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Flux density calibration

Spectral flux density calibration of a meridian instrument is carried out using a grid of calibration objects that relatively uniformly cover the available sky region in the elevation angle. By observing objects at different elevations, the calibration curve of the conversion factor between antenna temperature and spectral flux density versus the antenna elevation angle is constructed. This curve reflects variation of antenna effective area and short-wave atmospheric absorption depending on radio source elevation allowing for actual aberrations due to the transverse offset of the primary feeds from the electric axis of the telescope. To calculate spectral flux density, a technique described in detail in Aliakberov et al., 1985 and Udovitskiy et al., 2016 is used.

In addition to the known secondary calibration objects, the so-called "ratan" ones are also used for observations at low angles. The list of the secondary standards used and their parameters can be found in Kovalev et al., 1999 and Udovitskiy et al., 2016 or in the RATAN-600 Documentation section. The parameters of the calibration objects measured with maximum accuracy at frequencies from 50 MHz to 50 GHz are presented in Baars et al., 1977; Ott and Witzel 1994; Tabara & Inoue, 1980; Perley et al., 2013; and Perley et al., 2017
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