Issue EAS Publications Series Volume 8, 2003 Astronomy with High Contrast Imaging Page(s) 171 - 180 DOI 10.1051/eas:2003060

Astronomy with High Contrast Imaging
C. Aime and R. Soummer (eds)
EAS Publications Series, Vol. 8, 2003
DOI: 10.1051/eas:2003060

Color-differential astrometry with the NGST. Application to the spectroscopy of giant extrasolar planets

M. Vannier¹, R.G. Petrov¹, S. Bensammar² and B. Lopez<sup>3

1</sup>  Université de Nice-Sophia Antipolis, France
²  GEPI, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
³  Observatoire de la Côte d'Azur Département Fresnel UMR 6528, BP. 4229, 06034 Nice Cedex 4, France

Abstract
The color-differential astrometry method consists in measuring the variations of the photocenter position with wavelength. This yields spectral information on the spatial structure of an unresolved source, and could allow, among other applications, the direct detection and spectroscopy of extrasolar planets. We give some estimates of signal-to-noise ratio for CDA using the the NGST mid-infrared instrument (MIRI) spectrograph, assuming for the planetary luminosity either black-body models or recent synthetic spectra. Giant Planets around nearby Sun-like stars are potentially observable over a wide-range of orbital distances, if the precision on the measurement is limited by the fundamental noises. Space-based CDA would then be complementary, in terms of star-planet separation, to ground based interferometry and to coronography. This assumes, though, a proper chromatic stability of the instrument. This note introduces some possible methods for instrumental internal calibration, and presents a possible spatial design for a calibration by spatial modulation.

© EAS, EDP Sciences 2003

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