Spectroscopy of the Solar Corona Using Ground and Space-based Observations

Abstract

The outer solar atmosphere, the corona, is known for its million-degree temperature. The mystery surrounding the source of this high temperature is gradually being resolved with various theories, observations and models. However, the quest continues and the attempts to understand its detailed dynamics are in progress. Spectroscopy is a widely used technique to study the physical features of astronomical objects. The spectral line profile parameters are obtained and their features are examined. In this project, the coronal spectra from ground-based Fabry-Perot interferometric observations and space-based Hinode/Extreme ultraviolet Imaging Spectrometer (EIS) observations are studied. The various regions of the solar corona like active regions and coronal holes are analyzed. The primary aim is to study the intensity, Doppler velocity, line width and centroid, their inter-dependencies and their spatial and temporal variations. The Fabry-Perot interferograms were obtained during the total solar eclipse of 21 June 2001, observed from Lusaka, Zambia. The duration of the totality was 3 min 37 sec during which 14 interferograms were obtained. EIS is one of the three instruments onboard Hinode which observes the solar corona in the EUV band. The data can be obtained from different regions like the active regions, quiet sun, coronal holes, flares, prominences etc. in different wavelengths. Solarsoft/Interactive Data Language (IDL) is used for the data analysis. In the analysis using both the data, the Doppler velocity and the centroid obtained from the line profiles are mainly emphasized. It is observed that most of the line profiles have multiple components. A line profile is simulated by adding a stationary main component and a varying subsidiary component. The intensity, Doppler velocity and line width of the subsidiary component are changed to see how these two parameters affect the resultant Gaussian. The primary findings from the Fabry-Perot interferograms analysis are the variation of the abovementioned parameters during the totality and their correlations with the line width and the radial height. The nature of line profiles is studied in detail and it is seen how multiple components introduce asymmetry in them. The EIS spectral data were used to study the coronal active regions spread globally over the Sun for a duration of 13 years. The focus is on the Doppler velocity, centroid and line width, their inter-dependencies and cross-correlations with the solar cycle 24. The study is further extended to the coronal holes as well.