Download Disks - Osservatorio di Arcetri

Probing high-mass star formation
through different molecules
Riccardo Cesaroni
INAF - Osservatorio Astrofisico di Arcetri
High-mass  >8 MO  >103 LO  O-B star
1) The recipe of (OB) star formation: infall,
outflow, rotation  the role of accretion disks
2) OB star formation: observational problems
3) The search for disks: tracing rotation and infall
4) Results: disks in B stars; for O stars ALMA is
needed
The recipe of (OB) star formation:
infall, outflow, rotation
Infall of circumstellar material onto protostar
Two relevant timescales:
accretion: tacc = Mstar/(dM/dt)acc
contraction: tKH = GMstar/RstarLstar
Mstar > 6-10 MO  tacc > tKH (Palla & Stahler
1993)
High-mass stars reach ZAMS still accreting!
Spherical symmetry  Pradiation > Pram 
 stars > 6-10 MO should not form!??
Rotation and outflow may be the solution
(Yorke & Sonnhalter, Kruhmolz et al.):
Rotation+ang.mom.conserv.  Disk 
 focuses accretion 
 boosts ram pressure
Outflow  channels stellar photons 
 lowers radiation pressure
Detection of accretion disks is crucial
to understand O-B star formation
High-mass star observations
• Problems:





IMF  high-mass stars are rare
large distance: >450 pc  a few kpc ALMA sensitivity!
formation in clusters  confusion ALMA resolution!
rapid evolution: tacc=50 MO /10-3MOyr-1=5 104yr
parental environment profoundly altered
• Advantage:
 very luminous (cont. & line) and rich (molecules)!
ALMA spectral coverage!
Clump
UC HII
HMC
(CH3CN, HCOOCH3, NH3, HNCO, C2H5CN, etc. …)
The search for disks: where
0.5 pc
The search for disks: what
HMC LINE
TRACER
Emission
e.g. CH3CN,
CH3OH, HCO+
Absorption
e.g. NH3
Maser
e.g. H2O,
CH3OH
PROs
CONTRAs
Kinematics and
geometry of outflow
(expansion) and disk
(rotation)
Excellent tracers of
infall
Limited angular
resolution and
sensitivity 
ALMA needed
Bright, embedded
continuum source
needed  cm,
submm (ALMA)?
Unclear geometry &
kinematics
Very high angular
resolution (1 mas);
3D velocity field
Emission
line from
rotating
disk
HMC LINE
TRACER
Emission
e.g. CH3CN,
CH3OH, HCO+
Absorption
e.g. NH3
Maser
e.g. H2O,
CH3OH
PROs
Kinematics and
geometry of outflow
and disk
Excellent tracers of
infall
Very high angular
resolution (1 mas);
3D velocity field
CONTRAs
Limited angular
resolution and
sensitivity 
ALMA needed
Bright, embedded
continuum source
needed  cm,
submm (ALMA)?
Unclear geometry &
kinematics
Absorption
line from
infalling
envelope
HMC LINE
TRACER
Emission
e.g. CH3CN,
CH3OH, HCO+
PROs
Kinematics and
geometry of outflow
and disk
CONTRAs
Limited angular
resolution and
sensitivity 
ALMA needed
Bright, embedded
continuum source
needed  cm,
submm (ALMA)?
Global picture
unclear
All line tracers
must be used!
Absorption
e.g. NH3
Maser
e.g. H2O,
CH3OH
Excellent tracers of
infall
Very high angular
resolution (1 mas);
3D velocity field
Results of disk search
in B and late-O (proto)stars:
2 examples
L* Mdis Ddisk M*
k
(AU) (MO
(LO) (MO
)
)
IRAS20126 104
4 1600 7
G24.78 A1 5 104 130 5000 20
Spec.
Type
B0.5
O9.5
IRAS 20126+4104
Cesaroni et al.
Hofner et al.
Keplerian
Moscadelli etrotation:
al.
M*=7 MO
Moscadelli et al. (2005)
Furuya et al. (2002)
Beltran et al. (2004)
Beltran et al. (2005)
Furuya et al. (2002)
Beltran et al. (2004)
Beltran et al. (2005)
Furuya et al. (2002)
Beltran et al. (2004)
Beltran et al. (2005)
Keplerian rotation
around 20 MO star?
ALMA needed!
UC HII + dust
O9.5 (20 MO) + 130 MO
CH3OH masers
Mdyn= 19 MO
Beltran et al. (2004,2005)
Goddi et al. (in prep.)
