Asteroseismology of the ZZ Ceti star KUV 083684026

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

Overview l Introduction ¡ZZ Ceti stars ¡KUV 08368+4026 l New observations l Preliminary results of asteroseismology l Discussion on variations of FT l Future Plans

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

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

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

ZZ Ceti Star KUV 08368+4026 Discovered in Feb. 1996 With the 1. 9 m telescope at Haute Provence Observatory V=15. 55 mag B-V=0. 22 U-B=-0. 59 (Vauclair et. al. 1997)

l The FTs of 4 ZZ Ceti stars (G 29 -38, HL Tau 76, G 255 -2, KUV 08368+4026) show similar character, ¡large amplitudes ¡common frequencies (1. 6 m. Hz and 2. 0 m. Hz) ¡the similarity is probably the signature of some fundamental mechanism.

Location of the 4 ZZ Ceti stars on the Instability Strip HL Tau 76 KUV 08368+4026 G 255 -2 G 29 -38

Journal of new observations in B Date Observatory Telescope Frames Nights Feb. 1018. 2009 Lijiang 2. 40 m 6805 8 Dec. 1218. 2009 Xinglong 2. 16 m 1651 6 Dec. 2631. 2009 Lijiang 2. 40 m 2328 3 Dec. 2728. 2009 Xinglong 2. 16 m 815 1 Jan. 0717. 2010 SPM 1. 50 m 2771 7 Jan. 1219. 2010 Xinglong 2. 16 m 2745 6

2. 4 m Telescope of Lijiang 2. 16 m Telescope of Xinglong

Light Curve (Feb 2009)

Power spectrum (Feb 2009)

Period analysis： Period 04 (Lenz & Breger 2005)

Frequency List --------------------------Freq(μHz) Err Amp(mma) S/N --------------------------1386. 90 0. 04 3. 9 15. 04 3247. 77 0. 03 5. 3 15. 49 1454. 67 0. 05 3. 6 10. 06 3249. 11 0. 06 2. 7 7. 97 1976. 48 0. 02 10. 8 20. 88 3885. 53 0. 02 11. 1 17. 11 2159. 09 0. 06 2. 9 9. 38 3886. 74 0. 04 4. 7 7. 38 2498. 75 0. 02 10. 5 24. 90 3887. 73 0. 01 16. 7 26. 04 2500. 71 0. 02 8. 7 20. 78 5223. 79 0. 07 2. 3 7. 09 2757. 87 0. 07 2. 3 5. 63 5747. 68 0. 06 2. 9 9. 19 2759. 98 0. 05 3. 6 8. 82 6386. 52 0. 07 2. 6 8. 70 3245. 51 0. 06 2. 9 8. 76 7134. 37 0. 04 4. 6 16. 13 3246. 74 0. 01 13. 0 38. 44 --------------------------

Preliminary results of asteroseismology l 19 periods extracted l 8 eigenmodes founded l mode identification: l=1, 2 l triplets: average δf=1. 12 µHz →rotational period: P=3. 09 day l average ΔP=32. 6 s for l=1 → M=0. 6 -0. 7 M⊙ The 1. 6 m. Hz frequency found in 1996 disappeared.

Light Curves (Dec 2009 part 1)

Power Spectrum (Dec 2009 part 1)

Light Curve (Dec 2009 Part 2)

Power Spectrum (Dec 2009 Part 2)

Light Curve (Jan 2010)

Power Spectrum (Jan 2010)

Discussion on variations of FT Power spectrum (Feb 2009)

Power Spectrum (Dec 2009 part 1)

Power Spectrum (Dec 2009 Part 2)

Power Spectrum (Jan 2010)

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

Calculation of Total Power Runs Σ(An)2 2009. 2 1044. 1 2009. 12. 1 778. 5 2009. 12. 2 1146. 4 2010. 1 933. 5 (mma 2)

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

Power Spectrum (Dec 2009 + Jan 2010)

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

Future plans l To get high-precision stellar parameters (High-Resolution Spectroscopic data needed) l Call a WET Campaign for KUV 08368+4026 l Theoretical study with the white dwarf Modelling Code (Toulouse)

Vielen Dank!