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H$\alpha$ CCD spectra of the totally eclipsing short-period Algol U Sge were obtained with the Kitt Peak 0.9m Coud{\'e} Feed Telescope during two observing runs in May -- June 1993. These observations are part of a long-term project to investigate the physical properties and spatial distribution of the accretion structures in these interacting systems. The 140 H$\alpha$ spectra of U Sge analyzed in this work were all collected within nine orbital cycles and cover $\simeq$70\% of the orbit of the binary. Emission due to circumstellar gas, blended with the photospheric absorption of the two stars, can be seen in the observed profiles at phases outside of eclipse. The detailed study of the circumstellar gas in the short-period Algol systems requires that the circumstellar component of the H$\alpha$ line profile be deblended from the photospheric component. This is accomplished by subtracting a composite theoretical photospheric line profile from the observed profiles, the resulting difference profile represents all the emission and excess absorption arising from circumstellar gas in the system. The difference profiles of U Sge indicate the presence of circumstellar gas at all phases around the orbit. This gas is in the form of a transient accretion disk because double-peaked emission features can be seen at nearly all phases outside of eclipse. The radius of this transient disk can be estimated from the near-eclipse and in-eclipse difference profiles. This work marks the first time that detailed modeling of the out-of-eclipse emission and absorption from circumstellar gas has been done for this well studied system.
Electronic Abstract Submitted to the AAS for Jan 94 meeting at Washington DC.
