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.