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Testing the effects of opacity and the chemical mixture on the excitation of pulsations in B stars
SИbastien Salmon
Collaborators : J. MontalbАn, T. Morel, A. Miglio, M-A. Dupret, A. Noels

IAU, Beijing, August 2012


Pulsations across the HR diagram

OP/OPAL K mechanism

Galactic B AL OP / OP stars

MCs B stars Cephei - SPB

Ni thercity O opa s?


The Kappa mechanism

Second He partial ionization zone
(see Zhekavin 1959, Baker & Kippenhahn 1962)

OP/OPAL K mechanism

Galactic B AL OP / OP stars

MCs B stars Cephei - SPB

Ni thercity O opa s?


The Kappa mechanism
Iron group opacity bump Cephei : main-sequence B stars ; low-order p and g modes ; P ~ 2-8 h SPB : less massive ; high-order g modes ; P ~ 1-3 d
(see Moskalik & Dziembowski 1992; Cox et al. 1992; Dziembowski & Pamyatnykh 1993; Dziembowski, Moskalik & Pamyatnykh 1993)

OP/OPAL K mechanism

Galactic B AL OP / OP stars

MCs B stars Cephei - SPB

Ni thercity O opa s?


The iron bump
Very high number of atomic transitions of iron-group elements
[He-like] [Ne-like] [Ar-like]

e.g. for Fe

57%

Fe (%)

27% 17% 7.2 6.4 5.3

31%

4.4

log T

OP/OPAL K mechanism

Galactic B AL OP / OP stars

MCs B stars Cephei - SPB

Ni thercity O opa s?


Historical review...
Group Los Alamos
(first release by Cox & Stewart 1965)

Date Before 1991 1991

Chemical elements 12
(H-He-C-N-O-NeNa-Mg-Al-Si-Ar-Fe)

Physics input
Missed boundbound transitions of heavy elements

Result/Trouble Cepheids mass problem 300 % increase of iron bump of opacity : mech. of Ceph / SPBs Iron bump from OPAL

OPAL
(Rogers & Iglesias 1991,92)

14
(H-He-C-N-O-NeNa-Mg-Al-Si-S-ArCa-Fe)

Bound-bound transitions of heavy elements + spin-orbit interaction
Iron-group elements

OP
(Seaton et al. 1994)

1994 1996 2005

17
(OPAL ones + NiCr-Mn)

OPAL
(Iglesias & Rogers 1996)

21
(+ P-Cl-K-Ti-Ni-CrMn)

More elements + improved EoS New treatment of inner-shell transitions

OP (Badnell et al.
2005)

17

Iron bump enhanced by 18%

OP/OP K mP/OPAL O echanism

Galactic B AL rs Galactic P stars OP / O sta

MCs B stars MCs s-tar Cephei SPB

Ni thercity O opa s? Others?


... also for the chemical mixture
Chemical mixture: from GN93 (Grevesse & Noels 1993) to AGS05 (Asplund
& Grevesse & Sauval 2005) C, N, O 35-45%

AGS05 in combination with enlarges instabili strip and domain frequency (Miglio
al. 2007)

OP ty of
et

For a given Z, Fe 20%

!
OP/OP K mP/OPAL O echanism Galactic B AL rs Galactic P stars OP / O sta MCs B stars MCs s-tar Cephei SPB Ni thercity O opa s? Others?


Pulsating B stars : troubleshot ?
The anwer is no :
- Galactic hybrids (both Cep/SPB pulsations) => trouble to reproduce high period modes
(e.g. Pamyatnykh, Handler & Dziembowski 2004 ; Dziembowski & Pamyatnykh 2008 ; DaszynskaDaszkiewicz & Walczak 2010)

- B-type pulsators in the Magellanic Clouds ZSMC=0.0027 and ZLMC=0.0046 (metallicities from
Buchler 2008)

Z too low for excitation of pulations !
(e.g. Miglio et al. 2007)

OP/OP K mP/OPAL O echanism

Galactic PAL rs Galactic B AL OP / OP stars OP/O sta

MCs s-tar MCs B stars Cephei SPB

Ni thercity O opa s? Others?


