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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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