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Paper: Magnetism of Herbig Ae/Be stars
Volume: 449, Astronomical Polarimetry 2008: Science from Small to Large Telescopes
Page: 262
Authors: Wade, G. A.; Alecian, E.; Grunhut, J.; Catala, C.; Bagnulo, S.; Folsom, C. P.; Landstreet, J. D.
Abstract: Observations of magnetic fields of stars at the pre-main sequence phase can provide important new insights into the complex physics of the late stages of star formation. This is especially true at intermediate stellar masses, where magnetic fields are strong and globally organized, and therefore most amenable to direct study. Recent circularly-polarized spectroscopic observations of pre-main sequence Herbig Ae/Be stars have revealed the presence of organized magnetic fields in the photospheres of a small fraction of these objects. To date, 9 magnetic HAeBe stars have been detected, and those detections confirmed by repeated observations. The morphology and variability of their Stokes V signatures indicates that their magnetic fields have important dipole components of ∼kG strength, and that the dipole is stable on timescales of at least years. These magnetic stars exhibit a large range of stellar mass, from ∼2–13M, and diverse rotational properties, with v sin i from a few km/s to ∼ 200 km/s. Most magnetic HAeBe stars show approximately solar abundances; they clearly do not generally exhibit the strong and systematic peculiarities of the magnetic main sequence A and B type stars (the Ap/Bp stars). The observed fractional bulk incidence of magnetic HAeBe stars is about 7%, a value compatible with the incidence of magnetic intermediate-mass stars on the main sequence. This low incidence is at odds with formation scenarios generally involving magnetically-mediated accretion. The similarily between the magnetic properties of the pre-main sequence and main sequence intermediate-mass stars appears compatible with the hypothesis of a fossil origin of magnetism in these objects.
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