Hunting down the subdwarf populations

1. Hunting down the subdwarf populations Peter Nemeth KU Leuven, Belgium Bamberg, Germany; Sep 13, 2013

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

3. A Galex sample (Vennes et al. 2011) • ~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

4. The fitting method (XTGRID) 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

5. The fitting method (XTGRID) 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. Composite spectra Must be addressed, ~20 % of the sample shows a significant IR excess.

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

8. Temperature – gravity

9. Temperature – gravity

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

11. 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?

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? C. Binary: 4% Nitrogen: 70% C. Binary: 30% Nitrogen: 22% S. Charpinet, E. M. Green, A. Baglin et al.; 2010; A&A 516 L6

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?

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

15. Puzzling questions • How 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.

16. 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 can join at: http://stelweb.asu.cas.cz/~nemeth/work/sd1000/

17. Improvements in XTGRID • Rotational broadening; first application for CD-30 11223: 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. However, it is still demanding... • “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

18. MMT Spectra • Data for 8 BHB stars were provided by Betsy Green after the sdOB6 conference • MMT Blue Channel Spectrograph • R = 4500 • SNR ~ 200

19. Tlusty Models

20. Two conclusions • Spectral fitting with 30 elements is not a dream job • The effects of metal abundances and not just their presence are important:

21. Comparison with M22

22. Comparison with M22

23. Abundance patterns Grevesse & Sauval (1998) Solar abundances in Tlusty

24. Balloon 82000001 (HIP 65388) • HIP 65388 is the only star in Betsy’s sample that has FUSE observations. • Not much recent work is available on the star. • Tobin, W. 1986, A&A, 155, 326 • de Boer, K.S., Richtler, T., Heber, U. 1988, A&A, 202, 113 • Conlon, E.S., Brown, P.J.F., Dufton, P.L., Keenan, F.P. 1989, A&A, 224, 65 • Dissertation: Martin, J.C. 2006, AJ, 131, 3047 • Simbad: also PB 166 • Galactic coordinates: 109.3 +66.9 • Spectral type: sdB – B2 • V = 12.48 mag • vrad = -30 – -43 km/s • π = 6.45 mas (155 pc) ? • The star was observed by FUSE for 9890 sec in 2002 (PI Edward Fitzpatrick, Data ID: C1180701). According to the proposal the original intent was to carry out a complex abundance analysis in serach for the origins of halo subdwarfs. • Only one reference in MAST to the FUSE observation: • Gianninas, A., Bergeron, P., Dupuis, J., and Ruiz, M.T., 2010, ApJ, 720, 581 • Using the results from the optical spectrum, I fit the optical and UV data simultaneously. Still, for 2 months.

25. The optical data

26. A small part of the FUSE spectrum

27. Final remarks • Field BHB stars show a similar dichotomy like sdB stars. • BHB stars are interesting and might help us understand the formation of sdB stars. They are challenging and not well analised objects. • H/He fits are a quick way to derive atmospheric parameters, however if one is interested in metal abundances and precision spectroscopy, CNO and Fe must not be avoided in the structure calculations. • Element stratification might be responsible for some of the observed line profile inconsistencies and must be investigated.