Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007iaus..240..120g&link_type=abstract
Binary Stars as Critical Tools and Tests in Contemporary Astrophysics, International Astronomical Union. Symposium no. 240, he
Astronomy and Astrophysics
Astrophysics
Scientific paper
The lambda Boo stars are a fascinating class of stars :it is the only class of A-type stars with abundances lower than solar, in spite of the fact that they have the kinematical and photometric properties of Pop I stars. The most plausible theory, at present, to interpret this peculiar behaviour is based on the diffusion-accretion model proposed by Venn & Lambert (1990). The key point of this model is the existence of a surrounding disk of dust and gas which would be the remnant of the star formation material and from which the - metal depleted - gas is accreted, the metals being incorporated into the dust. The large variety of objects classified as lambda Boo and the lack of any relation between their physical parameters and the measured abundance anomalies, coupled with the recent detection of bright companions near several lambda Boo candidates (detected by ground-based speckle and our adaptive optics (AO) observations, as well as by the Hipparcos space experiment) prompted us to scrutinize all the high resolution spectra we could obtain to search the objects that have composite spectra: a combination of two similar spectra which can be confused with that of a single metal poor star when analyzed by adopting their average Teff, log parameters. The detection of duplicity is tricky because one of the characteristics of lambda Boo stars is the mean-high vsini which produces broad and shallow lines. We have developed a strategy to detect such composite spectra by selecting the spectral features which are more sensitive to duplicity. We apply this analysis to one more object: HD 204041,a "well known" lambda Boo star which is shown to be a further member of the " composite spectra " class.
Faraggiana Rosanna
Gerbaldi Michèle
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