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A&A
Volume 415, Number 2, February IV 2004
Page(s) L13 - L16
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040001


A&A 415, L13-L16 (2004)
DOI: 10.1051/0004-6361:20040001

Letter

No magnetic field variation with pulsation phase in the roAp star $\gamma$ Equulei

O. Kochukhov1, T. Ryabchikova1, 2 and N. Piskunov3

1  Institut für Astronomie, Universität Wien, Türkenschanzstraße 17, 1180 Wien, Austria
2  Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia
3  Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden

(Received 26 November 2003 / Accepted 5 January 2004)

Abstract
We present an analysis of 210 high-resolution time-resolved spectropolarimetric observations of the roAp star $\gamma$ Equ obtained over three nights in August and September 2003. Radial velocity variations due to p-mode non-radial pulsations are clearly detected in the lines of rare-earth elements, in particular $\ion{Pr}{iii}$, $\ion{Nd}{ii}$ and $\ion{Nd}{iii}$. In contrast, we find absolutely no evidence for the variation of the mean longitudinal magnetic field over the pulsation period in $\gamma$ Equ at the level of 110-240 G which was recently reported by Leone & Kurtz (2003). Our investigation of the variability of circularly polarized profiles of 13  $\ion{Nd}{iii}$ lines demonstrates that, at the 3 $\sigma$ confidence level, no magnetic field variation with an amplitude above $\approx$ 40-60 G was present in $\gamma$ Equ during our monitoring of this star.


Key words: stars: atmospheres -- stars: chemically peculiar -- stars: individual: $\gamma$ Equ -- stars: magnetic fields -- stars: oscillations

Offprint request: O. Kochukhov, kochukhov@astro.univie.ac.at

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