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)

Exström et al. (2012)

Two types of luminous Blue Supergiants (BSG)

MS BSG RSG

BSG

HD limit

with rotational mixing

at least one radial pulsation modeis excited

Radial pulsations are excited in BSGs returned from RSGs

Pulsations candistinguish thetwo types ofBlue Supergiants

Micro variations in blue Supergiants --- α Cygni variables

Sp. Type; A—B

log L/Lsun > 4.6

Semi-regular variations

Periods; ~10 – 100 daysDeneb(α Cyg)

Rigel(β Ori)

Pulsating BSGs must bereturned from Red Supergiants (RSGs)

Bresolin et al. (2004)

50 daysVariable blue supergiants in NGC 300

Stan

dard

dev

iatio

n

BSGs NGC 300

Bresolin et al. (2004)

Bresolin et al. (2004)

50 daysVariable blue supergiants in NGC 300

9000 K logL=5.3; 72.5 days

9250 K logL=5.1; 96.1 days

Two stars showregular light curves, ----- radial pulsations

D12

A10

Periods of excited radial pulsations

at least one modeis excited

A10D12 Predicted periods

are roughlyconsistent withobserved ones

Rigel

D12

A10

25

20M

Problem in Surface CNO abundances

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

H-burning by CNO cycle: 12C, 16O 14N

InitialN/C = 0.29N/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

Problem in Surface CNO abundances

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

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: 12C, 16O 14N

InitialN/C = 0.29N/O = 0.12

Internal mixing& wind mass loss

Surface N/C & N/O ratios increase

log(N/C)

log(N/O)

Den

eb

Rige

l

25M

Przybilla et al. (2010)

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

Schwarzschild criterion Ledoux criterion

Main sequence Main sequenceHe burning He burning

Age Age

Conv.

Conv.

Conv.

Conv.Conv.

Conv.Conv.

final mass final mass

Center

Surf.

Georgy et al. (2013)

Mi=25M

Mr

X (H

-frac

.)

0 M

Ledoux

Schwarzschild

Schwarzschild & Ledoux criterions for convective mixing

(μ=mean. mol.weight)

Ledoux

Schwarzschild

Schwarzschild Ledoux

Georgy et al. (2013)

2nd BSG stage

Just afterMS stage

Surf.

Surf.

N/C≈7N/C≈60

Schwarzschild Ledoux

conv. core conv. core

conv. conv.

Schwarzschild

Schwarzschild

Ledoux

Ledoux

Rige

l

Den

eb

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

SummaryPulsating 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 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 BSGsprovide good constraints on the internal mixing.

I wish homogeneous data for CNO abundances & photometry

of Blue supergiants in nearby galaxies

Stan

dard

dev

iatio

n

BSGs NGC 300 (1.9Mpc)

Bresolin et al. (2004)

N(pulsator)/N(non-pulsator) = τEV(redblue)/τEV(bluered)

Differences in N/C, N/O, 12C/13C between pulsators & non-pulsators Very good constraints on the models of mixing and mass loss