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					            Radio Astronomy
                PARI
 School of Galactic Radio Astronomy
                 And
Brevard College Pisgah Forest Institute
                          26 March 2011

Michael Castelaz, Ph.D.               Christi Whitworth
PARI Science Director                 Education Director
mcastelaz@pari.edu                    cwhitworth@pari.edu
Introduction to Light
             Production of Light
   Continuous Spectrum
   Thermal Radiation
    • (black body radiation)
    • Atomic collisions result excitation of atoms and in
      emission of energy at multiple frequencies.


   Emission Spectrum
   Excitation of electrons
    • High energy level
   Return to ground state produces emission of
    energy
    • Energy produced proportional to drop
Other colors of light we can’t see…
   Ionizing Radiation
    • UV
    • X-Rays
    • Gamma Rays

   Non-Ionizing Radiation
    • IR
    • Microwave
    • Radio
Multi-spectral Astronomy
    Discovery of Radio Astronomy
   Radio Waves first discovered by Hertz in
    1888

   Radio Astronomy born 1931
   Karl Jansky first detects extra terrestrial
    radio waves
    • Source: Galactic Center
   1937 Grote Reber first modern radio
    telescope
    • 1944 Reber publishes first radio map of sky
     Karl Guthe Jansky
   father of radio astronomy
Hired by Bell Labs in the late
  1920’s to determine the
    source of natural radio
         interference
   Jansky constructed a 20.5 MHz
    receiver on a large turntable antenna
    to isolate the direction of radio noise

   Sources of Radio Noise

    • Nearby storms

    • Distant storms

    • A faint hiss that repeated itself every 23
      hours 56 minutes – same rate that stars
      rise and set!
In 1933, Jansky identified the source of noise
  as the center of our galaxy, in Sagittarius
             Grote Reber

   Bell Labs was not interested in radio
    astronomy, so Jansky’s involvement
    ended

   Reber continued after Jansky, by
    constructing his own radio telescope
    in 1937

   Formed images of the radio sky at
    160 and 480 MHz
Reber’s 31.4 ft parabolic reflector
 Reber’s contour maps of the
Milky Way, at 160 and 480 MHz
Astronomy expands to the entire spectrum.
      Formation of Radio Waves
   Thermal Radiation

   Synchrotron Radiation
    • Relativistic e- in magnetic fields
   Bremstrahlung
    • “Breaking Radiation” e- /ion collisions
   Maser
    • Microwave Laser e- oscillations in molecular
      clouds
   Atomic Transitions (emission spectra)
    • Hydrogen e- spin flip
Formation of 21cm Radio waves
          (1420 MHz)
   Synchrotron (non-thermal)

    • Electrons or ions gyrating around magnetic
      fields emit radiation

    • Example: trapped charges in Jupiter’s
      magnetic fields emit radio (below)
• Synchrotron radio waves also come from
  supernova remnants and other galaxies
                             Pulsars
   highly magnetized neutron star, with a radius of 10-15 km,
   greater than mass than the Sun
   Radiation is beamed out along the magnetic poles and pulses of
    radiation are received as the beam crosses the Earth, in the
    same manner as the beam from a lighthouse causes flashes.



Vela Pulsar
              ESC to Stop
Galaxies and Blackholes




                          Measure Rotation of a Galaxy:
                          Discover 2 things:
                                 Missing Mass
                                 Central Blackhole
 Radio waves are VERY weak!
 Brightness = power/area

 Radio brightness measured in units of
  Janskys
       1 Jansky (Jy) = 10-26 W/m2
 Typical sources:

    • Sun: 10,000’s of Jy
    • Brightest Supernova Remnant: 1000’s Jy
    • Active Galactic Nuclei: 10-100 Jy
             Radio Telescopes
   Your car radio is an example of a simple
    antenna and receiver

   Radio waves cause free electrons in
    metal to oscillate

   Radio receivers amplify these
    oscillations

   Radio telescopes measure radio
    brightness as a ‘voltage’ on the sky
            The Ideal Telescope
   Directional antennae, such as reflectors,
    isolate the radio power from single
    sources, reduce confusing radiation
    from others

   Sensitive receivers with low noise
    figures, < 150 K.

