THE CHANGING SPECTRA OF FOUR SHELL STARS

Abstract

Since 1963 a program to observe the A-type stars in the Catalogue of Bright Stars at low dispersion has been under way (see Cowley 1968). During the course of this work spectrograms were obtained of four interesting A-type shell stars. All spectrograms were taken on Ila-O emulsion plates which were developed in a fine-grain developer. The spectrograms have a dispersion of 125 A/mm at Hy and are widened more than 0.7 mm. The observations were made at the Yerkes and McDonald Observatories. HR716(A) = ADS 1878(A) has a Henry Draper classification of A2. Bidelman (1943) classified it as an Al star, and he derived an absolute magnitude of -1.1. It was reclassified by Appenzeller (1967) as A2III based on a McDonald spectrogram taken in May 1966*. By September 25, 1966 the spectrum resembled 17 Leporis with sharp absorption lines of hydrogen, Fe n, Sen, Tin, and Can. The metallic lines were somewhat weaker than those seen in 17 Lep at its maximum shell phase and the hydrogen lines did not appear to have multiple components as are often seen in 17 Lep. The K-line type was about A2. Two plates taken in July and September of 1968 are very similar. The K line is narrower and weaker (approximately Al) and only X 3900 and