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

TL;DR

This study uses high-resolution spectropolarimetry to investigate the dynamic near-star environments of Herbig Ae/Be stars, revealing signatures that challenge traditional models and suggest a new optical-pumping explanation.

Contribution

The paper introduces a novel optical-pumping model to explain spectropolarimetric signatures, advancing understanding of circumstellar gas around young stars.

Findings

Detected variable spectropolarimetric signatures centered on spectral line absorptions.

Confirmed large spectroscopic variability over short and long timescales.

Observed dynamic stellar winds with bullets and streamers.

Abstract

The near-star environment around young stars is very dynamic with winds, disks, and outflows. These processes are involved in star and planet formation, and influence the formation and habitability of planets around host stars. Even for the closest young stars, this will not be imaged even after the completion of the next generation of telescopes decades from now and other proxies must be used. The polarization of light across individual spectral lines is such a proxy that contains information about the geometry and density of circumstellar material on these small spatial scales. We have recently built a high-resolution spectropolarimeter (R~13000 to 50000) for the HiVIS spectrograph on the 3.67m AEOS telescope. We used this instrument to monitor several young intermediate-mass stars over many nights. These observations show clear spectropolarimetric signatures typically centered on absorptive components of the spectral lines, with some signatures variable in time. The survey also confirms the large spectroscopic variability in these stars on timescales of minutes to months, and shows the dyamic bullets and streamers in the stellar winds. These observations were largely inconsistent with the traditional scattering models and inspired the development of a new explanation of their polarization, based on optical-pumping, that has the potential to provide direct measurements of the circumstellar gas properties.