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

2. Pannon Observatory and Visitor Center Bakonybél
K. U. Leuven - Nov. 9., 2012.

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
K. U. Leuven - Nov. 9., 2012.

4. Globular cluster CMD NGC 2880 Heber, U., 2009, ARA&A, 47, 211
Yi, S.K., 2008, ASPC, 392, 3
K. U. Leuven - Nov. 9., 2012.

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
K. U. Leuven - Nov. 9., 2012.

6. Structure of subdwarfs
sdB sdO
From Wikipedia
K. U. Leuven - Nov. 9., 2012.

7. Spectral classification
sdO – dominant H and He II absorption lines
sdB – dominant H lines, weak He I absorption lines
K. U. Leuven - Nov. 9., 2012.

8. A GALEX sample
K. U. Leuven - Nov. 9., 2012.

9. The sample 694 UV-excess objects, NUV-V < 0.5
7 observing runs,
~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
K. U. Leuven - Nov. 9., 2012.

10. The fitting method
Green: Model, T = K, log g = 5.6, log He = -1, log CNO = -2
Red: J , T = K, log g = 4.5, log He = -0.4
log C = -2.8, log N = -2.9, log O < -2.6
K. U. Leuven - Nov. 9., 2012.

11. The fitting method
Green: Model, T = K, log g = 5.6, log He = -1, log CNO = -2
Red: J , T = K, log g = 4.5, log He = -0.4
log C = -2.8, log N = -2.9, log O < -2.6
K. U. Leuven - Nov. 9., 2012.

12. Composite spectra
K. U. Leuven - Nov. 9., 2012.

13. Temperature – gravity
K. U. Leuven - Nov. 9., 2012.

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
K. U. Leuven - Nov. 9., 2012.

15. Luminosity distribution
K. U. Leuven - Nov. 9., 2012.

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
K. U. Leuven - Nov. 9., 2012.

17. Spectral evolution? Complicated.
UV flux induces convection, turbulence, mixing, wind ... lots of complications.
(Unglaub, 2008)
K. U. Leuven - Nov. 9., 2012.

18. Formation channels Canonical Hot-flasher Common Envelope
Roche Lobe Overflow
WD Mergers
Hot-flasher
Deep mixing
Shallow mixing
No mixing
K. U. Leuven - Nov. 9., 2012.

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?
K. U. Leuven - Nov. 9., 2012.

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
K. U. Leuven - Nov. 9., 2012.

21. References Zhang, X., Jeffery, S. C.; 2012, MNRAS, 419, 452
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
K. U. Leuven - Nov. 9., 2012.