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Carbon and Silicon in Normal a Stars and in Lambda Bootis Stars

Published online by Cambridge University Press:  12 April 2016

Hartmut Holweger  and
Sven Stürenburg
Hartmut Holweger
Affiliation:
Institut für Theoretische Physik und Sternwarte, Universität Kiel, Olshausenstrasse 40, W-2300 Kiel, Federal Republic ofGermany
Sven Stürenburg
Affiliation:
Institut für Theoretische Physik und Sternwarte, Universität Kiel, Olshausenstrasse 40, W-2300 Kiel, Federal Republic ofGermany

Abstract

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The anticorrelation of C and Si previously inferred from high-resolution spectroscopy of sharp-lined A stars classified as normal or mild Am is also found among the metal-deficient, more rapidly rotating λ Boo stars. The entire sample of program stars covers the range [C/Si] = − 1.14 (Sirius, mild Am star) to + 1.35 (HR 7400, λ Boo-type). Iron varies parallel with silicon. With respect to surface chemistry the λ Boo stars do not form a distinct group but rather represent the lower end in a continuous sequence of ‘metal’ abundance extending over more than 1.5 dex.

We argue that differential accretion of gas and dust in late stages of star formation or during the main-sequence phase is responsible for most of the abundance variations of the lighter elements up to the iron group. Enhanced or impeded accretion of dust leads to a metal-rich or metal-poor surface composition, respectively. The heavy trace elements Sr and Ba show additional anomalies indicating that other processes like gravitational and radiative separation are also involved.

Type
IV. Related Stars
Information
International Astronomical Union Colloquium , Volume 138: Peculiar versus Normal Phenomena in A-Type and Related Stars , 1993 , pp. 356 - 366
Copyright
Copyright © Astronomical Society of the Pacific 1993

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