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1 mm Polarization Science with CARMA

1 mm Polarization Science with CARMA. Chat Hull Collaborators: Dick Plambeck , Greg Engargiola , & all the CARMA staff 19 August 2011 URSI General Assembly XXX Istanbul, Turkey.

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1 mm Polarization Science with CARMA

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  1. 1 mm Polarization Science with CARMA Chat Hull • Collaborators: Dick Plambeck, Greg Engargiola, & all the CARMA staff 19 August 2011 • URSI General Assembly XXX • Istanbul, Turkey

  2. 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

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

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

  5. 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

  6. 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

  7. How do we make it work? Grad student

  8. 1 mm Dual-polarization Receivers SIS mixers Orthomode transducer Waveguide circular polarizer WBA13 I.F. amplifiers (1-9 GHz) 1 inch

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

  10. OMT construction

  11. Testing OMTs using 300 GHz network analyzer at Agilent

  12. Some OMTs have resonances…

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

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

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

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

  17. XY  RL Sky Receiver

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

  19. 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

  20. 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!

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

  22. XY phase fit results

  23. 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

  24. 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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