The Italian Panoramic Monochromator, recently installed at THEMIS, is
a post-focus instrument which, preserving all the telescope
spatial resolution (
), allows to obtain narrow-band
(FWHM = 21.5 mÅ at 5500 Å) monochromatic images of the solar
surface with high wavelength stability (better than 10
ms-1 in 10h) and spectral homogeneity of the field
(
10 ms-1). Although it is not long that the
instrument is operative, some improvements are already under study,
to overcome two present instrumental limitations: a too small field of
view and a too slow acquisition rate.
In principle, to increase the field, two makeshift solutions are possible. The first one consists in reducing, by means of a suitable optical interface, the effective focal length of the telescope, preserving the relative aperture: in this case the field increases at the expense of the spatial resolution. The second one consists in changing the optics of the instrument to increase the aperture of the beam incident on the interferometer: in this case the field increases at the expense of the spectral resolution. Both these solutions, however, cannot be adopted, due to mechanical constraints.
In the future the present interferometer will be replaced by a new one with a larger diameter, and larger and faster CCDs will be used. This solution will allow to increase the acquisition rate and the field of view, while preserving all the present spatial and spectral resolution.
Acknowledgements
Thanks are due to Prof. A. Righini for his useful suggestions, to Dr. G. Ceppatelli for having written the control software for the instrument, to Mr. G. Falcini and Mr. S. Paloschi for having built the mechanical structure and the electronic controls, to Mr. T. Grisendi and Mr. F. Fabiani for having secured part of the observations performed in Arcetri and for their contribution to the installation at THEMIS. Prof. A. Egidi, Prof. S. Cantarano and Dr. F. Berrilli have built the CCD acquisition systems and written their software; Dr. S. De Muro and the mechanical workshop of the Physics Department of "Tor Vergata" University have designed and built part of the mechanical supports necessary for the installation of the IPM at THEMIS.
This instrument was built with the contribution of the Consiglio Nazionale delle Ricerche (CNR), the Osservatorio Astrofisico di Arcetri, the Università di Firenze and the Università di Roma II.