Chemical composition of B-type stars: relevance
for hot star physics and chemical evolution of
the Galaxy
Thierry Morel
Liège University, Belgium
Outline
Generalities
The chemical composition of nearby B stars
Neon in B stars and relevance for solar physics
Usefulness of massive stars in the context of the chemical
evolution of the Galaxy
Mixing in B stars
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
Teff
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Effective temperature from ionisation equilibrium
Teff = 20000 K
Teff = 23000 K
Teff = 26000 K
Teff = 29000 K
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Effective temperature from ionisation equilibrium of various ions
Generalities
Chemical evolution of the Galaxy
Teff
logg
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
strong metal lines
ionisation balance
Balmer lines
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Surface gravities from fitting the wings of Balmer lines
Generalities
Chemical evolution of the Galaxy
Teff
logg
ξ
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
strong metal lines
no dependence abundances
vs line strength
ionisation balance
Balmer lines
idem
Generalities
Chemical evolution of the Galaxy
Teff
logg
ξ
Winds
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
strong metal lines
no dependence abundances
vs line strength
ionisation balance
Balmer lines
no
no (TLUSTY, DETAIL/SURFACE)
yes (FASTWIND, CMFGEN)
idem
Generalities
Chemical evolution of the Galaxy
Teff
logg
ξ
Winds
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
strong metal lines
no dependence abundances
vs line strength
ionisation balance
Balmer lines
no
no (TLUSTY, DETAIL/SURFACE)
yes (FASTWIND, CMFGEN)
idem
non-LTE
atmospheric structure no
no/yes
line formation
YES
yes
Generalities
Chemical evolution of the Galaxy
Teff
logg
ξ
Winds
The chemical composition of B stars
Mixing in B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
strong metal lines
no dependence abundances
vs line strength
ionisation balance
Balmer lines
no
no (TLUSTY, DETAIL/SURFACE)
yes (FASTWIND, CMFGEN)
idem
non-LTE
atmospheric structure no
no/yes
line formation
yes
YES
yes
no
3D
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
Teff
logg
ξ
Winds
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
strong metal lines
no dependence abundances
vs line strength
ionisation balance
Balmer lines
no
no (TLUSTY, DETAIL/SURFACE)
yes (FASTWIND, CMFGEN)
idem
non-LTE
atmospheric structure no
no/yes
line formation
yes
YES
3D
yes
no
Rotation
no
yes
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
OB stars are usually
fast rotators
Howarth et al. (1997)
Generalities
Chemical evolution of the Galaxy
Teff
logg
ξ
Winds
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
strong metal lines
no dependence abundances
vs line strength
ionisation balance
Balmer lines
no
no (TLUSTY, DETAIL/SURFACE)
yes (FASTWIND, CMFGEN)
idem
non-LTE
atmospheric structure no
no/yes
line formation
yes
YES
3D
yes
no
Rotation
no
yes
Chemical species
no Ne
no Li, Cr, Ni, …
Generalities
Chemical evolution of the Galaxy
Teff
logg
ξ
Winds
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Cool stars
Hot stars
excitation balance/Balmer lines
ionisation balance
strong metal lines
no dependence abundances
vs line strength
ionisation balance
Balmer lines
no
no (TLUSTY, DETAIL/SURFACE)
yes (FASTWIND, CMFGEN)
idem
non-LTE
atmospheric structure no
no/yes
line formation
yes
YES
3D
yes
no
Rotation
no
yes
Chemical species
no Ne
no Li, Cr, Ni, …
Abundance analysis
curve of growth/spectral synthesis idem
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Why are early B-type dwarfs well-suited for abundance studies?
They have weak winds contrary to O stars and stars that have evolved way off
the main sequence
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
de Jager et al. (1988)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
de Jager et al. (1988)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Why are early B-type dwarfs well-suited for abundance studies?
They have weak winds contrary to O stars and stars that have evolved way off
the main sequence
Their atmosphere can be modelled in LTE
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Hybrid approach (LTE model atmosphere + NLTE line formation) adequate for B
stars on the main sequence
Nieva & Przybilla (2007)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Why are early B-type dwarfs well-suited for abundance studies?
