Spectral energy distributions and best-fitting parameters for neutron star atmospheres composed of fusion ashes

This Zenodo record provides spectra of model atmospheres of hot neutron stars enriched with thermonuclear fusion ashes as  presented in the paper "Neutron star atmospheres composed of fusion ashes" by Valery F. Suleimanov, Juri Poutanen, and Klaus Werner, accepted for publication in Astronomy & Astrophysics (arXiv:2604.16650). Also the parameters with the fits by an analytical model are presented. 

There are 21 files of the type "sp_NAME_mxN1_gN2_nN3.dat". Here "NAME" is the used ash mixture and has five values, "ash1", "ash2", "ash3", "ash4", and "fe". The first four names correspond to the ashes presented in Table 1 of the cited paper, whereas "fe" means pure iron chemical composition.

Here we present not only the result corresponding to pure ashes, but also the spectra corresponding to the mixture of the given ash with the plasma having the solar H/He ratio and the solar abundance of heavy elements reduced by 100 times (solA01). N1 is the mass fraction of the given ash to the resulting chemical abundance of the model atmosphere so that  the mass fraction of a chemical element is determined through       mfr = N1*mfr(NAME) + (1-N1)*mfr(solA01). 

N2 encodes the surface gravity of the model atmospheres and has two values. N2=3 corresponds to log g = 14.3, and N2=0 corresponds to log g = 14.0.

N3 is the number of model spectra in this file. We computed model atmospheres for 25 relative bolometric fluxes F/F_Edd:  0.01, 0.03, 0.05, 0.07, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.02, 1.03, 1.04, 1.06. 

The Eddington flux is computed as F_Edd = cg/\kappa_e, where c is the speed of light, g is the surface gravity, and "\kappa_e" is the electron scattering opacity\kappa_e = 0.2*[1-(1-N2)*X_H] cm^2/g. Here X_H = 0.7374 is the hydrogen mass fraction in the plasma with the solar abundance. The effective temperature of each model "T_eff" can be calculated as T_eff = (F_Edd/ \sigma_SB)^(1/4) * (F/F_Edd)^(1/4), where \sigma_SB is the Stefan-Boltzmann constant.

For some of the mixtures, the models with high F/F_Edd ratio are not stable due to the radiation pressure force exceeding the surface gravity and therefore were not computed. Thus, the number of models, N3, depends on the composition. 

Every model spectrum has 380 lines and two columns. The first column is the photon energy in keV, the second one is the so called Eddington flux (H_E=F_E/4\pi) in units erg s^(-1) cm^(-2) keV^(-1) sr^(-1). Therefore, if N3=24, there are 380*24=9120 lines in the file named like "sp_NAME_mxN1_gN2_n24.dat".

There are 21 files "tab_NAME_mxN1_gN2.dat" presenting best-fit parameters of the spectral shape with the analytical model (Eq. 7 in the paper)F^fit_E =      w * pi * B_E(fc * T_eff),                                     if E < E_th,     w * pi * B_E(fc *T_eff) * \exp(-\tau_th * [E/E_th]^{-p}),     if E > E_th. Here B_E(fc * T_eff) is the Planck function of temperature T=fc*T_eff.  The NAME, N1, and N2 have the same meaning like in the spectral files. Every file has six columns. The first column (1) is the relative flux value, F/F_Edd, the other five columns are the fitting parameters:  (2) the dilution factor "w", (3) the color correction factor "fc", (4) the threshold energy "E_th" (in keV) of the absorption edge,  (5) the optical depth of the absorption edge at the threshold energy  "tau_th", and (6) the absorption exponent "p". The columns are separated by "&" symbols.