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What do we really know about ε Aurigae ?

What do we really know about ε Aurigae ?. Observational Constraints and Implications for the Evolutionary State of the F Star. Kloppenborg et al. (2010). Philip D. Bennett, Christine K. Wilson, and Jeffrey L. Hopkins.

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What do we really know about ε Aurigae ?

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  1. What do we really know about εAurigae? Observational Constraints and Implications for the Evolutionary State of the F Star Kloppenborg et al. (2010) Philip D. Bennett, Christine K. Wilson, and Jeffrey L. Hopkins 4 July 2012 11th Hvar Astrophysical Colloquium

  2. Authors & Collaborators • Philip Bennett – Saint Mary’s University • Christine Wilson – Saint Mary’s University • Jeffrey Hopkins – Hopkins Phoenix Observatory Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  3. Philosophy of Present Work Previous analyses of εAurigae have tended to focus on particular aspects of the problem Here, we seek the best estimates of the parameters consistent with all available observational evidence Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  4. What do we really know about ε Aur? … actually, quite a lot • Abundances • Spectroscopic Orbit • Angular Diameter • Eclipse Light Curve • Spectral Energy Distribution • Far Ultraviolet Spectrum • Baade-Wesselink Distance Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  5. Abundances • Hinkle & Simon (1987) found 12C/13C = 10 ± 3, which suggests a late evolutionary stage • Sadakane et al. (2010) carried out a differential abundance analysis of εAur compared to the A7 Iab supergiant HD 81471 • Total CNO in εAurand HD 81471 solar, with C & O under-abundant, and N over-abundant • Na slightly over-abundant • Sr slightly under-abundant • Y, Zr, & Ba slightly over-abundant & similar to αCar • These abundances are normal for massive SGs Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  6. Abundances II • These results confirm the only processing that has occurred in εAur is due to the CNO cycle • In particular, εAur shows NO signs of third dredge-up or s-process enhancements • Post-AGB stars have [C/Fe], [O/Fe] > 0, but for εAur (& other SGs), these elements are under-abundant • Post-AGB stars have [C/Fe] > [N/Fe], due to third dredge-up of C, and total CNO > solar, but this is not the case for εAur (which has solar total CNO) • Post-AGB stars typically have [s-process/Fe] > 1, but again, this is not so for εAur Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  7. Abundances III • Sadakane et al. conclude: • ε Aur abundances are normal for massive SGs except for a slight over-abundance of Y, Zr, Ba • NO evidence for post-AGB nature of F star  ε Aur is probably an F supergiant Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  8. Spectroscopic Orbit • We adopted the mean of the FOTEL & PHOEBE solutions of Chadima et aL. (2010): • Tmin = JD 245 5403.3 ± 1.1 [eclipse epoch] • P = 9890.62 ± 0.56 d [orbital period] • n = 2π/P =7.3526 ⨉ 10-9 s-1[mean motion] • e = 0.253 ± 0.014 [eccentricity] • ω = 42.25°± 3.6° [longitude of periastron] • K1 = 14.35 ± 0.32 km s-1 [primary orbit amplitude] • v0 = -2.26 ± 0.15 km s-1 [systemic velocity] Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  9. Spectroscopic Orbit II Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  10. Orbit Drawn to Scale • This figure shows the orbit of Chadima et al. (2010) drawn to scale • Top panel is a view looking down at the orbit plane • Middle is edge-on view • Bottom panel is as seen projected on the sky Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  11. Spectroscopic Orbit III Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  12. F Star Angular Diameter Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  13. ε Aurigae: Eclipse Light Curve Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  14. Eclipse Light Curve & Timings Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  15. Eclipse Light Curve & Timings II Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  16. Eclipse Light Curve & Timings III Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  17. Summary of Results (so far…) Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  18. Summary of Results (so far…) Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  19. Summary of Constraints Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  20. ε Aur: Summary of Constraints Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  21. Additional Constraints What other observational constrains can we apply to this binary? • Start with the spectral energy distribution (SED) • Distance estimates derived from the Baade-Wesselink method (Wilson et al., this meeting) Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  22. Spectral Energy Distribution • Spectrum is ~F0 supergiant • Moderately reddened: Av = 1.07 magnitudes • SED fits give Teff = 7000 K, θD = 2.2 mas • F star dominates between 1300 Å and 3 μm • < 1300 A: photons from hot source dominate • > 3 μm: dust emission dominates Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  23. Spectral Energy Distribution II Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  24. Spectral Energy Distribution III Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  25. The UV Continuum Problem • Note the ultraviolet spectrum for λ< 2000 Å disagrees with the models by 1 dex at 1500 Å • This is a model deficiency and NOT excess flux due to a hot star continuum, as claimed by Hoard et al. (2010) • The Lejeuene et al. (1997) models used here are LTE models and do not realistically represent the UV continuum of the F star. • To do this, we need non-LTE (NLTE) models Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  26. The UV Continuum Problem II • Do we see the hot star at all? • To examine this, we look at 2 hot star model spectra in the UV, reddened with Av= 1.07, and compare to the observed UV spectrum: • Early B star model (B1 V) with Teff=25000 K, and • Mid B star model (B5 V) with Teff=15000 K • Observed FUSE/HST/IUE spectrum of εAur • It is evident that the UV spectrm of εAur does not resemble a B star in shape, or lines present, or brightness (εAur is much fainter!) Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  27. A Comparison of UV Continua Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  28. NLTE Models of UV Continuum • We have modelled the UV spectrum of εAur with more appropriate models: NLTE models computed using Ivan Hubeny’s TLUSTY code • These NLTE models of the UV continuum included 33 levels of H-, H I, Si I, Mg I, Al I, Fe I, C I and S I • Equivalent LTE TLUSTY models were also computed Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  29. TLUSTY Model Results • NLTE models of the UV continuum included 33 levels of H-, H I, Si I, Mg I, Al I, Fe I, C I and S I • Equivalent LTE models were also computed • The LTE model had far too little continuum flux at λ < 1682 Å, the Si I 1D bound-free edge • In contrast, the NLTE models had too much continuum flux at these wavelengths. • Surprisingly, a linear combination of log FλofLTE & NLTE models agreed well with observations! Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  30. TLUSTY Model Comparisons Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  31. Subtracting the F Star Spectrum • With a reasonable model for the UV spectrum of the F star, we can subtract this from the observed far UV (FUV) spectrum with some emission lines appear • The result (black curve in next slide) is an emission line spectrum throughout the FUV • This tells us something is producing FUV photons (which an F star will not) • This is the long sought after hot companion! Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  32. FUV Spectrum with F Star Removed Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  33. Empirical Line Formation in Winds Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  34. Empirical Line Formation in Winds II Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  35. Observed FUV Spectrum & Model Wind Model (red), FUSE spectrum (blue) Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  36. Constraints from FUV Spectrum Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  37. Baade-Wesselink Distance Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  38. Baade-Wesselink Distance UBV photometry from 1990-2012 Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  39. Baade-Wesselink Distance Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  40. ε Aurigae: Best Solution Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  41. Summary of Constraints Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  42. ε Aurigae: Best Solution Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  43. ε Aurigae: Position in HRD Philip D. Bennett: 11th Hvar Astrophysical Colloquium

  44. Thank you! ) Philip D. Bennett, Christine K. Wilson, and Jeffrey L. Hopkins 4 July 2012 11th Hvar Astrophysical Colloquium

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