1. A Spectroscopic Survey of Bright DA(…) White Dwarfs Alexandros Gianninas, Pierre Bergeron Université de Montréal Jean Dupuis Canadian Space Agency Maria Teresa Ruiz Universidad de Chile

2. EUROWD 2010 2 Survey Initial survey aimed at studying ZZ Ceti instability strip (Gianninas et al. 2005, 2006) Serendipitous discovery of GD 362 (Gianninas et al. 2004) PhD thesis : expand survey to cover all DA white dwarfs in McCook & Sion catalog with V < 17.5 Motivation : study and understand and all bright (nearby) WD’s (see also posters by Limoges and Giammichele) Observational sample of 1495 WD’s

3. EUROWD 2010 3 Final tally Total spectra in final sample = 1334 89% complete, most missing spectra for stars in the southern hemisphere 706 total spectra obtained specifically for this project from 2003-2010

4. EUROWD 2010 4 S/N 52% with S/N > 70 78% with S/N > 50

5. EUROWD 2010 5 Analysis Standard spectroscopic technique using new Balmer-line profiles from Tremblay & Bergeron (2009) Other types require more in depth analyses:  DA+DB

6. EUROWD 2010 6 DA+DB

7. EUROWD 2010 7 Analysis Standard spectroscopic technique using new Balmer-line profiles from Tremblay & Bergeron (2009) Other types require more in depth analyses:  DA+DB  DA+dM (37)

8. EUROWD 2010 8 DA+dM Combine DA models with spectral templates of Bochanski et al. (2007)

9. EUROWD 2010 9 DA+dM

10. EUROWD 2010 10 Analysis Standard spectroscopic technique using new Balmer-line profiles from Tremblay & Bergeron (2009) Other types require more in depth analyses:  DA+DB  DA+dM (37)  DAO (29) → Gianninas et al. (2010), ApJ, 720, 581… hot off the press!

11. EUROWD 2010 11 DAO white dwarfs Distinguished by He II line at 4686 Å Bergeron et al. (1994) established that stratified atmospheres don’t work, need to use homogeneous models Most DAO’s in Bergeron et al. (1994) exhibit Balmer-line problem

12. EUROWD 2010 12 Solution to the Balmer-line problem Werner (1996) : add CNO (solar abundances) to model atmospheres with appropriate Stark broadening, cools upper layers of the atmospheres where core of Balmer lines is formed TLUSTY : computed new grid of models applying prescribed solution

13. EUROWD 2010 13 DAO white dwarfs

14. EUROWD 2010 14 Balmer-line problem Bergeron et al. (1994) only detected problem in DAO stars Only a few mentions of Balmer-line problem in normal DA stars With our sample: 18 hot DA stars (T eff > 40,000 K) exhibiting the Balmer-line problem Analagous models without helium

15. DAO models EUROWD 2010 15 Teff = 65 000 K log g = 7.5 log He/H = -3.0

16. EUROWD 2010 16 Hot DA’s with Balmer-line problem

17. EUROWD 2010 17 Cooling Sequence

18. EUROWD 2010 18 Balmer-line problem : FUSE Must be caused by the presence of metals in the atmosphere Searched FUSE archive for available FUV spectra of stars in our sample Selected lines of metallic ions (C, N, O, P, Si, S, Fe)

19. EUROWD 2010 19 Hot DA white dwarfs

20. EUROWD 2010 20 Hot DA’s with a few metals

21. EUROWD 2010 21 Hot DA’s with Balmer-line problem

22. EUROWD 2010 22 DAO white dwarfs

23. EUROWD 2010 23 DAO phenomenon Balmer-line problem solved Revised evolutionary scenario One question remains: why do DAO’s have helium?

24. EUROWD 2010 24 Mass loss Unglaub & Bues (2000) : mass loss driven by metals can maintain sufficient helium in the atmosphere to explain observed abundances in DAO stars “Wind limit” at about ~ 80,000 K, but we see DAO’s at cooler temperatures Helium sinks faster than metals Mass loss does not allow for diffusive equilibrium → no stratified atmospheres (except PG 1305, ~ 44, 000 K, below wind limit)

25. EUROWD 2010 25 post-AGB evolution Stellar Wind Initial abundance of Z DAO + BP DA + BP DA T eff Enough Z? No Yes Helium?YesNo