THE CHEMICAL-COMPOSITION OF 3 LAMBDA-BOOTIS STARS

Abundance analyses are reported for three certain members (λ Boo, 29 Cyg, π1 Ori) of the class of rapidly rotating, metal-poor A-type stars known as λ Boötis stars. Model atmosphere analysis of high-resolution, high signal-to-noise spectra shows that the metal deficiencies are more severe than previously reported: [Fe/H] = -2.0, -1.8, -1.3 for λ Boo, 29 Cyg, and π1 Ori, respectively. Other metals (Mg, Ca, Ti, and Sr) are similarly underabundant with Na often having a smaller underabundance. C, N, O, and S have near-solar abundances. Vega is shown to be a mild λ Boo star. The abundance anomalies of the λ Boo stars resemble those found for the interstellar gas in which the metals are depleted through formation of interstellar grains. It is suggested that the λ Boo stars are created when circumstellar (or interstellar) gas is separated from the grains and accreted by the star. The bulk of the interstellar grains comprises a circumstellar cloud or disk that is detectable by its infrared radiation.