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Protostars and Pre-Main Sequence Evolution

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Protostars and Pre-Main Sequence Evolution Protostars and Pre-Main Sequence Evolution Jos´eGarmilla Princeton University October 16, 2012 Outline Protostars Gravitational Collapse Accretion Phase Comparissons to Observations Pre-Main Sequence Evolution Convective and Radiative Contraction Deuterium Burning and the Stellar Birth Line Lithium Burning and Substellar Objects Degeneracy T Tauri Stars Conclusions Protostars Gravitational Collapse Bonnor-Ebbert Mass 4 −1=2 3=2 cs n T Mcrit = 1:18 = 1:82 M 1=2 3=2 104cm−3 10 K Psurf G The process starts with cores of M ∼ M , and R ∼ 0:1 pc. Three phases of collapse Isothermal Collapse Adiabatic Collapse Envelope Accretion Protostars Isothermal and Adiabatic Collapse 2 2 4 Gm dP 1 d r 64π acr 3 dT 4 + = − 2 2 ; Lr = − T 4πr dm 4πr dt 3κR dm dr 1 dL dE dv = ; r = − − P dm 4πr 2ρ dm dt dt 2 4 with bc: r = Lr = 0 at m = 0, P = Po LR = 4πR σTeff at m = M 2 −1=2 τ ≈ κR ρR, tdiff ≈ 3κR ρ(∆r) =c, tff ≈ (Gρ) Isothermal Phase: τ 1, ρ = 10−19{10−13gcm−3, efficient cooling, can assume constant temperature (T ≈ 10 K). Adiabatic Phase: τ & 1, tdiff tff, infrared radiation gets trapped, can ignore heat term in energy equation. Protostars Isothermal and Adiabatic Collapse Bodenheimer, 2011 Larson, 1969 Protostars Accretion Phase The central part of the core reaches quasi-hydrostatic equilibrium while the outer regions are still in isothermal collapse. 2 tKH ≈ GM =RL ∼ Myr 5 tacc ≈ M=M_ ∼ 10 yr tdiff tacc tKH , therefore L ≈ Lacc. Stahler et al., 1980 Dust sublimates at T ≈ 1500 K. Protostars Comparissons to Observations Kenyon et al., 1993 Bodenheimer, 2011 Non-thermal spectrum due wavelength Bodenheimer, 2011 dependent opacity. Luminosity Problem, for M = 0:5M Lacc ∼ 10L . Pre-Main Sequence Evolution Convective and Radiative Contraction In the interior, 3 κR Lr P @ ln T 4 > 16πGac mT @ ln P S −3:5 κK / ρT Thin Outer Radiative Zone with H−, 0:5 9 κH− / Zρ T 2 κ P = g p p 3 Palla & Staller, 1999 Pre-Main Sequence Evolution Convective and Radiative Contraction Bodenheimer, 2011 Stars above 6M are already in the main sequence when the accretion phase is over. Pre-Main Sequence Evolution Deuterium Burning and the Stellar Birthline Stahler, 1988 Deuterium Burns at 106 K 1H + 2D ! 3He + γ / f [D=H] ρT 11:8 [D=H] = 2 × 10−5, f = 1 Stahler, 1988 Pre-Main Sequence Evolution Deuterium Burning and the Stellar Birthline Burrows et al., 2003 Pre-Main Sequence Evolution Lithium Burning and Substellar Objects Burrows et al., 2003 Cores with M < 0:08M , can't burn Hydrogen Lithium Burns at 2:5 × 106 K 1H + 7Li ! 4He + 4He Burrows et al., 2003 Pre-Main Sequence Evolution Degeneracy Burrows et al., 2003 13 5=3 −2 Pe = 1:004 × 10 (ρ/µe ) dyne cm −8 3=2 −3 ρ = 2:4 × 10 µe T g cm Bodenheimer, 2011 Pre-Main Sequence Evolution T Tauri Stars Lada et al., 1999 Hα, high Li abundance (∼ 10−9H), nearby dark clouds, X-rays emission, strong Lada et al., 1999 magnetic fields (Zeeman splitting∼kilogauss). Infrared excess in CTTS, due to dusty disk. Pre-Main Sequence Evolution T Tauri Stars Lamm et al., 2005 Contraction, magnetic star disk interaction, stellar winds. Conclusions We have made a lot of progress in understanding the protostar and pre-main sequence phase of star foramtion. Many challenges remain: The luminosity problem, the role of magnetic fields, star disk interaction, stellar winds. References Stahler, S. W., ApJ 332, pp. 804, 1988. Palla, F., Stahler, S., ApJ 525, pp. 772, 1999. Burrows, A., Hubbard, W., Lunine, J., Liebert, J., Rev. of Modern Physics 73, pp. 719, 2001. Bodenheimer, Pirnciples of Star Formation, Springer, 2011..
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