Sensitivities

A. 3mm VLBI detection limits


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

Important: Depending on weather and elevation, Tsys and SEFD could be considerably higher!


Antenna and Receiver properties at 86 GHz:

Station Diameter (m) Tsys (K) Gain (K/Jy) Eta (%) SEFD (Jy) Comment
GBT 100.0 100.0 0.73 26 137
for nighttime observing
Effelsberg 80.0 (eff.)
140.0 0.14 7.7 1000 -
NOEMA (PdB) 43.9 100.0 0.39 71 260
10x15m
Pico Veleta 30.0 100.0 0.15 60 654
-
Yebes 40.0 180.0 0.09 20 2000
-
VLBA (8x25m) 25.0 100.0 0.04 22 2500
range is: 0.02-0.04 K/Jy
KVN (3x21m) 21.0 200.0 0.062 49 3226
for each 21m antenna
Onsala 20.0 190.0 0.049 43 3877
-
Metsähovi 14.0 300.0 0.010 19 30000 -
LMT (prelim) 50 240.0* 0.39 55 615
* DSB, single pol
GLT (prelim) 12 100 0.025 60 4000
-
ALMA 79.7 (eff.) 90.0 1.32 73 68.0 50x12m



7 sigma single baseline detection thresholds (all numbers in mJy):
link to: EVN Sensitivity calculator and GMVA Sensitivity Calculator

- PdBure Pico Veleta Yebes Onsala Metsähovi VLBA GBT KVN LMT ALMA37
Effelsberg 51
45
73
127
236
89-126
21
101
74
15
P. de Bure - 41
66
115
214
80-114
19
91
67
13
Pico Veleta - - 59
103
193
72-102
17
83
60
12
Yebes - - - 164 305
115-162
27
130
95
19
Onsala - - - - 534
201-284
47
228
166
33
Metsähovi - - - - -
374-528
87
424
309
62
VLBA - - - - -
167-236
33-47
160-226
116-165
25-35
GBT - - - - -
-
-
37
27
5
KVN - - - - -
-
-
-
132
26
LMT - - - - -
-
-
-
-
19


Baseline Sensitivity: to Effelsberg: 50-100 mJy
to IRAM 30m: 40-60 mJy
to GBT: 20-50 mJy
to ALMA: 5-20 mJy


Array Sensitivity: 0.90 mJy/hr (Europe+VLBA)
0.49 mJy/hr (Europe+VLBA+GBT)
0.22 mJy/hr (Europe+VLBA+GBT+ALMA)
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, the phase stability and atmospheric coherence time can vary between 10-180 seconds.
Assuming the following observing parameters:
  • Mode:
  • MK5B, 2048-16-2 (PFB), single polarisation
  • Bandwidth:
  • 500 MHz per polarisation
  • 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. ALMA, the LMT and the KVN are not yet included in the simulation.

    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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