Wednesday 03 Feb 2016: Seminar: Assessing Magnetospheric Accretion in Herbig Ae/Be Stars
Dr Alicia Aarnio - University of Michigan
Physics, 4th floor 14:00-15:00
In the last few years, large spectropolarimetric surveys have found low magnetic field detection rates in Herbig Ae/Be stars. It has also been recently noted that magnetic field structure and strength dramatically change with increasing stellar mass. These results are very suggestive that the mechanisms for accretion and outflow in Herbig Ae/Be star+disk systems may differ from the magnetospheric accretion paradigm as envisaged for T Tauri star+disk systems. We have performed a high resolution optical spectroscopic campaign of ~60 Herbig AeBe stars including some multi-epoch observations; the timescales sampled range from high cadence (~minutes) to observations taken over several years, to probe a wide range of kinematic processes. We find that the strength of variability increases with the cadence of the observations, and over all timescales sampled, the strongest variability occurs within the blueshifted absorption components of the Balmer series lines. We see no inverse P-Cygni profiles, traditionally indicative of ongoing accretion. We discuss the implications of these results in context of recent spectropolarimetric surveys for our understanding of how accretion is occurring in these objects, as well as ongoing radiative transfer modeling.