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Surface CNO abundance and Pulsation of Blue Subergiants tell about internal mixing and winds of massive stars Hideyuki Saio (Tohoku University, Sendai)

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Presentation on theme: "Surface CNO abundance and Pulsation of Blue Subergiants tell about internal mixing and winds of massive stars Hideyuki Saio (Tohoku University, Sendai)"— Presentation transcript:

1 Surface CNO abundance and Pulsation of Blue Subergiants tell about internal mixing and winds of massive stars Hideyuki Saio (Tohoku University, Sendai) in collaboration with Cyril Georgy (Keele University, UK) George Meynet (Geneva Observatory)

2 Exström et al. (2012) Two types of luminous Blue Supergiants (BSG) MS BSG RSG BSG HD limit with rotational mixing

3 Humphreys and Davidson (1994) H-D limit

4 at least one radial pulsation mode is excited Radial pulsations are excited in BSGs returned from RSGs Pulsations can distinguish the two types of Blue Supergiants

5 Micro variations in blue Supergiants --- α Cygni variables Sp. Type; AB log L/Lsun > 4.6 Semi-regular variations Periods; ~10 – 100 days Deneb (α Cyg) Rigel (β Ori) Pulsating BSGs must be returned from Red Supergiants (RSGs)

6 Kaufer et al. (1997) α Cyg (Deneb) 40 days 50 days

7 Richardson et al. (2011) P=17.8 days P=13.4 days log L = 5.2, T eff =8500 Deneb (α Cyg) Occasionally shows radial pulsations but different periods season to season --- the mean radius is different?

8 Bresolin et al. (2004) 50 days Variable blue supergiants in NGC 300 Standard deviation BSGs NGC 300 Bresolin et al. (2004)

9 50 days Variable blue supergiants in NGC K logL=5.3; 72.5 days 9250 K logL=5.1; 96.1 days Two stars show regular light curves, radial pulsations D12 A10

10 Lamers et al. (1998) LBVs (S Dor variables) show semi-regular micro variations (α-Cygni type variations) S Dor phase redder (LMC) log L = days

11 Periods of excited radial pulsations at least one mode is excited A10 D12 Predicted periods are roughly consistent with observed ones Rigel D12 A M

12 Observed period ranges and theoretical periods of excited modes Before RSG stage After RSG stage Observed period ranges are consistent with strange modes and oscillatory convection modes in models after the Red SG stage.

13 Problem in Surface CNO abundances Predicted surface CNO ratios of BSG 1st BSG stage 2nd BSG stage (no pulsation) (pulsations) N/C = N/O = H-burning by CNO cycle: 12 C, 16 O 14 N Initial N/C = 0.29 N/O = 0.12 Internal mixing & wind mass loss Surface N/C & N/O ratios increase log(N/C) log(N/O) 25M Rotational mixing mass loss

14 Problem in Surface CNO abundances Predicted surface CNO ratios of BSG 1st BSG stage 2nd BSG stage (no pulsation) (pulsations) N/C = N/O = Spectroscopic analyses: Deneb(α Cyg); N/C = 3.4, N/O= 0.65 Rigel(β Ori); N/C = 2.0, N/O=0.46 CNO ratios agree with the 1st BSG stage (before RSG) ; No pulsations are expected H-burning by CNO cycle: 12 C, 16 O 14 N Initial N/C = 0.29 N/O = 0.12 Internal mixing & wind mass loss Surface N/C & N/O ratios increase log(N/C) log(N/O) Deneb Rigel 25M Przybilla et al. (2010)

15 Surface CNO ratios of BSGs depend on the assumptions about internal mixing Rotational mixing : Initial rotation velocity (0.4×critial at ZAMS assumed) Chemical composition is obtained from Convective mixing: Two different criterions Schwarzschild criterion Ledoux criterion (μ=mean. mol.weight) with turbulent diffusion coefficient

16 Schwarzschild criterion Ledoux criterion Main sequence He burning Age Conv. final mass Center Surf. Georgy et al. (2013) M i =25M MrMr X (H-frac.) 0 M Ledoux Schwarzschild Schwarzschild & Ledoux criterions for convective mixing (μ=mean. mol.weight) Ledoux Schwarzschild

17 Ledoux Georgy et al. (2013) 2nd BSG stage Just after MS stage Surf. N/C7 N/C60 Schwarzschild Ledoux conv. core conv.

18 Schwarzschild Ledoux Rigel Deneb A10 D12 Ledoux criterion for convective mixing gives smaller N/C & N/O than Schwarzschild criterion log(N/C) log(N/O) Mass X N /X O

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20 Summary Pulsating blue supergiants (α Cygni variables) should be once red-supergiants and lost significant mass: Blue --> Red --> Blue evolution Discrepancies of CNO abundances: Models (Georgy et al. 2013): Schwarzschild criterion: N/C 60; N/O 4 X He 0.63 Ledoux criterion: N/C 7; N/O 1.6 X He 0.46 Spectroscopic analyses (Przybilla et al. 2010): Deneb; N/C=3.4, N/O=0.65, X He =0.32 Rigel; N/C=2.0, N/O=0.46, X He =0.37 NGC 300 D12; ??? A10; ??? Surface compositions & pulsations of BSGs provide good constraints on the internal mixing.

21 I wish homogeneous data for CNO abundances & photometry of Blue supergiants in nearby galaxies Standard deviation BSGs NGC 300 (1.9Mpc) Bresolin et al. (2004) N(pulsator)/N(non-pulsator) = τ EV (red blue)/τ EV (blue red) Differences in N/C, N/O, 12 C/ 13 C between pulsators & non-pulsators Very good constraints on the models of mixing and mass loss

22 Radial pulsations are excited in BSGs returned from RSG stage at least one mode is excited α Cygni variables were once RSGs Pulsations can distinguish the two types of Blue Supergiants

23 Model predictions: Schwarzschild criterion: N/C 60; N/O 4 Ledoux criterion: N/C 7; N/O 1.6 Spectroscopic analyses: Deneb; (N/C, N/O) = (3.4, 0.65) Rigel; = (2.0, 0.46) NGC 300 D12 = ??? A10 = ??? Accurate surface compositions and pulsation properties of blue supergiants constrain the assumptions on the internal mixing in massive stars.

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25 Surface CNO abundances Predicted surface CNO ratios Observed values: Deneb; (N/C, N/O) = (3.4, 0.65) Rigel; = (2.0, 0.46)

26 log Teff Schwarzschild criterion Ledoux criterion

27 Radial strange modes + Convection modes Deneb Convection modes have periods longer than radial modes


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