HD 178892 – a cool Ap star with extremely strong magnetic field

Free access article

Issue		A&A Volume 445, Number 3, January III 2006


Page(s)		L47 - L50
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200500222

A&A 445, L47-L50 (2006)
DOI: 10.1051/0004-6361:200500222

Letter

HD 178892 - a cool Ap star with extremely strong magnetic field

T. Ryabchikova^{1, 2}, O. Kochukhov³, D. Kudryavtsev⁴, I. Romanyuk⁴, E. Semenko⁴, S. Bagnulo⁵, G. Lo Curto⁵, P. North⁶ and M. Sachkov²

¹ Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Wien, Austria
e-mail: ryabchik@inasan.ru
² Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia
³ Department of Astronomy and Space Physics, Uppsala University Box 515, 751 20 Uppsala, Sweden
⁴ Special Astrophysical Observatory of RAS, Nizhnij Arkhyz 369167, Russia
⁵ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁶ Laboratoire d'Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire, 1290 Sauverny, Switzerland

(Received 25 October 2005 / Accepted 29 November 2005 )

Abstract
We report a discovery of the Zeeman resolved spectral lines, corresponding to the extremely large magnetic field modulus $\langle B_{\rm s}\rangle$ = 17.5 kG, in the cool Ap star HD 178892. The mean longitudinal field of this star reaches 7.5 kG, and its rotational modulation implies the strength of the dipolar magnetic component $B_{\rm p}\ge$ 23 kG. We have revised rotation period of the star using the All Sky Automated Survey photometry and determined P = 8.2478 d. Rotation phases of the magnetic and photometric maxima of the star coincide with each other. We obtained Geneva photometric observation of HD 178892 and estimated $T_{\rm eff}$ = $7700\pm250$ K using photometry and the hydrogen Balmer lines. Preliminary abundance analysis reveals abundance pattern typical of rapidly oscillating Ap stars.

Key words: stars: magnetic fields -- stars: chemically peculiar -- stars: individual: HD 178892

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