Sinking timescales for metals in white dwarf atmospheres

Sinking timescales for metals in white dwarf atmospheres

Sinking timescales calculated using the STELUM evolution code. We supply two grids of sinking timescales, labelled 'SV' and 'S3D'. In the SV grid, the depth of convective overshoot varies according to a specified 1D parametrisation, whereas in the S3D grid it is calibrated to the output of 3D simulations. For further details, see Buchan et al. 2025 ("Exogeological inferences from white dwarf pollutants: the impact of stellar physics").

The key variables which determine sinking timescales are the white dwarf's atmospheric composition, its surface gravity, and its effective temperature. The first two of these are specified in the file names. The file name format is GRID_ATM_LOGG.csv, where GRID is the grid type (either SV or S3D), ATM is the atmospheric composition (either H or He), and LOGG indicates the surface gravity, given in log cgs units, multiplied by 10 to remove the decimal place. For example, the file 'S3D_H_80.csv' describes values from the S3D grid, for white dwarfs with H-dominated atmospheres, and surface gravity of log(g) = 8.0. The S3D grid only includes H-dominated atmospheres.

Each file contains text in a comma-delimited csv format. The first column indicates a number of variables. The top row, labelled 'T:' indicates the effective temperature in Kelvin. The second row, labelled 'qcvz:', indicates the depth of the convective zone (including overshoot), expressed as log(1-(m/M)), where m is the mass interior to the base of the convective zone, and M is the total mass of the white dwarf. All other rows correspond to different metals, labelled by their atomic number, and indicate their sinking timescales in units of log(year). For example, reading the third column of S3D_H_80.csv, we find that at an effective temperature of 12000K, the depth of the convective zone is given by q=-13.165, and the sinking timescale of phosphorus (atomic number 15) is expressed as 0.544, which corresponds to 3.5 years (=10^0.544).