They have weak winds contrary to O stars and stars that have evolved way off
the main sequence
Their atmosphere can be modelled in LTE
No significant diffusion processes contrary to late B-type stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Why are early B-type dwarfs well-suited for abundance studies?
They have weak winds contrary to O stars and stars that have evolved way off
the main sequence
Their atmosphere can be modelled in LTE
No significant diffusion processes contrary to late B-type stars
They do not migrate far from their birth environments contrary to long-lived
stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Abundance properties of nearby B stars
Single, non-supergiant stars within ~1 kpc
with non-LTE abundance results in the
literature
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Abundance properties of nearby B stars
1D solar models
(Grevesse & Sauval 1998)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Abundance properties of nearby B stars
1D solar models
(Grevesse & Sauval 1998)
3D solar models
(Asplund et al. 2009)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Abundance properties of nearby B stars
1D solar models
(Grevesse & Sauval 1998)
3D solar models
(Asplund et al. 2009)
Meteorites
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Abundance properties of nearby B stars
1D solar models
(Grevesse & Sauval 1998)
3D solar models
(Asplund et al. 2009)
Meteorites
Abundances of OB stars generally found to
be subsolar: problem!
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Abundance properties of nearby B stars
1D solar models
(Grevesse & Sauval 1998)
3D solar models
(Asplund et al. 2009)
Meteorites
Abundances of OB stars generally found to
be subsolar: problem!
BUT
Recent results more in accordance with solar
values:
Nieva & Przybilla (2011)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Abundance properties of nearby B stars
1D solar models
(Grevesse & Sauval 1998)
3D solar models
(Asplund et al. 2009)
Meteorites
Abundances of OB stars generally found to
be subsolar: problem!
BUT
Recent results more in accordance with solar
values:
Nieva & Przybilla (2011)
Simón-Díaz (2010)
Nieva & Simón-Díaz (2011)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
The new solar abundances (Asplund et al. 2009)
1-D
3-D
log ε(C)
8.52±0.06
8.43±0.05
log ε(N)
7.92±0.06
7.83±0.05
log ε(O)
8.83±0.06
8.69±0.05
log ε(Ne)
8.08±0.06
7.93±0.10
log ε(Mg)
7.58±0.05
7.60±0.04
log ε(Si)
7.55±0.05
7.51±0.03
log ε(S)
7.33±0.11
7.12±0.03
log ε(Fe)
7.50±0.05
7.50±0.04
Z
0.0169±0.0013 0.0134±0.0008
-19%
-19%
-28%
-29%
+5%
-9%
-38%
+0%
-21%
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Conflict with helioseismology
3D
1D
Basu & Antia (2007)
Sound-speed and density profiles incorrectly reproduced
Convective zone too shallow (rb~0.7289 vs 0.7133 Rsun)
He abundance in convective zone too low (Ys~0.23 vs 0.25)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Conflict with helioseismology
Delahaye & Pinsonneault (2006)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Reasonable agreement with helioseismic data if Ne abundance increased by ~0.45
dex (+ slight adjustments of the other metals necessary)
Basu & Antia (2007)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Reasonable agreement with helioseismic data if Ne abundance increased by ~0.45
dex (+ slight adjustments of the other metals necessary)
Delahaye & Pinsonneault (2006)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Neon abundance in cool stars ill defined (estimated in corona): photospheric lines only
present in B stars
Cunha et al. (2006)
Dworetski & Budaj (2000)
Hempel & Holweger (2003)
Kilian (1994)
Morel & Butler (2008)
Sigut (1999)
Nieva & Przybilla (2011)
Nieva & Simón-Díaz (2011)
Asplund et al. (2005)
Grevesse & Sauval (1998)
Value necessary to solve the
‘solar model problem’
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Usefulness of OB stars to study the chemical evolution of the Galaxy
Stars visible at large distances even when unevolved: sample a significant part
of the Galactic disc
Tracers of the present-day chemical composition of the ISM, close to their
birthplace: complement studies of the cool star populations
Give access to some elements hard to determine (e.g., N) or even not present
in cool stars (e.g., Ne)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
GAIA is an ESA mission due to be
launched in June 2013.
