Part III. PhD course originally developed by René Liseau Updated to Master level course by Alexis Brandeker

Transcription

1 Part III Early stages in stellar tll evolution PhD ii ll d l db R éli PhD course originally developed by René Liseau Updated to Master level course by Alexis Brandeker

2 Part III Early stages in stellar tll evolution = star formation What will the course contain? Large topic; searching for papers with star formation in the title on ADS returns results (as of ). This third part of the course stretches over 7 lectures 90 min = s. (However, 5 hp = 133 h = s!) Clearly we have to be selective.

3 Book of choice: The Formation of Stars by Stahler and Palla, 2004 Large brick, bik 850 pages! Only subset will be covered. L15 General Overview / Pre collapse phase I Chapt. 1, 2, 4 L16 Pre collapse phase II Chapt. 3, 4, 9 L17 Collapse phase I Chapt. 9, 10

4 Book of choice: The Formation of Stars by Stahler and Palla, 2004 L18 Collapse phase II Chapt. 9, 10 L19 Circumstellar disks I Chapt. 11, 17 L20 Pre main sequence evolution, multiplicity Chapt. 11, 12 L21 Circumstellar disks II debris disks Chapt. 18

5 Homework / examination 3 problem sets with problems of varying degree of difficulty (for varying degree of grades!), to be handed in no later than Friday, June 20, 24:00 for higher grade than pass (E).

6 Literature projects in star formation Suggestions handed out earlier. Please feel free to make your own suggestion! Only one student per topic; first come, first served. To be presented on Monday, June 16, 10:00 14:00. 14:00.

7 Early stages in stellar tll evolution L15 General Overview / Pre collapse phase I L16 Pre collapse phase II L17 Collapse phase I L18 Collapse phase II L19 Circumstellar disks I L20 Pre main sequence evolution L21 Circumstellar disks II debris disks

8 How do we know that stars presently form?

9 ms lifetimes = nuclear times t Trapezium cluster θ Ori t Sun t BigBang t nuc 2 Mc L M α, α > 0

10 Relevant stellar evolution time scales : yr dynamical 2 3 O 2 1 O 5 ff = = R R M M G t ρ π yr 10 3 thermal 1 O 1 O 2 O 7 2 KH = = << L L R R M M RL GM t yr 10 1 main sequence nuc O O O = Δ = << L L M M L Mc t O L M L O

11 Where do stars form?

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14 What is the fraction of a galaxy s mass turned dinto stars, and locked dth there?

15 Global concepts (on galactic scales, in space and time) IMF Initial Mass Function N ( M ) dm n( M dm = NdM star star star ) star = D(IMF) 1 star SFR StarFormation Rate = M dm dt stars D (SFR ) = M yr o 1 SFE Star Formation Efficiency M stars M stars D(SFE) = 1 + M gas+ dust (%)

16 Local concepts (on cloud scales, in space and time) IMF Initial Mass Function SFR StarFormation Rate SFE Star Formation Efficiency

17 In general IMF Initial Mass Function What Form? SFR StarFormation Rate What Value? SFE Star Formation Efficiency What Time Dependence?

18 Pre collapse phase: The clouds out of which h stars form

19 Interstellar clouds Historical milestones 1784 Visual Eye (optical) Herschel, in: Construction of the Heavens: holes in the sky 1918 Imaging (optical) Curtis, PASP 30, 65, dark nebulae st detection: CH (optical) Swings & Rosenfeld, ApJ 86, st detection: CH + (optical) Douglas & Herzberg, ApJ 94, st detection: H I (21 cm) Ewen & Purcell, Nature 168, st detection: OH (18 cm) Weinreb et al., Nature 200, st detection: CMB (7.3 mm) Penzias & Wilson, ApJ 142, st detection: CO (2.6 mm) Wilson et al., ApJ 161, L multimode: MIR FIR IRAS sky survey 1989 multimode: NIR mm COBE sky survey 1995 multimode: NIR FIR ISO observatory 2003 multimode: MIR FIR Spitzer Space Telescope 2009 Multimode: FIR submm Herschel (again!) Space Observatory

20 Interstellar Molecular clouds: Galactic distribution Visual Obscuration CO emission i Distribution cf. also H I IRAS 100 μm et c CO (J = 1 0) Integrated Line Intensity Dame, Hartmann & Thaddeus, 2001, ApJ 547, 792

