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Molecular Opacities and Collisional Processes for IR/Sub-mm Brown Dwarf and Extrasolar Planet Modeling Phillip C. Stancil Department of Physics and Astronomy.

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Presentation on theme: "Molecular Opacities and Collisional Processes for IR/Sub-mm Brown Dwarf and Extrasolar Planet Modeling Phillip C. Stancil Department of Physics and Astronomy."— Presentation transcript:

1 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

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

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

4 Effective Temperatures and Spectral Classifications TiO, VO, CaH, MgH TiO depletion VO depletion FeH, Li, K, Na CrH Li  LiCl NaCl, RbCl, CsCl H 2 O condenses CO CH 4 N2N2 NH 3 Burrows et al. (2001) M - dwarfs EGP? 0.2 M  0.3M J 73 M J 15 M J

5 MgH in the Visible A-X: 10,091 transitions B-X: 10,649 transitions X, A, B levels: 313, 435, K 3000 K 2000 K 2000 K dusty A-X Weck et al. (2003), Skory et al. (2003) Wavelength (Å) 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 Substellar objects (brown dwarfs) have insufficient mass to maintain nuclear burning (~0.08 M  ~80 M J ) Lithium test for substellarity: presence of Li 6708 Å line Keck II spectrum of an L5 dwarf (Reid et al. 2000) No Li Li ? Wavelength (Å)  Stellar classifications based on optical/NIR spectra

8 1670 K 2000 K 2500 K 3330 K 1430 K Equilibrium abundances in a cool dwarf atmosphere (Lodders 1999 ) 10 4 /T ML Log of abundance

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 M J (800 K, 10 pc, T dwarf) theoretical spectra by Burrows et al. (2003) Weck et al. (2004) Wavelength (  m)  v=1  v=2  v=3 LiCl T=1000 K H 2 0 CH 4 NH 3 SIRTF JWST LTE spectra with 3,357,811 lines between 29,370 levels

11 Inclusion of LiCl in PHOENIX models gave no distinct features The maximum flux difference is 20% Spectrum is dominated by H 2 O opacity It will be hard to detect LiCl with SIRTF or JWST NaCl or KCl may be more promising Also, alkali-hydrides (NaH, KH) Models constructed for T eff =900, 1200, and 1500 K and log(g)=3.0 (young), 4.0, and 5.0 (old, > 1 Gyr) Solar metallicity L T T T

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

13  v=1  v=0 X-A NAH LTE spectra for rovibrational and electronic X-A transitions (Horvath et al. 2005, in prep.)  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 Burrows et al. (2001) LiCl NaH NaClKCl KH KH?

14 Non-LTE effects NLTE effects investigated for CO by: 1) Ayres & Weidemann in the sun (1989) 2) Schweitzer, Hauschildt, & Baron (2000) for M dwarfs NLTE effects might be expected for cool objects i. Non-Planckian radiation ii. Strong irradiation from companion iii. Slow collisional rates M8 model: T eff =2700 K CO  v=1

15 CO(v=1) + H  CO(v=0) + H MLT EGP Orion Peak 1 and 2 Dense cores

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. H 2 O, NH 3, CH 4  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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