Main objectives: ultra precise astrometric
data (positions, parallaxes, proper motions)
for ~109 objects down to V~20 mag.
Courtesy ESA
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
GAIA is an ESA mission due to be
launched in June 2013.
Main objectives: ultra precise astrometric
data (positions, parallaxes, proper motions)
for ~109 objects down to V~20 mag.
Equipped with broadband photometers
(BP/RP) for centroid correction and source
characterization.
Line-of-sight velocity provided for the
brightest sources by the RVS spectrograph
(8470-8740 Å, R=λ/∆λ~11,500). Also used
for source characterization.
Courtesy ESA
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
V = 12 mag: σπ~15 µarcsec at end of mission
Type
Sun-like
MV (mag) AV (mag) d (kpc) σd/d (%)
+4.8
0
0.3
~0.4
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
V = 12 mag: σπ~15 µarcsec at end of mission
Type
Sun-like
Clump giant
MV (mag) AV (mag) d (kpc) σd/d (%)
+4.8
+0.7
0
1
0.3
1.2
~0.4
~1.7
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
V = 12 mag: σπ~15 µarcsec at end of mission
Type
Sun-like
Clump giant
Cepheids
MV (mag) AV (mag) d (kpc) σd/d (%)
+4.8
+0.7
−3.3
0
1
3
0.3
1.2
2.9
~0.4
~1.7
~4.3
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
V = 12 mag: σπ~15 µarcsec at end of mission
Type
MV (mag) AV (mag) d (kpc) σd/d (%)
Sun-like
Clump giant
Cepheids
+4.8
+0.7
−3.3
0
1
3
0.3
1.2
2.9
~0.4
~1.7
~4.3
B2 V
B0 V
O9 V
−2.45
−4.0
−4.5
3
3
3
2.0
4.0
5.0
~2.9
~6.0
~7.5
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Evolution of abundances vs time
Sun formation
Now
Element Enrichment since Sun
formation (dex)
C
0.07
N
0.10
O
0.05
Fe
0.16
Ne
0.04
S
0.10
Si
0.08
Mg
0.04
Chiappini et al. (2003)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Evolution of abundances vs time
Sun formation
?
?
Now
?
Element Enrichment since Sun
formation (dex)
C
0.07
N
0.10
O
0.05
Fe
0.16
Ne
0.04
S
0.10
Si
0.08
Mg
0.04
Chiappini et al. (2003)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Evolution of slope of Galactic gradient vs time
?
Andrievsky et al. (2005)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Chemical gradient as seen from OB stars
Elements available:
C, N, O, Mg, Al, Si, S, Ne
No iron-peak elements
Daflon & Cunha (2004):
69 late O- to early B-type stars in 25 young
open clusters
−0.031 < slope (dex kpc-1) < −0.052
(similar to H II regions)
Daflon & Cunha (2004)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Daflon & Cunha (2004)
Andrievsky et al. (2004)
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Daflon & Cunha (2004)
Neon
Mixing in magnetic B stars
Current limitations
B-type stars apparently metal poor
with respect to the Sun
Andrievsky et al. (2004)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Daflon & Cunha (2004)
Neon
Mixing in magnetic B stars
Current limitations
B-type stars apparently metal poor
with respect to the Sun
Outer disk poorly sampled (9 stars in
7 clusters): strongly biases results
Andrievsky et al. (2004)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Daflon & Cunha (2004)
Neon
Mixing in magnetic B stars
Current limitations
B-type stars apparently metal poor
with respect to the Sun
~0.7 dex
Outer disk poorly sampled (9 stars in
7 clusters): strongly biases results
Large scatter at given Rg
Andrievsky et al. (2004)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Daflon & Cunha (2004)
Neon
Mixing in magnetic B stars
Current limitations
B-type stars apparently metal poor
with respect to the Sun
Outer disk poorly sampled (9 stars in
7 clusters): strongly biases results
Large scatter at given Rg
Andrievsky et al. (2004)
Interpretation very limited
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Daflon & Cunha (2004)
Neon
Mixing in magnetic B stars
Current limitations
B-type stars apparently metal poor
with respect to the Sun
Outer disk poorly sampled (9 stars in
7 clusters): strongly biases results
Large scatter at given Rg
Andrievsky et al. (2004)
Interpretation very limited
GAIA distances coupled with a
homogeneous abundance analysis of
a large sample of OB stars would
dramatically improve the situation
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Need for follow-up observations: only a few, weak metal lines in RVS spectral range
Rauw et al. (2008)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Fast rotation gives rise to:
Meridional currents and shear mixing
Transport of chemical elements
Hunter et al. (2008)
12 Msun
Mixing indicators in massive stars: He, B
and CNO.
