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 100.0 140.0 0.73 26 192
for nighttime observing
Effelsberg 80.0 (eff.)
140.0 0.14 7.7 1000 -
Noema (PdB) 45.0 100.0 0.41 71 244
10x15m
Pico Veleta 30.0 100.0 0.15 60 654
-
Yebes 40.0 180.0 0.10 22 1782
-
VLBA (8x25m) 25.0 100.0 0.04 22 2500
range is: 0.02-0.04 K/Jy
KVN (3x21m) 21.0 200.0 0.061 49 3279
for each 21m antenna
Onsala 20.0 190.0 0.049 43 3878
-
Metsähovi 14.0 200.0 0.010 18 20000 -
LMT (prelim) 50 240.0* 0.39 55 615
-
GLT (prelim) 12 180 0.032 78 5625
-
ALMA 70.7 (eff.) 75.0 1.00 70 74.9 37x12m



7 sigma single baseline detection thresholds (all numbers in mJy):
link to: EVN Sensitivity calculator1 (classic), and EVN Sensitivity calculator2 (new), and GMVA Sensitivity Calculator

- Noema Pico Veleta Yebes Onsala Metsähovi VLBA GBT KVN LMT ALMA37
Effelsberg 28
45
75
111
251
89-126
25
102
44
15
Noema - 23
37
55
124
44-62
12
50
22
8
Pico Veleta - - 61
90
203
72-102
20
82
36
12
Yebes - - - 148 336
118-168
33
136
59
21
Onsala - - - - 495
175-248
49
201
87
30
Metsähovi - - - - -
398-563
110
456
197
69
VLBA - - - - -
141-281
39-55
161-228
70-99
24-34
GBT - - - - -
-
-
45
19
7
KVN - - - - -
-
-
-
80
28
LMT - - - - -
-
-
-
-
12


Baseline Sensitivity: to Effelsberg: 15-100 mJy
to IRAM 30m: 12-90 mJy
to GBT: 12-50 mJy
to ALMA: 7-30 mJy


Array Sensitivity (1 sigma): 0.097 mJy/hr (Europe+VLBA)
0.063 mJy/hr (Europe+VLBA+GBT)
0.035 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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