is valid. Scanning the isochrones of every track set slug ships finds interpolated sums X + Y + C + N + O up to ~1.085 (MIST), although no tabulated MIST point exceeds 1. A sum above 1 makes the implied metallicity Z = 1 - X - Y negative (or smaller than the C + N + O it must contain), which quantities that take log(Z) – e.g. the nugis_lamers_00 WC wind velocity – cannot handle. If X + Y + C + N + O exceeds 1, this scales all five down by the same factor so that they sum to exactly 1 (so that Z = 1 - X - Y = C + N + O >= 0), preserving their ratios. A sum at or below 1, or a NaN sum, is left untouched. Corrupt track data, as opposed to interpolation artifacts, is caught when the tracks are loaded instead – see checkSurfaceAbundances() in TrackUtils.hpp.

Parameters:

props – A star’s properties, as produced by evaluating a track or isochrone; its hSurf/heSurf/cSurf/nSurf/oSurf entries are modified in place, and every other entry is untouched