Spectral flux from low-density photospheres - Low-temperature results

Previous studies of low-density, hydrogen-dominated, quasi-static photospheres (such as those of Type II supernovae) are extended to effective temperatures Te = 4000-6000 K. These temperatures include those at which hydrogen recombines at the densities investigated, corresponding to scale heights Delta R = (1-100) x 10 to the 14th cm. In addition to presenting results for the emergent spectral flux (required to obtain supernova distances via the Baade method), the validity of some assumptions previously made is demonstrated. It is shown that the level populations of hydrogen are governed solely by a balance between photoionization directly to and recombination directly from the continuum.