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

Outline Introduction ESPaDOnS observations (11 out-of-eclipse) Spectopolarimetry, Epsilon Aurigae ESPaDOnS observations (11 out-of-eclipse) An unusual observation 2006-02-08 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

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

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

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

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

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

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

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

ε Aur (F0Ia)

ESPaDOnS observations Date RJD Phase* RV [km/s] 2006 Feb 8 3774.92 0.93 13.99 2008 Aug 25 4704.04 0.02 9.00 2008 Oct 18 4757.92 0.03 8.40 2008 Dec 7 4807.82 7.82 2008 Dec 8 4808.83 7.81 2008 Dec 9 4809.83 7.80 2008 Dec 10 4810.83 7.79 2008 Dec 16 4817.05 7.71 2009 Feb 13 4875.71 0.04 7.01 2009 Feb 14 4876.70 7.00 2009 Feb 17 4879.85 6.96 * Periastron phase 0.0

H I (656.28 nm)

H I (656.28 nm)

H I (656.28 nm)

H I (656.28 nm)

H I (656.28 nm) Data have been rotated into the stellar frame of reference

H I (656.28 nm)

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

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 2006-02-08 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!

Thank you!

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

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

H I (656.28 nm)

H I (656.28 nm)

H I (656.28 nm)

Fe II 473.144 nm

Fe II 473.144 nm

Fe II 473.144 nm

Ca I (422.67 nm)

Ti II (450.83 nm)

Ti II (450.83 nm)

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)

http://science.howstuffworks.com/magnet3.htm

Equivalent width

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

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

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

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) =

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

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

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