Méthode nouvelle pour la mesure CCD du diamètre solaire avec un astrolabe - A new method for CCD measurements of the solar diameter with an astrolabe

摘要: Observing the Solar disk is a challenge and, as for past visual observations, we have many re sults depending on observers and/or instruments. This was due to differences in perceptions of Sun's limb, instrumental errors and atmospheric disturbances. After long series observations at Calern Observatory, Francis Laclare felt need more impersonal automatic measurements diameter. analog CCD (1989-1995), digital data acquisition processing tested by Paris Observatory group (F. Chollet V. Sinceac) during 1996 spring Observatory. Before starting new continuous campaign confirm eventual variations diameter solar flatness, aim find best definition edge. The test spent comparing different solutions that were tried two astrolabes Ca lern Observatory: "classical” one, outfitted with eleven zerodur ceramic prisms (S astrolabe), has been used twenty years other hand an instrument equipped varying angle prism (V astrolabe) enabling (385 1996) perfecting know how.
This article focusses techniques their feasibility. Two procedures tried: first one alternately direct reflected images (separated using revolving shutter front objective) second mathematically sorts out both components inside computer (an image being two-dimensionral array numbers). According principle astrolabe, measured quantity exact time crossing parallel altitude (defined angle) edge, i.e. merging Sun focal plane telescope where matrix stands. Here comes edge frame collection inflect points luminosity function along each 256 useful lines (the 512 pixels). means numerical derivation performed every line video camera which stand vertical possible. Then, frame, through points, parabola fitted, least squares method. top this materializes prospective characteristic point. sets such associated corresponding times acquisition, are collected contact may be obtained. also when crosses almucantar.
The results semi-diameter obtained derived from sixty mask seven without it, Astrolabe. They give mean value 959″39 ± 0″ 03 scatter 0 ″ 29.
It interesting remark values error bar do not depend whereas does it.
It noticed going method made systematic slightly shrinks diameter, but can known statistically correction easily done. Choosing will matter following article.
The main advantage procedure stressed, it enables store full further reference if possible, better future processing.