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

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 σ level, was performed for the Vega-like star ι Cen, for which we measured  G. In the prototype of Vega-like stars, the star β Pictoris, which shows conspicuous signs of chromospheric activity, a longitudinal magnetic field is measured only at ~1.5 σ level. We diagnosed a longitudinal magnetic field for the first time at a level higher than 3 σ 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 doublet displays several components in both H and K lines. From the measurement of circular polarization in all Balmer lines from H_β to H₈, we obtain  G. However, using only the H and K lines for the measurement of circular polarization, we are able to diagnose a longitudinal magnetic field at 2.8 σ level,  G.