HIGH-RESOLUTION SPECTROSCOPY OF LAMBDA-BOOTIS STARS AND DUSTY NORMAL A-STARS - CIRCUMSTELLAR GAS, ROTATION, AND ACCRETION

We present results of a high-S/N search for circumstellar Ca K lines in two classes of A stars: (i) metal-deficient stars of the lambda Bootis type whose surface anomalies are believed to be due to accretion of depleted gas, and (ii) stars known to possess circumstellar dust disks, including Vega and beta Pictoris. We derive T-eff and log g and combine model-atmosphere analysis with spectrum synthesis to determine projected rotational velocities, calcium abundances, and the motion of circumstellar gas with respect to the star. Narrow components in Ca K are present in five of the eleven lambda Boo stars studied. This exceptional high incidence suggests that the lambda Boo phenomenon is related to the presence of circumstellar gas. Specific topics discussed (Sect. 6) include: (1) a connection between rotation, the presence of detectable amounts of CS gas, and metal deficiency, (2) Vega and beta Pic as suspected lambda Boo stars, (3) lambda Boo stars as probable pre-main-sequence objects, and (4) episodes of massive accretion in beta Pic and in the lambda Boo star HR 4881.