High-mass stars from cradle to first steps:
a possible evolutionary sequence
(High-mass  M*>10M⊙  L*>104L⊙  B3-O)
1)
2)
3)
4)
5)
The environment of 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?
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
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 
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 
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 highmass 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) H2O masers without free-free: luminous but without
UC HII region
c) IRAS without H2O 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) H2O masers without free-free: luminous but without
UC HII region
c) IRAS without H2O and UC HII: protostellar phase?
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
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⊙
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
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
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
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
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
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
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
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
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
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
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
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
Beuther et al. (2002)
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
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 (?)
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 (?)
H2O maser
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 (?)
IRAS 23385+6053
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 (?)
HC
WC
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 (?)
Proposed evolutionary sequence
I.
II.
III.
IV.
V.
WC: dMacc/dt  10-5 M⊙/y squelches UC HII;
e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
HC: outflow+disk, non-spherical accretion?
e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
HC+ small UC HII: outflow+disk remnant,
UC HII begins expansion;
e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
HC+UC HII: outflow remnant, UC HII destroys HC;
e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
(UC)HII: HC is “evaporated”
IRAS 23385+6053
Proposed evolutionary sequence
I.
II.
III.
IV.
V.
WC: dMacc/dt  10-5 M⊙/y squelches UC HII;
e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
HC: outflow+disk, non-spherical accretion?
e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
HC+ small UC HII: outflow+disk remnant,
UC HII begins expansion;
e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
HC+UC HII: outflow remnant, UC HII destroys HC;
e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
(UC)HII: HC is “evaporated”
Proposed evolutionary sequence
I.
II.
III.
IV.
V.
WC: dMacc/dt  10-5 M⊙/y squelches UC HII;
e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
HC: outflow+disk, non-spherical accretion?
e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
HC+ small UC HII: outflow+disk remnant,
UC HII begins expansion;
e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
HC+UC HII: outflow remnant, UC HII destroys HC;
e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
(UC)HII: HC is “evaporated”
Proposed evolutionary sequence
I.
II.
III.
IV.
V.
WC: dMacc/dt  10-5 M⊙/y squelches UC HII;
e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
HC: outflow+disk, non-spherical accretion?
e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
HC+ small UC HII: outflow+disk remnant,
UC HII begins expansion;
e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
HC+UC HII: outflow remnant, UC HII destroys HC;
e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
(UC)HII: HC is “evaporated”
Proposed evolutionary sequence
I.
II.
III.
IV.
V.
WC: dMacc/dt  10-5 M⊙/y squelches UC HII;
e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
HC: outflow+disk, non-spherical accretion?
e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
HC+ small UC HII: outflow+disk remnant,
UC HII begins expansion;
e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
HC+UC HII: outflow remnant, UC HII destroys HC;
e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
(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