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Maser P olarization and Magnetic fields during Massive Star Formation. W. H. T. Vlemmings ASP 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 - PowerPoint PPT Presentation
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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 substates 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 com-
ponents (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 follow
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 CabinObservation
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
Sampler
WDMOpticalDMUX
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