Previous abstract Next abstract

Session 54 - Ground and Instrumentation Techniques and Catalogs.
Display session, Wednesday, June 12
Tripp Commons,

[54.02] The Origin of Solar and Stellar Image Aureole

J. M. Beckers (NSO/NOAO), C. Ftaclas (Michigan Technical U.)

The extended wings of the telescope point-spread-function affect the performance of solar and stellar reflecting coronagraphs used to study the faint envelopes of bright objects like the sun, planets, and stars. We are expanding an initial examination of the origin of these wings (Beckers, ``Scientific and Engineering Frontiers for 8 - 10 m Telescopes", Eds. M. Iye and T. Nishimura, 1995, 303 - 312) in order to obtain a quantitative evaluation of the observed point-spread-function and to derive the technical specifications for solar and stellar coronagraphs.

We include the following factors contributing to the point-spread-function wings : (i) the atmospheric seeing, including the effects of the finite inner scale of turbulence, (ii) the scattering by atmospheric aerosol particles, (iii) the atmospheric Rayleigh scattering, (iv) the scattering by small scale surface irregularities in the telescope optics (micro-ripple), (v) the scattering by dust in the telescope, (vi) the diffraction on the telescope aperture, and (vii) diffraction on objects partially obscuring the aperture (e.g. spiders). It is assumed that care is taken not to increase the point-spread-function wings by ghosting and scattering in the astronomical instrument and in its detector(s).

Using the resulting algorithms, we interpret observed stellar and solar image aureolae. The wavelength dependence of the point-spread-function wings is evaluated and applied to the performance estimates and technical specification definition of the CLEAR facility (CLEAR = ``Coronagraphic and Low Emissivity Astronomical Reflector"), a 4 meter class solar/stellar coronagraph presently under study.

Program listing for Wednesday