Modelling winds of really metal-poor carbon stars: Not as expected - - PowerPoint PPT Presentation

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Modelling winds of really metal-poor carbon stars: Not as expected - - PowerPoint PPT Presentation

Jun 18, 2023 363 likes •574 views

Modelling winds of really metal-poor carbon stars: Not as expected Lars Mattsson Dark Cosmology Centre, NBI, Copenhagen Anja Andersen (Dark) Bernhard Aringer (Vienna) Kjell Eriksson (Uppsala) Susanne Hfner (Uppsala) Carbon stars Mass

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Modelling winds of really metal-poor carbon stars: Not as expected

Lars Mattsson Dark Cosmology Centre, NBI, Copenhagen

Anja Andersen (Dark) Bernhard Aringer (Vienna) Kjell Eriksson (Uppsala) Susanne Höfner (Uppsala)

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Carbon stars

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Mass loss

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Low metallicity

Sloan et al. (2008, Science, 323, 354)

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Model

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Model

Mattsson et al. 2008, A&A, 484, L5

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Model

“Standard” model star:

  • Mass: 1 M8
  • Luminosity: log(L/L8) = 3.85 (~ 7080 solar lum.)
  • Surface temperature: Teff = 2800 K
  • Carbon excess: log(C-O) + 12 = 8.50
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[Fe/H] = 0.0

3.77 10-6 15.6 0.248

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[Fe/H] = -0.5

3.55 10-6 14.0 0.229

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[Fe/H] = -1.0

3.17 10-6 13.4 0.218

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[Fe/H] = -2.0

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[Fe/H] = -2.0

Ballistics!

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[Fe/H] = -2.0

Does a higher luminosity do the trick?

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[Fe/H] = -2.0

Does a higher luminosity do the trick?

Nope!

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[Fe/H] = -2.0

Log(L/L8) = 4.15

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[Fe/H] = -2.0

But changing the effective temperature...?

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[Fe/H] = -2.0

But changing the effective temperature...?

Not a chance!

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[Fe/H] = -2.0

Mattsson et al. 2010, A&A, 509, A14

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Molecules

Molecular opacity may change this scenario: O-enhancement: C + O → CO H + O → H2O, OH ?? N-enhancement: H + N → NH3 H + N + C → HCN

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Conclusion and

  • pen questions
  • There exist a critical metallicity below which the

necessary conditions for dust nucleation cannot be met.

  • O/N-enhancment may improve the conditions for

nucleation, but the critical metallicity seems inevitable.

  • If these stars have no dust-driven winds – how do they

lose their mass? Is there another mechanism?

  • Or do they not lose mass and go ka-boom as some

peculiar type of Type I-ish supernovae?

  • Any better ideas?!?