Absolute Magnitude Effects in Stellar Spectra

Abstract

IT is known from the fundamental work of Adams and Kohlschütter and their followers that certain pairs of lines in stellar spectra change in relative intensity with absolute luminosity, and this has formed the basis of the method of ‘spectroscopic parallaxes.’ The method has been hitherto empirical, stars of known luminosity being used as a basis to determine the luminosities of other stars from calibration curves. Saha's researches on high-temperature ionisation, whilst not removing the empirical basis, afforded a general qualitative explanation of many of the results observed. They showed that the lowered value of surface gravity g in giant stars as compared with dwarfs must cause reduced pressures in the atmospheres of giants with consequent increased ionisation and hence increased intensity of enhanced lines (Pannekoek, B.A.N., 19).