1. 1)The environment of star formation 2)Theory: low-mass versus high-mass stars 3)The birthplaces of high-mass stars 4)Evolutionary scheme for high-mass stars 5)Conclusion: formation by accretion? High-mass stars from cradle to first steps: a possible evolutionary sequence ( High-mass  M * >10M ⊙  L * >10 4 L ⊙  B3-O)

2. The environment of star formation Clouds: 10  100 pc; 10 K; 10  10 3 cm -3 ; Av=1  10; CO, 13 CO; n CO /n H 2 =10 -4 Clumps: 1 pc; 50 K; 10 5 cm -3 ; A V =100; CS, C 34 S; n CS /n H 2 =10 -8 Cores: 0.1 pc; 100 K; 10 7 cm -3 ; Av=1000; CH 3 CN, exotic species; n CH 3 CN /n H 2 =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: t KH =GM 2 /R * L * Accretion: t acc =(dM acc /dt)/M * –Low-mass stars: t KH > t acc –High-mass stars: t KH < t acc  High-mass stars reach ZAMS still accreting 

5. Low-mass VS High-mass “Standard” (Shu’s) picture: Accretion onto protostar Static envelope: n  R -2 Infalling region: n  R -3/2 Protostar: t KH =GM 2 /R * L * Accretion: t acc =(dM acc /dt)/M * –Low-mass stars: t KH > t acc –High-mass stars: t KH < t acc  High-mass stars reach ZAMS still accreting 

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

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: a)UC HIIs: OB stars are in clusters b)H 2 O masers without free-free: luminous but without UC HII region c)IRAS without H 2 O and UC HII: protostellar phase?

9. 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: a)UC HIIs: OB stars are in clusters b)H 2 O masers without free-free: luminous but without UC HII region c)IRAS without H 2 O and UC HII: protostellar phase?

10. Observations High-mass YSOs: A V > 10  radio  NIR needed Low angular resolution = single-dish = 10”  2’ Effelsberg, Nobeyama, IRAM, JCMT, CSO, NRAO NH 3, CO, 13 CO, CS, C 34 S, CH 3 C 2 H, CN, HCO+, … High angular resolution = interferometers = 0.3”  4” VLA, IRAM, Nobeyama, OVRO, BIMA, VLBI NH 3, CH 3 CN, CH 3 OH, SiO, HCO +, H 2 O, continuum

11. General results  Targets surrounded by dense, medium size clumps: 1 pc, 50 K, 10 5 –10 6 cm -3, 10 3 –10 4 M ⊙  Dense, small cores found close to/around targets: 0.1 pc, >10 7 cm -3, 40–200 K, 10–10 3 M ⊙

13. Clumps Traced by all molecules observed  real entities! M clump >M virial  large B (1mG) needed for equilibrium T K  R -0.5  heated by source close to centre n H 2  R -2.6  marginally stable dM acc /dt = M clump /t AD = 10 -3 –10 -2 M ⊙ /y  large accretion rates  clumps may be marginally stable entities ( ∼ 10 5 y)  accretion from clumps feeds embedded YSOs

14. Clumps Traced by all molecules observed  real entities! M clump >M virial  large B (1mG) needed for equilibrium T K  R -0.5  heated by source close to centre n H 2  R -2.6  marginally stable dM acc /dt = M clump /t AD = 10 -3 –10 -2 M ⊙ /y  large accretion rates  clumps may be marginally stable entities ( ∼ 10 5 y)  accretion from clumps feeds embedded YSOs

16. Clumps Traced by all molecules observed  real entities! M clump >M virial  large B (1mG) needed for equilibrium T K  R -0.5  heated by source close to centre n H 2  R -2.6  marginally stable dM acc /dt = M clump /t AD = 10 -3 –10 -2 M ⊙ /y  large accretion rates  clumps may be marginally stable entities ( ∼ 10 5 y)  accretion from clumps feeds embedded YSOs

18. Clumps Traced by all molecules observed  real entities! M clump >M virial  large B (1mG) needed for equilibrium T K  R -0.5  heated by source close to centre n H 2  R -2.6  marginally stable dM acc /dt = M clump /t AD = 10 -3 –10 -2 M ⊙ /y  large accretion rates  clumps may be marginally stable entities ( ∼ 10 5 y)  accretion from clumps feeds embedded YSOs

20. Clumps Traced by all molecules observed  real entities! M clump >M virial  large B (1mG) needed for equilibrium T K  R -0.5  heated by source close to centre n H 2  R -2.6  marginally stable dM acc /dt = M clump /t AD = 10 -3 –10 -2 M ⊙ /y  large accretion rates  clumps may be marginally stable entities ( ∼ 10 5 y)  accretion from clumps feeds embedded YSOs

21. Clumps Traced by all molecules observed  real entities! M clump >M virial  large B (1mG) needed for equilibrium T K  R -0.5  heated by source close to centre n H 2  R -2.6  marginally stable dM acc /dt = M clump /t AD = 10 -3 –10 -2 M ⊙ /y  large accretion rates  clumps may be marginally stable entities ( ∼ 10 5 y)  accretion from clumps feeds embedded YSOs