Products of CNO cycle brought up to the
surface because of rotational mixing:
nitrogen enrichment and (smaller) carbon
depletion.
Logarithmic ratio of N and C abundances
([N/C]) good probe of deep mixing.
Data from Heger & Langer (2000)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data
for Galactic stars
[N/C]<-0.2
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data
for Galactic stars
[N/C]<-0.2
-0.2<[N/C]<+0.2
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data
for Galactic stars
[N/C]<-0.2
-0.2<[N/C]<+0.2
+0.2<[N/C]<+0.6
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data
for Galactic stars
[N/C]<-0.2
-0.2<[N/C]<+0.2
+0.2<[N/C]<+0.6
+0.6<[N/C]<+1.0
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data
for Galactic stars
[N/C]<-0.2
-0.2<[N/C]<+0.2
+0.2<[N/C]<+0.6
+0.6<[N/C]<+1.0
[N/C]>+1.0
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data
for Galactic stars
vsini=400 km s-1
vsini=200 km s-1
vsini=100 km s-1
[N/C]<-0.2
-0.2<[N/C]<+0.2
+0.2<[N/C]<+0.6
+0.6<[N/C]<+1.0
[N/C]>+1.0
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data
for Galactic stars
vsini=400 km s-1
vsini=200 km s-1
vsini=100 km s-1
[N/C]<-0.2
-0.2<[N/C]<+0.2
+0.2<[N/C]<+0.6
+0.6<[N/C]<+1.0
[N/C]>+1.0
Generalities
Chemical evolution of the Galaxy
Literature data
for Galactic stars
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Literature data
for Galactic stars
τ Sco
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data for Galactic stars
HD 64760
HD 191423
ζ Oph
[N/C]<-0.2
-0.2<[N/C]<+0.2
+0.2<[N/C]<+0.6
+0.6<[N/C]<+1.0
[N/C]>+1.0
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Literature data for Galactic stars
Slowly-rotating MS stars with N excess
HD 64760
HD 191423
ζ Oph
[N/C]<-0.2
-0.2<[N/C]<+0.2
+0.2<[N/C]<+0.6
+0.6<[N/C]<+1.0
[N/C]>+1.0
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Large Magellanic Cloud
(Hunter et al. 2009)
[N/C]<-0.45
-0.45<[N/C]<-0.05
-0.05<[N/C]<+0.35
+0.35<[N/C]<+0.75
[N/C]>+0.75
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Large Magellanic Cloud
(Hunter et al. 2009)
Fast-rotating stars with normal N
[N/C]<-0.45
-0.45<[N/C]<-0.05
-0.05<[N/C]<+0.35
+0.35<[N/C]<+0.75
[N/C]>+0.75
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Large Magellanic Cloud
(Hunter et al. 2009)
Slowly-rotating MS stars with N excess
Fast-rotating stars with normal N
[N/C]<-0.45
-0.45<[N/C]<-0.05
-0.05<[N/C]<+0.35
+0.35<[N/C]<+0.75
[N/C]>+0.75
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Large Magellanic Cloud O stars
(Rivero González et al. 2011)
Neon
Mixing in magnetic B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Only a modest decrease of the rotational velocities of B stars from ZAMS to TAMS
Huang & Gies (2006)
Meynet & Maeder (2003)
Generalities
Chemical evolution of the Galaxy
Solar
The chemical composition of B stars
Mixing in B stars
Solar
Neon
Mixing in magnetic B stars
Literature data
for Galactic mainsequence B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
A population of N-enriched main sequence stars
Solar
Solar
Literature data
for Galactic mainsequence B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
A population of N-enriched main sequence stars
Higher incidence of magnetic stars ?
