2012/09/05 by Cyril Bazin, Bazin, Cyril, S. Koutchmy +1
Physics and Astronomy · Computer Science · #Solar and Space Plasma Dynamics #Solar Radiation and Photovoltaics #History and Developments in Astronomy
paper · pdf · doi:10.48550/arxiv.1209.1027
We consider the use of the commercially available Fabry-Perot etalons (FP)\nfor the imaging of the solar chromosphere in the H alpha line of HI. Three\netalons of 40, 60 and 90 mm diameter were accurately analysed. At normal\nincidence the maximum transmission wavelength as well as the finesse were\nevaluated. Polynomial curves precisely fitting the transmitted central\nwavelength variations when using a quasi-parallel beam from a point-like source\nare presented. Further calibrations have been done with photometric accuracy\nusing a laboratory set-up comprising i/ a 16 bits CCD camera; ii/ a Littrow\nspectrograph of a spectral power 110000 giving a linear dispersion of 0.0058\nnm/pixel and iii/ an artificial Sun used as a light source and iv/ precisely\nadjustable in position optical components, including the F-P etalons. In\naddition, a precise laboratory wavelength calibration was performed using a low\npressure deuterium 2D spectral lamp simultaneously illuminating the adjustable\nentrance slit using a splitter before. The variations of the FWHM of the\nspectral transmission variations as a function of the incidence angle of a\nparallel beam are also given for each etalon. Consequences resulting from the\nuse of a low but significant aperture/ratio are tentatively discussed for the\nfirst time. An application to a precise photometric work of solar physics\ninterest when using limb filtergrams is illustrated and discussed, with\nemphasis on the photometric accuracy resulting from the use of such etalons put\nbefore the entrance aperture of an imaging telescope. Monochromatic images of\nthe solar chromosphere shell in the vicinity of the polar and equatorial limbs\nwere made using a small telescope, in order to deduce the variation of the\ntypical average thicknesses at poles and equator interpreted as a prolateness\neffect of the chromospheric shell observed during the last minimum of solar\nactivity (2009).\n