Cool Stars 14 - Submitted Abstract # 95
This version created on 05 October 2006

Modelling spectroastrometric signatures of binary stars and
exo-planets


Boris Rockenfeller, Hamburger Sternwarte
Guenter Wiedemann, Hamburger Sternwarte

The technique of spectroastrometry so far allowed astronomers to
resolve flux distributions at angular scales of milli-arcseconds by
measuring the position centroid of high signal-to-noise long-slit
spectra.  We study the case of spatially unresolved binary point
sources in which differences in the spectra of the two components
(particularly strong emission and absorption lines) cause the position
centroid to vary with wavelength.  This reveals information about the
spatial flux distribution.  As a first step towards high precision
infrared observations, we have simulated the spectroastrometric
signatures that are expected for binary point sources.  Their
components consist of e.g.  main sequence stars, ultra cool dwarfs and
extra-solar planets.  Using modern adaptive optics in combination with
the largest telescopes available, spectroastrometry could
theoretically achieve a micro-arcsecond resolution.  However, any
distortion of the point-spread-function leads to significant artefacts
in the measured position centroid.  These artefacts can easily exceed
a real signal present in the observed target.  We have performed
simulations in order to reproduce and then remove these artefacts for
restoring the full spatial resolution.  The latter is given by the
signal-to-noise ratio and the width of the PSF.

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