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1 mm Polarization Science with CARMA

1 mm Polarization Science with CARMA. Chat Hull UC Berkeley, Radio Astronomy Laboratory Collaborators: Dick Plambeck , Greg Engargiola , & all the CARMA staff 12 October 2011 NSF Reverse Site Visit Washington, DC. 1 mm Polarization: Science Goals. Magnetic-field morphology in Class 0s

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1 mm Polarization Science with CARMA

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  1. 1 mm Polarization Science with CARMA Chat Hull UC Berkeley, Radio Astronomy Laboratory Collaborators: Dick Plambeck, Greg Engargiola, & all the CARMA staff 12 October 2011 NSF Reverse Site Visit Washington, DC

  2. 1 mm Polarization: Science Goals • Magnetic-field morphology in Class 0s • B-field vs. outflow direction • Using dust polarization and Goldreich-Kylafis effect • Polarization variability in Sgr A* • Probing time-variable accretion onto central BH • Collaborator interests • MHD turbulence

  3. 1 mm Dual-polarization Receivers SIS mixers Orthomode transducer Waveguide circular polarizer WBA13 I.F. amplifiers (1-9 GHz) 1 inch

  4. Hardware Testing

  5. Hardware Testing

  6. Calibration: Beam Polarization Percentage Position Angle

  7. Calibration: XY Phase

  8. First Results: NGC 1333-IRAS 4A

  9. First results: L1157

  10. CARMACombine Array for Research in Millimeter-wave AstronomyConsortium: Berkeley, Caltech, Illinois, Maryland, Chicago • Attributes • 6 ⨯10-m, 9 ⨯ 6-m, 8 ⨯ 3.5-m telescopes • Observations at 1mm, 3mm, and 1cm • Located in Cedar Flat, CA (near Bishop) • Science goals • Molecular emission in galaxies • Galaxy clusters • Protoplanetary debris disks • Dust polarization in star-forming regions

  11. Credit: Bill Saxton, Harvard-Smithsonian Center for Astrophysics

  12. First Target: NGC 1333 IRAS 4A CARMA observations SMA observations Girart+ 2006 • We want to search for “hourglass” shape of the B-field structure in the circumbinaryenvelope

  13. Class 0 Dust Polarization Credit: NASA, ESA, STScI,J. Hester and P. Scowen (Arizona State University)

  14. Why observe polarization? • B-fields play an important role in star formation • How important? • Are they strong (& ordered)? • Are they weak (& chaotic)? • B-fields  polarization • Dust grains align their spin axes with B-fields • Dust emission is strong at 1 mm

  15. How do we make it work? Grad student

  16. Turnstile-junction OMT 1 cm Navarrini & Plambeck 2006, IEEE-MTT, 54, 272-277

  17. OMT construction

  18. Unequal sidearm lengths in OMT can cause resonances (simulation)

  19. OMT tests at 4K(passbands, LO = 210-255 GHz in 1 GHz steps) OMT15 (good) OMT10 (bad)

  20. Polarizer construction Copper electroplated onto mandrel Aluminum mandrel Machined Soldered into waveguide flange 1 inch

  21. Final design: 2-section polarizer λ/2 retarder at 15° λ/4 retarder at 74.5° 0.047’’ diameter facets 0.006’’ deep

  22. XY  RL Sky Receiver

  23. Sample polarizer test data(mandrel machining errors) Fraction of linear radiation converted to RCP and LCP

  24. Polarization calibration • Two main steps to calibrate a polarimeter: • XY phase • The absolute phase offset between the RCP and LCP receivers of an antenna • Leakage terms • The fraction of LCP radiation detected in the RCP receiver, and vice versa

  25. XY phase calibration • How do we find an antenna’s XY phase? • Observe a strongly polarized source with known position angle • These don’t exist at mm wavelengths • We create our own by observing broadband noise from the ambient load through a wire-grid polarizer!

  26. XY phase calibration SKY (~60 K) WIRE-GRID POLARIZER AMBIENT LOAD (300 K) FEED HORN

  27. RF = 210 – 270 GHz IF = 1 – 9 GHz Baseband = 0.5 – 1.0 GHz τ2 1 mm signal path τ1 τ3,hi 10 GHz mixer Baseband mixer RF mixer 1– 5 GHz 5 – 9 GHz To digitizer, filter, & correlator 0.5 – 1.0 GHz 1 – 9 GHz RCP τ4 τ3,lo 1– 5 GHz LO 2 NOISE FILTER FILTER FILTER FILTER FILTER FILTER Feed horn Polarizer 1.75 – 4.25 GHz Correlated Noise Source All phases flat OMT Block downconverters 8-way splitters 1– 5 GHz 5 – 9 GHz To digitizer, filter, & correlator 0.5 – 1.0 GHz LCP 1 – 9 GHz 1– 5 GHz

  28. Status/conclusions • Dual-polarization receivers are installed on all 15 6- and 10-m telescopes • Full-Stokes (LL, LR, RL, RR) system is working • Observed NGC 1333-IRAS 4A as a commissioning test • XY phase offset is well understood • Leakages need to be determined better • Will soon install new Berkeley-made polarizers • Full-Stokes commissioning time will be in Oct., 2011

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