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The environment of star formation Theory: low-mass versus high-mass stars

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The environment of star formation Theory: low-mass versus high-mass stars

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  1. High-mass stars from cradle to first steps: a possible evolutionary sequence (High-mass  M*>10M⊙ L*>104L⊙ B3-O) • Theenvironmentof star formation • Theory: low-mass versus high-mass stars • The birthplaces of high-mass stars • Evolutionary scheme for high-mass stars • Conclusion: formation by accretion?

  2. The environment of star formation • Clouds: 10100 pc; 10 K; 10103 cm-3; Av=110; CO,13CO; nCO/nH2=10-4 • Clumps: 1 pc; 50 K; 105 cm-3; AV=100; CS, C34S; nCS/nH2=10-8 • Cores: 0.1 pc; 100 K; 107 cm-3; Av=1000; CH3CN, exotic species; nCH3CN/nH2=10-10 • YSOs signposts: IRAS, masers, UC HIIs

  3. Low-mass VS High-mass “Standard” (Shu’s) picture: Accretion onto protostar Static envelope: nR-2 Infalling region: nR-3/2 Protostar: tKH=GM2/R*L* Accretion: tacc=(dMacc/dt)/M* • Low-mass stars: tKH > tacc • High-mass stars: tKH < tacc  High-mass stars reach ZAMS still accreting 

  4. Low-mass VS High-mass • “Standard” (Shu’s) picture: • Accretion onto protostar • Static envelope: nR-2 • Infalling region: nR-3/2 • Protostar: tKH=GM2/R*L* • Accretion: tacc=(dMacc/dt)/M* • Low-mass stars: tKH > tacc • High-mass stars: tKH < tacc •  High-mass stars reach ZAMS still accreting 

  5. Problem: • Stellar winds + radiation pressure stop accretion at M*=8 M⊙ how can M*>8 M⊙ form? • Solutions: • Accretion with dM/dt(High-M*)>>dM/dt(Low-M*)=10-5 M⊙/y • Accretion throughdisks (+outflows) • Merging of many low-mass stars Observations of the natal environment of high-mass stars are necessary to solve this problem!

  6. The search for high-mass YSOs High-mass YSOs deeply embedded  observations more difficult than for low-mass YSOs (e.g. S254/7 SFR) Observational problem: to find suitable tracer and target 1) What to look for? High-density, high-temper. tracers  high-excitation lines, rare molecules, (sub)mm continuum 2) Where to search for? Young and massive targets: • UC HIIs: OB stars are in clusters • H2O masers without free-free: luminous but without UC HII region • IRAS without H2O and UC HII: protostellar phase?

  7. The search for high-mass YSOs • High-mass YSOs deeply embedded  observations more difficult than for low-mass YSOs (e.g. S254/7 SFR) • Observational problem: to find suitable tracer and target • 1)What to look for? High-density, high-temper. tracers  high-excitation lines, rare molecules, (sub)mm continuum • 2)Where to search for? Young and massive targets: • UC HIIs: OB stars are in clusters • H2O masers without free-free: luminous but without UC HII region • IRAS without H2O and UC HII: protostellar phase?

  8. Observations High-mass YSOs: AV > 10 radioNIR needed • Low angular resolution = single-dish = 10”2’ Effelsberg, Nobeyama, IRAM, JCMT, CSO, NRAO NH3, CO, 13CO, CS, C34S, CH3C2H, CN, HCO+, … • High angular resolution = interferometers = 0.3”4” VLA, IRAM, Nobeyama, OVRO, BIMA, VLBI NH3, CH3CN, CH3OH, SiO, HCO+, H2O, continuum

  9. General results • Targets surrounded by dense, medium size clumps: 1 pc, 50 K, 105–106 cm-3, 103–104 M⊙ • Dense, small cores found close to/around targets: 0.1 pc, >107 cm-3, 40–200 K, 10–103 M⊙

  10. Clumps Traced by all molecules observed  real entities! • Mclump>Mvirial  large B (1mG) needed for equilibrium • TKR-0.5 heated by source close to centre • nH2 R-2.6 marginally stable • dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y  large accretion rates • clumps may be marginally stable entities (∼105 y) • accretion from clumps feeds embedded YSOs

  11. Clumps • Traced by all molecules observed real entities! • Mclump>Mvirial large B (1mG) needed for equilibrium • TKR-0.5 heated by source close to centre • nH2 R-2.6 marginally stable • dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y  large accretion rates • clumps may be marginally stable entities (∼105 y) • accretion from clumps feeds embedded YSOs

  12. Clumps • Traced by all molecules observed  real entities! • Mclump>Mvirial large B (1mG) needed for equilibrium • TKR-0.5 heated by source close to centre • nH2 R-2.6 marginally stable • dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y  large accretion rates • clumps may be marginally stable entities (∼105 y) • accretion from clumps feeds embedded YSOs

  13. Clumps • Traced by all molecules observed  real entities! • Mclump>Mvirial large B (1mG) needed for equilibrium • TKR-0.5 heated by source close to centre • nH2 R-2.6 marginally stable • dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y  large accretion rates • clumps may be marginally stable entities (∼105 y) • accretion from clumps feeds embedded YSOs

  14. Clumps • Traced by all molecules observed  real entities! • Mclump>Mvirial large B (1mG) needed for equilibrium • TKR-0.5 heated by source close to centre • nH2 R-2.6 marginally stable • dMacc/dt = Mclump/tAD= 10-3–10-2 M⊙/y  large accretion rates • clumps may be marginally stable entities (∼105 y) • accretion from clumps feeds embedded YSOs