Solar
Solar
Literature data
for Galactic mainsequence B stars
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
A challenge and a key object: τ Sco (B0.2 V)
B~300 G
Stable, likely fossil field
Complex magnetic structure
Wind magnetically confined (P~41 d)
Strong, hard X-ray emission
Close to ZAMS
Intrinsically very slow rotator (veq ~ 6 km s-1)
[N/C] = –0.17±0.18 (Kilian 1992)
[N/C] = –0.04±0.21 (Hubrig et al. 2008)
[N/C] = –0.14±0.18 (Przybilla et al. 2008)
(Sun: –0.60±0.08)
Donati et al. (2006)
Nitrogen rich by a factor ~3, whereas
it should not be
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Models with dipolar field and magnetic braking
B=1 kG, with differential
rotation
B=1 kG, with solid body
rotation
Meynet et al. (2011)
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Are magnetic OB stars more prone to mixing?
Without a field detection
With a field detection
Morel (2011)
Conclusions
Chemical composition of nearby B stars
Often found subsolar, but situation improving.
No evidence that neon could solve the conflict between the new solar abundances and helioseismology.
Conclusions
Chemical composition of nearby B stars
Often found subsolar, but situation improving.
No evidence that neon could solve the conflict between the new solar abundances and helioseismology.
Usefulness of OB stars to study the chemical evolution of the Galaxy
Unevolved stars visible at large distances and tracers of the present-day abundance of the ISM, close to
their birthplace.
But current limitations: outer disk poorly sampled, large scatter at given galactocentric distance.
Prospects with GAIA: much more accurate distances (<<10% compared to up to 50%).
No abundance analysis possible from RVS spectra: need for ground-based follow up.
Accurate distances and detailed chemical information for both young and old populations will improve
our understanding of the chemical history of the Galaxy and how it formed/evolved: stringent
constraints on theoretical models.
Conclusions
Chemical composition of nearby B stars
Often found subsolar, but situation improving.
No evidence that neon could solve the conflict between the new solar abundances and helioseismology.
Usefulness of OB stars to study the chemical evolution of the Galaxy
Unevolved stars visible at large distances and tracers of the present-day abundance of the ISM, close to
their birthplace.
But current limitations: outer disk poorly sampled, large scatter at given galactocentric distance.
Prospects with GAIA: much more accurate distances (<<10% compared to up to 50%).
No abundance analysis possible from RVS spectra: need for ground-based follow up.
Accurate distances and detailed chemical information for both young and old populations will improve
our understanding of the chemical history of the Galaxy and how it formed/evolved: stringent
constraints on theoretical models.
Evidence for two populations of massive stars not explained by rotational mixing:
Fast rotators with no signature of mixing: binaries?
Slowly-rotating, main-sequence stars with a nitrogen excess: suggest that mixing efficiency is
underestimated. Link with magnetic fields emerging, but abundance studies of larger samples of stars
with a secure field (un)detection needed. No strict one-to-one correspondence between magnetic fields
and extra mixing: if any, relationship likely statistical.
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Effective temperature from theoretical calibrations of Si line ratios (σTeff ~ 1000 K)
ξ=5 km s-1
ξ=10 km s-1
ξ=15 km s-1
Generalities
Chemical evolution of the Galaxy
The chemical composition of B stars
Mixing in B stars
Neon
Mixing in magnetic B stars
Effective temperature from theoretical calibrations of Si line ratios (σTeff ~ 1000 K)
ξ=5 km s-1
ξ=10 km s-1
ξ=15 km s-1
EW(Si IV 4212)/EW(Si III 4813)=0.31
Teff~26300 K