Sensitivities

A. 3mm VLBI detection limits



Here we assume optimum weather conditions (low opacity, tau < 0.1, no clouds).

Note: Depending on weather, the zenith Tsys and the SEFD could be considerably worse!


Antenna and Receiver Characteristics:

Station Diameter (m) Zenith Tsys (K) Gain (K/Jy) Eta (%) SEFD (Jy)
Effelsberg 80.0 (eff.)
 130.0 0.140 7.7 929
Plateau de Bure 34.8 90.0 0.220 65 409
Pico Veleta 30.0 90.0 0.140 55 643
VLBA 25.0 100.0 0.034 19 2941
Onsala 20.0 300.0 0.049 43 6122
Metsähovi 14.0 300.0 0.017 30 17647



7 sigma single baseline detection thresholds (all numbers in mJy):

- Plateau de Bure Pico Veleta Onsala Metsähovi VLBA
Effelsberg 69
 86
 265
 450
 184
Plateau de Bure - 57
 176
 300
 122
Pico Veleta - - 221
 374
 153
Onsala - - - 1156 472
Metsähovi - - - - 801
VLBA - - - - 327


Highest Baseline Sensitivity: 57 mJy


Array Sensitivity: 21 mJy in 20 secs or 0.65 mJy in 12 hr adopting
(all European telescopes a duty cycle (time on source/total time) of 0.5.
  + 8 VLBA antennas) These numbers have to be increased by a

factor of exp(tau*A) , i.e. for tau=0.1

and airmass A= 1/sin (elv) = 2, the factor is 1.22

Depending on weather conditions, the phase stability and atmospheric
coherence time can vary between ~10 seconds and ~200 seconds.


Assuming the following observing parameters:


  • Mode:
    		• MKV/VLBA 512-8-2, single polarisation
  • Bandwidth:
    		• 128.0 MHz (512 Mbit/s)
  • Integration time:
    		• 20.0 sec (typical coherence time)
  • Threshold:
    		• 7.*sigma
  • Sampling:
    		• 2 Bit





    Useful formulae:

    Usefull Formulae



    B. Simulated uv-coverage for the Global 3mm-VLBI Array
    Below we show 3 types of uv-coverages for sources with different declinations. In these simulations we assumed 12 hrs of observing time, 50% duty cyle, and a VLBI array consisting of 5 European and 8 VLBA antennas (see table above).

    1. for a source at dec=70 (click here)
    2. for a source at dec=40 (click here)
    3. for a source at dec= 0 (click here)



    1. uv-plot of a source with a declination of 70 degree

    uv-plot, declination = 70 degree



    2. uv-plot of a source with a declination of 40 degree

    uv-plot, declination = 40 degree



    3. uv-plot of a source with a declination of 0 degree

    uv-plot, declination = 0 degree



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