Magnetic Fields on T Tauri Stars: Recent
Observational Results and Future Directions
Dr. Christopher Johns-Krull, University of California, Berkeley
Classical T Tauri stars (CTTS) are roughly solar mass, pre-main
sequence stars surrounded by active accretion disks. Theoretically,
accretion of disk material onto the stellar surface should be
controlled by a strong stellar magnetic field with a substantial dipole
component. Magnetic field observations of these stars present a unique
opportunity to test our understanding of magnetic accretion which is
invoked to explain such diverse objects as accreting white dwarfs and
black holes. Here, I will present new high resolution IR spectra for
several CTTS and NTTS (similarly young stars which lack circumstellar
accretion disks). Zeeman broadening of magnetically sensitive lines
indicates that all stars observed show evidence for mean surface
magnetic fields of 1 - 3 kG. I will also present high resolution,
optical spectropolarimetric observations for a subsample of these
stars. These observations show that the fields on CTTS are not large
scale dipoles. However, we do detect strong circular polarization
in accretion diagnostics suggesting that accretion onto the star does
occur primarily along large scale stellar magnetic fields.