Gamma Doradus stars: Evolutionary status

1. Gamma Doradus stars: Evolutionary status Andrea Miglio, Josefina Montalban & Sylvie Theado Institut d’Astrophysique, Liège Belgium

2. Plan of the talk -MS evolution -internal structure A “typical” gamma-Doradus Mass Age, Z, aMLT on HR location,TCZ,Xcore Effects of classical parameters Convection: MLT/FST semiconvection Effects of physical processes diffusion overshooting rotation Effects on the frequencies of g modes

3. γ Doradus

4. γ Doradus • Close in HRD location • Chemical peculiar stars: Am-Fm • (HD8801, HD114839 ) • Transition from low to high stellar • rotational velocity • Bohm-Vitense GAP • Lithium GAP • From convective to radiative • envelope • A7-F5 type stars • Teff: 7400 – 6500 K • [M/H]: -0.37 , +0.12 • Main Sequence Stars • Multiple Photometric (a few millimagnitudes) • and spectroscopic (2-4 km/s) variables: • low degree and high order g-modes: P=0.3-3 d • g Dor instability strip (IS) overlap dScuti IS : • HD 8801 (Henry & Fekel, 2005), HD114839, HD184914 (MOST), • HD49434 (Uytterhoeven et al. 2008), COROT data … • Overlap solar like oscillations domain

5. k convective core H,He He Fe ad rad convective envelope  p Sl NBV p g 1 A “typical” star in the g dor inst strip

6. tth ~ Pat the bottom of convective envelope for gDor “Convective Blocking” excitation mechanism (Guzik et al. 2000). In the frozen-in convection approximation: tconv > P Tcz ~ 200000 – 480000 K Teff ~ 7400 – 6500 K 1 A “typical” star in the g dor inst strip Transition layer Log(tth) g Dor g modes

7. 2 Effects of “classical parameters” Mass: 1.4 – 1.8 M Main Sequence Z=0.02 aMLT=1.8 No Diff Observational instability strip (Handler & Shobbrook 2002) Observational points (Henry et al 2005)

8. 2 Effects of “classical parameters” Age and Mass: Tcz Convective Core Mass 1.45 1.40 1.60 1.55 1.50

9. 2 Effects of “classical parameters” Chemical Composition: Measured Metallicity: [M/H]~ -0.37 to +0.12

10. 2 Effects of “classical parameters” The aMLT parameter: aMLT=1.8

11. The aMLT parameter: aMLT=1.8 aMLT=1.6 2 Effects of “classical parameters”

12. The aMLT parameter: aMLT=1.8 aMLT=1.6 2 Effects of “classical parameters” aMLT=1.4

13. 2 Effects of “classical parameters” Tcz increases when aMLT increases if the CZ is deep enough. If low density, even high aMLT does not increase Fconv aMLT does not affect the size of the convective core

14. 2 Effects of “classical parameters” aMLT=2 aMLT=1.5 aMLT=1 aMLT=1.87 Warner et al. 2003 Convective blocking requires high aMLT, BUT in that HRD region, 2-3D numerical Simulations suggest aMLT < aMLT() Dupret et al. 2004

15. 3.Convection Treatment • MLT : L=aMLT Hp, one-eddy approx. • FST : L=z+a*Hp CGM96, full spectrum of turbulence. • Low efficient convection: Fcon(FST) ~ 0.3 Fcon(MLT) • and • Efficient convection: Fcon(FST) ~ 10 Fcon(MLT)

16. 3.Convection Treatment

17. 3. Physical processes “classical” parameters Structure of γ Dor 1. Semiconvection 2. Diffusion 3. Overshooting 4. Rotation

18. 3.2 Semiconvection Evolution of Mcc during MS Masses considered: 1.25 ≤ M/M≤ 1.8 Higher masses: Mccshrinks Lower masses:Mccgrows Age

19. 3.2 Semiconvection CNO cycle becomes dominant source of hydrogen burning discontinuity in chemical composition profile Growing convective core

