Granulation in stars. solar granulation. Thomas IAU GA Beijing, Aug Wednesday, January 2, 13

Transcription

1 Granulation in stars Thomas IAU GA Beijing, Aug 2012 solar granulation

2 granulation in the Sun

3 the solar signal... SOHO/NASA activity granulation pulsation

4 the solar background... simple model noise + background + pulsation activity pulsation granulation

5 the solar background... simple model noise + background + pulsation activity pulsation granulation

6 the frequency of maximum power e.g., Brown et al. or Kjeldsen & Bedding empirical adiabatic case/ ideal gas seismic scaling relation Huber et al νmax, Δν, (Teff) R, M, L (e.g. Kallinger et al for red giants)

7 the solar background... simple model noise + background + pulsation background parameters activity pulsation τ... time scale σ... amplitude ϛ... normalisation constant granulation

8 the Harvey model zoo... original Harvey (1985) model Mathur et al time more realistic version time Bayesian model comparison (Kallinger et al, in prep.)

9 granulation and faculae simple model noise + background + pulsation pulsation granulation faculae

10 granulation in red-giant stars

11 background in red-giant stars Red

12 background in red-giant stars ~4R8

13 background in red-giant stars ~4R8 ~6R8

14 background in red-giant stars ~4R8 ~6R8 ~10R8

15 background in red-giant stars ~4R8 ~6R8 ~10R8 ~23R8

16 the Kepler sample 1025 RG in LC mode (long cadence, ~30min) Q0-10, ~900d (νmax μHz) 75 stars in SC mode (short cadence, ~1min) Q5-8, ~1yr (νmax μHz)

17 timescales background timescales 1000 LC SC scale almost uniformly with pulsation timescales (over >3 orders of magnitude) ν gran, ν fac (µhz) faculae granulation νgran νmax faculae νfac νmax ν/ν max 0.5 granulation see also Mathur et al. (2011) ν max (µhz)

18 amplitudes signal in the spectrum variance in the time series pulsation energy (Apuls) 10 5 background energy (Abg) Power density (ppm 2 /µhz) A 2 bg A 2 puls Frequency (µhz)

19 amplitudes (i.e. energies) 4 2 LC A bg (ppm) SC unity A bg /A puls A puls (ppm)

20 amplitudes (i.e. energies) 4 2 LC A bg (ppm) SC unity A bg /A puls A puls (ppm)

21 diminished dipole modes PDS A l=1 / A l= Frequnency (µhz) ν max (µhz) PDS 1 see also Mosser et al. (2011) Frequnency (µhz)

22 what about other stars

23 granulation in A-type stars?

24 the classical approach... mowing the grass pre-whiten down to the white noise FG Vir (Breger et al. 2004) V588 Mon (Kallinger et al. 2008)

25 δsct stars entering the space age >1000 independent pulsation peaks? ~422 independent pulsation peaks? (Garcia Hernandez et al. 2009) (Poretti et al. 2009) -> very high mode degree!?!

26 are these > 1000 frequencies pulsation modes? Δν 3d -1 in the range 5-30d -1 8 radial orders HD50844@CoRoT l m=0 m 0 total

27 can we observe high-l modes in the integrated light? (l,m) = (1,0) (2,1) (3,1) observable (4,2) (6,3) (8,4) observable?

28 disk-averaging factor Daszynska-Daszkiewicz et al, 2006

29 disk-averaging factor % ~1% 7 ~0.3% Daszynska-Daszkiewicz et al, 2006

30 what are the amplitudes we have to look for? 100% 1% (l=5) 0.3% (l=7)

31 what else could it be?

32 striking similarities HD50844 red giant slope = 4

33 coloured-noise model HD50844 HD ~125 surviving frequencies (>1000) ~65 surviving frequencies (~422) Kallinger & Matthews 2010

34 but is it a common phenomena? δsct stars@kepler I think so!

35 time scales are consistent HD50844 HD174939

36 convective envelope in simple stellar models amplitudes cell size (and not the depth!!!)

37 what about more advanced models? grid of 3D convection simulations comparison with Kepler RG s sim obs Regner Trampedach Mathur et al. 2011

38 conclusions only since recently we have the data available to measure granulation properties in a large variety of stars there appears to be a tight relation between pulsation and granulation timescales as well as amplitudes these might serve as a valuable input for 3D modelling of convection granulation seems to play a role also in A-type stars first models seems to tentatively reproduce what we observe but we just started to do this business

39 thank you...