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Parkes

Parkes. “The Dish”. M83. 19’. Parkes. “The Dish”. VLA, Very Large Array New Mexico. 300 metres. Arecibo Telescope… in Puerto Rico. 91 metres. GBT Green Bank West Virginia … the newest… … and last ( perhaps )… … big dish Unblocked Aperture. LOFAR “elements”.

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Parkes

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  1. Parkes “The Dish”

  2. M83 19’

  3. Parkes “The Dish”

  4. VLA, Very Large Array New Mexico

  5. 300 metres Arecibo Telescope… in Puerto Rico

  6. 91 metres GBT Green Bank West Virginia … the newest… … and last (perhaps)… … big dish Unblocked Aperture

  7. LOFAR “elements”

  8. http://www.astron.nl/press/250407.htm

  9. LOFAR image at ~ 50MHz (Feb 2007)

  10. Dipole + ground plane: a model conducting ground plane

  11. i2pft I e o Dipole + ground plane equivalent to dipole plus mirror image i2pft -I e o

  12. 4x4 array of dipoles on ground plane - the ‘LFD’ element h s s (many analogies to gratings for optical wavelengths)

  13. Beam Reception Pattern 4x4 Tuned for 150 MHz sin projection

  14. ‘sin projection’ gives little weight to sky close to horizon !

  15. As function of angle away from Zenith ZA = 0 deg 15 30 45 60 75

  16. i2pft I e o h h 2 P(q) ~ sin [2ph cos(q)/l] q = zenith angle equivalent to dipole plus mirror image i2pft -I e o (maximize response at q=0 if h=l/4 )

  17. As function of frequency 4x4 Patterns • ZA = 30 deg • tuned for 150 MHz • 120 150 • 180 210 240

  18. Atacama L Millimeter Array Very Large Array USA Westerbork Telescope Netherlands

  19. VLBA Very Long Baseline Array for: Very Long Baseline Interferometry

  20. LBA: Long Baseline Array in AU EVN: European VLBI Network(more and bigger dishes than VLBA)

  21. ESO Paranal, Chile

  22. * *** (biblical status in field)

  23. More references: • Synthesis Imaging in Radio Astronomy, 1998, ASP Conf. Series, Vol 180, eds. Taylor, Carilli & Perley • Single-Dish Radio Astronomy, 2002, ASP Conf. Series, Vol 278, eds. Stanimirovic, Altschuler, Goldsmith & Salter • AIPS Cookbook, http://www.aoc.nrao.edu/aips/

  24. LOFAR + MWA VLA ALMA GMRT ground based radio techniques 350m 10 MHz ATCA

  25. 1) Thermal 2) Non-Thermal Radio “Sources” Spectra: • Thermal • emission mechanism related • to Planck BB… electrons have • ~Maxwellian distribution • 2) Non-Thermal • emission typically from • relativistic electrons in • magnetic field… electrons • have ~power law energy • distribution Flux Density Distinctive Radio Spectra ! Frequency MHz

  26. Nonthermal

  27. Thermal M81 Group of Galaxies Visible Light Radio map of cold hydrogen gas

  28. (from P. McGregor notes)

  29. Inwhere In~ Sn/W can assign “brightness temperature” to objects where “Temp” really has no meaning…

  30. Brightest Sources in Sky Flux Density [Jansky] Frequency MHz (from Kraus, Radio Astronomy)

  31. Radio `source’ • Goals of telescope: • maximize collection of energy (sensitivity or gain) • isolate source emission from other sources… (directional gain… dynamic range) Collecting area

  32. Incident waves Radio telescopes are Diffraction Limited

  33. Incident waves Radio telescopes are Diffraction Limited Waves arriving from slightly different direction have q Phase gradient across aperture… When l/2, get cancellation: Resolution = q ~ l/D

  34. Celestial Radio Waves?

  35. Actually……. Noise …. time series Time Fourier transform Frequency

  36. F.T. of noise time series Frequency Narrow band filter B Hz Frequency Envelope of time series varies on scale t ~ 1/B sec Time

  37. Observe “Noise” …. time series V(t) Time Fourier transform Frequency

  38. …want “Noise Power” … from voltage time series => V(t)2 then average power samples “integration” V(t) Time Fourier transform Frequency

  39. Radio sky in 408 MHz continuum (Haslam et al)

  40. Difference between pointing at Galactic Center and Galactic South Pole at the LFD in Western Australia Power ~4 MHz band Frequency

  41. thought experiment… Cartoon antenna 2 wires out (antennas are “reciprocal” devices… can receive or broadcast)

  42. thought experiment… Black Body oven at temperature = T

  43. Black Body oven at temperature = T thought experiment… R

  44. Black Body oven at temperature = T thought experiment… … wait a while… reach equilibrium… at T R warm resistor delivers power P = kT B (B = frequency bandwidth; k = Boltzmann Const)

  45. R real definition… Measure Antenna output Power as “Ta” = antenna temperature Ta temp = T warm resistor produces P = kT B = Pa = kTa B

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