The Near-Star Environment: Spectropolarimetry of Herbig Ae/Be Stars

David M. Harrington
Jeff R. Kuhn
Institute for Astronomy
University of Hawaii
dmh@ifa.hawaii.edu


     The near-star environment (inner 10's of stellar radii) around young stars is thought to be very dynamic.  There is evidence of accretion, outflows, ionized disk structures, and stellar winds, many times happening simultaneously.  Since these spatial scales, for even the closest young stars, correspond to angular scales much less than one milliarcsecond, they will not be imaged even after the completion of the next generation of telescopes decades from now.  However, the polarization of scattered light across individual resolved spectral lines contains information about the geometry and asymmetry of circumstellar material on these spatial scales.  We have recently built a high-resolution spectropolarimeter (R~13000 to 30000) for the HiVIS spectrograph on the 3.67m AEOS telescope for this purpose. In 2006-2007, we used this instrument to observe the H-alpha line of several young Herbig Ae/Be stars many times per night, sometimes continuously, over 26 nights.  These observations show clear spectropolarimetric signatures at the 0.2% to 1% level that are variable in time.  This confirms the previously reported detections and shows the level of variability in these signatures.  The analysis of this variability will constrain the small-scale changes in the near-star environment.  The survey also confirms the large spectroscopic variability of the H-alpha line in these stars on timescales of minutes to months, and shows the dyamic ÒbulletsÓ and ÒstreamersÓ in the winds of some of these young stars.