Spectropolarimetry of the H-alpha line in Herbig Ae/Be stars

Abstract

Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS telescope, we have obtained a large number of high precision spectropolarimetrc observations (284) of Herbig AeBe stars collected over 53 nights totaling more than 300 hours of observing. Our sample of five HAeBe stars: AB Aurigae, MWC480, MWC120, MWC158 and HD58647, all show systematic variations in the linear polarization amplitude and direction as a function of time and wavelength near the H-alpha line. In all our stars, the H-alpha line profiles show evidence of an intervening disk or outflowing wind, evidenced by strong emission with an absorptive component. The linear polarization varies by 0.2% to 1.5% with the change typically centered in the absorptive part of the line profile. These observations are inconsistent with a simple disk-scattering model or a depolarization model which produce polarization changes centered on the emmissive core. We speculate that polarized absorption via optical pumping of the intervening gas may be the cause.

Accepted for publication in ApJ Letters

References in corpus (2)

• On the difference between Herbig Ae and Herbig Be stars
• The new HiVIS spectropolarimeter and spectropolarimetric calibration of the AEOS telescope

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• Spectropolarimetric observations of Herbig Ae/Be Stars I: HiVIS spectropolarimetric calibration and reduction techniques
• Scattering Polarization of Hydrogen Lines in Weakly Magnetized Stellar Atmospheres I. Formulation and Application to Isothermal Models
• Calibrating and Stabilizing Spectropolarimeters with Charge Shuffling and Daytime Sky Measurements
• Ultraviolet Spectropolarimetric Diagnostics of Hot Star Magnetospheres
• Spectropolarimetry of massive stars: Requirements and potential from today to 2030