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