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

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

3. Nonthermal

4. Ka = Ta / Sn = Aeff /2k [K/Jy]
Example 3: Array
High redshift quasar with
continuum flux density Sn = 1 mJy
(Ta = Sn Aeff /2k)
Ka = Ta / Sn = Aeff /2k [K/Jy]
= K/Jy Parkes
= 6 x 0.1 = 0.6 K/Jy ACTA
rms = DS = (fac)(Tsys /Ka)/(B tint)1/2
ATCA (B=128 MHz): 1 mJy = 5 rms means DS = 0.2 mJy
rms = DS = (fac)(Tsys /Ka)/(B tint)1/2
= (1.4)(30/0.6)/(B tint)1/2
tint = (70/0.0002)2/(128x106)
~ 16 min

5. ARRAYS:
Sensivity depends
on collecting area
Angular resolution
~ l/D D

6. Ka = Ta / Sn = Aeff /2k [K/Jy]
Example 3: Array
High redshift quasar with
continuum flux density Sn = 1 mJy
(Ta = Sn Aeff /2k)
Ka = Ta / Sn = Aeff /2k [K/Jy]
= K/Jy Parkes
= 6 x 0.1 = 0.6 K/Jy ACTA
rms = DS = (fac)(Tsys /Ka)/(B tint)1/2
ATCA (B=128 MHz): 1 mJy = 5 rms means DS = 0.2 mJy
rms = DS = (fac)(Tsys /Ka)/(B tint)1/2
= (1.4)(30/0.6)/(B tint)1/2
tint = (70/0.0002)2/(128x106)
~ 16 min

7. Sensivity depends
on collecting area
Angular resolution
~ l/D D

8. Maps from Arrays (or Aperture Synthesis Telescopes):
intensities indicated in ‘units’ of `milli-Jansky per beam’ [why?]
can compute noise level sJy using radiometer equation
can compute beam size from Q ~ l/D so W ~ pQ2/4 sterad
best to think of ‘mJy/beam’ as Intensity, In = 2kTB/l2
then, uncertainty is DTB ~ sJy /W
IMPORTANT: lose surface brightness sensitivity when dilute the
aperture by separating the array telescopes !!!
Hurts ability to see diffuse emission.

9. Fourier Transform Effect of observing complex source with a ‘beam’
Strength
Angle
Fourier Transform
Effect of observing complex source with a ‘beam’
Zoom of FT

10. view convolution of source with beam as filtering in the Spatial Frequency Domain
Fourier Transform
Zoom of FT
Filter

11. The `microwave sky’ (all sky picture from
WMAP map.gfsc.nasa.gov)
Example of importance of
Spatial Frequency Content

13. L = 1

14. L = 2

15. L = 10

16. L = 50
(spatial frequency)

17. L = 210

18. Interference Fringes and “Visibility” …. (Visibilities)
The term “visibility” has its origin in optical interferometry, where fringes of unresolved sources has high “fringe visibility.” The term “visibilities” in radio astronomy generally refer to a set of measurements of the visibility function of a celestial source.

19. Simple cross correlation
radio interferometer:
on-axis source

21. M
Radio `source’ L
Interferometer
Response
Angle, Q
Consider:
‘point source’ response … full amplitude, but fringe ambiguity
‘resolved source’ response … source fills + and – fringes => signal
cancels and response -> 0.

23. The fringe spacing and orientation corresponding to a single ‘u-v’ point:

24. U-V sampling comes from forming interferometers among all pairs of telescopes in the array:
Locations on Earth
Instantaneous UV Coverage
Earth rotation

26. See: www.narrabri.atnf.csiro.au/astronomy/vri.html
to access the Virtual Radio Interferometer simulator.

28. “Dipoles”