Context :

Aims : X-ray bursting neutron stars in low mass X-ray binaries constitute an appropriate source class to constrain masses and radii of neutron stars , but a sufficiently extended set of corresponding model atmospheres is necessary for these investigations .

Methods : We computed such a set of model atmospheres and emergent spectra in a plane-parallel , hydrostatic , and LTE approximation with Compton scattering taken into account .

Results : The models were calculated for six different chemical compositions : pure hydrogen and pure helium atmospheres , and atmospheres with solar mix of hydrogen and helium , and various heavy element abundances Z = 1 , 0.3 , 0.1 , and 0.01 Z _ { \odot } .
For each chemical composition the models are computed for three values of surface gravity , \log g =14.0 , 14.3 , and 14.6 , and for 20 values of the luminosity in units of the Eddington luminosity , L / L _ { Edd } , in the range 0.001–0.98 .
The emergent spectra of all models are redshifted and fitted by a diluted blackbody in the RXTE /PCA 3–20 keV energy band , and corresponding values of the color correction ( hardness factors ) f _ { c } are presented .

Conclusions : Theoretical dependences f _ { c } – L / L _ { Edd } can fitted to the observed dependence K ^ { -1 / 4 } – F of the blackbody normalization K on flux during cooling stages of X-ray bursts to determine the Eddington flux and the ratio of the apparent neutron star radius to the source distance .
If the distance is known , these parameters can be transformed to the constraints on neutron star mass and radius .
The theoretical atmosphere spectra can also be used for direct comparison with the observed X-ray burst spectra .