An Etymological Dictionary of Astronomy and Astrophysics

An approximation in the treatment of photoionized → H II regions, whereby secondary ionizing photons are absorbed immediately very close to their site of emission. The secondary photons, produced by → radiative recombinations directly to the → ground states, are thus ignored with respect to the ionizing photons emitted by the → exciting star. The OTS approximation requires that the ionized gas be sufficiently dense so that secondary ionizing photons are very likely absorbed within the H II region.

Etymology (EN): → on; → spot; → approximation.

Etymology (PE): Nazdineš, → approximation; dar “in,” from Mid.Pers. andar, → intra-.