Beaming in on some stimulating issues in stellar evolution Richards - PowerPoint PPT Presentation

Beaming in on some stimulating issues in stellar evolution Richards (JBO) with thanks to Araya, Babkovskaia, Bains, Bartkiewicz, Cohen, Desmurs, Diamond, Edris, Etoka, Flood, Gledhill, Green, Gray, Harvey-Smith, Hoffman, Imai, Lekht, Hutawarakorn Kramer, Mashadar, Matsuura, Mendoza-Torres, Murakawa, Pestalozzi, Szcerba, Szymczak, van Langevelde, Vlemmings, Yates et al. ● Masers a probes of physical process ● Star formation ● Mass loss from evolved stars ● Supernova remnants ● VLBI as part of multi-scale, multi- λ data ● Thousand-AU filaments ● Zeeman splitting of (almost) everything ● Overdense overmagnetised overexcited clumps ● Silicate-carbon star solved ● SNR shocks

Conditions for Microwave Amplification of Stimulated Emitted Radiation ● Excited state overpopulated with respect to lower state ● Probability ∝ λ 4 - Non-thermal emission ( T B >10 17 K recorded in Orion KL flare) ● Pump usually collisional or radiative (MIR e.g. warm dust) - Depends on transition, typically 10 12 < n <10 16 m -3 , 50< T <2000 K - Cloud collapse, shock fronts, warm dense shielded clumps etc. ● Usually amplifies ambient radiation ( τ < 0) ● Beaming (spatial and spectral) means narrow, bright lines - few µ as < d < 100 mas, 0.3 < ∆ V < 1.0 km s -1 ● Zeeman splitting (if magnetic, typically µ T < B < 0.1 mT) ● Non-paramagnetic (H 2 O, SiO, CH 3 OH) ∆ VZ < ∆ Vth ● Paramagnetic OH can have ∆ VZ > ∆ Vth

Direct evidence – pulsar amplification! ● Pulsed 1720-MHz OH emission towards PSR B1641-45 ( Weisberg+ 05 ) ● H II region G339.1-0.4 in foreground - V LSR -45 km s -1 emission is synchronised with PSR (period 0.5 s) - ∆ V on-pulse 2 km s -1 , off 2-3 km s -1 - Conjugate 1612-MHz absorption behaves similarly - τ -0.05 (i.e. gain 1.05) ● 1665,1667, 1612 MHz absorption deeper on-pulse than off ● Off-pulse lines at -100 to -120 km s -1 not seen on-pulse ● -30 km s -1 lines in absorption on-pulse, in emission off-pulse ● 1665, 1667 MHz absorption non-LTE ratio ● Pulsar beam selects very narrow column with different conditions from average in whole Parkes beam

Spatial beaming

What mases? (in the Milky Way) ● Warm/hot shielded environments ● cm-wave masers from SiO, H 2 O, OH, CH 3 OH, H 2 CO ● Star-forming regions ● Cloud collapse - Molecules sublimed off grains in early stages ● Outflows and discs around (not so) Young Stellar Objects - (Comets not discussed here – resolved out by interferometry) - (Cyclotron masers predicted from WD planets Willes&Wu 05 ) ● Evolved stars ● Circumstellar envelopes of AGB stars and Red Supergiants - Classic 'onion shell' model is sprouting... - PPNe and biconical/bipolar outflows ● (mm-wave masers e.g. SiS ( Fonfr í a Exp ó sito+06) , HCN, CO) ● Supernova Remnants

