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.

• D - the compact configuration with just the D array for maximum sensitivity. This configuration is best suited for detection experiments and coarse mapping. It provides the lowest phase noise and highest sensitivity.
• C - the next most compact configuration provides a fairly complete coverage of the uv-plane (low sidelobe level) and is well adapted to be combined with D for low angular resolution studies ($\sim$3.5$''$ at 100GHz, $\sim$1.5$''$ at 230GHz) and with B for higher resolution ($\sim$1.7$''$ at 100GHz, $\sim$0.7$''$ at 230GHz). C alone is also well suited for snapshot size measurements and for detection experiments at low source declinations.
• B - the second most extended configuration yields $\sim$1.2$''$ at 100GHz and, in combination with A provides an angular resolution of $\sim$1.0$''$ at 100GHz. It is mainly used for relatively strong sources.
• A - the most extended configuration is well suited for mapping or size measurements of very compact, strong sources. It provides a resolution of $0.8''$ at 100GHz, $\sim$0.35$''$ at 230GHz.

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.

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. 

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