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Hideyuki Saio (Tohoku University, Sendai) in collaboration with

Surface CNO abundance and P ulsation of B lue S ubergiants 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).

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Hideyuki Saio (Tohoku University, Sendai) in collaboration with

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  1. Surface CNO abundanceand 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. Two types of luminous Blue Supergiants (BSG) MS  BSG  RSG BSG HD limit with rotational mixing Exström et al. (2012)

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

  4. Micro variations in blue Supergiants --- α Cygni variables Sp. Type; A—B 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)

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

  6. Variable blue supergiants in NGC 300 50 days Two stars show regular light curves, ----- radial pulsations 9000 K logL=5.3; 72.5 days D12 9250 K logL=5.1; 96.1 days A10 Bresolin et al. (2004)

  7. Periods of excited radial pulsations at least one mode is excited D12 25 A10 20M A10 D12 Predicted periods are roughly consistent with observed ones Rigel

  8. Problem in Surface CNO abundances Surface N/C & N/O ratios increase H-burning by CNO cycle: 12C, 16O  14N Internal mixing & wind mass loss Predicted surface CNO ratios of BSG 1st BSG stage 2nd BSG stage (no pulsation) (pulsations) N/C = 3.2 60 N/O = 0.88 4.2 Initial N/C = 0.29 N/O = 0.12 25M log(N/C) mass loss Rotational mixing log(N/O)

  9. Problemin Surface CNO abundances Surface N/C & N/O ratios increase H-burning by CNO cycle: 12C, 16O  14N Internal mixing & wind mass loss Predicted surface CNO ratios of BSG 1st BSG stage 2nd BSG stage (no pulsation) (pulsations) N/C = 3.2 60 N/O = 0.88 4.2 Initial N/C = 0.29 N/O = 0.12 Rigel 25M Deneb log(N/C) 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 log(N/O) Przybilla et al. (2010)

  10. 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 with turbulent diffusion coefficient Convective mixing: Two different criterions Schwarzschild criterion Ledoux criterion (μ=mean. mol.weight)

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

  12. Just after MS stage Ledoux Schwarzschild conv. conv. Surf. Surf. 2nd BSG stage Schwarzschild Ledoux N/C≈60 N/C≈7 conv. core conv. core Georgy et al. (2013)

  13. Ledoux criterion for convective mixing gives smaller N/C & N/O than Schwarzschild criterion Schwarzschild D12 Ledoux A10 log(N/C) Schwarzschild Ledoux Deneb XN/XO log(N/O) Rigel Mass

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

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

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