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Spatial Resolution

Four primary 6 antenna configurations (see Table [*]) are available that can be combined to produce maps with different angular resolution. All four configurations are usually scheduled during the course of a year. During the summer period (May until September) each antenna undergoes a thorough maintenance and the interferometer is operated in the 5 antenna D configuration (equal to the 6 antenna D configuration given in Table [*] but without station N02).


Table: Plateau de Bure 6 antenna configurations
Configuration Stations
D W08 W05 E03 N02 N07 N11
C W12 W09 E04 E10 N11 N17
B W27 W12 E12 E23 N20 N46
A W27 E04 E24 E68 N29 N46

The combinations, named AB, BC, CD are reasonably suited for all declinations above 0$^\circ$ (see Tables [*] to [*]). For lower source declinations, the beam becomes increasingly elliptical. Sources lower than -25$^\circ$ declination cannot reasonably be observed from Plateau de Bure.

The four configurations can be used in different combinations to achieve complementary sampling of the uv-plane, and to improve on angular resolution and sensitivity. Mosaicing is usually done with D or CD, but the combination BCD can also be requested for high resolution mosaics.

The antenna half-power beam size is $50''$ at 100GHz and the shortest possible antenna spacing is 24m to avoid collisions between two antennas. Even taking into account projection effects that shorten the effective baseline, sources larger than about $15''$ are already heavily resolved at 100GHz. In these cases, additional short-spacing observations should be acquired by observing a raster- or OTF- (On-The-Fly) map using the IRAM 30m telescope1. The short-spacing information can then easily be added to the uv-tables obtained from the interferometer by means of the GILDAS MAPPING software.

Tables [*]-[*] give a summary of beam sizes for natural weighting and various observing frequencies. Observing was supposed to be limited to 6 hours before and after transit and to elevations higher than 20 degrees. Typical uv-coverages and resulting beam shapes for the six-element array are shown in Fig. [*] (D and CD), [*] (BCD and BC), and [*] (A and AB).


Table: Beam sizes for configuration D
Dec. 85 GHz 115 GHz 230 GHz PA
  Maj. Min. Maj. Min. Maj. Min.  
80 6.41 5.88 4.74 4.35 2.37 2.17 92
60 6.45 5.45 4.77 4.03 2.38 2.01 96
40 6.45 5.54 4.77 4.09 2.38 2.04 104
20 6.13 6.04 4.53 4.46 2.26 2.23 91
0 7.35 6.12 5.43 4.52 2.71 2.26 -18
-20 11.43 5.68 8.44 4.20 4.22 2.10 -6


Table: Beam sizes for configuration CD
Dec. 85 GHz 115 GHz 230 GHz PA
  Maj. Min. Maj. Min. Maj. Min.  
80 4.48 4.15 3.31 3.06 1.65 1.53 -90
60 4.35 3.86 3.21 2.85 1.60 1.42 86
40 4.44 4.02 3.28 2.97 1.64 1.48 89
20 4.42 4.21 3.26 3.11 1.63 1.55 40
0 5.41 4.23 4.00 3.12 2.00 1.56 6
-20 8.38 3.82 6.19 2.82 3.09 1.41 -178


Table: Beam sizes for configuration BC
Dec. 85 GHz 115 GHz 230 GHz PA
  Maj. Min. Maj. Min. Maj. Min.  
80 2.12 1.96 1.56 1.45 0.78 0.72 79
60 2.15 1.86 1.59 1.37 0.79 0.68 80
40 2.20 1.93 1.62 1.42 0.81 0.71 69
20 2.40 1.96 1.77 1.45 0.88 0.72 37
0 3.39 1.99 2.50 1.47 1.25 0.73 -166
-20 4.60 1.89 3.40 1.40 1.70 0.70 6


Table: Beam sizes for configuration AB
Dec. 85 GHz 115 GHz 230 GHz PA
  Maj. Min. Maj. Min. Maj. Min.  
80 1.21 1.12 0.89 0.83 0.44 0.41 84
60 1.21 1.05 0.89 0.77 0.44 0.38 74
40 1.25 1.06 0.92 0.78 0.46 0.39 59
20 1.40 1.06 1.03 0.78 0.51 0.39 37
0 1.74 1.02 1.28 0.75 0.64 0.37 22
-20 2.66 0.98 1.97 0.72 0.98 0.36 10


Table: Beam sizes for configuration A
Dec. 85 GHz 115 GHz 230 GHz PA
  Maj. Min. Maj. Min. Maj. Min.  
80 0.97 0.91 0.71 0.67 0.35 0.33 76
60 0.99 0.86 0.73 0.64 0.36 0.32 61
40 1.07 0.87 0.79 0.64 0.39 0.32 44
20 1.29 0.84 0.95 0.62 0.47 0.31 31
0 1.70 0.78 1.25 0.57 0.62 0.28 22
-20 2.58 0.74 1.91 0.54 0.95 0.27 12

Figure: uv-plane coverage and beamshapes for the D and CD (6 antenna) configurations. Contour levels are at 5%, 10%, 20%, and 50%. Frequency is 100GHz.
\includegraphics[height=.9\textheight]{pdbi-intro-d} \includegraphics[height=.9\textheight]{pdbi-intro-cd}
Figure: uv-plane coverage and beamshapes for the BCD and BC (6 antenna) configurations. Contour levels are at 5%, 10%, 20%, and 50%. Frequency is 100GHz. Note the different scaling of the uv-plane with respect to Fig. [*]
\includegraphics[height=.9\textheight]{pdbi-intro-bcd} \includegraphics[height=.9\textheight]{pdbi-intro-bc}
Figure: uv-plane coverage and beamshapes for the AB and A (6 antenna) configurations. Contour levels are at 5%, 10%, 20%, and 50%. Frequency is 100GHz. Note the different scaling of the beam maps with respect to Figs. [*] and [*]
\includegraphics[height=.9\textheight]{pdbi-intro-ab} \includegraphics[height=.9\textheight]{pdbi-intro-a}


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Gildas manager 2014-10-21