Aperture Synthesis of Hipparcos Transit Data

Extract

The ESA Hipparcos astrometry satellite did not contain an imaging detector (such as a CCD) but used a modulating grid of alternating transparent and opaque bands to modulate the light from a given object. The Fourier coefficients of the modulated detector signal were the basis for the astrometric and photometric processing leading to the Hipparcos Catalogue. These coefficients are included (for a subset of the stars) in the CD-ROM version of the Hipparcos Catalogue as the ‘Hipparcos Transit Data’. In this work, the Transit Data are used in a completely different and novel application: the modulation components from a single scan are considered to be equivalent to the interference fringes from an interferometer oriented along the scan direction and having baselines of 0, ≃ 10 and ≃ 20 cm and a wavelength of 550 nm. Using all the scans collected over the mission lifetime, it is possible to use the complex visibilities (containing bothamplitude and phase information) calculated from the Transit Data to createaperture synthesis images of various type of objects such as visual or orbiting binary systems. More information, including sample images, can be found in: Quist C.F., Lindegren L., Söderhjelm S., 1997, Using HipparcosTransit Data for Aperture Synthesis Imaging, Hipparcos Venice ‘97 Symposium, ESA SP-402 (in press).