Spectropolarimetric observations of Herbig Ae/Be stars. II. Comparison of spectropolarimetric surveys: HAeBe, Be and other emission-line stars.
HARRINGTON D.M. and KUHN J.R.
Abstract (from CDS):
The polarization of light across individual spectral lines contains information about the circumstellar environment on very small spatial scales. We have obtained a large number of high-precision, high-resolution spectropolarimetric observations of Herbig Ae/Be, Classical Be and other emission-line stars collected on 117 nights of observations with the Hi-Resolution Visible spectropolarimeter at a resolution of R = 13, 000 on the 3.67 m Advanced Electro-Optical System telescope. We also have many observations from the ESPaDOnS spectropolarimeter at a resolution of R = 68, 000 on the 3.6 m Canada-France-Hawaii Telescope. In roughly ∼2/3 of the so-called "windy" or "disky" Herbig Ae/Be stars, the detected Hα linear polarization varies from our typical detection threshold near 0.1% to over 2%. In all but one HAe/Be star, the detected polarization effect is not coincident with the Hα emission peak but is detected in and around the obvious absorptive part of the line profile. The qu-loops are dominated by the polarization in this absorptive region. In several stars, the polarization varies in time mostly in the absorptive component and is not necessarily tied to corresponding variations in intensity. This is a new result not seen at lower resolution. In the Be and emission-line stars, ten out of a sample of 30 show a typical broad depolarization effect but four of these ten show weaker effects only visible at high resolution. Another five of 30 show smaller amplitude, more complex signatures. Six stars of alternate classification showed large amplitude (1%-3%) absorptive polarization effects. These detections are largely inconsistent with the traditional disk-scattering and depolarization models.