tih in subdwarfs p. f. bernath department of chemistry, university of waterloo, waterloo, ont.,...
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TiH IN SUBDWARFS
P. F. BernathDepartment of Chemistry, University of Waterloo,
Waterloo, Ont., Canada N2L 3G1C.W. Bauschlicher, Jr
NASA Ames Research Center, Moffett Field, CA 94035M. Dulick
National Solar Observatory, Tucson, AZ 85726-6732R.S. Ram
Department of Chemistry, University of Arizona, Tucson, AZ 85721
C.M. Sharp, J.A. Milsom and A. BurrowsSteward Observatory, University of Arizona, Tucson,
AZ 85721
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Stellar Classification (Kitt Peak)
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O > 25 000 K
B 11000 - 25000 K
A 7500 - 11000 K
F 6000 - 7500 K
G 5000 - 6000 K
K 3500 - 5000 K
M 2000 - 3500 K
L 1400 - 2000 K
T < 1400 K? (Not to
scale)
Stellar Spectral Classification System (“normal” oxygen-rich stars)
Sta
rs
Brown Dwarfs
Jupiter-like Planets
GG
00112233445566778899
Sun: G2 V (6000 K, dwarf)
Luminosity (Size): I (Supergiant), II, III (Giant), IV, V (dwarf)
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M Dwarf SpectraT = 3500 K
H2O
As the surface temperature drops TiO A-X saturates, VO B-X, FeH F-X and H2O appear.
Kirkpatrick et al. ApJ 402, 643 (1993)
TiO A3Φ-X3Δ
T=3500 K
T=2900 K
VO B4Π-X4Σ-
FeH F4Δ-X4Δ
H2O
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L Dwarf Spectra
Kirkpatrick et al. ApJ 519, 802 (1999)
T=1800 K
T=1600 K
T=1300 K
As the temperature drops further metal oxides are converted to metal hydrides and CrH appears.
CrH 0-0 A6Σ-X6Σ
FeH 1-0 F4Δ-X4Δ
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T Dwarf Spectra (ε Indi Ba)
Strauss et al. ApJ 522, L61 (1999)
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Sub-Dwarf Spectra
Gizis, AJ 113, 806 (1997)
Sub-dwarfs are metal-poor stars or brown dwarfs. Metal hydrides (one metal) are enhanced relative to metal oxides (two “metals”), e.g., CaH enhanced relative to TiO.
Burgasser, 2003, 2004 TiH?
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TiH 4Φ-X4Φ System
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CrH & FeH Molecular Opacities
Strategy: Combine experimental energy levels and extrapolated levels (guided by theory) with line strengths obtained from an ab initio electronic transition dipole moment.e.g., Dulick et al. ApJ 594, 651
(2003)
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CrH Lifetimes
Obs.
0.94
1.03
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Calculations (Bauschlicher)
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TiH Calculations Hönl-London factors 4Φ-4Φ transition
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TiH Cross sections
Line-by-line calculation of cross sections at 10 atm, 3000 K (red) and 1 atm, 2000 K (black) plus water (in blue) for 10 atm, 3000 K
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TiH & TiO Abundances
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“Conclusion”
Burrows does not find the comparison between the observations and the simulations to be convincing for the detection of TiH!
Burgasser ApJ, 614, L73 (2004)