1. Asteroseismology of the ZZ Ceti star KUV 08368+4026
Chun LI
(Beijing Normal University, China)
Collaborators:
J.N. Fu, G. Vauclair, L. Fox Machado, M. Alvarez, J. Su, R. Michel, X.H. Yang, Y. Li, Y.P. Zhang, N. Dolez
Aug.16-20, 2010 Tübingen

2. Overview Introduction New observations
ZZ Ceti stars
KUV
New observations
Preliminary results of asteroseismology
Discussion on variations of FT
Future Plans

3. Introduction of ZZ Ceti Stars
ZZ Ceti stars (DAV white dwarfs):
－the lowest Teff among the 4 classes of variable white dwarfs (DAV, DBV, DQV, GW Vir)

4. Pure instability strip
(Li & Fu, 2010, in preparation)

5. The DAVs (ZZ Ceti) 148 members (Castanheira et al. 2010)
Periods: 100 – 1500 s
Internal stucture:
C/O core, He layer, H envelope
Instability: κ-mechanism
Teff: ~12500 K  ~11000 K;
Pulsation modes: g modes

6. ZZ Ceti Star KUV 08368+4026 (Vauclair et. al. 1997)
Discovered in Feb.1996
With the 1.9m telescope at Haute Provence Observatory
V=15.55 mag
B-V=0.22
U-B=-0.59
(Vauclair et. al. 1997)

8. show similar character,
The FTs of 4 ZZ Ceti stars
(G29-38, HL Tau 76, G255-2, KUV )
show similar character,
large amplitudes
common frequencies (1.6 mHz and 2.0 mHz)
the similarity is probably the signature of some fundamental mechanism.

9. Location of the 4 ZZ Ceti stars on the Instability Strip
HL Tau 76
KUV
G255-2
G29-38

10. Journal of new observations in B
Date
Observatory
Telescope
Frames
Nights
Feb
Lijiang
2.40 m
6805 8
Dec
Xinglong
2.16 m
1651 6
Dec
2328 3
Dec
815 1
Jan
SPM
1.50 m
2771 7
Jan
2745

11. 2.4m Telescope of Lijiang
2.16m Telescope of Xinglong

12. Light Curve (Feb 2009)

13. Power spectrum (Feb 2009)

14. Period analysis：
Period04
(Lenz & Breger 2005)

15. Frequency List
Freq(μHz) Err Amp(mma) S/N
Freq(μHz) Err Amp(mma) S/N

16. Preliminary results of asteroseismology
19 periods extracted
8 eigenmodes founded
mode identification: l=1, 2
triplets: average δf=1.12 µHz
→rotational period: P=3.09 day
average ΔP=32.6 s for l=1
→ M= M⊙
The 1.6mHz frequency found in 1996 disappeared.

17. Light Curves (Dec 2009 part 1)

18. Power Spectrum (Dec 2009 part 1)

19. Light Curve (Dec 2009 Part 2)

20. Power Spectrum (Dec 2009 Part 2)

21. Light Curve (Jan 2010)

22. Power Spectrum (Jan 2010)

23. Discussion on variations of FT
Power spectrum (Feb 2009)

24. Power Spectrum (Dec 2009 part 1)

25. Power Spectrum (Dec 2009 Part 2)

26. Power Spectrum (Jan 2010)

27. Amplitude variation Time scale of variation: weeks Explanation:
Not a evolutionary effect
Interaction of rotation and pulsation?
Interaction of convection and pulsation?

28. Calculation of Total Power
Runs
Σ(An) (mma2)
2009.2
1044.1
778.5
1146.4
2010.1
933.5

29. Amplitude variation also be found in HS 0507+0434B
(See the Poster of Fu et al.)

30. Power Spectrum (Dec 2009 + Jan 2010)

31. Periods were resolved.
However, it is very difficult to do the mode identification

33. Future plans
To get high-precision stellar parameters (High-Resolution Spectroscopic data needed)
Call a WET Campaign for
KUV
Theoretical study with the white dwarf Modelling Code (Toulouse)

34. Vielen Dank!