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T Tauri Stars: An Overview
Colette Salyk
Ge132
What is a T Tauri star?
• 1st Answer: Observational
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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
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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
•  = 6562.8 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
•  = 6707.76 Å ; 2P3/2 ->2S1/2
•  = 6707.91 Å ; 2P1/2 ->2S1/2
• Li fragile, destroyed when in contact with
high temperatures at base of convecting
region of stars, so strong Li = young
• In TTSs, log[nLi] = 3 ; similar to meteorites
(in sun, log[nLi] = 1; log[nH]≡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
–  = 3968.5 Å
– 2S1/2 <-2P1/2
• Ca II K
–  = 3933.7 Å
– 2S1/2 <-2P3/2
• Fe I
–  = 4062.4 Å ; 3P1 <-3S1
–  = 4132.1 Å ; 3F2 <- 3F3
– 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?)