Astron. Astrophys. 327, 1137-1146 (1997)

Abundance analysis of roAp stars

IV. HD 24712 ^*

T.A. Ryabchikova ¹, J.D. Landstreet ^{2, 5}, M.J. Gelbmann ³, G.T. Bolgova ¹, V.V. Tsymbal ⁴ and W.W. Weiss <sup>3

1</sup> Institute for Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia (e-mail: ryabchik@inasan.rssi.ru)
² Astronomy Department, University of Western Ontario, London, Ontario N6A 3K7, Canada (e-mail: jlandstr@phobos.astro.uwo.ca)
³ Institute for Astronomy, Univ. Vienna, Türkenschanzstr. 17, A-1180 Vienna, Austria (e-mail: last name@galileo.ast.univie.ac.at)
⁴ Simferopol State University, Crimea, Ukraine
⁵ Guest Observer at Las Campanas Observatory, which is operated by the Carnegie Institution of Washington

Received 20 May 1997 / Accepted 1 July 1997

Abstract

We present the first abundance analysis of the rapidly oscillating chemically peculiar star HD 24712, and determine a = 7250 K, = 4.3, and = 1 km s^-1. Microturbulence seems to be entirely simulated by a magnetic field with a polar field strength of 4.4 kG and of dipolar structure, both of which are supported by our polarimetric observations.

Rotation of HD 24712 and a spotty surface distribution of the elements result in different mean abundances for different (magnetic) phases.

Our results do not support the hypothesis of a monotonic correlation between the amplitude of abundance variations and the atomic number Z, and we present arguments in favour of one of the rotation periods (P_rot = 12:d4610) discussed in the literature.

Rare earth elements are the most overabundant elements relative to the sun, and they have the largest abundance amplitude during a rotation cycle; only Mg has a larger amplitude. For HD 24712 we find a clear overabundance of Co while most of the other iron peak elements are underabundant.

A comparison of the abundance pattern with the other three roAp stars analyzed so far by us concludes the paper.

A systematic difference between surface gravities obtained from spectroscopy and from both asteroseismology and evolutionary tracks is found for the roAp stars HD 24712, Cir and Equ.

Key words: stars: abundances chemically peculiar magnetic field oscillations pulsations individual: HD 24712

* Based on observations obtained with the Canada-France-Hawaii telescope, operated by the National Research Council of Canada, the Centre Centre National de la Recherche Scientifique de France, and the University of Hawaii, and on observations obtained at CARSO, Las Campanas, Chile

Send offprint requests to: Werner W. Weiss

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Contents

• 1. Introduction
• 2. Observations
• 3. Reduction of spectra
• 4. The period of the magnetic, spectrum and light variations
• 5. The magnetic field of HD 24712
• 6. The model atmosphere
• 7. Abundance analysis
  • 7.1. Light elements: C to Ca
  • 7.2. Iron peak elements: Sc to Ni
  • 7.3. s -process elements: Sr, Y, In and Ba
  • 7.4. Rare Earth elements: La to Er
• 8. Evolutionary status
• 9. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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