The Na I-like Spectra of Potassium and Calcium, KIX and CaX

From about 50 observed lines, in the range from 60 to 600 Å, in each of the spectra K IX and Ca X, term values are obtained forns, np, ndandnfup to highn-values. The series are perfectly regular and expressed by Ritz formulae which permit their extension to arbitraryn-values. The ionization limits are determined by means of an isoelectronically extrapolated polarization formula applied to thenfseries with the result:El(K IX) = 1 418 058 ± 20 cm-1andEl(Ca X) = 1 704 054±30 cm-1. We give, also, complete lists of the potassium and calcium lines of different ionization stages measured on our spectrograms, obtained with a 5-m grazing-incidence spectrograph and a condensed vacuum spark. The potassium list contains 230 lines from 230 to 41 Å, about half of which have been classified in the spectra from K VII to K XII. The corresponding figures for calcium are 294 lines from 217 to 35 Å of Ca VII to Ca XIII. The uncertainty in the wavelengths is estimated to be less than 0.005 Å.