1. Spectrally-polarized features of ε Aurigae: In and out of eclipse
Graduate colloquium
May 6, 2013
Spectrally-polarized features of ε Aurigae: In and out of eclipse
Presented by Kathy Geise
Thank you to
Robert Stencel, University of Denver
Nadine Manset, CFHT, Kamuela, Hawaii
Canada-France-Hawaii telescope

2. Research goals Hypothesis Methods Broader impacts
The eclipsing disk material originates from the visible star in this binary stellar system
Methods
Differential (time series) analysis of spectropolarimetric data before, during and after eclipse
Broader impacts
Unique “laboratory” to study a planet-forming disk and binary system evolution

3. Outline System overview Polarization refresher
QU frame to stellar frame of reference
ESPaDOnS observations (50+ epochs)
Data rotation, radial velocity correction
Automated spectral (absorption) line fitting
Automatic Routine for line Equivalent widths in stellar Spectra (ARES) Sousa et al. (2007)
Results: Polarized atomic species

4. Epsilon Aurigae, system overview
Spectroscopic single lined binary
Line polarization intrinsic to F star
Additional spectropolarimetric features during eclipse
AJC April 17, 2013

5. Stokes parameters Stokes vector
Before I show you a sample of the data, I need to explain the Stokes parameters. Light can be represented by 4 parameters
– One for the Intensity (all photons)
– Two for linear polarization
– One more for circular polarization
• Those parameters are called Stokes parameters
Often represented as a 4 vector
Linear polarization is usually caused by scattering (on electrons, or dust grains) in an asymmetric envelope
Circular polarization is usually caused by magnetic fields
Stokes vector

6. Calculate %p and P.A. from Stokes parameters
Bagnulo et al. (2009)

7. Stokes frame to stellar reference frame

9. Rotation angle
Motion along a line with a position angle of ± 6.85 degrees
Rotate observations 27 degrees into the stellar frame
Kloppenborg et al. 2010
AJC April 17, 2013

10. Rotation angle
Simulated rotation

11. Rotated QU data Fe II Fe II rotated
Rotation matrix from Code, A. & Whitney B. (1995)

12. Sousa et al. (2007)

13.
Fitted with single Gaussian

14. IDL Routine Polarization peaks ≥ 4σ Hack line list ARES output file
species

15. IDL Routine

16. IDL Routine

17. IDL Routine

18. Next Steps Expand line list to include full range of wavelengths
All epochs
Eclipse species?
Analyze position angle
Analyze scattering behavior when the F star is not uniformly eclipsed

19. Thank you
This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency.