The Spectroscopic Orbit of AU Monocerotis.

The system of AU Monocerotis is formed by a B5 star, which is partially eclipsed at the principal minimum, and a star of type near FO whose spectrum is observed oniy during eclipse. The orbital ele- ments derived from the Hei lines are the following: K = 32.2 km/sec; w = 34O~; e = 0.13; `y = + 11.8 .km/sec; a sin i = 4.9 X 10~, km; andf(m) = 0.04 0. The velocity-curve which corresponds to these ele- ments, drawn through the theasurements from the H lines and the appearance of the spectrograms be- tween phases 8.776 and 10.505 days, suggests the existence of a flow of relatively cool gas from the at- mosphere of the secondary star toward the B5 component-a phenomenon which is similar to the one de- scribed by Struve for SX Cassiopeiae