Anatomy of B stars

Invited talk at Argelander Institute fur Astronomie, Bonn, Germany

Transcript

1. Ehsan Moravveji (KU Leuven) The Anatomy of B stars
 from Asteroseismic Perspective Conny Aerts Peter Papics Santiago Triana
2. Ignore the atmosphere Sub-surface Iron and Nickel Opacity Mixing in the whole radiative envelope Details of the overshoot layer (only 2% in radius) Sorry: g-modes do not penetrate into the convective core! The image scales with the size of different regions of our SPB star KIC 10526294, inferred from seismic modelling. Angular momentum transport between core and envelope
3. Enhanced Iron Opacity and Instability Strips of Massive Stars
5. Enhancing Iron Opacity: OP Monochromatic Data [1,2,3,4] [1] Seaton M. J. et al., 1992, MNRAS [2] Seaton M. J. 2005, MNRAS [3] Badnell N. R. et al. 2005, MNRAS [4] Hu H., et al. 2011, MNRAS [5] Moravveji (2015, MNRAS, in press) (βFe ,βNi ) = (1.0,1.0) = (1.75,1.0) = (1.75,1.75) Three new opacity tables in OPAL Type I format [5]: κi (ν) = βi κbf i (ν)+κff i (ν)+κbb i (ν) ( )× 1−exp −hν / k B T ( ) ( ) κnet (ν) =κes + κi (ν), where i=H, He, C, N, O, ..., Fe, Ni i=1 17 ∑ 1 κ = 1 dB / dT 1 κnet (ν) dB(ν,T) dT 0 ∞ ∫ dν. All codes, and new opacity tables are available on bitbucket: op_mono
6. Iron- and Nickel-Enhanced Opacity Tables (βFe ,βNi ) = (1.0,1.0) = (1.75,1.0) = (1.75,1.75) [1] Moravveji (2015, MNRAS Lett); [2] Paxton et al. (2011, 2013, 2015, ApJS); [3] Townsend & Teitler (2013, MNRAS); [4] Nieva F. & Przybilla N. 2012, A&A MESA [2] + GYRE [3] Initial mass = 2.5 M⦿ to 25 M⦿ Composition: Zini=0.014, Xini = 0.71 [4] Mixture: Asplund et al. (2009) Three new opacity tables in OPAL Type I format [1]:
7. What is the Instability Strip? [1] Pamyatnykh (1999); [2] Saio (2011); [3] Walczak et al. (2015); [4] Paxton et al. (2015); ❖ Pulsationally Unstable regions on HRD or Kiel diagram ❖ The boundary depends on the input physics, e.g. mass, mixture, metallicity, opacity (OP vs. OPAL) ❖ Choice of boundary is subjective ❖ Number of unstable modes evolves along tracks
 ❖ Classical vs. new picture!
8. Extended Instability Strips: Radial Modes [1] Pamyatnykh (1999); [2] Saio (2011); [3] Walczak et al. (2015); [4] Paxton et al. (2015); [5] Moravveji (2015, MNRAS, in press)
9. Extended Instability Strips: Dipole Modes [1] Pamyatnykh (1999); [2] Saio (2011); [3] Walczak et al. (2015); [4] Paxton et al. (2015); [5] Moravveji (2015, MNRAS, in press)
10. Late-O β Cep Stars on the Kiel Diagram [3] [1] HD 46202 (O9V) [2] EPIC 202060092 (O9V:p) Q: How to explain observed variability in these two stars? A: Only if Iron (and/or Nickel) opacity is enhanced by ~75%. [1] Briquet et al. (2011); [2] Buysschaert et al. (2015) [3] Moravveji (2015, MNRAS, in press)
11. β Cep - SPB Hybrids on the Kiel Diagram ★ Hybrids simultaneously show both SPB and Cep variability 
 ★ 8 confirmed hybrids from literature + 3 new stars from BRITE mission ★ Hybrid instability domain grows
 ★ ~75% Iron opacity increase from lab measurement agrees with the mode excitation in OB stars
12. Gravity-Modes and Mixing Processes
13. Observed Period Spacings Across HRD F-type: ~ 60 Dor stars [1]
 A-type binary: both components [2]
 B-type: 3 SPB stars [3] Subdwarf B stars: 9 stars [4]
 
