When does an a star turn into an ap star?

Details When does an a star turn into an ap star? When does an a star turn into an ap star?

Aug 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003basbr..23q.111f&link_type=abstract

Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p. 111-111

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Scientific paper

Ap stars present high abundance of rare earth elements. These overabundances are understood as the result of radiative diffusion. In the model, the rare earth elements are pushed to the surface by selective radiation pressure as the wavelength where the radiation field is maximum coincides with the wavelength where the rare earths opacities peak. Radiation pressure is helped by the lack of convection in A star envelopes and by the inhibition of turbulence promoted by the magnetic fields. A fundamental question in the investigation of Ap stars is when, in the evolution process, does an A star turn into an Ap star? Previous work by Abt (1979) and Abt & Cardona (1983) have suggested that A stars turn into Ap stars as they age. Later, other workers have questioned this result (see for instance North, 1993). All of the work done after Abt & Cardona was done based on photometric data rather than spectroscopy. Our goal is to solve this controversy studing the ratio of Ap to A stars on open clusters of different ages. Another way to investigate when a A star turns into an Ap star is to study visual multiples. We have obtained classification spectra of 430 late B, A and early F-type stars in 18 open clusters and 120 visual multiples. The spectra were obtained with 4 Å resolution with Cassegrain spectrographs on 1.5m CTIO, 1.52m ESO and 1.6m LNA telescopes. We are further studing if there is a relation between the ratio of Ap to A stars in open clusters and rotational velocities. Preliminary results of Vsin i of B and A stars in the open cluster IC 2602 will be presented.

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