On the Threshold: Astrometric Optical Interferometry in Space with POINTS

POINTS (Precision Optical INTerferometry in Space) would measure the angular separation of two stars, separated by about 90 deg on the sky, with a nominal measurement error of 5 microarcseconds (μas). See Figure 1 for an artist’s rendition of the instrument mounted on the NASA MMS. A discussion of some astrophysical applications of POINTS is given by Reasenberg et al. (1988) and in less detail by Reasenberg (1984). For a pair of mag 10 stars, an observation would require about 10 minutes; the instrument would measure daily the separation of two stars for each of about 60 pairs of stars. A random sequence of such measurements, if suitably redundant, contains the closure information necessary to detect and correct time-dependent measurement biases to well below the nominal measurement accuracy. The 90 deg target separation permits absolute parallax to be determined, obviating the need for adjacent zero-parallax objects and making possible parallax measurements in all directions.