 dipole (l=1) prograde or retrograde 
 g-modes
 [1] Van Reeth et al. (2015, A&A) [2] Schmid et al. (2015, A&A) [3] Papics et al. (2012, 2014, 2015, A&A) [4] Ostensen et al. (2014, A&A) Prograde (left) and retrograde (right) 
 dipole g-modes in KIC 2710594 ( Dor) ΔP n,ℓ = P n+1,ℓ − P n,ℓ
14. Observed Period Spacings Across HRD KIC 10080943: Binary. Both components exhibit rotationally-split g-mode period spacings! F-type: ~ 60 Dor stars [1]
 A-type binary: both components [2]
 B-type: 3 SPB stars [3] Subdwarf B stars: 9 stars [4]
 
 dipole (l=1) prograde or retrograde 
 g-modes
 [1] Van Reeth et al. (2015, A&A) [2] Keen & Schmid et al. (2015) [3] Papics et al. (2012, 2014, 2015, A&A) [4] Ostensen et al. (2014, A&A) ΔP n,ℓ = P n+1,ℓ − P n,ℓ
15. Observed Period Spacings Across HRD F-type: ~ 60 Dor stars [1]
 A-type binary: both components [2]
 B-type: 3 SPB stars [3] Subdwarf B stars: 9 stars [4]
 
 dipole (l=1) prograde or retrograde 
 g-modes
 [1] Van Reeth et al. (2015, A&A) [2] Schmid et al. (2015, A&A) [3] Papics et al. (2012, 2014, 2015, A&A) [4] Ostensen et al. (2014, A&A) ΔP n,ℓ = P n+1,ℓ − P n,ℓ
16. Observed Period Spacings Across HRD KIC-10553698A: Subdwarf B star in binary system. Clear mode trapping for l=1, 2 g-modes F-type: ~ 60 Dor stars [1]
 A-type binary: both components [2]
 B-type: 3 SPB stars [3] Subdwarf B stars: 9 stars [4]
 
 dipole (l=1) prograde or retrograde 
 g-modes
 [1] Van Reeth et al. (2015, A&A) [2] Schmid et al. (2015, A&A) [3] Papics et al. (2012, 2014, 2015, A&A) [4] Ostensen et al. (2014, A&A) ΔP n,ℓ = P n+1,ℓ − P n,ℓ
17. Miglio et al. (2008, MNRAS) Zhang Q. S. (2013, ApJ) Moravveji et al. (2015, A&A) Moravveji (2015, EAS Conf. Proc., in press) Viallet et al. (2013, 2015, A&A) Simplified Mixing Scheme • Convective mixing (MLT) • Overshoot (ad-hoc) • Extra mixing in radiative envelope (ad-hoc)
18. Consequences of Extra 
 Mixing in the Envelope N2 ∝(∇ad − ∇+ ∇ µ ) Mixing in radiative envelope modifies the -gradient Mode periods depend on the exact shape of Buoyancy frequency P n,ℓ ∝ N(r) r dr 0 R ∫ # $ % & ' ( −1
19. Evolution of Period Spacing
20. [1] Pápics et al. (2014, A&A) [2] Moravveji et al. (2015, A&A) [3] Triana et al. (2015, ApJ) KIC 10526294 [1, 2, 3] ★ B8.3 V ★ log Teff=11 500 ± 500 K ★ log g = 4.1 ± 0.2 [cm2 sec-1] ★ vrot ≲ 18 [km sec-1] ★ Prot ≈ 188 [days] The first, richest SPB, modelled so far!
 Wait for the second …
21. To Mix or Not to Mix? [1] Pápics et al. (2014, A&A) [2] Moravveji et al. (2015, A&A) [3] Triana et al. (2015, ApJ) χNo Mixing 2 ≈11χMixing 2 2 for fitting frequencies Thus, extra mixing in the envelope is needed, even for slow rotators D mix ≈ 55 to 100 (cm2 sec−1)
22. [1] Moravveji (2015, EAS Conf. Proc.)
 [2] Dziembowski & Pamyatnykh (1991, A&A Lett.) Eigenfunctions Resolve the Near-Core Regions
23. Miglio et al. (2008, MNRAS) Moravveji et al. (2015, A&A) Moravveji (2015, EAS Conf. Proc.) Viallet et al. (2013, 2015, A&A) Overshooting Mixing Profile (a) Exponential Overshoot:
 mixing is r-dependent, gives smoother Buoyancy
 
