Astrophysical Estimate of Ionisation Potential of Vanadium

Abstract

IN a previous letter (NATURE, June 9, 1928) I outlined the method by which estimates of ionisation potentials might be derived from the spectra of Cepheid variables. Many of the lines emitted by ionised atoms are intensified at or near maximum luminosity phase and diminish in intensity as the star passes through the phase of minimum light. Many arc lines, on the other hand, show the reverse tendency. By comparing the behaviour of certain ionised lines with spark lines due to titanium, scandium, strontium, and barium, the ionisation potentials of which are known, it has been possible to estimate this constant for iron, yttrium, and lanthanum (loc. cit.), and quite recently for vanadium. From the periodic changes in intensity of the ionised line λ4205.07 I have obtained for the ionisation potential of vanadium 6.74 volts, the final figure being extremely uncertain.