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 – 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

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

Hardware Testing

Percentage Position Angle Calibration: Beam Polarization

Calibration: XY Phase

First Results: NGC 1333-IRAS 4A

First results: L1157

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

Credit: Bill Saxton, Harvard-Smithsonian Center for Astrophysics

First Target: NGC 1333 IRAS 4A We want to search for “hourglass” shape of the B-field structure in the circumbinary envelope Girart CARMA observations SMA observations

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

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

How do we make it work? Grad student

Turnstile-junction OMT Navarrini & Plambeck 2006, IEEE-MTT, 54, cm

OMT construction

Unequal sidearm lengths in OMT can cause resonances (simulation)

OMT tests at 4K (passbands, LO = GHz in 1 GHz steps) OMT10 (bad ) OMT15 (good)

Polarizer construction Aluminum mandrel Copper electroplated onto mandrel MachinedSoldered into waveguide flange 1 inch

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

XY  RL Sky Receiver

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

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

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!

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

1 mm signal path Block downconverte rs 8-way splitters RF = 210 – 270 GHz IF = 1 – 9 GHz Baseband = 0.5 – 1.0 GHz Feed horn Polarizer OM T RC P 1 – 9 GHz 5 – 9 GHz 1 – 5 GHz RF mixer Baseband mixer 10 GHz mixer LO – 4.25 GHz LCP 0.5 – 1.0 GHz NOISE Correlated Noise Source All phases flat To digitizer, filter, & correlator FILT ER 1 – 5 GHz τ4τ4 τ 3,hi τ 3,lo τ2τ2 τ1τ1 1 – 9 GHz 5 – 9 GHz 1 – 5 GHz 0.5 – 1.0 GHz FILT ER 1 – 5 GHz To digitizer, filter, & correlator

Status/conclusions Dual-polarization receivers are installed on all 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