1. Turbulence, orbits, evolution MERLIN observations of H 2 O masers in outer Galactic SFR S128A Anita Richards, AVO/JBO Evgueni Lekht, Eduardo Mendoza-Torres, INAOEP Jim Cohen, Matt Crocker, JBO Vladimir Samodourov, LPI

2. S128A ● 8-9 kpc (16 from Galactic centre) ● Haschick & Ho (1985) ● Colliding CO ● 2 HII regions ● 2 H 2 O masers ● 2+ IR sources S Per

3. Monitoring ● Puschino 22-GHz since 1955 ● Relatively stable ● Three main features ● MERLIN 1998, 1999 ● <10 mas resolution ● FoV ~ primary beam! ● ~50-mas absolute astrometry S Per

4. Spatial complexity ● Colour - separate region (MERLIN) ● Log scale ● 1998-1999 ● Single-dish blending not serious (at these epochs) in most regions... S Per

5. Line drifts ● SD peak blueshifts ~-0.1 km/s/yr ● Resolved - similar ● All regions ● -0.5 km/s/yr B1 B2 B3 B5 B4

6. Variability ● Unsaturated maser DV-2 ~ ln F0 ● Brightening - steep narrowing - pump rate increases? ● Dims again - shallower re- broadening - near saturation as pump rate falls? ● Why?

7. New maser region ● C - several arcsec from suggested CO front

8. Maser motions B ● Brightest r ~3 au, no systematic shift ● Centroid shifts 3 mas to ESE - 100 km/s???

9. Maser structure A ● Features seen in 1998, 1999 in A2 ● Individual clouds have linear structure ● No systematic velocity gradient ● ~15 km/s range of V LSR

10. Colliding clouds CO clouds collide in 3 dimensional space.. Cloud nearer us must be pushing back on background cloud Hence blue-shifted acceleration of masers? About half of 1998 maser features have 1999 matches No systematic proper motions Mostly undetectable (1 mas/yr ~ 50 km/s) Apparent 100 km/s shift probably pattern speed e.g. compression wave going past? Heating/shock compression - masers seen if at favourable angle? Any evidence for turbulence?

11. Compressible &/or chaotic ● Line shifts and time-variability give Strouhal No <<1 (Lekht et al. 1999) for 1 au clouds ● Consistent with compressible or chaotic turbulence on scales up to 300 au ● MERLIN shows cloud radii 3 - 150 au ● Strelnitski et al. 2002 - fractal analysis ● Number density non-integer function of volume ● Approximate by s = dM/dV ~ r d-d0 ● d0 = 2 for 2D projection, d is fractal dimension ● d = d(log s )/d(log r ) + d0 ● Measure average surface density s for increments of spot separation r

12. Strelniski examples

13. S128A ● Line shifts and time-variability give Strouhal No <<1 ● Mean slope d(log s )/d(log r ) = -1.77 (0.04) = d - d0 ● d0 = 2 ● d = 0.23 (0.04)

14. Bohigas et al. 2003 Star formation in S128A

15. Masers and hot cores? ● Previously, IR nebulosity N0 close to masers A ● N2 close to maser region B ● Now maser region C found close to N3! ● Any direct association of masers with YSO? ● Need to investigate potential outflows ● Any masers in discs? ● look for large linear velocity gradient ● One candidate ● M* ~ (dVlsr/dR) 2 x R 3 /888 Msun (Vlsr km/s, R au) ● dVlsr/dR = 0.437(0.044) km/s/au, R=47(12) au ● M* = 22(3) Msun if edge-on, Keplerian ● More likely just a Gaussian cloud????

16. Disc candidates