NonLTE Models for Hot Stars Added Complications Complete

Non-LTE Models for Hot Stars Added Complications Complete Linearization Line Blanketed, Non-LTE Models 1

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Massive Hot Stars www. ster. kuleuven. ac. be/~coralie/ghost 3_bouret. pdf 3

Interesting Complications 10% of OB stars 4

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 + …) 5

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 6

Model Atmospheres for Hot Stars 7

TLUSTY/SYNSPEC • OSTAR 2002: Lanz & Hubeny 2003, Ap. JS, 146, 417 • BSTAR 2006: Lanz & Hubeny 2007, Ap. JS, 169, 83 • Web site: http: //nova. astro. umd. edu/ • TLUSTY – atmosphere SYNSPEC – detailed spectrum • Versions available for accretion disks 8

Line Blanketed Non-LTE Models for Hot Stars by Hubeny & Lanz (1995, Ap. J, 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 of crucial – full CL treatment and ALI – use fast ALI treatment 9

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 10

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) 11

Line Blanketing: OSTAR 2002 • 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 12

NLTE populations: OSTAR 2002 • He (left), C (right) ionization vs. tau for Teff = 30, 40, 50 k. K (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 13

OSTAR 2002: Lyman Jump & Teff • Top to bottom: Teff = 55, 50, 45, 40, 35, and 30 k. K • Lyman jump gradually weakens with increasing temperature and disappears at 50 k. K • Weakening and disappearance of Lyα, Si IV 1400, C IV 1550, etc. at hot end 14

OSTAR 2002: 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 15

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) 16

NLTE (TLUSTY) vs. LTE (ATLAS) • (Teff, log g) = (40 k. K, 4. 5), (35 k. K, 4. 0), (30 k. K, 4. 0) (thick lines), compared to Kurucz models with the same parameters (thin histograms) 17

OSTAR 2002 & BSTAR 2006 • grad/g vs. Teff and log g Thick and dashed line = Eddington limit for solar and zero metallicity • BSTAR 2006 grid (filled) and OSTAR 2002 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 18 (left to right)

BSTAR 2006 vs. ATLAS • (Teff, log g) = (25 k. K, 3. 0), (20 k. K, 3. 0), (15 k. K, 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 19

BSTAR 2006 vs. ATLAS • NLTE effects most important for analysis of specific lines (NLTE – black, LTE – red) 20