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Phillip C. Stancil Department of Physics and Astronomy Center for Simulational Physics

Molecular Opacities and Collisional Processes for IR/Sub-mm Brown Dwarf and Extrasolar Planet Modeling. Phillip C. Stancil Department of Physics and Astronomy Center for Simulational Physics The University of Georgia Lexington, KY; May 3, 2005. Collaborators. Astrophysics:.

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Phillip C. Stancil Department of Physics and Astronomy Center for Simulational Physics

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  1. Molecular Opacities and CollisionalProcesses for IR/Sub-mm Brown Dwarf and Extrasolar Planet Modeling Phillip C. Stancil Department of Physics and Astronomy Center for Simulational Physics The University of Georgia Lexington, KY; May 3, 2005

  2. Collaborators Astrophysics: Atomic/molecular: Chemistry: • N. Balakrishnan • Adrienne Horvath • Andy Osburn • Stephen Skory • Philippe Weck • Benhui Yang • Kate Kirby • Brian Taylor • T. Leininger • F. X. Gadéa • Peter Hauschildt • Andy Schweitzer Funding: NASA

  3. Introduction Opacities for LTE spectral models Electronic transitions Rovibrational transitions Collisional excitation for non-LTE Summary Outline

  4. Effective Temperatures and Spectral Classifications 0.2 M M - dwarfs CO TiO, VO, CaH, MgH TiO depletion VO depletion FeH, Li, K, Na CrH Li  LiCl NaCl, RbCl, CsCl H2O condenses 15 MJ N2 73 MJ CH4 0.3MJ EGP? NH3 Burrows et al. (2001)

  5. MgH in the Visible 4000 K A-X 3000 K 2000 K • A-X: 10,091 transitions • B-X: 10,649 transitions • X, A, B levels: 313, 435, 847 2000 K dusty Wavelength (Å) Weck et al. (2003), Skory et al. (2003) PHOENIX models

  6. CaH in the Visible • A-X: 26,888 transitions • Also, B-X, C-X, D-X, E-X transitions Weck, Stancil, & Kirby (2003) • Problem: with new CaH line data, models are a factor of 10 smaller than M dwarf observations

  7. Keck II spectrum of an L5 dwarf (Reid et al. 2000) • Stellar classifications based on optical/NIR spectra • Substellar objects (brown dwarfs) have insufficient mass to maintain nuclear burning (~0.08 M ~80 MJ) • Lithium test for substellarity: presence of Li 6708 Å line Li ? No Li Wavelength (Å)

  8. 2000 K 3330 K Equilibrium abundances in a cool dwarf atmosphere (Lodders 1999) 2500 K 1670 K 1430 K Log of abundance M L 104/T

  9. However, for T<1600 K, Li is converted to LiCl (LiOH) • Li test not useful for the coolest L dwarfs or T dwarfs • Lodders (1999) and Burrows et al. (2001) suggested that the LiCl fundamental vibrational band at 15.8 m should be looked for; total Li elemental abundance could be obtained • Problem I. LiCl feature at 15.8 m previously inaccessible from ground or space • Problem II. Current spectral models lack alkali-molecule opacities due to lack of molecular line lists • Solution I. Space-based IR observatories: Spitzer, JWST, Herschel, TPF • Solution II. Line lists are being calculated in our group: LiCl, NaH, …, and incorporated into the stellar atmosphere code PHOENIX

  10. 25 MJ (800 K, 10 pc, T dwarf) theoretical spectra by Burrows et al. (2003) H20 CH4 NH3 SIRTF JWST LiCl T=1000 K LTE spectra with 3,357,811 lines between 29,370 levels v=1 v=2 v=3 5 10 20 30 Weck et al. (2004) Wavelength (m)

  11. T T • Inclusion of LiCl in PHOENIX models gave no distinct features • The maximum flux difference is 20% • Spectrum is dominated by H2O opacity • It will be hard to detect LiCl with SIRTF or JWST • NaCl or KCl may be more promising • Also, alkali-hydrides (NaH, KH) L T • Models constructed for Teff=900, 1200, and 1500 K and log(g)=3.0 (young), 4.0, and 5.0 (old, > 1 Gyr) • Solar metallicity

  12. New Spitzer IR Observations M3.5 L8 EGP T1/T6 EGP Roellig et al. (2004) TrES-1: Charbonneou et al. (2005) HD 209458B: Deming et al. (2005)

  13. NAH LTE spectra for rovibrational and electronic X-A transitions (Horvath et al.2005, in prep.) v=0 X-A v=1 • Future mid- to far-IR observations of L/T dwarfs (and maybe extrasolar giant planets) may be able to detect NaH, NaCl, KCl, and other molecular alkali species NaH LiCl NaCl KCl KH? KH Burrows et al. (2001)

  14. Non-LTE effects • NLTE effects investigated for CO by: • Ayres & Weidemann in the sun (1989) • Schweitzer, Hauschildt, & Baron (2000) for M dwarfs • NLTE effects might be expected for cool objects • Non-Planckian radiation • Strong irradiation from companion • Slow collisional rates M8 model: Teff=2700 K CO v=1

  15. CO(v=1) + H  CO(v=0) + H T L M EGP Dense cores Orion Peak 1 and 2

  16. CO(v=1,j=0) + H  CO(v’=0,j’=0-25) + H

  17. Summary • Advances in brown dwarf (BD) and extrasolar giant planet (EGP) spectra modeling requires line lists of ``new’’ molecules, e.g. hydrides (CrH, FeH), alkalis (NaCl, KH, KCl, …), … • Non-LTE (NLTE) effects may play a role in the coolest objects, e.g. H2O, NH3, CH4 • NLTE effects are likely for atomic lines, e.g. Na 3s3p • Non-local chemical equilibrium (NLCE) may need consideration: ionization, dissociation, recombination, association  CO is overabundant by a factor of 100 in the T dwarf Gl 229B

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