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

Stellar Classification (Kitt Peak)

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)

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

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

T Dwarf Spectra (ε Indi Ba)

Strauss et al. ApJ 522, L61 (1999)

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?

TiH 4Φ-X4Φ System

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)

CrH Lifetimes

Obs.

0.94

1.03

Calculations (Bauschlicher)

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

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

TiH & TiO Abundances

“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)