Spectra of binaries classified as λ Bootis stars^*

¹ Dipartimento di Astronomia dell' Università di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy
² Institut d'Astrophysique, 98 bis Bld. Arago, 75014 Paris, France e-mail: gerbaldi@iap.fr
³ Université de Paris Sud XI
⁴ Istituto Nazionale per l'Astrofisica - Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy e-mail: bonifaci@ts.astro.it
⁵ European Southern Observatory(ESO), Alonso de Cordoba 3107, Vitacura, Casilla 19001, Santiago 19, Chile e-mail: fpatrick@eso.org
⁶ Observatoire de Paris-Meudon, DASGAL, 5 place Jules Janssen, 92195 Meudon, France e-mail: Patrick.Francois@obspm.fr

Corresponding author: R. Faraggiana, faraggiana@ts.astro.it

Received: 16 January 2001
Accepted: 11 July 2001

Abstract

High angular resolution observations have shown that some stars classified as λ Boo are binaries with low values of angular separation and magnitude difference of the components; therefore the observed spectrum of these objects is a combination of those two components. These composite spectra have been used to define spectroscopic criteria able to detect other binaries among stars classified as λ Boo. The application of this method to HD 111786 is presented: the contribution of 5 components to the observed spectrum is demonstrated by the shape of the O I 7774 Å feature. This result makes unreliable any attempt to perform an abundance analysis of this object which therefore must be definitely rejected from the class of the peculiar λ Boo stars. This approach allowed us also to recognize that the SB2 star HD 153808 is in reality a triple system.