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1) Are disks predicted? Theories of HM SF
2) Are disks observed? Search methods
3) Observational evidence disks VS toroids
4) Open questions and the future: ALMA, etc.
Search for Disks around YoungHigh-Mass Stars
Riccardo CesaroniINAF-Osservatorio Astrofisico di Arcetri
Existence of disks: Theory
Disks are natural outcome of infall + angular momentum conservation, however:
• B field magnetic braking, pseudo disks?• Ionization by OB stars photoevaporation?• Tidal interaction with cluster truncation?• Merging of low-mass stars destruction?
Disks in OB protostars might not exist!
Good news: all theories predict circumstellar disks! Different models of high-mass star formation (core accretion, competitive accretion, …), but all predict circumstellar disks of ~100-1000 AU
See e.g. Bonnell 2005, Krumholz et al. 2007, Keto 2007, Kuiper et al. 2010
stars up to 137 MO through disk accretion
1 pc clump collapsecompetitive accretion
Bonnell (2005)
Zoom in
time
core accretionin 0.2 pc clump
Krumholz et al. (2007)
disk
50 AU
molecular gas
ionized gas
density & velocity of gas around O9 star (Keto 2007)
Bad news: all theories predict circumstellar disks!
Disks existence not sufficient to choose SF theory
Disks may keep memory of formation process disks properties needed to discriminate between SF models
< 100 AU resolution necessary, i.e. < 0.1” ALMA, EVLA, eMERLIN, VLBI, VLTI, …
The search for disks
Many searches in the last decade need targets & toolsSelection criteria for targets:• Bolometric (IRAS) luminosity > several 103 LO
high-mass (proto)star• Association with outflow likely disk?• Presence of massive (> 10 MO), compact (< 0.1 pc)
molecular core deeply embedded (young) high-mass object
• In some cases maser and/or UCHII OB stars
Tools adopted:• Thermal lines of rare (low-abundance) molecules trace high-
density, high-temperature gas in disk• H2O, CH3OH, OH, SiO maser lines mas resolution• (sub)mm continuum disk mass• IR continuum/lines disk emission and absorption• cm continuum and RRL ionised accretion flow
Diagnostic:• Flattened (sub)mm core perpendicular to jet/outflow• Velocity gradient perpendicular to associated outflow• Peculiar (Keplerian) pattern in position-velocity plot• Dark silouhette in near-IR against bright background• Elongated emission in the mid-IR perpendicular to bipolar
reflection nebula
CepA HW2Jimenez-Serra et al. (2007,2009)
PV plot along disk
Keplerian rotation about 18 MO star
thermal jet
disk
B field (23 mG)CH3OH masers
Vlemmings et al.(2010)
SO2
600 AU
1000 AU
rel. D
ec.
[m
as]
NGC7538 IRS1 N Pestalozzi et al. (2004, 2009)
model of Keplerian disk
around 31 MO star
CH3OH maser
PV plotalong disk
diskplane
M17Chini et al. (2004)
Nuerberger et al. (2007)
2.2 µmcontinuum
H2 jetdisk
2 µm lines
4.5µmemission
disk
J23056+6016Quanz et al. (2010)
H K’bipolarnebula
12COblue outflow lobe
red & blueC18Odisk
Major problems:• Velocity gradient may be expansion instead of rotation• Outflow multiplicity and/or precession• Masers sample only few lines of sight• (sub)mm & IR continuum: no kinematical info• IR lines: so far limited spectral resolution
Possible solutions:• High angular & spectral resolution accurate PV plots
Keplerian rotation (close enough to star)• Maser proper motions 3D velocity
Combine as many tools as possible!
IRAS 20126+4104Cesaroni et al.Hofner et al.
Sridharan et al.Moscadelli et al.
Image: 2µm cont.
--- OH maser
H2O masers
1000 AU
Keplerian rotation+infall:
M*=10 MOMoscadelli et al. (2010)
CH3OH H2O200 AU
jet
disk+jetdisk
Distance measurement to IRAS 20126+4104 withH2O maser parallax (Moscadelli et al. 2010)
d = 1.64±0.05 kpc
Observational results
• Evidence for rotation/flattening in ~42 molecular cores:~26 disks Keplerian rotation in ~10 of these
~16 rotating toroids velocity gradient perpendicular to outflow/jet, but not Keplerian
PV plots of candidateKeplerian disks
in high-mass stars
13CO
-0.5”0.5”1” 0NH3(1,1)
CH3OH
IRAS23151
NGC7538
IRAS20126
CepAHW2CH3OH
NGC7538S
DCN
C17O
AFGL5142
AFGL490
IRAS18566
M17
W33A
CO v=2-0
disk
disk
disk
model 2.2µm VLT
diskmodel2.2µm VLT
model 2.2µm VLTI
disk
IR detected disks
AFGL2591
2.1µm speckle
2.2µm Subaru
J23056 IRAS20126
M17UC1
M17
19µm SubaruHD200775
IRAS13481
2.2µm UKIRT
Kraus+2010
Quanz+2010
Sridharan+2005
Steinecker+2006
Nielbock+2007
Kraus+2010
Okamoto+2009
Velocity fields of rotating toroids
C
G24 A1
G24 A2
G31.41
G19.61G10.62
G327
G351
G305
G28.20
CH3CN
CH3CN
CH3CNNH3 NH3
Toroids• M > 100 MO
• R ~ 10000 AU• L > 105 LO O (proto)stars• small tacc/trot
non-equilibrium, circum-cluster structures
Disks• M < a few 10 MO
• R ~ 1000 AU• L ~ 104 LO B (proto)stars• large tacc/trot
equilibrium, circumstellar structures
disks
toroidsBeltran et al. (2010)
Open questions
• When do disks appear? 1 disk/toroid in IR-dark cloud• Role of magnetic field? 2 toroids with B parallel to
rotation axis B may play crucial role• Why no (Keplerian) disks seen in O stars?
