Maser Polarization 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 KVN Single Dish Polarization

Background : Zeeman Effect Occurs when the degeneracy of magnetic substates is broken under the influence of B field Zeeman splitting –~ 10 3 larger in paramagnetic molecules –OH : paramagnetic –SiO, H 2 O, CH 3 OH : 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 B  cos .  : angle between B and maser propagation direction –B field direction Magnetic transitions  m F =  1 give rise to Elliptically polarized components (V ~ B  cos , Q ~ -Bsin 2  ). Polarization vector  B Magnetic transitions  m F = 0 give rise to Linearly polarized components (Q ~ Bsin 2  ). 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 observation H 2 O and methanol maser observations are increasing. SiO maser polarization observations are rare. –Orion IRc2 : magnetic field along the disk (Plambeck+ 2003)

HMSF : OH masers 1.6 GHz, Paramagnetic Trace ~10 5 – 10 8 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| ~ mG at 10 8 – 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 Faraday 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|  n 0.49 over wide density scale B remains partly coupled to the gas up to very dense region. Dynamical importance of B during HMSF process in shaping outflows and jets.

KVN Data Acquisition System 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 –|d LR – d* RL | < 5% (10%) at K (Q) Simultaneous Dual Frequency Polarimetry Lee,S.-S.+ in prep

I/I o V/I Amp(Q+jU)/I Phs(Q+jU) To Do Spectroscopy Polarimetry using DFB+DSM –DFB Quantization Correction, Post Doppler Correction –H 2 O, CH 3 OH Single Dish observations 86, 129GHz Test VLBI Polarization –Multi-epoch H 2 O Calibration Procedure –Noise source –P-Cal System