Combining visibilities from the giant meterwave radio telescope and the Nancay radio heliograph

High dynamic range snapshot images of the solar corona at 327 MHz

¹ Observatoire de Paris, LESIA, 5 place Janssen, 92190 Meudon, France e-mail: claude.mercier@obspm.fr
² Inter-University Centre for Astronomy and Astrophysics, PO Bag 4, Ganeshkhind, Pune-411007, India
³ NCRA - TIFR, PO Bag 3, Ganeshkhind, Pune University Campus, Pune-411007, India
⁴ Physical Research Laboratory, Astronomy & Astrophysics Division, Navrangpura, Ahmedabad-380009, India

Received: 13 June 2005
Accepted: 1 October 2005

Abstract

We report first results from an ongoing program of combining visibilities from the Giant Meterwave Radio Telescope () and the Nancay Radio Heliograph () to produce composite snapshot images of the sun at meter wavelengths. We describe the data processing, including a specific multi-scale  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 emphasize that snapshot images of a complex object such as the sun, obtained by combining data from both instruments, are far better than images from either instrument alone, because their uv-coverages are very complementary.