 
 (b) Step-Function Overshoot:
 constant mixing, 
 gives steeper buoyancy
 D over (r) = D conv exp −2r f ov H p ( ) D over (r) = D conv , R core ≤ r ≤αov H p
24. Which Overshoot Profile? [1] Pápics et al. (2014, A&A) [2] Moravveji et al. (2015, A&A) [3] Stancliffe et al. (2015, A&A) 2 for fitting frequencies Exponential overshooting is preferred. Two more stars are in the pipeline:
 HD 50230 (CoRoT) and KIC 7760680. 
 χStep 2 ≈ 2.3χExp 2 Best f ov = 0.017 Best αov = 0.21
25. Asteroseismic Modelling of Slowly Rotating SPBs
26. Rotational Splittings
 & Counter-Rotation! [1] - Efficient angular momentum transport - Mechanism: Internal Gravity Waves [2], 
 or heat-driven waves [3, 4].
 
 [1] Triana et al. (2015, ApJ) [2] Rogers et al. (2013, ApJ) [3] Lee & Saio (1993, MNRAS) [4] Lee et al. (2015, MNRAS)
27. Getting Even Richer!
 KIC 7760680 ★ The decreasing pattern in the period 
 spacing is a signature of rotation
 ★ Great potential to study angular 
 momentum transport from core to 
 the envelope
 ★ The sub-structure (dips) reveal mixing 
 properties
 ★ Quantifying rotational mixing
 ★ Rotation suppresses overshooting? [1] Lee & Saio (1997, ApJ) [2] Townsend (2000, 2003, 2005, MNRAS) [3] Bouabid et al. (2013, MNRAS) [4] Pápics et al. (2015, ApJL)
 [5] Van Reeth et al. (2015a, b, A&A) Detailed Seismic 
 Modelling
28. [1] Lee & Saio (1997, ApJ) [2] Townsend (2000, 2003, 2005, MNRAS) [3] Ballot et al. (2010, A&A) [4] Bouabid et al. (2013, MNRAS) ★It has N=36 observed dipole g-modes ★Unknown surface rotation frequency ★Traditional approximation of rotation [1, 2, 4]. ★Optimising rotation rate, ηrot, to match number 
 of observed modes ★GYRE takes ~2 min to optimise ηrot per each model ★Then, we can compute 2 for fitting frequencies Extremely Rough Results:
 KIC 7760680 Thus, thorough asteroseismic modelling of rotating SPBs is possible
29. Extremely Rough Results:
 KIC 7760680 M = 3.45M sun f ov = 0.020 Z = Z sun = 0.014 D mix =10 [cm2 sec−1] X core = 0.60 ηrot = 3.26% Ωsurf = 0.468 [d−1] v rot = 57.9 [km sec−1] vsini = 62± 5 [km sec−1] # $ % & % Yet, no thorough modelling is attempted.
 Much better models will come out soon
30. Ignore the atmosphere Fe and Ni are more opaque than we compute! Quantifying mixing even for very slow rotators Resolving thermal & chemical structure of overshooting zone Sorry: g-modes do not penetrate into the convective core! The image scales with the size of different regions of our SPB star KIC 10526294, inferred from seismic modelling. Angular momentum transport: solid- body rotation
32. Extended Instability Strips: Quadrupole Modes [1] Pamyatnykh (1999); [2] Saio (2011); [3] Walczak et al. (2015); [4] Paxton et al. (2015); [5] Moravveji (2015, MNRAS, in press)
36. Paxton et al. (2015, ApJS)