1. European Southern Observatory
Disk-mediated accretion in a high-mass YSO and dynamical history in Orion BN/KL
CIRIACO GODDI
European Southern Observatory
Main collaborators
Lincoln Greenhill
Harvard-Smithsonian Center for Astrophysics
Lynn Matthews
MIT Haystack Observatory
Liz Humphreys
European Southern Observatory
Claire Chandler
National Radio Astronomy Observatory

2. Focus on two questions to address in HMSF
Which are the physical properties of Disk/Outflow interfaces?
Sizes/Structures of Disks
Acceleration and Collimation of Outflows
Balance of forces vs radius (gravity/radiation/magnetic field)
Do dynamical interactions among high-mass YSOs play an important role within dense protoclusters?
What might help?
Direct imaging at R < 102 AU
- Gas structure & dynamics, magnetic fields, etc.
- Radio/mm interferometers generally unable to probe inside AU
Multi-epoch observations of radio continuum sources
- 3-D velocities of high-mass YSOs: hints on cluster dynamical evolution
- Long temporal baselines required for measurable position displacements

3. The closest massive SFR: Orion BN/KL
D = 4186 pc
(Kim et al. 2008)
L ~ 105 L
O(200) km s-1
outflow (H2)
(Kaifu et al. 2000)
BN/KL
Trapezium
What is powering Orion BN/KL?

4. A High Density Protocluster in BN/KL
H2 P[FeII]
HST/Nic
Schultz et al. 1999
BN/KL
BN and IRc sources
20 IR peaks distributed over 20”
BN and IRc2 brightest IR sources, but not enough to power the nebula!
Source I
12.5um, Keck (θ≈0.5”) BN
IRc2
Greenhill et al. 2004
7mm - VLA
Reid et al. 2007; Goddi et al. submitted
Obscured up to 22 μm (AV ≥300)
Ionized disk with R~40 AU (λ7mm)
Source I 1”
Zooming into the center of the nebula, we identify a cluster of IR sources,
The most prominent IR sources are BN and Irc2, which however are not bright enough to explain the high luminosity of BNKL
Source I is a luminous, massive, embedded YSO

5. The case of the high-mass YSO “Source I” in Orion BN/KL
Collection of λ7mm observations of Source I at R<1000 AU
SiO v=0 J=1-0 (VLA)
T~1000 K, n < 107 cm-3
λ7mm cont (VLA)
T=104 K
SiO v=1,2 J=1-0 (VLBA)
T~2000 K, n=1010±1 cm-3
Goddi et al.
Greenhill et al.
Matthews et al.
150 AU
Transition Instrument Observations Resolution
28SiO (v=1,2 J=1-0) VLBA epochs over AU
28SiO (v=0 J=1-0) VLA epochs in 10 yrs AU
7 mm continuum VLA epochs in 8 yrs AU
Dataset

6. Radio Source I drives a “Low-Velocity” NE-SW outflow
7mm SiO v=0+H2O 1.3cm (VLA )
18 km/s
Dec (arcsec)
500 AU
Proper motions of SiO maser spots over 4 epochs
open Q: what confines flow?
open Q: what enables 102x spread in density implied by species overlap?
<Voutflow>
18 km s-1
Rinn
100 AU
Rout
1000 AU
Mass-loss
~10-6 M⊙ yr-1
Tdyn
500 yr
RA (arcsec)
100 AU<R<1000 AU
Greenhill, Goddi, et al., in prep.

7. Long-term VLBA imaging study of Source I
Integrated Intensity
over time
SiO v=1,2
1010±1 cm K
O(1000) Jy km s-1 peak
T=21 months, ΔT~1 month
R<100 AU
Isolated Features
North Arm
East Arm
South Arm
West Arm
Western Bridge
Eastern Bridge
Dark Band
Streamers
Matthews, Greenhill, Goddi, et al ApJ,708, 80

8. Time-series of VLBA moment 0 images of SiO v=1,2 masers over 2 years
Integrated Intensity epoch-by-epoch
T=21 months, ΔT~1 month
R<100 AU
Physical flow of O(1000) independent clumps
Radial flow (four arms)
Transverse flow(bridge)
Interpretation:
bipolar outflow (limbs)
disk rotation
Matthews, Greenhill, Goddi, et al ApJ,708, 80
R<100 AU
Matthews, Greenhill, Goddi, et al. submitted

9. 3-D velocity field of SiO (v=1,2) maser emission
O(1000) Proper Motions
3-11 mo. lifetimes
3 & 4 month tracks
43395 spots (0.22 km s-1)
Vpmo=0.8–24 km s-1
V3D=5.3–25.3 km s-1
<V3D>=14 km s-1
3-D Velocities:
v = 5-25 km/s
Vave = 14 km/s
Role of magnetic fields from curvature of p.mo trajectories
VLOS rotation
NE / SW axis
red/blue arms
declining rotation curve
∇VLOS in bridge
Two loci.
Limb and front edge of flow.
Bipolar funnel flow.
Outflow.
Rotation and expansion in the bridge
Backside emission
Matthews, Greenhill, Goddi, et al. submitted

