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Astron. Astrophys. 329, 155-160 (1998)

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On the new [FORMULA] Bootis-type spectroscopic binary systems HD 84948 and HD 171948 *

E. Paunzen 1, U. Heiter 1, G. Handler 1, R. Garrido 2, E. Solano 3, W.W. Weiss 1 and M. Gelbmann 1

1 Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, A-1180 Wien, Austria (surname@astro.ast.univie.ac.at)
2 Instituto de Astrofisica de Andalucia, CSIC, P.O. Box 3004, E-18080 Granada, Spain (garrido@iaa.es)
3 INSA; ESA IUE Observatory, P.O. Box 50727, E-28080 Madrid, Spain (esm@vilspa.esa.es)

Received 11 July 1997 / Accepted 27 August 1997

Abstract

We report the discovery of two new [FORMULA] Bootis-type spectroscopic binary systems (HD 84948 and HD 171948).

High resolution spectra were analyzed in order to derive abundances as well as astrophysical quantities. It resulted in extreme (HD 171948) and moderate (HD 84948) underabundances of Na, Mg, Si, Ca, Sc, Ti, Cr and Fe with respect to the Sun, thus establishing all four individual stars as true members of the [FORMULA] Bootis group. These two systems are therefore the first spectroscopic binary systems where both components are [FORMULA] Bootis-type stars. Furthermore, we have discovered [FORMULA] Scuti type pulsation for one component of HD 84948 making this star particularly interesting for further observations.

Since many authors have used the rotational velocity for discriminating [FORMULA] Bootis stars (v sin i [FORMULA] 50 kms-1 ), we note that both components of HD 171948 are the slowest (v sin i [FORMULA] 20 kms-1 ) rotating [FORMULA] Bootis-type stars known so far.

Using the Hipparcos data, we are able to rule out the diffusion/mass-loss mechanism as origin for these two systems. Pre- as well as Main Sequence evolutionary tracks for the age determination yield consistent results with the predictions of the diffusion/accretion theory, establishing both systems as being very close to the Main Sequence. A determination of the orbital elements and/or an asteroseismological investigation of HD 84948 could provide an independent proof of our results.

Key words: binaries: spectroscopic – stars: chemically peculiar; early type; individual: HD 84948; HD 171948

* Based on observations obtained at the Osservatorio Astronomico di Padua-Asiago, McDonald Observatory, the Sierra Nevada Observatory and with the Hipparcos satellite

Send offprint requests to: E. Paunzen

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© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997
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