The evolutionary paths of the massive O and B type stars are often defined by angular momentum transformations that involve circumstellar gas disks. This circumstellar gas is revealed in several kinds of observations, and I will describe a series of investigations of the hydrogen line emission from such disks.
By examining three sets of spectra of the active mass-transfer binary system RY Scuti, I determined masses of 7.1 +/- 1.2 M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the massive companion that is hidden by an accretion torus. I will also present a cartoon model of the complex mass flows in the system.
Using optical spectroscopy and X-ray flux data, I investigated the mass transfer processes in four massive X-ray binaries (a massive B star with mass flowing onto a compact, neutron star companion). The B-supergiant system LS I +65 010 transfers mass via stellar winds. In the other three binaries (LS I +61 303, HDE 245770, and X Per), an outflowing circumstellar disk is responsible for the mass transfer, and in all three systems, the disk appears to be truncated by gravitational interactions with the compact companion. During the course of the analysis of the X-ray binaries, I developed numerical models for estimating the size of the Be star disks using just the H-alpha equivalent width.
Finally, I will present the results of a three year spectroscopic survey of both the H-alpha and H-gamma regions of 128 Be stars. I find that the median fractional variation in the equivalent width of the disk emission lines is 15% over a two year period. I also find that two-thirds of the sample displays evidence of Fe II emission or absorption resulting from surrounding circumstellar material. Many candidates for non-radial pulsation and binary systems are also found. I will also describe a voluminous appendix in which spectra and notes for all of the sample stars are presented.