A.B., Astronomy, UC Berkeley, 1936.
M.A., Astronomy, Harvard, 1938.
Ph.D., Astronomy, Harvard, 1943.
Principal interest has been in study of chemical compositions of stars and gaseous nebulae and in the atomic and radiative processes involved therein. Much effort was placed on elemental abundances in the sun and how they compared with chondritic meteorites. More recently, particular emphasis has been directed to so-called planetary nebulae which are the ejecta of dying stars when their cores contract to white dwarfs and the outer envelopes are blown off into the interstellar medium. Elemental abundances give important clues to nuclear processes occurring during last stages of the life of a star like the sun, the composition of the interstellar medium at the epoch when the progenitor star was formed, and condensation of refractory elements in solid grains. Although high accuracy has been achieved in abundance analyses of most stars, many challenges remain in the nebular problem. Geometrical and density irregularities in nebular structure, insufficient knowledge of the ultraviolet radiative flux of the exciting star, the fact most atoms are observed in only a few of their possible ionization stages, and inaccuracies in atomic parameters all produce difficulties. Fortunately, we have access to the high dispersion Hamilton echelle spectrograph at Lick Observatory and supplementary IR, UV and radio frequency data are becoming available. Much of the effort is inspired by a close cooperation with the Queens' University in Belfast group who are making accurate calculation of the relevant atomic parameters. Observations are interpreted with the aid of theoretical nebular models that can accommodate many of the constraints imposed by the observations.
Aller, L.H. , 1994 Ap.J., 432, 427. Abundances, Planetary Nebulae, and Stellar Evolution.
Aller, L.H., and Hyung, S., 1995 MNRAS, 273, 973. The optical spectrum of NGC 7009.
Keenan, F.P., Aller, L.H., Bell, K.L., Hyung, S., McKenna, F.C. and Ramsbottom, C.A. 1996 MNRAS, 281, 1073. Auroral and Nebular Emission Lines of [SII] in the Optical Spectra of Planetary Nebulae.
Hyung, S., and Aller, L.H. 1997 ApJS, 108, 503. The Spectrum of the Planetary Nebula NGC 6884.