1. TiH IN SUBDWARFS P. F. Bernath Department of Chemistry, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 C.W. Bauschlicher, Jr NASA Ames Research Center, Moffett Field, CA 94035 M. Dulick National Solar Observatory, Tucson, AZ 85726-6732 R.S. Ram Department of Chemistry, University of Arizona, Tucson, AZ 85721 C.M. Sharp, J.A. Milsom and A. Burrows Steward Observatory, University of Arizona, Tucson, AZ 85721

2. Stellar Classification (Kitt Peak)

3. 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) Stars Brown Dwarfs Jupiter-like Planets G 0123456789 Sun: G2 V (6000 K, dwarf) Luminosity (Size): I (Supergiant), II, III (Giant), IV, V (dwarf)

4. M Dwarf Spectra T = 3500 K H2OH2O As the surface temperature drops TiO A-X saturates, VO B-X, FeH F-X and H 2 O appear. Kirkpatrick et al. ApJ 402, 643 (1993) TiO A 3 Φ-X 3 Δ T=3500 K T=2900 K VO B 4 Π-X 4 Σ - FeH F 4 Δ-X 4 Δ H2OH2O

5. 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 A 6 Σ-X 6 Σ FeH 1-0 F 4 Δ-X 4 Δ

6. T Dwarf Spectra (ε Indi Ba) Strauss et al. ApJ 522, L61 (1999)

7. 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?

8. TiH 4 Φ-X 4 Φ System

9. 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)

10. CrH Lifetimes Obs. 0.94 1.03

11. Calculations (Bauschlicher)

12. TiH Calculations Hönl-London factors 4 Φ- 4 Φ transition

13. 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

14. TiH & TiO Abundances

15. “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)