Combining visibilities from the Giant Meterwave Radio Telescop and the Nancay Radio Heliograph : High dynamic range snapshot images of the solar corona at 327 MHz

Abstract

We report first results from an ongoing program of combining visibilities from the GiantMeterwave Radio Telescope (GMRT) and the Nancay Radio Heliograph (NRH) to produce composite snapshot images of the sun at meter wavelengths. We describe the data processing, including a specific multi-scale CLEAN algorithm. We present results of a) simulations for two models of the sun at 327 MHz, with differing complexity b) observations of a complex noise storm on the sun at 327 MHz on Aug 27 2002. Our results illustrate the capacity of this method to produce high dynamic range snapshot images when the solar corona has structures with scales ranging from the image resolution of 49 ′′ to the size of the whole sun. We find that we cannot obtain reliable snapshot images for complex objects when the visibilities are sparsely sampled.