Spatial Resolution

Three primary 10 antenna configurations (see Table ) are available that can be combined to produce maps with different angular resolution. All three configurations are usually scheduled during the course of a year (see Table ). During the summer period (May until September) each antenna undergoes a thorough maintenance and the interferometer is operated in a 9 antenna D configuration.

Table: Configurations of the ten-antenna array

Name	Stations
10A	W27	W23	W08	E68	E24	E16	E03	N46	N29	N20
10C	W23	W20	W09	E23	E18	E10	E03	N20	N17	N11
10D	W12	W08	W05	E10	E04	N17	N13	N09	N05	N02
9D	W12	W09	W05	E10	E04	–	N13	N09	N05	N02

The general properties of these configurations (numbers refer to a source at 20$^\circ$ declination) are:

• D – the compact configuration with just the D array for maximum sensitivity. This configuration is best suited for detection experiments and coarse mapping (resolution $\sim 3.9''$ at 100 GHz and $\sim 1.7''$ at 230 GHz). This configuration provides the lowest phase noise and highest sensitivity.
• C – the intermediate configuration provides a fairly complete coverage of the uv-plane (low sidelobe level) and is well adapted to combine with D for low angular resolution studies ($\sim$2.6$''$ at 100 GHz, $\sim$1.1$''$ at 230 GHz) and with A for higher resolution ($\sim$1.4$''$ at 100 GHz, $\sim$0.6$''$ at 230 GHz). C alone ($\sim$2$''$ at 100 GHz, $\sim$0.9$''$ at 230 GHz) is also well suited for snapshot and size measurements, and for detection experiments at low source declination.
• A – the most extended configuration alone is well suited for mapping or size measurements of compact, strong sources. It provides a resolution of $1.0''$ at 100 GHz, $\sim$0.4$''$ at 230 GHz.

The three configurations can be used in different combinations to achieve complementary sampling of the uv-plane, and to improve on angular resolution and sensitivity. The combinations AC, ACD, and CD are well suited for all declinations above 0$^\circ$ . For lower source declinations, the beam becomes increasingly elliptical. Sources lower than -25$^\circ$  declination cannot reasonably be observed from Plateau de Bure. Mosaicing is usually done with D or CD, but the combination ACD can also be requested for high resolution mosaics.

The antenna half-power beam size is 50 $^{\prime\prime}$ at 100 GHz and the shortest possible antenna spacing is 24 m to avoid collisions between two antennas. Even taking into account projection effects that shorten the effective baseline, sources larger than about 15 $^{\prime\prime}$ are already heavily resolved at 100 GHz. In these cases, additional short-spacing observations should be acquired by observing a raster- or OTF- (On-The-Fly) map using the IRAM 30 m 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. (see also Section).