An interesting property of the Meridian Circle was noted and studied by us since the beginning of the programme in a parallel work. It is well-known that the image profile of refractor instruments, like the Valinhos Meridian Circle, suffers distortions because of the objective chromatic aberration. This effect provokes that, in the focal plane of the instrument (in which the CCD is placed), a composition of several Gaussians (which are the intersections of the flux distribution formed at higher wavelengths) is actually observed. We display in Fig. 14 an observed flux distribution and a tentative pure Gaussian fit. As expected, the Gaussian does not fit the "wings" of the profile well since there is a non-negligible contribution from wavelengths other than the one for which focus is made.
Thus, the image profile reflects to a large extent intrinsic properties of the observed objects as modulated by the optical system. We are working to simulate the true (observed) profiles and expect some correlation between the profile shape and spectral type. This can be a future tool to obtain quick spectral information in the single-filter observations of the Meridian Circle, limited to the brightest stars that are better sampled.
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