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

EUROWD 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

EUROWD Final tally Total spectra in final sample = % complete, most missing spectra for stars in the southern hemisphere 706 total spectra obtained specifically for this project from

EUROWD S/N 52% with S/N > 70 78% with S/N > 50

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

EUROWD DA+DB

EUROWD 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)

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

EUROWD DA+dM

EUROWD 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!

EUROWD 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

EUROWD 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

EUROWD DAO white dwarfs

EUROWD 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

DAO models EUROWD Teff = K log g = 7.5 log He/H = -3.0

EUROWD Hot DA’s with Balmer-line problem

EUROWD Cooling Sequence

EUROWD 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)

EUROWD Hot DA white dwarfs

EUROWD Hot DA’s with a few metals

EUROWD Hot DA’s with Balmer-line problem

EUROWD DAO white dwarfs

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

EUROWD 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)

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