Effect of the chemical mixture
We made a compilation (from literature) of chemical abundances of B stars for the SMC (Salmon et al. 2012) + a stability analysis of stellar models with that mixture

Z

SMC

=0.0027

OP/OP K mP/OPAL O echanism

Galactic PAL rs Galactic B AL OP / OP stars OP/O sta

MCs s-tar MCs B stars Cephei SPB

Ni thercity O opa s? Othersity opac ?


Effect of the chemical mixture
We made a compilation (from literature) of chemical abundances of B stars for the SMC (Salmon et al. 2012) + a stability analysis of stellar models with that mixture

Z

SMC

=0.0027

Z 0.007 to excite Cep modes ~2.5 ZSMC Z > 0.004 to excite SPB modes ~ 1.5 ZSMC

OP/OP K mP/OPAL O echanism

Galactic PAL rs Galactic B AL OP / OP stars OP/O sta

MCs s-tar MCs B stars Cephei SPB

Ni thercity O opa s? Othersity opac ?


Increasing the opacity

10 M model OP/OPAL K mP/OPAL m mechanis O echanism OP/O Galactic B AL Galactic PAL rs GaOP / OP stars lOctic AL OP/O sta a P/O OP MCs B istarPB MCs e s-tars Cepheistars Ceph S SPB Ni thercity O opaci? Others? Others ty Ni opa s? opac


Increasing the opacity
We made an ad hoc increase of the Ni opacity (also of Fe and Cr/Mn opacities, see Salmon et al. 2012 ; see also Jeffery & Saio 2006 in the case of the sdBs)

Z

SMC

=0.0027

log P (d)

OP/OP K mP/OPAL O echanism

Galactic PAL rs Galactic B AL OP / OP stars OP/O sta

MCs B stars MCs s-tar Cephei SPB

Ni thercity O opa s? Othersity opac ?


Increasing the opacity
We made an ad hoc increase of the Ni opacity (also of Fe and Cr/Mn opacities, see Salmon et al. 2012 ; see also Jeffery & Saio 2006 in the case of the sdBs)

Z

SMC

=0.0027

log P (d) by 2 in the Ni region => excitation of both Cep and SPB modes at Z
SMC

OP/OP K mP/OPAL O echanism

Galactic PAL rs Galactic B AL OP / OP stars OP/O sta

MCs B stars MCs s-tar Cephei SPB

Ni thercity O opa s? Othersity opac ?


Increasing the opacity
We made an ad hoc increase of the Ni opacity (also of Fe and Cr/Mn opacities, see Salmon et al. 2012 ; see also Jeffery & Saio 2006 in the case of the sdBs)

Z

SMC

=0.0027

log P (d) by 1.5 in the Ni region => increases instability domain to higher periods at ZGalaxy=0.014 (metallicity from Przybilla, Nieva & Butler 2008) OP/OP K mP/OPAL O echanism Galactic PAL rs Galactic B AL OP / OP stars OP/O sta MCs B stars MCs s-tar Cephei SPB Ni thercity O opa s? Othersity opac ?


Conclusion
An underestimation < 2 of Ni opacity could explain the difficulties encountered for B-type pulsators of the Galaxy and Magellanic Clouds

This is strengthened by the facts : - Ni opacity is partially extrapolated from Fe opacity in OP computations - recent results from computations of Ni opacity and plasma laboratory measurements (Turck-ChiХze et al., LIAC 2012) We thus call for a reexamination of Ni opacity computations

OP/OP K mP/OPAL O echanism

Galactic PAL rs Galactic B AL OP / OP stars OP/O sta

MCs B stars MCs s-tar Cephei SPB

Ni thercity O opa s? Othersity opac ?