21 Interstellar Molecular clouds: Galactic distribution CO (J = 1 0) Integrated Line Intensity (K km s 1 ) Dame, Hartmann & Thaddeus, 2001, ApJ 547, 792

22 Interstellar Molecular clouds: Galactic distribution CO (J = 1 0) Radial velocity (LSR) Dame, Hartmann & Thaddeus, 2001, ApJ 547, 792

23 E up /k B = 5.5 K

24 Interstellar Molecular clouds: Solar neighbourhood ihb h (within 1 kpc)

25 Interstellar Molecular clouds: Solar neighbourhood ihb h (within 1 kpc)

26 Interstellar Molecular clouds: Solar neighbourhood ihb h (within 1 kpc) Scale Height, H Molecular Mass, M 75 pc M o Surface Density, Σ 1 M o pc -2 Mass Density, ρ(z 0 ) M o pc -3 Particle Density, n(z 0 ) 0.1 H 2 cm -3

27 Interstellar Molecular clouds: Individual id clouds (solar neighbourhood) h Type R n M Δv T Cores (pc) (cm -3 ) (M o ) (km s -1 ) (K) and Stars Diffuse ? Low-mass Dark Low-mass Giant Massive and Low-mass Average Property Depends On Molecular Tracer? CO (J = 1 0) Myers 1991, in: Molecular Clouds, James & Millar (eds.), p. 1

28 Interstellar Molecular clouds: Individual id clouds (solar neighbourhood) h Type R n M Δv T Cores (pc) (cm -3 ) (M o ) (km s -1 ) (K) and Stars Low-Mass T Tauri Massive... Large OB Small NH 3 (J,K = 1,1) OB Myers 1991, in: Molecular Clouds, James & Millar (eds.), p. 1

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30 Interstellar Dark clouds and cores Barnard 1927, Univ.Chicago Press Catalogue of 349 dark objects in the sky Bok & Reilly 1947, ApJ 105, 255 Globules size = 5arcsec to 60 arcsec Lynds 1962, ApJS 7, 1 DCs 1802 north of δ = 33 o Hartley et al. 1986, AAS 63, 27 DCs 1101 south of δ = 33 o Clemens & Barvainis, i 1988, ApJS JS68, 257 < north of δ = 33 o observational selection effects?

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32 Interstellar Dark clouds and cores Optical selection based on optical obscuration = extinction Empirically (Bohlin, Savage & Drake 1978, 21-2 N (H I + 2H 2) = AV cm where the extinction by dust in magnitudes 10 A = 2.5 log e τ V or, in general, A λ = 1.086τ λ τ λ V what is A( λ)? (``extinction curve ) ApJ 224, 132) : Rieke & Lebofsky (1985, ApJ 288, 618): A / E(B - V) = 3.09 V most widely used is is fit within 0.55 λ 2.2 μm to better than 0.5% by (0.3to 10 μm) A / AV = λ λ 1.539λ λ λ +

33 Interstellar Dark clouds and cores Optical selection based on optical obscuration A λ = 2.5 log e τ i.e. A λ τ so what is A( λ)? τ λ λ = 1.086τ λ Dependence on what physics? Rieke & Lebofsky curve applicable where? Is A(λ) a function of the time, i.e. A(λ, t)? Example: White et al. 2000, AA 364, 741

34 Interstellar Dark clouds and cores λ = 0.55 μm A V > 100 mag!!! Optical photographic plates & CCD images: A m V << 100 N(H) ~ A V saturation N(H) ~ A V calibration? gas mass vs dust mass ``normal m g /m d = 100 How well established? How relate A V and N(H 2 )? White et al. 2000, AA 364, 741

35 Interstellar Dark clouds and cores Molecular line observations Benson & Myers 1989, APJS 71, Barnard/Lynds objects NH 3 (1,1) Clemens et al. 1991, APJS 75, Clemens/Barvainis cores CO (2 1) Bourke et al. 1995, MNRAS 276, Hartley et al. cores NH 3 (1,1), (2,2) Lemme et al. 1996, AA 312, Clemens/Barvainis i NH 3 (1,1), (2,2) 2) Dust continuum observations Launhardt & Henning 1997, AA 326, CB 1.3 mm Osterloh et al. 1997, ApJS JS110, CB mm Shirley et al. 2000, ApJS 131, L & CB 450 μm & 850 μm Visser et al. 2001, AJ 124, CB & L 850 μm

36 In extragalactic applications, one uses CO and N(H2 ) = X CO TRdV where X CO = (1 5) 10 CO 20 cm -2 is the Conversion Factor /(K km s -1 )

37 Interstellar Dark clouds and cores More observational results: Mean aspect ratio ~ 2, but prolate? oblate? > 50% of cores have IRAS source no difference globules / embedded cores Core with IRAS source broader lines larger size without IRAS source narrow / thermal widths smaller more evolved? younger?

