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Post Info TOPIC: Ap stars
Blobrana


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RE: Ap stars
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Title: Multiplicity of rapidly oscillating Ap stars
Authors: M. Schoeller, S. Correia, S. Hubrig, D. W. Kurtz

Rapidly oscillating Ap (roAp) stars have rarely been found in binary or higher order multiple systems. This might have implications for their origin. We intend to study the multiplicity of this type of chemically peculiar stars, looking for visual companions in the range of angular separation between 0.05" and 8". We carried out a survey of 28 roAp stars using diffraction-limited near-infrared imaging with NAOS-CONICA at the VLT. Additionally, we observed three non-oscillating magnetic Ap stars.
We detected a total of six companion candidates with low chance projection probabilities. Four of these are new detections, the other two are confirmations. An additional 39 companion candidates are very likely chance projections. We also found one binary system among the non-oscillating magnetic Ap stars. The detected companion candidates have apparent K magnitudes between 6.8 and 19.5 and angular separations ranging from 0.23" to 8.9", corresponding to linear projected separations of 30-2400AU.
While our study confirms that roAp stars are indeed not very often members of binary or multiple systems, we have found four new companion candidates that are likely physical companions. A confirmation of their status will help understanding the origin of the roAp stars.

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ksushil970


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Magnetic Ap stars are stars in the ethereal class B9-A0 that have great magnetic dipole fields whose alliance is inclined with respect to the rotation axis (oblique dipole). These stars also show irregular profusions of the elements Si, Cr, Fe, and rare earths that are distributed unevenly across the stellar surface. This uneven distribution is believed to be due to the diffusion mechanism first proposed by Michaud.



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Blobrana


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Title: The evolution of Ap stars
Authors: P. North (1), J. Babel (2), D. Erspamer (3) ((1) Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, (2) Neuchâtel, Switzerland, (3) St-Maurice, Switzerland)

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 measured by us) is reviewed as well.

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