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

• f Stimulated Emitted Radiation
• Excited state overpopulated with respect to lower state
• Probability ∝ λ4
• Non-thermal emission (TB >1017 K recorded in Orion KL flare)
• Pump usually collisional or radiative (MIR e.g. warm dust)
• Depends on transition, typically 1012<n<1016 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 µas < d < 100 mas, 0.3 < ∆V < 1.0 km s-1
• Zeeman splitting (if magnetic, typically µT < B < 0.1 mT)
• Non-paramagnetic (H2O, SiO, CH3OH) ∆VZ < ∆Vth
• Paramagnetic OH can have ∆VZ > ∆Vth

Direct evidence – pulsar amplification!

• Pulsed 1720-MHz OH emission towards PSR B1641-45

(Weisberg+ 05)

• HII region G339.1-0.4 in foreground
• VLSR -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, H2O, OH, CH3OH, H2CO
• 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 (Fonfría Expósito+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 H2O 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 < Mcompanion ≲ 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, H2O masers observed since 1990 or earlier
• Model suggests large (µm) dust grains – accretion in disc?

V778 Cyg C✸ with H2O masers

C✸ V778 Cyg H2O masers colour - VLSR

V778 Cyg C✸ with H2O masers

C✸ V778 Cyg H2O masers colour - VLSR VLSR v. major axis

V778 Cyg C✸ with H2O masers

C✸ V778 Cyg H2O masers colour - VLSR Location of C✸ wrt masers

V778 Cyg C✸ with H2O masers

m=2 warped disc Babkovskaia

Low as well as high mass starformation

• High-mass YSOs rapidly

excite molecular environment

• Widespread detection of bright

H2O, CH3OH masers

• Weak methanol masers found

towards outer lobes of

• utflows in lowish-mass SFR

NGC 1333 (Kalenskiĭ+ 06)

• 44-GHz and higher class 1

masers (collisionally pumped?)

• Class 0 low-mass YSO have

H2O 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

H2O, CH3OH masers

• Weak methanol masers found

towards outer lobes of

• utflows in lowish-mass SFR

NGC 1333 (Kalenskiĭ+ 06)

• 44-GHz and higher class 1

masers (collisionally pumped?)

• Class 0 low-mass YSO have

H2O 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
• rthogonal to jet
• Keplerian rotation, enclosed

mass 5 M⊙

• 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 VLSR grad.120 km/s/pc
• CH3OH filiament 4990 km/s/pc
• ver 380 AU against UCHII
• Disc? Shock?

Methanol and OH

Methanol and OH

• OH copropagation models
• 6, 1.6 GHz mainlines associated
• 50-75 K
• 4.7, 1.7 GHz associated
• >100 K, higher nOH
• ≿15 mas OH ⇔ CH3OH
• Why not exact coincidence?
• 1.6 GHz OH quenched at lower

nT than CH3OH Szymczak+ 04

• CH3OH needs deeper N
• Inversion survives higher nT than

1.6 GHz OH (Szymczak+ 04)

• but velocity dispersions similar
• CH3OH 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
• H2O in 3 regions imaged by

MERLIN 98, 99

• Some close to UCHII
• 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
• H2O 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
• H2O in 3 regions imaged by

MERLIN 98, 99

• Some close to UCHII
• 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
• H2O traces CO cloud shock?

1994

Shock in Mira U Ori

1999

• H2O masers MERLIN 4 epochs
• Similar extent (30-40 AU), Vpeak
• Drastic changes in
• Apparent angle of shell

elongation

• Relative positions of red/blue

components

• Many bright maser spots have

larger measured sizes

• s ∝TB

(-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 ?

Shock in Mira U Ori

• H2O masers MERLIN 4 epochs
• Similar extent (30-40 AU), Vpeak
• Drastic changes in
• Apparent angle of shell

elongation

• Relative positions of red/blue

components

• Many bright maser spots have

larger measured sizes

• s ∝TB

(-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

45 50 55 60 65 70 75 200 400 600 45 50 55 60 65 70 75 200 400 600 45 50 55 60 65 70 75 200 400 600

Radial offset (mas) V elocity (kms

−1 )

• PPN OH 17.7-2.0
• MERLIN OH1612

(Bains+ 03)

• Monitoring shows

flare Szymczak

• EVN: interaction with
• utflow at PA 10°
• Similar angle from IR

polarimetry (Gledhill 05)

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 H2O (Richards+ 99); VLBI OH mainline (contours)
• MERLIN OH polarization

S Per (Red Supergiant)

• MERLIN H2O (Richards+ 99); VLBI OH mainline (contours)
• MERLIN OH polarization
• Circular polarization ⇒ B‖
• Strength in µT
• Linear polarization vector at PolA
• If θ > 55°, PolA ‖ B⊥
• else PolA ⊥ B⊥
• ∆PolA typically 16o per clump
• Faraday rotation?
• fractional ionisaton ≤~10-6
• Linear pol seen from near side only
• Pol. from far side scrambled?
• But conflicting theories
• Inferred B‖ strength
• PolA varies with path length
• ISM Faraday rotation

θ

B B⊥ B‖

• OH 1612 polarization

vectors

• Dipole magnetic field
• Axis p.a. ~20o
• S approaching
• (Szymczak+)

VX Sgr OH/H2O consistent symmetry

• OH 1612 polarization

vectors

• Dipole magnetic field
• Axis p.a. ~20o
• S approaching
• (Szymczak+)
• H2O ~spherical

(Murakawa+ 03)

• Lower density bicone

(▲ ● ), similar axis

VX Sgr OH/H2O consistent symmetry

• OH 1612 polarization

vectors

• Dipole magnetic field
• Axis p.a. ~20o
• S approaching
• (Szymczak+)
• H2O ~spherical

(Murakawa+ 03)

• Lower density bicone

(▲ ● ), similar axis

VX Sgr OH/H2O consistent symmetry

• VLBA H2O Zeeman

splitting model Vlemmings et al 05

A preferred axis without rotation?

