Maser Polarization and Magnetic fields during Massive Star Formation W. H. T. Vlemmings ASP...
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Transcript of Maser Polarization and Magnetic fields during Massive Star Formation W. H. T. Vlemmings ASP...
Maser Polarization and Magnetic fields during Massive Star Formation
W. H. T. VlemmingsASP Conference Series, Vol. 387, 2008
Do-Young Byun
Outline
• Theoretical Background– Zeeman Effect– Para- and non-paramagnetic Species
• Observational results on HMSF– OH, H2O, Methanol
• Summary• KVN Single Dish Polarization
Background : Zeeman Effect
• Occurs when the degeneracy of magnetic sub-states is broken under the influence of B field
• Zeeman splitting– ~ 103 larger in paramagnetic molecules – OH : paramagnetic– SiO, H2O, CH3OH : non-paramagnetic
– Z > D for paramagnetic case• Z : Zeeman splitting, D : Doppler Line Width
– Z < D for non-paramagnetic case
Large Zeeman Splitting : paramagnetic species
• Z > D : no theoretical ambiguity– Zeeman components are well separated and resolved.
No significant influence on each other.
– B field Strength• Observed splitting directly gives Bcos.• : angle between B and maser propagation direction
– B field direction• Magnetic transitions mF = 1 give rise to Elliptically polarized
components (V ~ Bcos, Q ~ -Bsin2). Polarization vector B• Magnetic transitions mF = 0 give rise to Linearly polarized
components (Q ~ Bsin2). Polarization vector || B
• Z < D : Complex – B field direction
• < crit ~ 55, Polarization vector || B
• > crit ~ 55, Polarization vector B• 90 flip of EVPA• Cannot directly determine B field direction
– B field strength • B field strength depends on circular pol. fraction
and maser saturation level.• need to know saturation level
Small Zeeman Splitting : non-paramagnetic species
Observational Results on High Mass Star Formation
• Most information on small scale magnetic field information has come from OH maser observa-tion
• H2O and methanol maser observations are in-creasing.
• SiO maser polarization observations are rare.– Orion IRc2 : magnetic field along the disk (Plam-
beck+ 2003)
HMSF : OH masers
• 1.6 GHz, Paramagnetic• Trace ~105 – 108 cm-3 density region• direct measurement of |B|
– |B| ~ 1mG , up to ~40mG (Fish&Reid 2007)
• Observation toward Cep A (Bartkiewicz+ 2005) – The B direction derived from circular pol. seems to fol-
low ambient B-field, not outflows
• B field measurements using 6 and 13GHz OH maser– Consistent with 1.6GHz measurements– Suffer less from Faraday Rotation than 1.6GHz
HMSF: H2O masers• First discovery of H2O Zeeman
splitting with single dish (Fiebig & Gusten 1989)
• High resolution circular pol.– Typically, |B| ~ 15-150mG at
108 – 1011 cm-3
– |B| ~ 650mG in Cep A HW2 (Vlemmings+ 2006b)
• Linear Pol– Typically 2%– Rapid change in direction over
small scale
HMSF: 6.7GHz Methanol masers
• Pol. observations of the 6.7G and 12G masers are rare.– Polarization fraction ~ 1.5% – First 6.7GHz polarization map
of W3(OH) (Vlemmings+ 2006c)
– Better probes of B direction than OH because of less Fara-day rotation
– Difficult to determine |B| due to Small Zeeman Splitting
Pol. Map of W3(OH)- Methanol : Contours and Black lines- OH : Triangles and Red lines
HMSF: mm Methanol masers
• Lin. Pol. fraction of up to 40% using IRAM 30m. (Wiesemeyer+ 2004)– Lin. Pol detection : 10/14 (Class I), 3/7 (Class II)– Cir. Pol detection towards 2 Class I sources
HMSF: Summary
• |B| n0.49 over wide density scale
• B remains partly coupled to the gas up to very dense re-gion.
• Dynamical importance of B during HMSF process in shap-ing outflows and jets.
Receiver Cabin
Observation Building
43 GHz FE
22 GHz FE
Down Con-
verter
Down Con-
verter
Receiver system DAS Clock Field system
GUI
Control PC
1 pps Distributor
100 MHz Distributor
10 MHz Distributor
10 MHz Distributor
1 pps Distributor
5 MHz
10 MHz
100 MHz
1 pps
1.4 GHz
ClockSystem
H-maser
GPS
Digital O/E
WDMOptical
MUX
DigitalE/O
Sampler
SamplerWDM
OpticalDMUX
DigitalSpectro-meter
Mark5B
DIR-1000
DigitalFiltersDown
Con-verter
Down Con-
verter
Sampler
Sampler
LCP
RCP
StokesI,Q,U,V
KVN Data Acquisition Sys-tem
• 4 Samplers– 4 Receiver Outputs with 512MHz bandwidth– 2bit quantization
• Digital Filter Bank (DFB)– 16x16MHz Streams :– Total Band Width : 256MHz bandwidth
• E.g. 1x256MHz, 2x128MHz, 4x64MHz, 8x32MHx, 16x16MHz
• Digital Spectrometer (DSM)– FX Type Correlator– Auto and Cross Power Spectrum– Wide : 4x512MHz Streams– Narrow : Max 8 streams w/ 4K channels
Continuum Observation
• Polarization Observation at K and Q– 3C454.3 Monitoring– MFPOL (Multi-Freq Polarization Observation)– MOGABA (Monitoring of Gamma-ray Bright AGN)
• Sensitivity of Linearly Polarization Flux– |Q+jU| ~10mJy (~15mJy) at K(Q) for 15 min obs.
• Phase Stability– Random Error < 0.2 (0.3) deg at K (Q)– Systematic Error < 2 deg at K/Q
• Instrumental Cross Pol– |dLR – d*RL| < 5% (10%) at K (Q)
• Simultaneous Dual Frequency Polarimetry Lee,S.-S.+ in prep
I/Io V/I
Amp(Q+jU)/I Phs(Q+jU)
To Do• Spectroscopy Polarimetry using DFB+DSM
– DFB Quantization Correction, Post Doppler Correc-tion
– H2O, CH3OH Single Dish observations
• 86, 129GHz Test • VLBI Polarization
– Multi-epoch H2O
• Calibration Procedure– Noise source– P-Cal System