Interferometry and Circular PolarisationMeasurements in Radio Astronomy

The Fifth International Congress for Radio Astronomy The European Radio Astronomy Club

Sept. 3-5, 2009

David E. Fields and Stanley KurtzTamke-Allan Observatory

SARA

Interferometry and CircularInterferometry and Circular Polarisation PolarisationMeasurementsMeasurements in Radio in Radio Astronomy Astronomy

The Fifth International Congress for Radio Astronomy The European Radio Astronomy Club

Sept. 3-5, 2009

David E. Fields and Stanley KurtzTamke-Allan Observatory

SARA

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Tamke-Allan Observatory

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In the dome: 8”RefractorTelescope

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Our primary deep-skyscope:

Meade LX-200 12” ReflectorGo-To capability

Computer Controlled

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Our Classroom

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Astronomy Camp

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Kid’sAstronomy

Day

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RSCCMulticultural

Day

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www.roanestate.edu/obs

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Planet View: Loss of the Skies

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Perseid Meteors

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Local View: Loss of the Skies

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NRAO in Green BankNRAO in Green Bank

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GBT Feed ArmGBT Feed Arm

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False Kiva, Canyonlands NP, UT

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Spitzer’s Milky Way

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What emits radio waves?What emits radio waves?

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Recipe for Radio WavesRecipe for Radio Waves

1. Hot Gases1. Hot Gases

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Electron accelerates as it passes near a proton.

EM waves are released

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Optical and radio features from hot gases

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Radio free-free emission

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Omega Nebula – star formation with Blu-opt,Gr-IR,R-L band

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2. Atomic and molecular transitions2. Atomic and molecular transitions(spectral lines)(spectral lines)

Recipe for Radio WavesRecipe for Radio Waves

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Hydrogen spectral lines in opticalHydrogen spectral lines in optical

434 nm486 nm656 nm

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Single-frequency spin flip:

Electron accelerates to a lower energy state(with emission of energy; e.g., 1420 MHz radio

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NGC 628

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M33, m5.7,triangulum

Spiral Galaxy

Optical +Radio (HI)image

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3. Moving electrons and magnetic3. Moving electrons and magneticfieldsfields

Recipe for Radio WavesRecipe for Radio Waves

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Electrons accelerate around magnetic field lines

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• Radio Sun

• Coronal MassEjections (CMEs)

• Magnetic solarcycles

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Solar Magnetic Field Strength andStructure

Active region showing strong shear: radioimages show high B and very high temperatures

from Lee et al (1998)

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from J. Lee

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Type U bursts observedby Phoenix/ETH andthe VLA.

SolarFlares

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• Largest explosions onthe Sun

• Large portion of theSolar Coronadestabilizes and isejected at speeds of 200-2000 km/s

• Accelerate chargedparticles to close to thespeed of light

• Major drivers of “spaceweather” effects

– Can take down powergrids, induce currents inoil pipelines, disruptnavigaton

Coronal Mass Ejections (CMEs)Optical lightSOHO/LASCO

cdaw.gsfc.nasa.gov/CME_list/

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Magnetic Butterfly Cycle

http://science.nasa.gov/headlines/y2001/ast15feb_1.htm

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The Sunspot Cycle(butterflies)

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Other ‘stellar’ signal:Cass A SNR

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Cass A in Radioland

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Consider Pulsars

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Cygnus A – 800 million LY distant

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Jet Mechanism:

• Accretion of gas ontoa massive centralblack hole releasestremendous amountsof energy

• Magnetic fieldcollimates outflow andaccelerates particlesto close to the speedof light

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ngc 4565polarization

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Questions for ERAC• What is the polarization of an accretion jet?• What is the polarization of Jovian B fields?• How can we study the spatial and temporal

variation of solar B fields?• What is the influence of the solar wind on

Jovian emission?• What can we understand from measuring

polarization and frequency?• How can we communicate with satellites?• Can we invent new tools for studying solar

emissions?

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RF polarizationcharacteristics

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Plane EM wave

How might we generate this wave?

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Amateur Radio Astronomy• Use of polarization measurements in RA

can yield information about physicalmechanisms

• Polarization important consideration forJupiter, solar, and distant radio jetemissions

• Polarized signals are accessible byamateurs

• Antenna construction is not too difficult

• The Pequod is afloat on a sea ofpossibilities

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How might we generate this wave?

Hint – think electron in magnetic field

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2 types of circularpolarization

63Phi is the important variable.

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This view isperpendicular to

the B field

Now consider the view along the B field…

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Consider E-vector for planeand circular polarization

Now thinkantennas!

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Can we study Jovian emission in CP?

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CP studies at 20.5 MHz?

Moby Dish and the Pequod ready for sailing?

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PreS’easter

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Post S’easter

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Radio Telescopes• Come in two basic flavors:

Arrays

Green Bank Telescope, WV Very Large Array, NM

Single Dish

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A Ku band analogue (intensity)interferometer

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Basic electronics

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Monitoring Output

One may monitor diode output (SLD at about 1GHz) with a meter or chart recorder orcomputer software (after digitization).

Fast digitizer: CompUSA video grabber withUSB output: SKU 318714

Can we hope to motorizethis interferometer?

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Don’t forget the mechanics

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Motor controllers can be handor computer-driven

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Some student tryinterferometry from TAO

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With computer control,multipoint scans are possible

(this is 5x5 points, about 5degrees of sky, from TAO.

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LNBs are Circular polarization-sensitive

Can we verify these data?

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Building a CP Ku-BandTransmitter

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High-tech CP generators

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The Intensity (amplitude)interferometer is operational

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Proposal: With dual square-lawdetectors we can have adifferential CP detector

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Proposal: Solar Studies –CP at Ku band

• Front-end development OK• Signal combiner details OK• Analysis techniques OK• Collaboration• More next year?