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Turbulence, orbits, evolution MERLIN observations of H 2 O masers in outer Galactic SFR S128A

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. S128A. 8-9 kpc (16 from Galactic centre) Haschick & Ho (1985)

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Turbulence, orbits, evolution MERLIN observations of H 2 O masers in outer Galactic SFR S128A

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  1. Turbulence, orbits, evolution MERLIN observations of H2O 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 H2O 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. Spatialcomplexity • Colour - separate region (MERLIN) • Log scale • 1998-1999 • Single-dish blending not serious (at these epochs) in most regions... S Per

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

  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 VLSR

  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 ~ rd-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. Star formation in S128A Bohigas et al. 2003

  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 R3/888 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

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