Mdyn= 55 MO
= Mstar+Mgas
absorption
UC HII
infall and rotation!
(dM/dt)infall > (dM/dt)HIIquench
but HII exists  infall in disk!
Goddi et al. in prep.
H2O maser
proper motions
accretion is finished!??
ALMA needed
Conclusions
• Robust evidence of disks in B (proto)stars and perhaps
in late O (proto)stars star formation by accretion as
in low-mass stars
• No disk found yet in early O (proto)stars  perhaps
observational bias? perhaps other star formation
mechanisms possible?
Only ALMA will tell:
 High sensitivity & resolution  large distances
 Sub-mm lines  high-T tracers  100 AU region
 Wide bandwidth  outflow, infall, and rotation tracers
simultaneously
infall and rotation!
(dM/dt)infall > (dM/dt)HIIquench
but HII exists  infall in disk!
Furuya et al. (2002)
Beltran et al. (2004)
Beltran et al. (2005)
Results of disk search
Two types of objects found:
Disks in B stars
Toroids in O stars
• M < 10 MO
• R ~ 1000 AU
• L ~ 104 LO
• (dM/dt)star ~ 10-4 MO/yr
• trot ~ 104 yr
• tacc ~ M/(dM/dt)star ~ 105 yr
 tacc >> trot
 equilibrium, circumstellar
structures
• M > 100 MO
• R ~ 10000 AU
• L >> 104 LO
• (dM/dt)star > 10-3 MO/yr
• trot ~ 105 yr
• tacc ~ M/(dM/dt)star ~ 104 yr
 tacc << trot
 non-equilibrium, circumcluster structures
The elusive disks in early O (proto)stars
Observational bias? For Mdisk= Mstar/2, a Keplerian
disk in a 50 MO star can be detected up to:
 continuum sensitivity:
d < 1.7 [Mstar(MO)]0.5 ~ 12 kpc
 line sensitivity:
d < 6.2 Mstar(MO) sin2i/W2(km/s) ~ 8 kpc
 spectral + angular resolution:
d < 14 Mstar(MO) sin2i/[D(’’)W2(km/s)] ~ 19 kpc
 disks in all O stars should be detectable
up to the galactic center
Caveats!!!
One should consider also:
• rarity of O stars  ALMA sensitivity
• confusion with envelope  ALMA resolution
• Chemistry  ALMA spectral coverage
• confusion with outflow/infall  ALMA resol.
• non-keplerian rotation
• disk flaring
• inclination angle
• …
infall and rotation!
(dM/dt)infall > (dM/dt)HIIquench
but HII exists  infall in disk!
Lstar = 103-105 LO
 Tdust = 65 K (Lstar/105LO)0.2 (R/0.1pc)0.4
 Tdust > 100 K for R < 0.1 pc
 Grain mantles evaporated
 chemical enrichment of gas phase: hot cores
 wide choice of molecular probes: CH3OH,
CH3CN, HCOOCH3, etc. …
Jets/outflows 
 shocks: H2O, SiO, HCO+, etc. …
Clump
UC HII
HMC
Core
IRAS 20126+4104
Edris et al. (2005)
Sridharan et al. (2005)
NIR & OH masers
disk
G192.16-3.82
Shepherd & Kurtz (1999)
2.6mm cont.
disk
CO outflow
G192.16-3.82
Shepherd & Kurtz (1999)
Shepherd et al. (2001)
3.6cm cont. & H2O masers
Simon et al. (2000): TTau stars
Velocity maps (CO J=21)
Cep A HW2
Torrelles et al. (1998)
Patel et al. (2005)
… but see Comito & Schilke
for a different interpretation
IRAS 18089-1732
Beuther et al.
(2004, 2005)
Gibb et al. (2002)
Olmi et al. (2003)
Olmi et al. (1996)
Furuya et al. (2002)
Beltran et al. (2004)
CH3CN(12-11)
Gibb et al. (2002)
Olmi et al. (2003)
Beltran et al. (2005)
Disks & Toroids
O stars
M*
(MO)
7
6-10
15-20
40
20…
-
B stars
L
Mdisk
Ddisk
(LO) (MO)
(AU)
IRAS20126 104
4
1600
G192.16
3 103
15
1000
M17
?
>110
20000
NGC7538S 104 100-400 30000
G24.78 (3) 7 105 80-250 4000-8000
G29.96
9 104 300
14000
G31.41
3 105 490
16000