[en] A number of topics relating to astrophysical observations that have already been made or are currently planned of spectral features, mostly emission lines, in the x ray and gamma ray region of the electromagnetic spectrum are investigated. These topics include the production of characteristic x ray and gamma ray lines by nonthermal ions, spectral features induced by processes occurring in strong magnetic fields, and the positron annihilation line at 0.5 MeV. The rate of x-ray production at 6.8 keV by the 2p to 1s transition in fast hydrogen- and helium-like iron ions, following both electron capture to excited levels and collisional excitation, is calculated. The cross section for electron-ion Coulomb collisions in strong fields is also calculated