SUSI Baselines

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Looking north along the SUSI baseline from the central stations. Each siderostat station (right) has a smaller electronics box alongside. The C14 dome and SUSPECT building are on the left, with AT antennas in the background.

The baselines

SUSI has been designed to operate with baselines ranging from 5m to 640m, with intermediate baselines forming a geometric progression increasing in steps of ~40%. This corresponds to a range of resolution from 20 milli-arc seconds (mas) to 70 micro-arc seconds at a (blue) wavelength of 450nm. The low resolution limit provides an overlap with the angular resolution attainable with speckle and non-redundant mask interferometry with large conventional telescopes. The 640m length of the baseline array, chosen to resolve a sample of hot O-type stars, provides SUSI with the highest angular resolution of any existing or currently proposed interferometer or interferometric array.

The Table below lists the preferred SUSI baselines, matching one station from the north side of the array with one from the south side. Baselines which are currently operational are shown in boldface. Note that there is no station N2, but there is an additional station E1 located 10m east of the centre of the main linear array. This is the first station of a potential east-west arm.

Ideally the interferometer baselines should be horizontal. The site chosen for SUSI has a small gradient and the two arms were designed to have slightly different non-zero gradients which were chosen to minimise the maximum vertical height difference over the array. The largest height difference occurs for the stations at the two ends of the array and is ~1.1m.

SUSI's "preferred" baselines.
Baselines in boldface are currently operational.
Baseline Length (m)Stations employed

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Another view of the central portions of the SUSI baseline, showing one station forming the stub of an eastern arm.

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