Exploring the outer emission corona spectroscopically by using Visible Emission Line Coronagraph (VELC) on board ADITYA-L1 mission

Abstract

It is very important to make the spectrographic observations of the outer emission corona in number of emission lines simultaneously in view of the results of the observations made in [Fe x] 6374 A, [Fe xi] 7892 A, [Fe xiv] 5303 A and [Fe xiii] 10,747 A coronal emission lines with the 25 cm coronagraph at Norikura Observatory in Japan. At ground based observatories, availability of number of hours of clear sky for coronagraphic observations is limited due to aerosols scattering and scattering from the internal coronagraph reflections. A space based coronagraph Visible Emission Line Coronagraph (VELC) on board ADITYA-L1 has been planned to perform spectroscopy in 3 out of the 4 emission lines mentioned above. Here, we discuss the various requirements for the parameters of the payload, given the specifications of the satellite, to observe the outer emission corona reliably with good Signal to Noise Ratio (SNR), realize the projected scientific goals and make the mission a great success.