The emission line spectrum of the eclipsing variable AR Pavonis

The bright line spectrum of AR Pav is described. During eclipse the intensity of the H lines weakens relative to the nebular lines; He I weakens more, while He ii 4686 nearly disappears. Stratification as in a planetary nebula is suggested. In the P Cyg structure of the Balmer lines the red component is always stronger than the violet, but equality is approached for over 100 days following eclipse. The separation of the components narrows during eclipse by an amount which varies in different cycles. Outside eclipse the mean separation obeys Struve's relation V3 P- for gaseous rings. A model of a thick ring subject to differential rotation is considered and proffles computed geometrically for various types of eclipse. The observed narrowing of components is not reproduced in this model. As an alternative an expanding ring is considered briefly, and this model predicts symmetrical narrowing during eclipse.