1. DU Graduate colloquium February 25, 2015
An analysis of the most polarized atomic lines in out-of-eclipse observations of the bright star epsilon Aurigae
Presented by Kathy Geise
Thank you to
Paul Hemenway, Jennifer Hoffman,
Mark Siemens, Robert Stencel,
Nadine Manset (CFHT, Hawaii)
My topic today…
Thank my research advisor Dr. Stencel and our collaborator in Hawaii, Nadine Manset
Canada France Hawaii Telescope

2. Outline Introduction ESPaDOnS observations (11 out-of-eclipse)
Spectopolarimetry, Epsilon Aurigae
ESPaDOnS observations (11 out-of-eclipse)
An unusual observation
Spectropolarimetry may be used to break degeneracies found in intensity-only data
Conclusions / Next steps
Eps Aur system overview
Research goals
Polarized light & Stokes parameters
Dipole scattering polarization

3. Spectropolarimetry
Wavelength and polarization are the bits of information attached to every photon that reveal the most about formation and history
Spectropolarimetry
Combines spectra with polarimetry in one device
Spectra
sort photons by wavelengths
Polarimetry
unravels the physics of their history from the emission site all the way to the observer

4. AU
disk
Distance uncertain; mass of objects uncertain; q is mass ratio q1/q2 q1 is primary
F star
Contributes visible spectral features consistent with designation
Variable in brightness, absorption EW, line profiles, polarization
B star embedded in dusty disk
Contributes spectral features for a short time during eclipse
Not to scale

5. Sky frame N E Kloppenborg et al. 2010, Nature
Frames of reference, interferometrically resolved Kloppenborg et al 2010
On the sky, north up east left
Stellar frame rotation axis is up
Kloppenborg et al. 2010, Nature

6. Stellar frame Kloppenborg et al. 2010, Nature
Frames of reference, interferometrically resolved Kloppenborg et al 2010
On the sky, north up east left
Stellar frame rotation axis is up
Kloppenborg et al. 2010, Nature
Stellar frame

7. Polarized Light Stokes parameters
Position angle in Stokes reference frame translates to position angle on the sky

8. Asymmetries and polarization for unresolved objects
Spherical
Disk
Net polarization
No net polarization
From Bjorkman, K. (2012)

9. α Lep (F0Ib)
Alpha Leporis is a supergiant star at a distance of about 680 parsec. (Wiki)
Luminosity class Ib is less luminous than Ia supergiant designation

10. ε Aur (F0Ia)

11. ESPaDOnS observations
Date
RJD
Phase*
RV [km/s]
2006 Feb 8
0.93
13.99
2008 Aug 25
0.02
9.00
2008 Oct 18
0.03
8.40
2008 Dec 7
7.82
2008 Dec 8
7.81
2008 Dec 9
7.80
2008 Dec 10
7.79
2008 Dec 16
7.71
2009 Feb 13
0.04
7.01
2009 Feb 14
7.00
2009 Feb 17
6.96
* Periastron phase 0.0

12. H I ( nm)

13. H I ( nm)

14. H I ( nm)

15. H I ( nm)

16. H I ( nm)
Data have been rotated into the stellar frame of reference

17. H I ( nm)

19. Adapted from Tan 1985; Cha et al. 1994
CHA Guang-we, TAN Hui-song, XU Jun, LI Yong-sheng
Not to scale
Adapted from Tan 1985; Cha et al. 1994

20. Conclusions / Next steps
Persistent linear polarization associated with F star in OOE observations
Resonant scattering from gas species
Absorption lines and polarization are variable
PA largely low angles, possible ring of circumstellar material
Unusual spectrum
New blue-shifted spectral feature in Hα
Different PA in line core and wings
Polarization suggests equatorial enhancement in blue-shifted (outflow) material
Next step – finish paper!

21. Thank you!

23. Epsilon Aurigae 2009-2011 eclipse
Description
Date
RJD
Phase
1st contact
2009 Aug 16
5066
0.056
2nd contact
2010 Feb 22
5250
0.074
Mid-eclipse
2010 Jul 22
5384
0.088
3rd contact
2011 Feb 27
5639
0.114
4th contact
2011 Aug 26
5703
0.120
Stencel 2012

24. Research goals Goals Methods Broader impacts
Show that 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
Goals
Show that 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

25. H I ( nm)

26. H I ( nm)

27. H I ( nm)

28. Fe II nm

29. Fe II nm

30. Fe II nm

31. Ca I ( nm)

33. Ti II ( nm)

34. Ti II ( nm)

35. Coherent
Absorption (by atomic species) followed by emission
Final atomic state same as initial atomic state
Emitted frequency of light the same as absorbed frequency of light (coherent, no energy loss)
Scattering cross section σ may be different than absorption cross section κ
Observed polarization depends upon number of scatterers, scattering angle, “polarizability” of transition
Ignace (2006)

38. Equivalent width

39. Scattering from bound electrons – classical vs
Scattering from bound electrons – classical vs. quantum mechanical models
Scattering cross section (classical model)
Scattering cross section (quantum mechanical model)
Scattering cross section is a function of frequency
S  P  S transition (no electron spin; no fine structure splitting)
Omega is the angular frequency of the perturbing wave
Tau_e is approximately the time for light to travel a distance equal to the classical electron radius
Enters the equation from the classical damping constant in the equation of motion
Transition between quantum states represent ‘natural frequencies’
Phi_L Lorentz profile
Need QM model to explain observed polarization in unpolarizable transitions
Transitions between quantum states: i, j
Cross section for resonance scattering becomes
The absorption oscillator strength, fij, corrects for the many electron transitions governed by quantum mechanical rules
ΦL(ν) is the Lorentz function

40. Scattering from bound electrons – quantum mechanical model
Transitions between quantum states: i, j
Cross section for resonance scattering becomes
The absorption oscillator strength, fij, corrects for the many electron transitions governed by quantum mechanical rules
Transition between quantum states represent ‘natural frequencies’
Phi_L Lorentz profile
Need QM model to explain observed polarization in unpolarizable transitions

41. Transition between quantum states represent ‘natural frequencies’
Phi_L Lorentz profile

42. Scattering from bound electrons – quantum mechanical model
Lorentz profile
Sum of the Einstein coefficients between the lower state i and all states k below it
The DAMPING RATE gamma (Stenflo 2005) =

43. Polarization and asymmetries for unresolved objects
Bjorkman, K. (2012)

44. AU
disk
Distance uncertain; mass of objects uncertain; q is mass ratio q1/q2 q1 is primary
F star
Contributes visible spectral features consistent with designation
Variable in brightness, absorption EW, line profiles, polarization
B star embedded in dusty disk
Contributes spectral features for a short time during eclipse
Not to scale

45. AU
disk
Distance uncertain; mass of objects uncertain; q is mass ratio q1/q2 q1 is primary
F star
Contributes visible spectral features consistent with designation
Variable in brightness, absorption EW, line profiles, polarization
B star embedded in dusty disk
Contributes spectral features for a short time during eclipse
Not to scale