M. Gerbaldi

λ Bootis stars with composite spectra

We examine the large sample ofλ Boo candidates collected in Table 1 of Gerbaldi et al. (2003) to see how many of them show composite spectra. Of the 132 λ Boo candidates we identify 22 which definitely show composite spectra and 15 more for which there are good reasons to suspect a composite spectrum. The percentage of λ Boo candidates with composite spectra is therefore >17% and possibly considerably higher. For such stars the λ Boo classification should be reconsidered taking into account the fact that their spectra are composite. We argue that some of the underabundances reported in the literature may simply be the result of the failure to consider the composite nature of the spectra. This leads to the legitimate suspicion that some, if not all, the λ Boo candidates are not chemically peculiar at all. A thorough analysis of even a single one of the λ Boo candidates with composite spectra, in which the composite nature of the spectrum is duly considered, which would demonstrate that the chemical peculiarities persist, would clear the doubt we presently have that the stars with composite spectra may not be λ Boo stars at all.

The field Am and ρ Puppis-like stars: Lithium and heavier elements

With observations at the Canada-France-Hawaii telescope, photospheric abundances of two evolved field Am stars, τ UMa and HR 178, have been determined for Li, Al, Si, S, Fe, Ni, and Eu by model abundance analysis. Thanks to these new determined abundances and the HIPPARCOS mission, making it possible to better estimate the evolutionary stage of field stars, one can consider the influence of evolution on the abundances of Am stars. No abundance trend for Al, Si, S, and Fe is found during Main Sequence evolution, up to its very last phases. The abundance of Li is, generally, cosmic. Large Li deficiencies may be observed in the very last phases (the “hook” region of the H-R diagram) and, too, on the red side of the Am phenomenon region where the ρ Puppis-like stars lie.

Peculiar am Stars after Hipparcos

The Hipparcos mission has made possible to constrain the positions of the nearby stars in the HR diagram with high accuracy. We reconsider the evolutionary status of the Am stars, as given by their position in the HR diagram; we discuss the measured abundance anomalies in function of the age and mass of the star.

Training in Astronomy

Astronomy offers a unique opportunity for promoting the science teaching in its present crisis. Astronomy can be introduced at various levels and become the medium by which both primary science education and public understanding of science are stimulated.

λ Boo Stars in the Orion OB1 Association

The origin of the photospheric underabundances detected in the Pop I A-type stars, the λ Boo stars, is interpreted as the signature of the last evolution of a star before to reach the main sequence. In order to test this hypothesis, UV observations of λ Boo candidates in the young Orion OBI Association have been made.