Masers get everywhere ● SiO masers: velocity, distance, evolution etc. ● 5/14 RSG in Scutum star cluster ( Nakashima+ 06 ) ● 5 bulge/disc globular clusters ( Matsunaga+06 ) - First masers from M ⊙ stars now ( t = 10 Gy) on AGB? ● Following V838 Mon 2002 nova-like eruption ( Deguchi+05 ) - SiO seen in photosphere reaches 1.6 R ✸ at 20 km s -1 ● A few rare C ✸ with silicate dust have H 2 O masers ● MERLIN obs V778 Cyg ( Szcerba+ 06; Babkovskaia+ 06 ) - Phase-referenced; maser:C ✸ separation ≈ 75 AU - Disc gradient ≈ 0.3 km s -1 AU -1 - 0.06 < M companion ≲ few M ⊙ Lower limit from Keplerian rotation; upper from stellar evolution ● - Masers in warped disc around main-sequence companion - Captured from O-rich stage of primary >> 15 yr ago Silicate features, H 2 O masers observed since 1990 or earlier ● - Model suggests large ( µ m) dust grains – accretion in disc?

V778 Cyg C ✸ with H 2 O masers C ✸ V778 Cyg H 2 O masers colour - V LSR

V778 Cyg C ✸ with V LSR v. major axis H 2 O masers C ✸ V778 Cyg H 2 O masers colour - V LSR

V778 Cyg C ✸ with H 2 O masers C ✸ V778 Cyg Location of C ✸ H 2 O masers wrt masers colour - V LSR

V778 Cyg m=2 warped disc C ✸ with Babkovskaia H 2 O masers

Low as well as high mass starformation ● High-mass YSOs rapidly excite molecular environment ● Widespread detection of bright H 2 O, CH 3 OH masers ● Weak methanol masers found towards outer lobes of outflows in lowish-mass SFR NGC 1333 ( Kalenski ĭ + 06 ) ● 44-GHz and higher class 1 masers (collisionally pumped?) ● Class 0 low-mass YSO have H 2 O masers ( Furuya+ 01, 03 ) ● VLBI monitoring suggests interaction with medium or disc ( Moscadelli+ 05 )

Low as well as high mass starformation ● High-mass YSOs rapidly excite molecular environment ● Widespread detection of bright H 2 O, CH 3 OH masers ● Weak methanol masers found towards outer lobes of outflows in lowish-mass SFR NGC 1333 ( Kalenski ĭ + 06 ) ● 44-GHz and higher class 1 masers (collisionally pumped?) ● Class 0 low-mass YSO have H 2 O masers ( Furuya+ 01, 03 ) ● VLBI monitoring suggests interaction with medium or disc ( Moscadelli+ 05 )

Methanol/OH disc around 5 M ⊙ YSO ● IRAS20126+4104 ( Edris+ 05 ) ● Class II 6.7 GHz methanol ● 1665 MHz OH ● Black contours ● Radiocontinuum jet ● Masers trace ~800-AU disc orthogonal to jet ● Keplerian rotation, enclosed mass 5 M ⊙

Methanol and OH ● W3(OH) 3100 AU filament ● OH 6.0 GHz - Etoka+ 05 ● OH 4.7 GHz ● Methanol 6.7 GHz

Methanol and OH ● W3(OH) 3100 AU filament ● OH 6.0 GHz - Etoka, Cohen, Gray 05 (MERLIN) ● OH 4.7 GHz contours ● Methanol 6.7 GHz contours - Harvey-Smith & Cohen 05,06 (M) - 12 GHz similar ( Moscadelli+ 02, V) ● Red symbols ground-state OH - Wright+ 04 (VLBI) ● 13.4 GHz OH ( Baudry+Diamond98 ) ● Position accuracy of a few AU ● MERLIN sensitive up to 1000 AU ● Overall V LSR grad.120 km/s/pc ● CH 3 OH filiament 4990 km/s/pc over 380 AU against UCH II - Disc? Shock?