22. Hot Cores (HCs) Hot (100–200 K) cores often found close to UC HIIs: H 2 O masers and high energy lines  large n H 2 and T K many rare molecules  evaporation from dust grains T K  R -3/4  inner energy source L IRAS  10 4 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

23. Hot Cores (HCs) Hot (100–200 K) cores often found close to UC HIIs: H 2 O masers and high energy lines  large n H 2 and T K many rare molecules  evaporation from dust grains T K  R -3/4  inner energy source L IRAS  10 4 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

27. Hot Cores (HCs) Hot (100–200 K) cores often found close to UC HIIs: H 2 O masers and high energy lines  large n H 2 and T K many rare molecules  evaporation from dust grains T K  R -3/4  inner energy source L IRAS  10 4 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

29. Hot Cores (HCs) Hot (100–200 K) cores often found close to UC HIIs: H 2 O masers and high energy lines  large n H 2 and T K many rare molecules  evaporation from dust grains T K  R -3/4  inner energy source L IRAS  10 4 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

32. Hot Cores (HCs) Hot (100–200 K) cores often found close to UC HIIs: H 2 O masers and high energy lines  large n H 2 and T K many rare molecules  evaporation from dust grains T K  R -3/4  inner energy source L IRAS  10 4 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

40. Hot Cores (HCs) Hot (100–200 K) cores often found close to UC HIIs: H 2 O masers and high energy lines  large n H 2 and T K many rare molecules  evaporation from dust grains T K  R -3/4  inner energy source L IRAS  10 4 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

41. Beuther et al. (2002)

42. Hot Cores (HCs) Hot (100–200 K) cores often found close to UC HIIs: H 2 O masers and high energy lines  large n H 2 and T K many rare molecules  evaporation from dust grains T K  R -3/4  inner energy source L IRAS  10 4 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

43. Warm cores (WC) Mostly towards IRAS sources with [25-12]<0.57 : warm (50 K) but dense and massive (10–10 2 M ⊙ ) luminous (L IRAS  10 4 L ⊙ )  high-mass YSOs few H 2 O 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 (?)

45. Warm cores (WC) Mostly towards IRAS sources with [25-12]<0.57 : warm (50 K) but dense and massive (10–10 2 M ⊙ ) luminous (L IRAS  10 4 L ⊙ )  high-mass YSOs few H 2 O 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 (?)

46. H 2 O maser

47. Warm cores (WC) Mostly towards IRAS sources with [25-12]<0.57 : warm (50 K) but dense and massive (10–10 2 M ⊙ ) luminous (L IRAS  10 4 L ⊙ )  high-mass YSOs few H 2 O 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 (?)

49. IRAS 23385+6053

50. Warm cores (WC) Mostly towards IRAS sources with [25-12]<0.57 : warm (50 K) but dense and massive (10–10 2 M ⊙ ) luminous (L IRAS  10 4 L ⊙ )  high-mass YSOs few H 2 O 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 (?)

51. WC HC

54. Warm cores (WC) Mostly towards IRAS sources with [25-12]<0.57 : warm (50 K) but dense and massive (10–10 2 M ⊙ ) luminous (L IRAS  10 4 L ⊙ )  high-mass YSOs few H 2 O 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 (?)

55. Proposed evolutionary sequence I.WC: dM acc /dt  10 -5 M ⊙ /y squelches UC HII; e.g. IRAS 23385+6053: 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 10 5 L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 10 5 L ⊙, 100 K, 3 10 3 M ⊙ V.(UC)HII: HC is “evaporated”

56. IRAS 23385+6053

57. Proposed evolutionary sequence I.WC: dM acc /dt  10 -5 M ⊙ /y squelches UC HII; e.g. IRAS 23385+6053: 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 10 5 L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 10 5 L ⊙, 100 K, 3 10 3 M ⊙ V.(UC)HII: HC is “evaporated”

59. Proposed evolutionary sequence I.WC: dM acc /dt  10 -5 M ⊙ /y squelches UC HII; e.g. IRAS 23385+6053: 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 10 5 L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 10 5 L ⊙, 100 K, 3 10 3 M ⊙ V.(UC)HII: HC is “evaporated”

61. Proposed evolutionary sequence I.WC: dM acc /dt  10 -5 M ⊙ /y squelches UC HII; e.g. IRAS 23385+6053: 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 10 5 L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 10 5 L ⊙, 100 K, 3 10 3 M ⊙ V.(UC)HII: HC is “evaporated”

63. Proposed evolutionary sequence I.WC: dM acc /dt  10 -5 M ⊙ /y squelches UC HII; e.g. IRAS 23385+6053: 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 10 5 L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 10 5 L ⊙, 100 K, 3 10 3 M ⊙ V.(UC)HII: HC is “evaporated”

64. Conclusions High-mass YSOs are associated with: large accretion rates outflows and circumstellar disks High-mass stars could form through accretion as much as low-mass stars