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 i n two classes of A stars: (i) metal-deficient stars of the lambda Boot is type whose surface anomalies are believed to be due to accretion of depleted gas, and (ii) stars known to possess circumstellar dust disk s, including Vega and beta Pictoris. We derive T-eff and log g and com bine model-atmosphere analysis with spectrum synthesis to determine pr ojected rotational velocities, calcium abundances, and the motion of c ircumstellar gas with respect to the star. Narrow components in Ca K a re present in five of the eleven lambda Boo stars studied. This except ional high incidence suggests that the lambda Boo phenomenon is relate d to the presence of circumstellar gas. Specific topics discussed (Sec t. 6) include: (1) a connection between rotation, the presence of dete ctable amounts of CS gas, and metal deficiency, (2) Vega and beta Pic as suspected lambda Boo stars, (3) lambda Boo stars as probable pre-ma in-sequence objects, and (4) episodes of massive accretion in beta Pic and in the lambda Boo star HR 4881.