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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 aurigae

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


Authors collaborators
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


Philosophy of present work
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


What do we really know about aur
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


Abundances
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


Abundances ii
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


Abundances iii
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


Spectroscopic orbit
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


Spectroscopic orbit ii
Spectroscopic Orbit II

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Orbit drawn to scale
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


Spectroscopic orbit iii
Spectroscopic Orbit III

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


F star angular diameter
F Star Angular Diameter

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Aurigae eclipse light curve
ε Aurigae: Eclipse Light Curve

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Eclipse light curve timings
Eclipse Light Curve & Timings

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Eclipse light curve timings ii
Eclipse Light Curve & Timings II

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Eclipse light curve timings iii
Eclipse Light Curve & Timings III

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Summary of results so far
Summary of Results (so far…)

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Summary of results so far1
Summary of Results (so far…)

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Summary of constraints
Summary of Constraints

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Aur summary of constraints
ε Aur: Summary of Constraints

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Additional constraints
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


Spectral energy distribution
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


Spectral energy distribution ii
Spectral Energy Distribution II

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Spectral energy distribution iii
Spectral Energy Distribution III

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


The uv continuum problem
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


The uv continuum problem ii
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


A comparison of uv continua
A Comparison of UV Continua

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Nlte models of uv continuum
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


Tlusty model results
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


Tlusty model comparisons
TLUSTY Model Comparisons

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Subtracting the f star spectrum
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


Fuv spectrum with f star removed
FUV Spectrum with F Star Removed

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Empirical line formation in winds
Empirical Line Formation in Winds

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Empirical line formation in winds ii
Empirical Line Formation in Winds II

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Observed fuv spectrum model
Observed FUV Spectrum & Model

Wind Model (red), FUSE spectrum (blue)

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Constraints from fuv spectrum
Constraints from FUV Spectrum

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Baade wesselink distance
Baade-Wesselink Distance

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Baade wesselink distance1
Baade-Wesselink Distance

UBV photometry from 1990-2012

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Baade wesselink distance2
Baade-Wesselink Distance

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Aurigae best solution
ε Aurigae: Best Solution

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Summary of constraints1
Summary of Constraints

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Aurigae best solution1
ε Aurigae: Best Solution

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Aurigae position in hrd
ε Aurigae: Position in HRD

Philip D. Bennett: 11th Hvar Astrophysical Colloquium


Thank you

Thank you!

)

Philip D. Bennett, Christine K. Wilson, and Jeffrey L. Hopkins

4 July 2012 11th Hvar Astrophysical Colloquium