TPF-I SWG Report - Exoplanet Exploration Program - NASA

C HAPTER 5
5.8.4 Angular Resolution and Imaging
The imaging properties of nulling arrays are discussed in Section 4.9. Angular resolution—essentially the
width of the main peak in the point spread function—is distinct from the IWA discussed in Section 5.8. A
key feature of the stretched X-array is its excellent angular resolution, resulting from the long imaging
baselines. Figure 5-25 compares synthesized dirty maps for the regular X-array 2:1 and the stretched X-
array 6:1. The IWA is the same in each case, but the angular resolution is improved by a factor of 3. The
angular resolution scales linearly with wavelength and is inversely proportional to the array size, as
illustrated in Table 5-3.
High angular resolution is highly desirable for (1) separating the contributions of multiple planets; (2)
rapid and unambiguous orbit determinations; and (3) discrimination against lumps in the exozodiacal
disk.
For previous arrays with relatively poor angular resolution, image deconvolution was considered to be a
major issue, since there can be substantial overlap between the PSFs of different sources. Sidelobes and
satellite peaks can combine to produce false peaks or mutually cancel and prevent detection. The greatly
enhanced angular resolution of the stretched X-array (Fig. 5-25b) minimizes these overlaps, and it should
go a long way to retiring these issues.
Figure 5-25. (a) Dirty map of two planets (indicated by the × symbols), synthesized from multichannel
observations of an X-array 2:1 array configuration (70 × 35 m); (b) Equivalent dirty map
for the stretched X-array 6:1 configuration (210 × 35 m).
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