Optical characteristics and capabilities of the successive versions of Meudon and Haute Provence H$\alpha$ heliographs (1954-2004)

Abstract

H$\alpha$ heliographs are imaging instruments designed to produce monochromatic images of the solar chromosphere at fast cadence (60 s or less). They are designed to monitor efficiently dynamic phenomena of solar activity, such as flares or material ejections. Meudon and Haute Provence observatories started systematic observations in the frame of the International Geophysical Year (1957) with Lyot filters. This technology evolved several times until 1985 with tunable filters allowing to observe alternatively the line wings and core (variable wavelength). More than 6 million images were produced during 50 years, mostly on 35 mm films (catalogs are available on-line). We present in this paper the optical characteristics and the capabilities of the successive versions of the H$\alpha$ heliographs in operation between 1954 and 2004, and describe briefly the new heliograph (MeteoSpace) which will be commissioned in 2023 at Calern observatory.