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

IntroductionZZ Ceti starsKUV 08368+4026

New observationsPreliminary results of asteroseismologyDiscussion on variations of FTFuture Plans

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)

Pure instability strip

(Li & Fu, 2010, in preparation)

The DAVs (ZZ Ceti)148 members (Castanheira et al. 2010)Periods: 100 – 1500 sInternal 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+4026Discovered in Feb.1996With the 1.9m telescope at Haute Provence ObservatoryV=15.55 magB-V=0.22U-B=-0.59(Vauclair et. al. 1997)

The FTs of 4 ZZ Ceti stars

(G29-38, HL Tau 76, G255-2, KUV08368+4026)

show similar character,large amplitudescommon frequencies (1.6 mHz and 2.0 mHz) the similarity is probably the signature of some

fundamental mechanism.

KUV08368+4026

G29-38

HL Tau 76

G255-2

Location of the 4 ZZ Ceti stars on the Instability Strip

Journal of new observations in BDate Observatory Telescope Frames Nights

Feb.10-18.2009

Lijiang 2.40 m 6805 8

Dec.12-18.2009

Xinglong 2.16 m 1651 6

Dec.26-31.2009

Lijiang 2.40 m 2328 3

Dec.27-28.2009

Xinglong 2.16 m 815 1

Jan.07-17.2010

SPM 1.50 m 2771 7

Jan.12-19.2010

Xinglong 2.16 m 2745 6

2.4m Telescope of Lijiang 2.16m Telescope of Xinglong

Light Curve (Feb 2009)

Power spectrum (Feb 2009)

Period analysis：Period04

(Lenz & Breger 2005)

Frequency List

---------------------------------------------------

Freq(μHz) Err Amp(mma) S/N

---------------------------------------------------

1386.90 0.04 3.9 15.04

1454.67 0.05 3.6 10.06

1976.48 0.02 10.8 20.88

2159.09 0.06 2.9 9.38

2498.75 0.02 10.5 24.90

2500.71 0.02 8.7 20.78

2757.87 0.07 2.3 5.63

2759.98 0.05 3.6 8.82

3245.51 0.06 2.9 8.76

3246.74 0.01 13.0 38.44

----------------------------------------------------

-------------------------------------------------

Freq(μHz) Err Amp(mma) S/N

--------------------------------------------------

3247.77 0.03 5.3 15.49

3249.11 0.06 2.7 7.97

3885.53 0.02 11.1 17.11

3886.74 0.04 4.7 7.38

3887.73 0.01 16.7 26.04

5223.79 0.07 2.3 7.09

5747.68 0.06 2.9 9.19

6386.52 0.07 2.6 8.70

7134.37 0.04 4.6 16.13

-------------------------------------------------

Preliminary results of asteroseismology

19 periods extracted8 eigenmodes foundedmode identification: l=1, 2triplets: average δf=1.12 µHz

→rotational period: P=3.09 dayaverage ΔP=32.6 s for l=1

→ M=0.6-0.7 M ⊙

The 1.6mHz 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)

Power spectrum (Feb 2009)

Discussion on variations of FT

Power Spectrum (Dec 2009 part 1)

Power Spectrum (Dec 2009 Part 2)

Power Spectrum (Jan 2010)

Amplitude variation

Time scale of variation: weeksExplanation:

Not a evolutionary effectInteraction of rotation and pulsation?Interaction of convection and pulsation?

Calculation of Total Power

Runs Σ(An)2 (mma2)

2009.2 1044.1

2009.12.1 778.5

2009.12.2 1146.4

2010.1 933.5

Amplitude variation also be found in HS 0507+0434B(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

To get high-precision stellar parameters (High-Resolution Spectroscopic data needed)

Call a WET Campaign for

KUV 08368+4026Theoretical study with the white dwarf

Modelling Code (Toulouse)

Vielen Dank!