• At high resolution most CSE show some axisymmetry
• No evidence for rotation in wind down to < km/s
• Maser polarization: magnetic field energy ~ kinematic energy
• But what is dynamo without stellar surface rotation?
• Blackman+ 01: α−ω dynamo?
• Differential rotation in layers, fast core, convection
• Dipole field in wind channels dust grains?
• But how transport B but not ω?
• Dust clumps more accelerated than less dusty OH regions
• Dust in CSE hotter than gas so Greenstein-Whittet effect doesn't work
• Soaker & Zoabi 02 : α2 turbulent dynamo
• Not enough to influence whole wind – unless also weak dipole
• Hartquist+ : Field frozen into clumps
• AGB stars have rotatingWD core – but RSG don't!
• Low mass companions to low-mass stars?
• Debris discs around high-mass stars?

• 34 - -46 km/s

Evidence for clumps

• S Per H2O sub-sonic 5-year drift

(MERLIN)

• Spectral

peak at VLSR

• f clump in

1994, 1999

• Vanishes in

1995-6 (Lekht+05)

• Accident of

excitation or beaming?

Evidence for density-bounded clumps

• Direct measurement of H2O cloud sizes
• MERLIN detects 85-100% emission
• Each cloud <1 – few velocity coherence lengths (∆Vth)
• 〈R(H2O clouds)〉~ R (Miras~1 AU, RSG ~10 AU)
• Maser conditions, mass loss rates ⇒ n(H2O cloud) ~50x n(OH gas)
• Maser emission survives ~Rcloud/cs (Miras <yr, RSG decades)
• Identifiable patterns, accelerating expansion proper motions
• Actual clouds must survive shell crossing time – 10-100 yr
• BOH ~ 0.2BH2O at same distance from star
• Frozen-in B ∝n~0.3 - 0.5 (Mouschouvias 87)
• Extrapolate BOH to PPNe stellar surface: sub-Tesla field
• Consisent with direct measurement of B (Jordan+ 05)

SFR density/magnetic field differentials

• Cep A H2O ring traced by

Gallimore+03 (MERLIN)

SFR density/magnetic field differentials

• Cep A H2O ring traced by

Gallimore+03 (MERLIN)

• Polarization measured by

Vlemmings+06 (VLBA)

• 25-65 µT
• PolA 90°change in SE

suggests θ~55°

• But small-scale B||

reversals – shock compression

• T~1150 K, decelerated

expansion, indicates stationary C-type shock

• Nearby H2O maser n, B

enhanced wrt OH (Bartkewiecz+05) consistent with shock

Detailed studies of SNR

• W28 (Hoffman+05)
• MERLIN, VLBA 1720 MHz
• 1-pc maser arc
• Aligned with shock front

(radio continuum)

• Full polarization
• Maser and synchrotron
• pol. angles consistent
• Well-ordered magnetic field
• OH in post-shock CO arc
• Similar results for W44
• but PolA || synchrotron B
• B close to critical angle?

Detailed studies of SNR

• W28 (Hoffman+05)
• MERLIN, VLBA 1720 MHz
• 1-pc maser arc
• Aligned with shock front

(radio continuum)

• Full polarization
• Maser and synchrotron
• pol. angles consistent
• Well-ordered magnetic field
• OH in post-shock CO arc
• Similar results for W44
• but PolA || synchrotron B
• B close to critical angle?

Future developments

• Interferometric follow-up of Galactic Plane surveys
• More phase-referenced VLBI (including VERA)
• Align epochs, different species
• Parallax e.g. U Her OH (Vlemmings), UX Cyg H2O

(Kurayama+05)

• eVLBI/e-MERLIN
• Faster follow-up of flares etc.
• Less correlator restrictions
• Wide band, narrow channels, full polarisation, wide field...
• Star + SiO + water at 22 + 43 GHz
• Resolve mass loss from stellar surface
• Track clumps over several years through dust formation region
• Carry on up the spectrum – ALMA, VLTI...
• Data mining – is red peak of OH mainlines in CSE

systematically flatter?

JAMES I

Futures

• Follow-up of Galactic

Plane surveys

• Associated with

CORNISH (HII @ 5 GHz), GLIMPSE etc.

• Methanol Multi Beam:

first full survey of Galactic Plane with Parkes & Lovell

• 469 detections so

far, 200 new

• Many on far side of

Galaxy, furthest at 19.6 kpc from Sun

• ATCA and/or

MERLIN follow-up of 125 sources to date

Find the star!

Find the star!

α Ori MERLIN+VLA 5GHz VLA 43 GHz Morris et al.

Central dust disc in OH231

• MIDI 8-13.5 µm

(Matsuura+ 06)

• Baseline angles

OB1, OB4

• 40-50 AU disc/ring
• Circumbinary?
• Silicate absorption
• Only blue-shifted

OH detected

• Resolved out?
• Strong scattering

screen?

• Ionised outflow