... spectrum . ... The photons we detect originate in the outermost layers, or atmosphere, of the star. In order to interpret stellar spectra, it is necessary to construct models which accurately represent the structure of a stellar atmosphere and the transfer of radiation from the stellar interior into interstellar space. For the study of helium stars and other stellar remnants, we in Armagh use several computer programs, of which sterne and spectrum are the most important. sterne . ...