Non-LTE Models for Hot Stars

1. Non-LTE Models for Hot Stars Added ComplicationsComplete LinearizationLine Blanketed, Non-LTE Models

3. Massive Hot Starswww.ster.kuleuven.ac.be/~coralie/ghost3_bouret.pdf

4. Interesting Complications

5. Complete Linearization (CL)(Auer & Mihalas 1969) • Linearized versions of - transfer equation- radiative equlilibrium- hydrostatic equilibrium- conservation of particle number- statistical equilibrium • Use matrix operations in a Newton – Raphson correction scheme (iterative) • Used for H + He models (Mihalas + …)

6. Complete Linearization (Auer & Mihalas 1969) • Always works but expensive in computer time …varies as(NF+NL+NC)3 x ND x Niter • NF = # frequency points (~106) • NL = # atomic energy levels • NC = # constraint equations (~3) • ND = # depth points • Niter = # iterations to convergence

7. Model Atmospheres for Hot Stars

8. TLUSTY/SYNSPEC • OSTAR2002:Lanz & Hubeny 2003, ApJS, 146, 417 • BSTAR2006:Lanz & Hubeny 2007, ApJS, 169, 83 • Web site:http://nova.astro.umd.edu/ • TLUSTY – atmosphereSYNSPEC – detailed spectrum • Versions available for accretion disks

9. Line Blanketed Non-LTE Models for Hot Stars by Hubeny & Lanz (1995, ApJ, 439, 875) • Uses hybrid CL + ALI scheme(Accelerated Lambda Iteration:solve for J = Λ[S] using approximate Λ-operator plus a correction term from prior iteration) • Divide frequency points into groups ofcrucial – full CL treatment andALI – use fast ALI treatment

10. Non-LTE Opacity Distribution Functions • Group all transitions:parity energy • Make superlevels for each group (~30 per ion) • Assign single NLTE departure coefficient to each superlevel

11. Non-LTE Opacity Distribution Functions • For each pair of superlevel transitions, get total line opacity in set frequency intervals • Represent in model as an ODF • Alternatively use Opacity Sampling(Monte Carlo sampling of superline cross sections)

12. Line Blanketing: OSTAR2002 • Low tau: top curves are for an H-He model, and the temperature is progressively lower when increasing the metallicity • Large tau:reverse is true at deeper layers

13. NLTE populations: OSTAR2002 • He (left), C (right) ionization vs. tau for Teff = 30, 40, 50 kK(top to bottom) • LTE = dashed lines • NLTE: numbers tend to be lower in lower stages (overionized by the strong radiation field that originates in deep, hot layers) and conversely higher in higher stages

14. OSTAR2002: Lyman Jump & Teff • Top to bottom:Teff = 55, 50, 45, 40, 35, and 30 kK • Lyman jump gradually weakens with increasing temperature and disappears at 50 kK • Weakening and disappearance of Lyα, Si IV 1400, C IV 1550, etc. at hot end

15. OSTAR2002: Lyman Jump & g • Top to bottom, > 912 Å:log g = 4.5, 4.25, 4.0, 3.75, 3.5 • Order reversed for < 912 Å • Saha eqtn.: low ne, low neutral H, less b-f opacity

16. Lyman Jump & metallicity • Z / ZSUN = 2, 1, 1/2, 1/5, 1/10 (bold line) • Strong absorption 1000 – 1600 Å balanced by higher flux < 912 Å in metal rich cases(flux constancy)

17. NLTE (TLUSTY) vs. LTE (ATLAS) • (Teff, log g) = (40 kK, 4.5), (35 kK, 4.0), (30 kK, 4.0) (thick lines), compared to Kurucz models with the same parameters (thin histograms)

18. OSTAR2002 & BSTAR2006 • grad/g vs.Teff and log gThick and dashed line = Eddington limitfor solar and zero metallicity • BSTAR2006 grid (filled) and OSTAR2002 grid (open) • Evolutionary tracks (Schaller et al. 1992) are shown for initial masses of 120, 85, 60, 40, 25, 20, 15, 12, 9, 7, 5, and 4 MSUN(left to right)

19. BSTAR2006 vs. ATLAS • (Teff, log g) = (25 kK, 3.0), (20 kK, 3.0), (15 kK, 3.0) (black lines); compared to Kurucz models, same parameters (red histograms) • In near UV, LTE fluxes are 10% higher than NLTE • Lower NLTE fluxes result from the overpopulation of the H I n = 2 level at the depth of formation of the continuum flux, hence implying a larger Balmer continuum opacity

20. BSTAR2006 vs. ATLAS • NLTE effects most important for analysis of specific lines(NLTE – black,LTE – red)