On the Threshold: Astrometric Optical Interferometry in Space with POINTS

Abstract

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.