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Paper: The Importance of Spectroscopic Binary Systems for the λ Bootis Phenomenon
Volume: 333, Tidal Evolution and Oscillations in Binary Stars: Third Granada Workshop on Stellar Structure
Page: 259
Authors: Paunzen, E.; Iliev, I.Kh.; Barzova, I.S.; Heiter, U.; Kamp, I.; Claret, A.
Abstract: We present high-resolution spectroscopic observations of the four λ Boötis type spectroscopic binary systems HD 64491, HD 84948, HD 141851 and HD 171948. This group of objects comprise of nonmagnetic, metal-weak, Population I, late B- to early F-type stars. For HD 64491 and HD 141851, estimates of the orbital period were derived. Whereas for the other two systems, detailed abundances and orbital elements are presented. The Hipparcos data reveal that the Galactic space motions of both systems are typical of those of Population I objects. The photometric data from the Hipparcos mission confirm the pulsation previously discovered for HD 84948 with a period of about 110 minutes and a V-amplitude of about 14 mmag. For HD 84948, we estimate from the mass ratio an age of about 1 Gyr, ruling out a possible Pre-Main-Sequence status. HD 171948 has an age of about 0.01 to 0.1 Gyr which is close to the Zero- Age Main Sequence. We therefore conclude that the λ Boötis phenomenon can be found continuously from very early stages to the Terminal-Age Main Sequence. These results together with those found in the literature are discussed in the light of the proposed theories explaining this phenomenon. The most acknowledged models include diffusion as main mechanism together either with mass-loss or with accretion of circumstellar material.
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