Mean period of pulsating white dwarfs as a spectroscopy-independent thermometer Anjum S. Mukadam, University of Washington Collaborators: M. H. Montgomery (UTx), D. E. Winget (UTx), S. O. Kepler (UFRGS, Brasil), J. C. Clemens (UNC), P. Szkody (UW), B. T. Gänsicke (UWr, UK) Animations from whitedwarf.org (T. Metcalfe, HAO)

Plan of Talk Introduction to pulsating white dwarfs and ZZ Ceti stars Correlating ZZ Ceti pulsation period with temperature Successful application of this new spectroscopy-independent technique to determine temperature Can we apply this technique to accreting ZZ Ceti stars?

Asteroseismology Pulsations  Only systematic way to study the stellar interior Pulsations are observed in different types of stars in various stages of evolution ZZ Ceti stars

White dwarfs show non-radial g-modes due to their high density with periods of 50s to 1400s Pulsation modes are discrete & characterized by quantum numbers (k,l,m) similar to atomic orbitals Pulsations reach the inner 99% of a white dwarf star (Montgomery & Winget 1999) Animations from whitedwarf.org (T. Metcalfe, HAO)

ZZ Ceti stars (DAVs) Hydrogen atmosphere white dwarf variables

Two flavours of ZZ Ceti stars (DAVs) T eff = 11000K P ~ 1000s T eff = 12000K P ~ 200s Time (s) Fractional Intensity Cool ZZ Ceti (cDAV) Hot ZZ Ceti (hDAV)

Mean Period vs. Spectroscopic Temperature

Pulsation Period: Means of measuring T eff ? WMP = T eff WMP = T eff

Spectroscopy vs. Weighted Mean Period Internal uncertainty ~200K / 1200K (17% of the width) Mass & Temperature are not entirely independent Dependence on model atmosphere & method used to determine T eff from the spectrum. Internal uncertainty ~10-60s / 1300s (<5% of the width) Mass does not affect pulsation period Relatively simple and model-independent measurement

Weighted Mean Period as a temperature scale We can think of the weighted mean period (WMP) as an effective temperature scale. If we restrict our T eff determination to units of seconds in the WMP scale, we become completely independent of spectroscopic T eff uncertainties. Average T eff uncertainty reduces from 17% to <5% (Mukadam et al. 2006, ApJ, 640, 956)

Pulsation amplitude across the instability strip

Comparison to previous work from 2002 Log Total Power Kanaan et al Mukadam et al. 2006

Mean pulsation amplitude vs. Mean period (serves as temperature) HotCool

ZZ Ceti stars lose amplitude before pulsations shut down at the red edge! HotCool

Accreting pulsating white dwarfs found! A ZZ Ceti star was discovered in a cataclysmic variable (van Zyl et al. 1998). Interesting systems to study the effect of accretion on pulsations Instability strip for accretors Use seismology to learn about the pulsating white dwarf in the cataclysmic variable

Accreting ZZ Ceti instability strip Statistically significant sample needed (10 accreting ZZ Ceti stars known to date) Spectroscopic temperature to the primary white dwarf implies simultaneously fitting: –White dwarf with Balmer absorption lines –Hot spot/ hot belt on the white dwarf –Accretion disk with emission lines

Preliminary results from HST UV time-resolved spectroscopy Accreting ZZ CetiT eff (K) (Spec) Period, Amplitude (~ Å) SDSSJ s, 78 mma 1 SDSSJ s, 23.4 mma s, 48.3 mma s, mma 1 SDSSJ s, 46 mma 1 (Szkody et al (in prep); Mukadam et al. 2005, BAAS, 207, 70.01)

Can we apply this technique to accreting pulsators?

Don’t know yet…. Need a few years of theoretical and observational development in this new and upcoming sub-discipline to answer reliably.

Conclusion Mean pulsation period seems very promising as an effective temperature scale for the non-interacting white dwarf pulsators. This technique remains to be proven for the accreting pulsators.