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)
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 = YSOs signposts: IRAS, masers, UC HIIs
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
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
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!
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?
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?
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
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 ⊙
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 -2 M ⊙ /y large accretion rates clumps may be marginally stable entities ( ∼ 10 5 y) accretion from clumps feeds embedded YSOs
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 -2 M ⊙ /y large accretion rates clumps may be marginally stable entities ( ∼ 10 5 y) accretion from clumps feeds embedded YSOs
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 -2 M ⊙ /y large accretion rates clumps may be marginally stable entities ( ∼ 10 5 y) accretion from clumps feeds embedded YSOs
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 -2 M ⊙ /y large accretion rates clumps may be marginally stable entities ( ∼ 10 5 y) accretion from clumps feeds embedded YSOs
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 -2 M ⊙ /y large accretion rates clumps may be marginally stable entities ( ∼ 10 5 y) accretion from clumps feeds embedded YSOs
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 -2 M ⊙ /y large accretion rates clumps may be marginally stable entities ( ∼ 10 5 y) accretion from clumps feeds embedded YSOs
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
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
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
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
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
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
Beuther et al. (2002)
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
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 G WCs may be “class 0” high-mass sources (?)
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 G WCs may be “class 0” high-mass sources (?)
H 2 O maser
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 G WCs may be “class 0” high-mass sources (?)
IRAS
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 G WCs may be “class 0” high-mass sources (?)
WC HC
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 G WCs may be “class 0” high-mass sources (?)
Proposed evolutionary sequence I.WC: dM acc /dt M ⊙ /y squelches UC HII; e.g. IRAS : 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS : 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G : L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G : L ⊙, 100 K, M ⊙ V.(UC)HII: HC is “evaporated”
IRAS
Proposed evolutionary sequence I.WC: dM acc /dt M ⊙ /y squelches UC HII; e.g. IRAS : 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS : 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G : L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G : L ⊙, 100 K, M ⊙ V.(UC)HII: HC is “evaporated”
Proposed evolutionary sequence I.WC: dM acc /dt M ⊙ /y squelches UC HII; e.g. IRAS : 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS : 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G : L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G : L ⊙, 100 K, M ⊙ V.(UC)HII: HC is “evaporated”
Proposed evolutionary sequence I.WC: dM acc /dt M ⊙ /y squelches UC HII; e.g. IRAS : 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS : 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G : L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G : L ⊙, 100 K, M ⊙ V.(UC)HII: HC is “evaporated”
Proposed evolutionary sequence I.WC: dM acc /dt M ⊙ /y squelches UC HII; e.g. IRAS : 10 4 L ⊙, 40 K, 370 M ⊙ II.HC: outflow+disk, non-spherical accretion? e.g. IRAS : 10 4 L ⊙, 200 K, 10 M ⊙ III.HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G : L ⊙, 200 K, 10 3 M ⊙ IV.HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G : L ⊙, 100 K, M ⊙ V.(UC)HII: HC is “evaporated”
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