10. Model of Source I R =10-100 AU R=100-1000 AU
Rotating disk with R~50 AU
=> v=1,2 SiO masers in bridge + 7mm cont
Wide-angle, rotating wind from the disk
=> v=1,2 SiO masers in four arms
R= AU
Collimated outflow at v~20 km s-1
=> v=0 SiO maser proper motions
Toy-model
Resolved the launch/collimation region of outflow
Identified a good example of disk-mediated accretion

11. 500 years ago BN and I were as close as 50-100 AU!
Dynamical Interaction in BN/KL
Close Passage between Source I and BN
7mm, VLA (θ≈0.05”),3 epochs in 7 years
12.5um, Keck (θ≈0.5”)
VI≈15 km/s
VBN≈26 km/s
ONC-absolute p.mo.
P.mo of BN relative to I BN
Greenhill et al. 2004 I
IF I DONT INCLUDE THE NEXT SLIDE, I NEED TO INCLUDE HERE:
Source I is the binary (M=20MS,A=10AU) and BN the escaper 2”
Smin(BN-I)=0.11”±0.18”, Tmin(BN-I)=550±10 yr
500 years ago BN and I were as close as AU!
Goddi et al. submitted
See also Gomez et al. 2008

12. Triple-system decay in BN/KL
Formation of a binary among the most massive bodies
Binary and third object both are ejected with high speed
- VBN~2VI ➟ Source I is the binary and BN the escaper
Linear momentum conservation
MIVI=MBNVBN => VBN=2VI => MI=2MBN and MBN=10M
Mass of Source I MI=20M
Mechanical energy conservation
½(MIVI2+MBNVBN2) = GM1IM2I/2a
Binary orbital separation a<10 AU
Which are mass and orbit of the binary?
Goddi et al. submitted; see also Gomez et al. 2008
The positive kinetic energy is compensated by the negative binding energy associated with the binary
Source I is a massive (20M) and tight (<10 AU) binary
Adapted from Reipurth 2000

13. Can the original disk(s) survive the collision?
The encounter between a pre-existing binary (Source I) and a single (BN) enhances chances to retain the circumbinary disk I BN
N-body simulation
Initial systems (binary+single):
1) Mbin=10+10M, Abin=10 AU
2) Msing=10M, S(bin-sing)=500AU
Results from 1000 cases:
Ejections in 16% of cases
Impact Periastron ~tens of AU
Vbin=15 km/s, Vsing=30 km/s
Abin=4 AU, Egrav~ erg
After 50yrs from the encounter
After 500yrs from the encounter
Goddi et al. submitted
Egrav bin=5x1047erg
Ekin BN+I=2x1047erg
EH2-flow=4x1047erg
-The main problem is to avoid the intruder and the more massive companion to stick together in a new binary and eject the low-mass companion M binary required to avoid swapping of low-mass companion
-The “hardening” of the binary would provide enough energy to account for the kinetic energy of both runaway stars and the fast H2 outflow
Work in progress
Ongoing N-body simulations to assess effects of stellar encounters on disks
Mdyn cluster ~20M >Mdyn sio ~8M
-dynamical effect of non-gravitational forces?
The “hardening” of the binary would provide enough energy to account for the kinetic energy of both runaway stars and the fast H2 outflow!
; see also Zapata et al. 2009

14. CONCLUSIONS
Source I is the best example of “resolved” accretion/outflow structure in HMSF
Laboratory to test processes (e.g., balance of B, L, G) at high-masses and constrain theories (e.g., disk-wind models)
Evidence of a complex dynamical history in Orion BN/KL
Is BN/KL “non-standard” or is this common in young clusters ? Studies with new EVLA and ALMA needed in other HMSFRs!
2 LESSONS LEARNED
1) Whatever is the actual history of Source I in BN/KL, our detailed study will drive people to figure out the balance of physics in a massive YSO when B, L, G are all at work
2) Is BN/KL “non-standard” or dynamical events common in massive, dense protoclusters?

15. Candidate physical mechanisms driving the disk-wind
Disk Photoionization (Hollenbach et al.1994)
For M*~8 M, an ionized wind is set beyond the radius of the masers:
cs < vesc . Unlikely.
Dust-mediated radiation pressure (Elitzur 1982):
Dust and gas are mixed at R<100 AU: Lmod=105 L, Ṁmod=10-3 M yr-1
Gas-φ SiO. Too little dust. Unlikely.
Line-Driven winds (Drew et al. 1998):
vw≥400 km/s, ρw<<10-14 g cm-3 inconsistent with vmas<30 km/s, ρmas>10-14 g cm-3
MHD disk-winds (Konigl & Pudritz 2000):
Maser features are detected along curved and helical filaments, indicating that
magnetic fields may play a role in launching and shaping the wind
Most likely.

16. Do SiO masers trace physical gas motion?
Supportive evidence:
Two independent kinematic components
Slow evolution of clump morphology
Inconsistent with shock propagation in inhomogeneous medium
Small scatter of centroids about linear proper motions
Consistency of Vlos
Similar appearance over a range of physical conditions
Morphological evolution of individual maser features over 2 yrs