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Issue A&A
Volume 446, Number 3, February II 2006
Page(s) 1089 - 1094
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20053794

A&A 446, 1089-1094 (2006)
DOI: 10.1051/0004-6361:20053794

Accurate magnetic field measurements of Vega-like stars and Herbig Ae/Be stars

S. Hubrig1, R. V. Yudin2, 3, M. Schöller1 and M. A. Pogodin2, 3

1  European Southern Observatory, Casilla 19001, Santiago 19, Chile
    e-mail: shubrig@eso.org
2  Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, 196140 Saint-Petersburg, Russia
3  Isaac Newton Institute of Chile, St.-Petersburg Branch, Russia

(Received 8 July 2005 /Accepted 19 September 2005)

Abstract
We obtained accurate circular spectropolarimetric observations of a sample of Vega-like and Herbig Ae/Be stars with FORS 1 at the VLT in an attempt to detect their magnetic fields. No magnetic field could be diagnosed in any Vega-like star. The most accurate determination of a magnetic field, at 2.6 $\sigma$ level, was performed for the Vega-like star $\iota$ Cen, for which we measured $\left<B_z\right>=-77\pm30$ G. In the prototype of Vega-like stars, the star $\beta$ Pictoris, which shows conspicuous signs of chromospheric activity, a longitudinal magnetic field is measured only at ~1.5 $\sigma$ level. We diagnosed a longitudinal magnetic field for the first time at a level higher than 3 $\sigma$ for the two Herbig Ae stars HD 31648 and HD 144432 and confirm the existence of a previously detected magnetic field in a third Herbig Ae star, HD 139614. Finally, we discuss the discovery of distinctive Zeeman features in the unusual Herbig Ae star HD 190073, where the $\ion{Ca}{ii}$ doublet displays several components in both H and K lines. From the measurement of circular polarization in all Balmer lines from H$_\beta$ to H8, we obtain $\left<B_z\right>=+26\pm34$ G. However, using only the $\ion{Ca}{ii}$ H and K lines for the measurement of circular polarization, we are able to diagnose a longitudinal magnetic field at 2.8 $\sigma$ level, $\left<B_z\right>=+84\pm30$ G.


Key words: stars: pre-main sequence -- stars: magnetic fields -- stars: individual: HD 31648 -- stars: individual: HD 139614 -- stars: individual: HD 144432 -- stars: individual: HD 190073

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