  15. Clumps • Traced by all molecules observed  real entities! • Mclump>Mvirial large B (1mG) needed for equilibrium • TKR-0.5 heated by source close to centre • nH2 R-2.6 marginally stable • dMacc/dt = Mclump/tAD= 10-3–10-2 M⊙/y  large accretion rates • clumps may be marginally stable entities (∼105 y) • accretion from clumps feeds embedded YSOs

  16. Hot Cores (HCs) Hot (100–200 K) cores often found close to UC HIIs: • H2O masers and high energy lines  large nH2 and TK • many rare molecules  evaporation from dust grains • TKR-3/4  inner energy source • LIRAS  104 L⊙  embedded OB star • a few HCs contain UC HIIs!  OB stars • rotating circumstellar disks found in some HCs • molecular outflows from several HCs  HCs host young ZAMS high-mass stars

  17. Hot Cores (HCs) • Hot (100–200 K) cores often found close to UC HIIs: • H2Omasers and high energy lines large nH2 and TK • many rare molecules evaporation from dust grains • TKR-3/4  inner energy source • LIRAS  104 L⊙  embedded OB star • a few HCs contain UC HIIs!  OB stars • rotating circumstellar disks found in some HCs • molecular outflows from several HCs •  HCs host young ZAMS high-mass stars

  18. Hot Cores (HCs) • Hot (100–200 K) cores often found close to UC HIIs: • H2Omasers and high energy lines large nH2 and TK • many rare molecules evaporation from dust grains • TKR-3/4  inner energy source • LIRAS  104 L⊙  embedded OB star • a few HCs contain UC HIIs!  OB stars • rotating circumstellar disks found in some HCs • molecular outflows from several HCs •  HCs host young ZAMS high-mass stars

  19. Hot Cores (HCs) • Hot (100–200 K) cores often found close to UC HIIs: • H2Omasers and high energy lines large nH2 and TK • many rare molecules evaporation from dust grains • TKR-3/4  inner energy source • LIRAS  104 L⊙ embedded OB star • a few HCs contain UC HIIs!  OB stars • rotating circumstellar disks found in some HCs • molecular outflows from several HCs •  HCs host young ZAMS high-mass stars

  20. Hot Cores (HCs) • Hot (100–200 K) cores often found close to UC HIIs: • H2Omasers and high energy lines large nH2 and TK • many rare molecules evaporation from dust grains • TKR-3/4  inner energy source • LIRAS  104 L⊙ embedded OB star • a few HCs contain UC HIIs!  OB stars • rotating circumstellar disks found in some HCs • molecular outflows from several HCs •  HCs host young ZAMS high-mass stars

  21. Hot Cores (HCs) • Hot (100–200 K) cores often found close to UC HIIs: • H2Omasers and high energy lines large nH2 and TK • many rare molecules evaporation from dust grains • TKR-3/4  inner energy source • LIRAS  104 L⊙ embedded OB star • a few HCs contain UC HIIs!  OB stars • rotating circumstellar disks found in some HCs • molecular outflows from several HCs • HCs host young ZAMS high-mass stars

  22. Beuther et al. (2002)

  23. Hot Cores (HCs) • Hot (100–200 K) cores often found close to UC HIIs: • H2Omasers and high energy lines large nH2 and TK • many rare molecules evaporation from dust grains • TKR-3/4  inner energy source • LIRAS  104 L⊙ embedded OB star • a few HCs contain UC HIIs!  OB stars • rotating circumstellar disks found in some HCs • molecular outflows from several HCs • HCs host young ZAMS high-mass stars

  24. Warm cores (WC) • Mostly towards IRAS sources with [25-12]<0.57: • warm (50 K) but dense and massive (10–102 M⊙) • luminous (LIRAS  104 L⊙) high-mass YSOs • few H2O masers (no OH masers)  prior to HC phase • no cm continuum emission  hypercompact HII? • weak evidence for disks and outflows • interesting candidate: the case of G24.78+0.08 •  WCs may be “class 0” high-mass sources (?)

  25. Warm cores (WC) • Mostly towards IRAS sources with [25-12]<0.57: • warm (50 K) but dense and massive (10–102 M⊙) • luminous (LIRAS  104 L⊙) high-mass YSOs • few H2Omasers (no OH masers)  prior to HC phase • no cm continuum emission  hypercompact HII? • weak evidence for disks and outflows • interesting candidate: the case of G24.78+0.08 •  WCs may be “class 0” high-mass sources (?)

  26. H2O maser

  27. Warm cores (WC) • Mostly towards IRAS sources with [25-12]<0.57: • warm (50 K) but dense and massive (10–102 M⊙) • luminous (LIRAS  104 L⊙) high-mass YSOs • few H2Omasers (no OH masers)  prior to HC phase • no cm continuum emission  hypercompact HII? • weak evidencefor disks and outflows • interesting candidate: the case of G24.78+0.08 •  WCs may be “class 0” high-mass sources (?)

  28. IRAS23385+6053

  29. Warm cores (WC) • Mostly towards IRAS sources with [25-12]<0.57: • warm (50 K) but dense and massive (10–102 M⊙) • luminous (LIRAS  104 L⊙) high-mass YSOs • few H2Omasers (no OH masers)  prior to HC phase • no cm continuum emission  hypercompact HII? • weak evidencefor disks and outflows • interesting candidate:the case of G24.78+0.08 •  WCs may be “class 0” high-mass sources (?)