   Large collecting areas increase gain and
    resolution

   Resolution: roughly 57.3 λ/D degrees
    (λ: observing wavelength, D: diameter
    of aperture)
Pisgah Astronomical Research Institute
               PARI
26 West
4.6 Meter Smiley
     Reception of Radio Waves
   Radio waves cause oscillation of free
    e- in metals

   Dish reflector antennas localize the
    source and exclude background noise

   Radio signal intensity is measured as
    voltage
Reception of Radio Waves
               Signal Path

        Receiver Feed Horn

         Amplifier
                          Smiley PC
       Mixer


                                      Antenna
Spectrometer
                                      Control
     Internet and Guest Astronomer
                Signal Path
   Receiver: radio waves reflected by dish
    are focused here

   Amplifier: one or more amplifiers
    increase the signal strength

   Mixer: Re-tunes the sky frequency of
    oscillations so electronic devices on the
    signal path can act on it

   Spectrometer: device for measuring the
    radio power across the spectrum as
    seen by the receiver
                     102000
                     100000
    Flux Data Unit    98000
                      96000
                      94000
                      92000
                      90000
                      88000
                      86000
                      84000
                              0   50             100   150
                                   Frequency Offset




   Spectrometer output
    • Spectrum: received power vs. radio
      frequency

    • Continuum: sum of power over all
      frequencies (area under spectrum)
At 21-cm wavelengths, PARI’s 26-m and
4.6-m (Smiley) antennas have resolutions
of 0.5 and 2.5 degrees respectively
        Other radio telescopes




100-m telescope in Greenbank, WV,
has a resolution of 7 minutes of arc
(see www.nrao.edu)
300-m telescope in Arecibo, Puerto Rico
has a resolution of 2.4 minutes of arc
(see www.naic.edu)
Interferometers synthesize a larger antenna




  Very Large Array, New Mexico,
  has a resolution of 1.4 seconds of arc
  (www.nrao.edu)
Very Long Baseline Array, a continent-sized
interferometer, has a resolution of 0.005 seconds of arc
       Radio Astronomy at Home
   Radio astronomy can be performed
    at your home institution!

   Packages are available from $120 to
    $5000
NASA’s Radio Jove antenna receives 20.1 MHz
          and converts it to audio
    (see http://radiojove.gsfc.nasa.gov/)
The Radio Jove receiver output can
be piped to the internet using Radio
 Skypipe (see www.radiosky.com)
Small Radio Telescope

2.3-m antenna receives
1420 MHz continuum
and spectral-line


See web.haystack.mit.edu/SRT/
and http://www.cassicorp.com/
4.6 Meter Smiley
          they were

in the lab.”
                             Pulsars
   highly magnetized neutron star, with a radius of 10-15 km,
   greater than mass than the Sun
   Radiation is beamed out along the magnetic poles and pulses of
    radiation are received as the beam crosses the Earth, in the
    same manner as the beam from a lighthouse causes flashes.



Vela Pulsar
              ESC to Stop
Galaxies and Blackholes




                          Measure Rotation of a Galaxy:
                          Discover 2 things:
                                 Missing Mass
                                 Central Blackhole
                                        Very Large Array




•   Unusual plume-like structure around a quasar at z=0.411
•   Overall linear size 196/h kpc (Hubble constant H = 100h
    km/s/Mpc)
•   Jet is extremely twisted and knotty
•   Possible bent counterjet in North lobe
•   Structure unusually distorted on all scales
•   VLA 4.9 GHz image at 0.9 arcsec resolution
Radio Telescopes
Receivers

       radio signal




                      radio
                      signal
Radio
signals
focused on
antenna
Feed

   Baffle
Radio Signal
Infrared Movie…
                             Jupiter

                  Infrared
Visible




          Radio
          they were

in the lab.”

				
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posted:11/25/2011
language:English
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