T Tauri Stars: An Overview Colette Salyk Ge132

What is a T Tauri star? 1st Answer: Observational –Hydrogen Balmer and Ca II H and K emission –Often emission of Fe I –Forbidden [O I] and [S II] emission –Strong Li absorption –IR -> sub-mm excess –UV excess –Found in dusty regions- proper motions correlated –Off main sequence –Sometimes associated with disks and/or outflows

What is a T Tauri star? 2nd Answer: Theoretical –Low-mass (0.2-2 M  ) young (PMS) star –Class II –Often accompanied by disk of gas and dust –Active (star/disk interactions, fast rotation) –Sometimes releasing mass via polar outflows

IR Excess Near-IR: hot inner disk: dust and gas mid-IR -> sub-mm: dusty disk emission Solar + accretional energy

H  emission n=3->n=2 transition = Å Requires high energy photons, close to star (also seen in solar chromosphere) Used to model accretion –Asymmetric shape –Doppler broadening >100 km/s (supersonic)

Strong Li I Absorption = Å ; 2 P 3/2 -> 2 S 1/2 = Å ; 2 P 1/2 -> 2 S 1/2 Li fragile, destroyed when in contact with high temperatures at base of convecting region of stars, so strong Li = young In TTSs, log[n Li ] = 3 ; similar to meteorites (in sun, log[n Li ] = 1; log[n H ]≡12)

Forbidden [O I] & [S II] emission Very low emission probabilities->low density environment Probe outer regions of polar jets Doppler broadened ->high speeds Blueshifted (red part partially hidden)

Ca II H & K, Fe I emission Ca II H – = Å – 2 S 1/2 <- 2 P 1/2 Ca II K – = Å – 2 S 1/2 <- 2 P 3/2 Fe I – = Å ; 3 P 1 <- 3 S 1 – = Å ; 3 F 2 <- 3 F 3 –Probably due to resonant fluorescence All similar to solar chromosphere, but actually due to extended atmosphere and star/disk interactions

Implications / The Future Initial Mass Function ( N(M) ) –Effect of environment on formation Mass of disk correlations? (environment, mass of parent star, age) Young Star/Disk Interactions –Magnetic fields –Accretion –Mass loss Evolution timescales –How long do outflows/disks last? –(How long do planets have to form?)