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Hunting down the subdwarf populations

Hunting down the subdwarf populations. Peter Nemeth Roy Østensen and Joris Vos KU Leuven, Belgium; In collaboration with Stephane Vennes and Adela Kawka Astronomical Institute of the Czech Republic. SDOB6; Tucson AZ, USA; May 20, 2013. A GALEX sample. How it got started.

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Hunting down the subdwarf populations

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  1. Hunting down the subdwarf populations Peter Nemeth Roy Østensen and Joris Vos KU Leuven, Belgium; In collaboration with Stephane Vennes and Adela Kawka Astronomical Institute of the Czech Republic SDOB6; Tucson AZ, USA; May 20, 2013

  2. A GALEX sample

  3. How it got started • Classical nova X-ray spectra • New model atoms from Topbase and NIST • Chi-by-eye fitting

  4. The sample • ~700 UV-excess objects, NUV-V < 0.5 • 7 observing runs at KPNO and ESO, 2007-2011 • Low-resolution, optical spectroscopy • ~200 targets, 6 new WDs • 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

  5. 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

  6. 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

  7. Composite spectra Must be addressed, ~20 % of the sample shows a significant IR excess.

  8. Composite spectra Must be addressed, ~20 % of the sample shows a significant IR excess.

  9. Temperature – gravity

  10. Temperature – gravity

  11. He abundance H. Edelmann, U. Heber, H.-J. Hagen et al.; 2003, A&A, 400, 939

  12. 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 • Are C&N class sdB and He-sdO stars related?

  13. 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 • Are C&N class sdB and He-sdO stars related? C. Binary: 4% Nitrogen: 70% C. Binary: 30% Nitrogen: 22% S. Charpinet, E. M. Green, A. Baglin et al.; 2010; A&A 516 L6

  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 • Are C&N class sdB and He-sdO stars related?

  15. Luminosity distribution* * before GAIA Correlates with observed mass distribution, eg. SPY (Lisker et al. 2005)

  16. Abundance evolution? Speculations... 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. Abundance evolution? Complicated... UV flux induces convection, turbulence, mixing, wind ... lots of complications. eg.: Unglaub, 2008

  18. 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? • These questions remain and need more attention.

  19. The SD1000 Collaboration • Spectroscopy for the largest possible sample for a better statistics and distribution. • Homogeneous analysis to find subtle trends and correlations among surface parameters. • ERC: From inhomogeneous data? • Find connections to RGs and WDs • Provide a statistically significant sample for GAIA and derive absolute luminosities and masses. • Find binary fractions and correlations between surface and binary parameters. • Collaborators needed...

  20. New improvements in XTGRID • Rotational broadening; first application for CD 3011223: v sin(i) ~170 km/s Vennes et al. (2012); Geier et al. (2013) • Simultaneous fit and radial velocity correction for multiple datasets • Efforts to speed-up model calulations with Iron-peak elements by adjusting opacity sampling parameters • “ICHANG”; examine the ionization balance • ... and numerous bug fixes New directions: • Abundance stratification • Resolve lower mass MS companions in the IR • Radial velocities from composite spectra

  21. Highlight from Paper III: GALEX J2349+3844 is a short-period eccentric binary Kawka et al.; in prep.

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