38 Molecular Probes of T kin and n(h 2 ) n(h 2 ) Genzel 1990, in: The Physics of Star Formation and Early Stellar Evolution, Lada & Kylafis (eds.), NATO ASI 342, p T kin

39 T kin n(h 2 ) Genzel 1990, in: The Physics of Star Formation and Early Stellar Evolution, Ld Lada & Kylafis (eds.), NATO ASI 342, p

40 Interstellar Dark clouds and cores Rotation Cloud dv/dr j * Reference (km s -1 pc -1 ) (km s -1 pc) Rosette Blitz & Thaddeus 1980 Mon R Blitz 1978 W Thronson et al Orion Kutner et al typical GMC < 0.05 <15 various; Blitz 1980 typical DC Goodman et al * for q = 0.5 and j = J/ M = q R 2 Ω j(sol sys) = km s 1 pc

41 Interstellar Dark clouds and cores Magnetic fields spectral lines Region Method B obs (μg) Intercloud Medium Faraday rotation 5 Diffuse Cloud Zeeman H I 7 Dark Cloud Zeeman H I 5 10 Zeeman OH GMC Zeeman H I 10 Massive Core Zeeman OH Maser Spots Zeeman H 2 O 10 4 Table adapted from Myers 1991

42 Interstellar Dark clouds and cores Zeeman OH 18 cm * Bourke et al. 2001, ApJ 554, 916 Zeeman OH 18 cm * Crutcher 1999, ApJ 520,706 * 1665, 1667 MHz

43 Interstellar Dark clouds and cores Magnetic fields continuum e.g., 800 μm m map of linear polarisation see also: Ward Thompson et al. 2000, ApJ 537, L L Wolf et al. 2003, ApJ 592, 233 also giveb field B strength: 257 μg 3 CB (+3 CB)

44 Interstellar Dark clouds and cores Time scales ages The `dynamical time scale R crosscommunication communication (δp) pc tdyn Myr v at the signal speed c -1 s km s The isothermal sound speed DC: Myr 1/ 2 1/ 2 P Γ k T cs m = ρ μ GMC: Myr H 3 in molecular clouds, with Γ = and μ = 2.4, Blitz 1993 and 5 Elmegreen Myr* -1 c = 0.07 T km s s Cloud Age Method Reference >20 Myr OB: n(stellar generations) > 1 Blaauw 1964, ARAA 2, 213 >10 Myr 34 open clusters/clouds Leisawitz et al. 1989, ApJS 70, 731 * `star forming lifetime

45 Structure of interstellar clouds 10pc 0.1pc 0.01pc

46 Structure of interstellar clouds continuous power laws structure clumps inhomogeneous fractals

47 Structure of interstellar clouds continuum azimuthally averaged isothermal power law fits ρ( r) r ρ( r) r α α, α 0, r r, α = 2, r > r 0 0 Motte et al. 1998, AA 336, 150

48 Inhomogeneous structure of interstellar clouds continuum Motte et al. 1998, AA 336, 150 clump mass spectrum dn m γ dm with two values of γ See also 850 μm map by Johnstone et al. 2000, ApJ 545, 327

49 Inhomogeneous structure of interstellar clouds Observational evidence from spatial distribution of FIR/submm lines Neutral Carbon [ C I ] 609 μm Ionised Carbon [ C II ] 157 μm

50 ρoph (L1688) in [C I] 609 μm, [C II] 157 μm and 13 CO 2.7 mm Kamegai et al. 2003, ApJ 589, 378

51 Inhomogeneous structure of interstellar clouds Observational evidence from spatial distribution of FIR/submm lines Neutral Carbon [ C I ] 609 μm Ionised Carbon [ C II ] 157 μm External UV radiation penetrates to large depths (e.g., Swiss cheese model) clump interclump contrast: > 10 0 to 10 2 in density < 10-1 to 10-2 in mass