Characterising the magnetic fields of the Herbig Ae/Be stars HD97048, HD150193, HD176386, and MWC480

Abstract

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 <B_z>. 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.

8 pages, 9 figures, 5 tables, accepted for publication in A&A

References in corpus (2)

• A study of the magnetic field in the photospheric and circumstellar components of Herbig Ae stars
• Molecular hydrogen in the circumstellar environments of Herbig Ae/Be stars probed by FUSE

Cited by in corpus (8)

• Temperaments of young stars: Rapid mass-accretion rate changes in T Tauri and Herbig Ae stars
• RoboPol: A four-channel optical imaging polarimeter
• HARPS spectropolarimetry of Herbig Ae/Be stars
• Measuring the mass accretion rates of Herbig Ae/Be stars with X-shooter
• Investigating the origin and spectroscopic variability of the near-infrared HI lines in the Herbig star VV Ser
• Linking Signatures of Accretion with Magnetic Field Measurements - Line Profiles are not Significantly Different in Magnetic and Non-Magnetic Herbig Ae/Be Stars
• Magnetic fields of Herbig Ae/Be stars
• Shaping core dynamos in A-type stars: The role of dipolar fossil fields