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Spectroscopy and the evolution of hot subdwarf stars

Spectroscopy and the evolution of hot subdwarf stars. Peter Nemeth Astronomical Institute of the Czech Republic. Pannon Observatory and Visitor Center Bakonyb él. Subdwarf stars?. The Hertzsprung-Russell diagram Red Giants, White dwarfs. Stellar evolution Stellar populations

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Spectroscopy and the evolution of hot subdwarf stars

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  1. Spectroscopy and the evolution of hot subdwarf stars Peter Nemeth Astronomical Institute of the Czech Republic

  2. Pannon Observatory and Visitor CenterBakonybél

  3. Subdwarf stars? • The Hertzsprung-Russell diagram • Red Giants, White dwarfs. • Stellar evolution • Stellar populations • Cool/hot subdwarfs • Globular cluster CMD • EHB stars. • Heavy traffic of evolved stars around the EHB

  4. Globular cluster CMD NGC 2880 Heber, U., 2009, ARA&A, 47, 211 Yi, S.K., 2008, ASPC, 392, 3

  5. What we know • Progenitor MS mass between 1 and ~5 Mʘ • Evolved, core helium burning stars • Thin hydrogen layer • Many in binaries with MS or WD companions • Direct evolution towards white dwarfs

  6. Structure of subdwarfs sdB sdO From Wikipedia

  7. Spectral classification • sdO – dominant H and He II absorption lines • sdB – dominant H lines, weak He I absorption lines

  8. A GALEX sample

  9. The sample • 694 UV-excess objects, NUV-V < 0.5 • 7 observing runs, 2007-2011 • ~200 targets • Low-resolution, optical spectroscopy • Modeling with TLUSTY-SYNSPEC • Paper I: 52 stars, interpolation in 3 grids, H, He • Paper II: 180 stars, steepest-descent with a constant level structure, H, He, CNO

  10. The fitting method Green: Model, T = 40 000 K, log g = 5.6, log He = -1, log CNO = -2 Red: J2059+4232, T = 20 700 K, log g = 4.5, log He = -0.4 log C = -2.8, log N = -2.9, log O < -2.6

  11. The fitting method Green: Model, T = 40 000 K, log g = 5.6, log He = -1, log CNO = -2 Red: J2059+4232, T = 20 700 K, log g = 4.5, log He = -0.4 log C = -2.8, log N = -2.9, log O < -2.6

  12. Composite spectra

  13. Temperature – gravity

  14. Abundances • Multiple dichotomies • Can abundance patterns indicate the evolution or other properties, like pulsations, of these stars? • HST STIS shows high abundances of iron-peak elements, but not much Fe. (O’Toole & Heber, 2006) • Slow, rapid and hybrid pulsators are well separated, but not preictable

  15. Luminosity distribution

  16. Spectral evolution? Canonical Hot-flasher e.g.: Zhang X., Jeffery S. C., 2012, MNRAS, 419, 452 e.g.: Miller Bertolami M. M. et al., 2008, A&A, 491, 253

  17. Spectral evolution? Complicated. UV flux induces convection, turbulence, mixing, wind ... lots of complications. (Unglaub, 2008)

  18. Formation channels • Canonical • Common Envelope • Roche Lobe Overflow • WD Mergers • Hot-flasher • Deep mixing • Shallow mixing • No mixing

  19. Puzzling questions • How do subdwarfs form? Which formation scenarios are viable and what are their contributions to the observed SD distribution? • What drives the mass-loss on the RGB? • He-sdO  ?  sdB • How clean is the observed population from ELM WD, post-AGB, CSPN stars?

  20. The SD1000 Collaboration • We need spectroscopy for a large sample • Repeat (and later extend) the analysis in a homogeneous way • Derive homogeneous parameters • Collaborations are important because subdwarfs link RGs to WDs • GAIA will provide distances and masses • Find binaries

  21. References • Østensen, R.H.; Comm. in Asteroseismology, 2008, 159, 75 • Heber, U.; ARA&A, 2009, 47, 211 • sdB sdO page on Wikipedia • Zhang, X., Jeffery, S. C.; 2012, MNRAS, 419, 452 • Miller Bertolami, M. M. et al.; 2008, A&A, 491, 253 • Yi, S.K.; 2008, ASPC, 392, 3 • O’Toole, S.J; Heber, U.; 2006, A&A, 452, 579 • Unglaub, K.; 2008, A&A, 486, 923

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