Ionized by OB stars? Unlikely: too slow and rotation in ionized gas detected in G10.62 (Keto & Wood 2005)
Truncated by tidal interactions in cluster? Maybe, but numerical simulations needed
Too far? ALMA and EVLA should tell us!Too deeply embedded in toroids? Optically thin (low
abundance i.e. high density) tracers needed, but line forest may fool even ALMA! VLBI of masers may help
IRDC18223-3Fallscheer et al. (2009)
CH3OH
5000 AU
disk model
small-scalevelocity field
large-scale bipolar outflow
disk-modelvelocity field
0.2 pc
Open questions
• When do disks appear? 1 disk/toroid in IR-dark cloud• Role of magnetic field? 2 toroids with B parallel to
rotation axis B may play crucial role• Why no (Keplerian) disks seen in O stars?
Ionized by OB stars? Unlikely: too slow and rotation in ionized gas detected in G10.62 (Keto & Wood 2005)
Truncated by tidal interactions in cluster? Maybe, but numerical simulations needed
Too far? ALMA and EVLA should tell us!Too deeply embedded in toroids? Optically thin (low
abundance i.e. high density) tracers needed, but line forest may fool even ALMA! VLBI of masers may help
G31.41+0.31
Cesaroni et al.in prep.
W51e2
Tang et al.(2009)
Keto&
Klaassen(2008)
Girart et al.(2009)
Open questions
• When do disks appear? 1 disk/toroid in IR-dark cloud• Role of magnetic field? 2 toroids with B parallel to
rotation axis B may play crucial role• Why no (Keplerian) disks seen in O stars?
Ionized by OB stars? Unlikely: too slow and rotation in ionized gas detected in G10.62 (Keto & Wood 2005)
Truncated by tidal interactions in cluster? Maybe, but numerical simulations needed
Too far? ALMA and EVLA should tell us!Too deeply embedded in toroids? Optically thin (low
abundance i.e. high density) tracers needed, but line forest may fool even ALMA! VLBI of masers may help
tidal destructionrotational period
photo-evaporation
Cesaroni et al. (2007)
Open questions
• When do disks appear? 1 disk/toroid in IR-dark cloud• Role of magnetic field? 2 toroids with B parallel to
rotation axis B may play crucial role• Why no (Keplerian) disks seen in O stars?
Ionized by OB stars? Unlikely: too slow and rotation in ionized gas detected in G10.62 (Keto & Wood 2005)
Truncated by tidal interactions in cluster? Maybe, but numerical simulations needed
Too far? ALMA and EVLA should tell us!Too deeply embedded in toroids? Optically thin (low
abundance i.e. high density) tracers needed, but line forest may fool even ALMA! VLBI of masers may help
Assumptions:HPBW = Rdisk/4
FWHMline = Vrot(Rdisk)
Mdisk Mstar
same <Ncol> in all disks
TB > 20 K
obs. freq. = 230 GHz
5 hours ON-source
spec. res. = 0.2 km/s
S/N = 20
edge
-on
i = 35
°
circumstellardisks
Keplerian
Assumptions:HPBW = Rdisk/4
FWHMline = Vrot(Rdisk)
Mdisk Mstar
same <Ncol> in all disks
TB > 20 K
obs. freq. = 230 GHz
5 hours ON-source
spec. res. = 0.2 km/s
S/N = 20
no s
tars
edge
-on
i = 35
°
Simulations of disksaround 8 MO star
Krumholz et al. (2007)
NH3 with EVLA
CH3CN(12-11) with ALMA
cont.+
line
cont.subtr.
Open questions
• When do disks appear? 1 disk/toroid in IR-dark cloud• Role of magnetic field? 2 toroids with B parallel to
rotation axis B may play crucial role• Why no (Keplerian) disks seen in O stars?
Ionized by OB stars? Unlikely: too slow and rotation in ionized gas detected in G10.62 (Keto & Wood 2005)
Truncated by tidal interactions in cluster? Maybe, but numerical simulations needed
Too far? ALMA and EVLA should tell us!Too deeply embedded in toroids? Optically thin (low
abundance i.e. high density) tracers needed, but line forest may fool even ALMA! VLBI of masers may help
Furuya et al. (2008)
CH3CN
Sanna et al. (2010)
rotating toroid deeply embedded disk?
CH3OH masers
1.3cm cont.