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
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 10-1000 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
The closest massive SFR: Orion BN/KL D = 4186 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?
A High Density Protocluster in BN/KL HST/Nic H2 P[FeII] 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! Schultz et al. 1999 Source I BN 1” IRc2 Greenhill et al. 2004 7mm - VLA Source I • Obscured up to 22 μm (AV ≥300) • Ionized disk with R~40 AU (λ7mm) 12.5um, Keck (θ≈0.5”) Reid et al. 2007; Goddi et al. submitted Source I is a luminous, massive, embedded YSO
The case of the high-mass YSO “Source I” in Orion BN/KL Collection of λ7mm observations of Source I at R<1000 AU SiOv=0 J=1-0 (VLA) T~1000 K, n< 107 cm-3 λ7mm cont (VLA) T=104 K SiOv=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 Dataset Transition Instrument Observations Resolution 28SiO (v=1,2 J=1-0) VLBA 35 epochs over 2001-03 0.1 AU 28SiO (v=0 J=1-0) VLA 5 epochs in 10 yrs 25-100 AU 7 mm continuum VLA 3 epochs in 8 yrs 25 AU
Radio Source I drives a “Low-Velocity” NE-SW outflow 7mm SiOv=0+H2O 1.3cm (VLA ) 18 km/s Dec (arcsec) 500 AU Proper motions ofSiO maser spots over 4 epochs RA (arcsec) 100 AU<R<1000 AU Greenhill, Goddi, et al., in prep.
Long-term VLBA imaging study of Source I Integrated Intensity over time SiOv=1,2 1010±1 cm-3 1000-3000 K O(1000) Jy km s-1 peak T=21 months, ΔT~1 month R<100 AU Isolated Features North Arm West Arm Eastern Bridge Dark Band East Arm Western Bridge Streamers South Arm Matthews, Greenhill, Goddi, et al. 2010 ApJ,708, 80
Time-series of VLBA moment 0 images of SiOv=1,2 masers over 2 years IntegratedIntensityepoch-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. 2010 ApJ,708, 80 R<100 AU Matthews, Greenhill, Goddi, et al. submitted
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 • VLOS rotation • NE / SW axis • red/blue arms • declining rotation curve • ∇VLOS in bridge Role of magnetic fields from curvature of p.mo trajectories Matthews, Greenhill, Goddi, et al. submitted
Model of Source I R =10-100 AU R=100-1000 AU Toy-model • Collimated outflow at v~20 km s-1 • => v=0 SiO maser proper motions • 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 • Resolved the launch/collimation region of outflow • Identified a good example of disk-mediated accretion
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”) ONC-absolute p.mo. P.mo of BN relative to I BN VBN≈26 km/s Greenhill et al. 2004 I VI≈15 km/s 2” Smin(BN-I)=0.11”±0.18”, Tmin(BN-I)=550±10 yr 500 years ago BN and I were as close as 50-100 AU! Goddi et al.submitted See also Gomez et al. 2008
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 Which are mass and orbit of the binary? • 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 Source I is a massive (20M) and tight (<10 AU) binary Adapted from Reipurth 2000 Goddi et al. submitted; see also Gomez et al. 2008
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 After 50yrs from the encounter 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~5 1047 erg I Egrav bin=5x1047erg Ekin BN+I=2x1047erg EH2-flow=4x1047erg After 500yrs from the encounter • Work in progress • Ongoing N-body simulations to assess effects of stellar encounters on disks • Mdyn cluster ~20M>Mdynsio ~8M • -dynamical effect of non-gravitational forces? BN I The “hardening” of the binary would provide enough energy to account for the kinetic energy of both runaway stars and the fast H2 outflow! Goddi et al. submitted ; see also Zapata et al. 2009
CONCLUSIONS • Source I is the best example of “resolved” accretion/outflow structure in HMSF • Laboratory to test processes (e.g., balanceofB, L, G) at high-massesand constraintheories (e.g., disk-windmodels) • 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!
Candidate physical mechanisms driving the disk-wind • Disk Photoionization(Hollenbachet al.1994) • For M*~8 M, an ionized wind is set beyond the radius of the masers: • cs < vesc . Unlikely. • Dust-mediatedradiationpressure(Elitzur 1982): • Dust and gas are mixed at R<100 AU: Lmod=105 L, Ṁmod=10-3 M yr-1 • Gas-φSiO. Too little dust.Unlikely. • Line-Drivenwinds(Drew et al. 1998): • vw≥400 km/s, ρw<<10-14g cm-3 inconsistentwithvmas<30 km/s, ρmas>10-14g cm-3 • MHD disk-winds(Konigl & Pudritz 2000): • Maser features are detectedalongcurved and helicalfilaments, indicatingthat • magneticfieldsmay play a role in launching and shaping the wind • Most likely.
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 Morphologicalevolutionofindividual maser featuresover2yrs