منابع مشابه
The Evolution of Ap Stars
The many peculiarities of Ap stars (not only chemical ones , but also magnetic field and slow rotation) may vary during the main-sequence evolution of these stars. We review here briefly the evidences found in the last thirty years for such evolution , with an emphasis on the more recent research. The position in the HR diagram of low mass Ap stars with a significant surface magnetic field (as ...
متن کاملBehaviour of calcium abundance in Am-Fm stars with evolution
Calcium abundance in the atmosphere of Am stars is examined as a function of their evolutionary state within the main sequence. New spectroscopic abundances as well as abundances obtained photometrically by Guthrie (1987) are used, since they are mutually quite consistent. The main result of this work is that, contrary to earlier suggestions, calcium abundance does not tend to be larger in evol...
متن کاملRotation and evolution of A stars: looking for progenitors of cool Ap stars
We explore to what extent the study of the projected rotational velocities of normal A stars might reveal the existence of progenitors of cool Ap stars, i.e. of slowly rotating normal young A stars. Since according to a recent work, magnetic Ap stars with masses ranging from 1.7 to 2.5 M are never found on the ZAMS in the HR diagram, but have completed at least 30% of their MS lifetime, one may...
متن کاملRapidly oscillating Ap stars versus non-oscillating Ap stars
The positions in the HR diagram and the kinematic characteristics of rapidly oscillating and non-oscillating chemically peculiar stars are obtained using new Hipparcos proper motions and parallaxes, and our own radial velocity measurements. We find that rapidly oscillating stars, as a group, are (−0.47±0.34) mag above the zero-age main sequence (ZAMS), while the non-oscillating stars are (−1.20...
متن کاملAM CVn stars
I review our observational and theoretical knowledge of AM CVn stars, focusing on recent developments. These include newly discovered systems, the possibility that two recently discovered extremely short period objects are AM CVn stars and an update on X-ray, UV an optical studies. Theoretical advances include the study of the details of both the donor and accretor, and the physics of the heliu...
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ژورنال
عنوان ژورنال: International Astronomical Union Colloquium
سال: 2002
ISSN: 0252-9211
DOI: 10.1017/s0252921100016225