Methanol and OH ● OH copropagation models ● 6, 1.6 GHz mainlines associated - 50-75 K ● 4.7, 1.7 GHz associated - >100 K, higher n OH ● ≿ 15 mas OH ⇔ CH 3 OH ● Why not exact coincidence? ● 1.6 GHz OH quenched at lower nT than CH 3 OH Szymczak+ 04 ● CH 3 OH needs deeper N - Inversion survives higher nT than 1.6 GHz OH ( Szymczak+ 04 ) - but velocity dispersions similar ● CH 3 OH evaporates before OH - Regional chemical differences likely

Water filament tracing cloud collision? ● S128 SFR ● ~17 kpc from Gal. centre - Outside spiral density waves - No local SNe history ● Colliding CO clouds ● H 2 O in 3 regions imaged by MERLIN 98, 99 ● Some close to UCH II ● Some trace jet bow-shocks ● But also 900-AU filament with parallel companion - 15 km/s velocity dispersion - Possible 'proper motion' 100 km/s: pattern speed? - Distinctive fractal scales ● H 2 O traces CO cloud shock?

Water filament tracing cloud collision? ● S128 SFR ● ~17 kpc from Gal. centre - Outside spiral density waves - No local SNe history ● Colliding CO clouds ● H 2 O in 3 regions imaged by MERLIN 98, 99 ● Some close to UCH II ● Some trace jet bow-shocks ● But also 900-AU filament with parallel companion - 15 km/s velocity dispersion - Possible 'proper motion' 100 km/s: pattern speed? - Distinctive fractal scales ● H 2 O traces CO cloud shock?

Shock in Mira U Ori ● H 2 O masers MERLIN 4 epochs ● Similar extent (30-40 AU), V peak ● Drastic changes in 1994 ● Apparent angle of shell elongation ● Relative positions of red/blue components ● Many bright maser spots have larger measured sizes ● s ∝ T B (-1 - -2) in other AGB stars ● Not consistent with beaming from spherical cloud 1999 ● Shocked slab? ● Strong complex circular polarization (B~0.35 T) ( Vlemmings et al 2005 ) (VLBA) ● Stellar shock compression ?

Shock in Mira U Ori ● H 2 O masers MERLIN 4 epochs ● Similar extent (30-40 AU), V peak ● Drastic changes in ● Apparent angle of shell elongation ● Relative positions of red/blue components ● Many bright maser spots have larger measured sizes ● s ∝ T B (-1 - -2) in other AGB stars ● Not consistent with beaming from spherical cloud ● Shocked slab? ● Strong complex circular polarization (B~0.35 T) ( Vlemmings et al 2005 ) (VLBA) ● Stellar shock compression ?

Shocking bipolarity ● PPN OH 17.7-2.0 ● MERLIN OH1612 ( Bains+ 03 ) ● Monitoring shows flare Szymczak ● EVN: interaction with 600 600 600 outflow at PA 10 ° Radial offset (mas) ● Similar angle from IR 400 400 400 polarimetry ( Gledhill 05 ) 200 200 200 0 0 0 45 45 45 50 50 50 55 55 55 60 60 60 65 65 65 70 70 70 75 75 75 − 1 ) V elocity (kms

Zijlstra et al. 2002 ● Interaction of lighter wind with equatorial density enhancement ● Chimney effect? ( Icke, Mellema ) ● No disc, no rotation required!

S Per (Red Supergiant) ● MERLIN H 2 O ( Richards+ 99 ); VLBI OH mainline (contours) ● MERLIN OH polarization

S Per (Red Supergiant) ● MERLIN H 2 O ( Richards+ 99 ); VLBI OH mainline (contours) ● MERLIN OH polarization ● Circular polarization ⇒ B ‖ ● Strength in µ T ● Linear polarization vector at PolA ● If θ > 55 °, PolA ‖ B ⊥ ● else PolA ⊥ B ⊥ ● ∆ PolA typically 16 o per clump ● Faraday rotation? ● fractional ionisaton ≤~ 10 -6 ● Linear pol seen from near side only ● Pol. from far side scrambled? ● But conflicting theories B ⊥ ● Inferred B ‖ strength B B ‖ ● PolA varies with path length θ ● ISM Faraday rotation