20. + A growing convective core SEMICONVECTION IN LOW-MASS MAIN SEQUENCE STARS ! Gabriel and Noels (1977), Crowe and Mitalas (1982), Merryfield (1995) The way the boundary of the mixed region is computed If extra-mixing is considered different chemical composition profiles are found

21. 3.2 Diffusion effects at borders of convective regions Change in chemical composition profile , C.Envelope Diffusion of H,He Opac Opac He Diff

22. 3.2 Diffusion C.Envelope Settling of Z Steep Z gradient at Rcz Semiconvection e.g. Bahcall et al. (2001) ApJ 555 ? Effect on excitation of g-modes Opacity “bump” ! Radiative accelerations M/M= 1.5

23. 3.2 Diffusion C.Envelope Radiative Forces “Iron” convective zone Richard, Michaud & Richer (2001) ApJ 558 Depth of convective envelope ? Effect on excitation of g-modes 2 Semiconvective regions ? M/M= 1.5

24. 3.2 Diffusion C.Core Diffusion of H,He Smoother X profile Effects on period spacing of g modes M/M= 1.5

25. 3.2 Diffusion C.Core Diffusion of H,He,Z Middle of main-sequence Z accumulates outside core boundary Semiconvetion again! (As in previous figure from Richard et al (2001)) M/M= 1.5

26. 3.3 Overshooting Boundary of convective region: Uncertainties in the models Role of overshooting: Amount of overshooting Dependence on the mass? on chemical composition? Definition no overshooting / overshooting mass domain Different extension of the mixed region and (T,P) stratification

27. 3.3 Overshooting - Mcc Larger not just mixed region - Different Mcc(Age) - Different effect depending on mass Different location and sharpness of c.comp. gradient Effects on

28. 3.3 Overshooting Central region 1.55 M

29. 3.3 Overshooting In the overshooting region: or where M/M= 1.55

30. 3.3 Overshooting Below the convective envelope In overshooting region if Change in properties of region where excitation mech. is at work ? M/M= 1.55

31. 3.3Rotation V sin i ~ 3-135 km/s R* ~ 1.5 R rot ~ 2.5 – 150 mHz wosc ~ 4.– 40 mHz Coriolis force dominates the mode’s dynamics De Cat et al. 2006, A&A 449

32. 3.3Rotation 1. Equatorial wave guide 2. Rotational splitting far from uniform splitting as  ~ w0 3. Photometric amplitude ratios cannot be used as diagnostic of the degree Townsend (2003) Proc. IAU 215

33. 3.3 Rotation: mixing “Mimicking” rotational mixing with a turbulent diffusion coefficient Mathis & Zahn (2004)

34. 3.3 Rotation: mixing Effects on: HD diagram Std DTURB Ov 0.1 Std DTURB Ov 0.1 He Diff

35. M=1.6 M Xc=0.7 Xc=0.5 Xc=0.3 Xc=0.1 4. Periods of high order g-modes Miglio, Montalbán, Noels, Eggenberger (2008) MNRAS, 386, 1487 first order asymptotic theory constant sharp features in clear deviations from constant ? Information in periodicity and amplitude

36. 4. Periods of high order g-modes White Dwarfs Mode trapping due to μgradients in the envelope e.g. Brassard et al., ApJS 80, 1992 Main sequence intermediate mass models Due to evol. of c.c models presents sharp features in Expected deviations from constant location “sharpness”

37. 4. Periods of high order g-modes B(r)~0.1 Age B(r)~0.25 M=1.6 M T~9 1/T~0.1 T~4 1/T~0.25

38. 4. Periods of high order g-modes effects of “extra-mixing” processes e.g. - Overshooting - Diffusion sensitive to detailed shape of the µ gradient region: position & sharpness

39. 5. Summary A “typical” gamma-Doradus Convective env. & conv core Excitation: T base conv. envelope diffusion Mass Age, Z, aMLT , HR location overshooting MLT/FST rotation Periods of g modes: probes of central ch. comp. gradient large effects of rotation on P, visibility, mode id !