S. Hubrig, M. Schoeller, I. Ilyin, C. R. Cowley, Z. Mikulasek, B. Stelzer, M. A. Pogodin, R. V. Yudin, M. Cure
Our knowledge of the presence and the role of magnetic fields in
intermediate-mass pre-main-sequence stars remains very poor.
We present the magnetic properties of four Herbig Ae/Be stars that have not
been previously studied in detail.
Our results for the three Herbig Ae/Be stars HD97048, HD150193, and HD176386
are based on multi-epoch low-resolution spectra obtained in spectropolarimetric
mode with FORS2 mounted on the VLT. New high-resolution polarimetric spectra
were obtained for MWC480 with the SOFIN spectrograph installed at the Nordic
Optical Telescope. We discuss 41 FORS2 low-resolution observations of the
Herbig Ae/Be stars HD97048, HD150193, and HD176386 and determine their
rotational periods. Using stellar fundamental parameters and the longitudinal
magnetic field phase curves, we place constraints on the magnetic field
geometry. Three high-resolution circularly polarised SOFIN spectra obtained for
MWC480 were measured using the moment technique where wavelength shifts between
right- and left-hand side circularly polarised spectra are interpreted in terms
of a longitudinal magnetic field .
Our search for periodicities resulted in P=0.693d for HD97048, P=1.317d for
HD150193, and P=0.899d for HD176386. The magnetic field geometry can likely be
described by a centred dipole with a polar magnetic field strength B_d of
several hundred Gauss. The longitudinal magnetic-field measurements of MWC480
reveal the presence of a strong kG field, which was undetected in our previous
low-resolution polarimetric observations with FORS1. A weak magnetic field was
detected in the circumstellar components of the Ca II H&K lines and the Na I D
lines, indicating a complex interaction between the stellar magnetic field and
the circumstellar environment.
View original:
http://arxiv.org/abs/1111.2186
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