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| Paper: |
High Resolution Spectropolarimetry of the Hα Line:
Obscured Stars and Absorptive Polarization |
| Volume: |
449, Astronomical Polarimetry 2008: Science from Small to Large Telescopes |
| Page: |
295 |
| Authors: |
Harrington, D. M.; Kuhn, J. R. |
| Abstract: |
The near-star environment around obscured stars is very dynamic. Many
classes of stars show evidence for winds, disks, inflows and outflows
with many phenomena occurring simultaneously. These processes are
involved in stellar evolution, star and planet formation, and influence
the formation and habitability of planets around host stars. Even for
the nearest stars, this region will not be imaged even after the
completion of the next generation of telescopes. Other methods for
measuring the physical properties of circumstellar material must be
developed. The polarization of light across spectral lines is a
signature that contains information about the circumstellar material on
these small spatial scales. We used the HiVIS (R=13 000 to 50 000) and
ESPaDOnS (R=68 000) spectropolarimeters to monitor several classes of
stars on over a hundred nights of observing from 2004-2008. In 10/30
classical Be stars, the traditional broad depolarization morphology is
reproduced, but with some additional absorptive effects in 4 of these 10
stars. In Herbig Ae/Be stars roughly 2/3 of the stars (14/20) with
strong absorptive components (either central or blue-shifted) showed
clear spectropolarimetric signatures typically centered on absorptive
components of the spectral lines. They were typically 0.3% to 2% with
some signatures being variable in time. Post-AGB and RV Tau type evolved
stars showed very strong absorptive polarimetric effects (5/6 PAGB and
4/4 RV Tau) very similar to the Herbig Ae/Be stars. These observations
were inconsistent with the traditional scattering models and inspired
the development of a new explanation of the observed polarization. This
new model, based on optical-pumping, has the potential to provide direct
measurements of the circumstellar gas properties. |
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