A speckle interferometry survey of λ Bootis stars^*

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
² Centro Galileo Galilei, Apartado de Correos 565, 38700 Santa Cruz de la Palma, Canary Islands, Spain
³ Dipartimento di Astronomia, Università degli Studi di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy
⁴ Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy

Corresponding author: E. Marchetti, emarchet@eso.org

Received: 18 December 2000
Accepted: 14 February 2001

Abstract

A search for duplicity of λ Boo stars has been made by using the speckle camera installed at the Telescopio Nazionale Galileo. The operation mode and the reduction procedure allow one to obtain not only the separation, but also the magnitude difference between the components; the latter parameter is fundamental for determining the degree of contamination from the secondary component of a binary system and thus the importance of the veiling effect that produces absorption lines weaker than normal. Two stars, HD 38545 and HD 290492, are close binaries with values of the separation and of the magnitude difference such that only a composite spectrum can be observed. For another 15 λ Boo candidates, observed with negative results, the upper limits of a possible companion separation are given.