Imaging of the Solar Atmosphere in K-Band through Single-Dish Observations

Alberto Pellizzoni, INAF - Osservatorio Astronomico di Cagliari

Single-dish mapping of the brightness temperature of the solar atmosphere in the radio band reveals free-free emission mostly originated by processes in local thermodynamic equilibrium plasma. In particular, long-term diachronic observations of the solar disk in K-band represents an effective tool to characterise the vertical structure and physical conditions of the solar chromosphere both for quiet and active regions, during their evolution at different phases of the solar cycle. We are performing continuum imaging of the solar chromosphere at 18-26.5 GHz (spatial resolution ~1 arcmin) by the 32-m diameter Medicina radio telescope and by the 64-m diameter Sardinia Radio Telescope (SRT), as a first scientific demonstration test for the potentialities of Italian single-dish antennas in this field. After a first test campaign aimed at defining and optimising hw/sw solar imaging requirements for the radio telescopes, the system will be fully ready in 2020 for systematic monitoring of the Sun providing: (1) accurate measurement of the brightness temperature of the quiet Sun radio component, presently poorly known in the 20-26 GHz range, and representing a significant constraint for atmospheric models; (2) characterisation of the flux density, spectral properties and long-term evolution of dynamical features (active regions, coronal holes, loop systems, streamers and the coronal plateau); (3) prediction tools for powerful flares through the detection of peculiar spectral variations in active regions, as a valuable forecasting aid for the Space Weather hazard network. We plan to publish our solar images on a dedicated web site, just after each solar observing session to ease their full exploitation by the wide multi-wavelength solar community, empowering both physical modelling and Space Weather forecast. We will present K-band solar images obtained during our early observations and prospects for joint observations with other facilities.