Development of Fast Imaging Solar Spectrograph and Observation of the Solar Chromosphere

다국어 초록 (Multilingual Abstract)

Traditionally, solar observations have been performed by ground-based instruments. Next to the photosphere, the solar chromosphere has been studied well for a long time. It is well known from high-resolution observations that chromospheric features are fine structured, short lived, and dynamic. In obtaining physical parameters, spectrograph-based observations are more effective than filter-based observations. Through imaging spectroscopy using a spectrograph, chromospheric features and dynamics can be revealed. The biggest telescope, New Solar Telescope (NST), was recently built at Big Bear Solar Observatory. NST has a capability of high spatial resolution, 0.08′′ at 500nm, with the aid of Adaptive Optics. As one post-focus instrument of NST, an imaging spectrograph, called Fast Imaging Solar Spectrograph (FISS) was proposed and constructed by Korean researchers to study the solar chromosphere.
This thesis mainly describes our contribution to the development of this spectrograph and early results. FISS is a grating-based spectrograph with high spectral resolution, high time cadence, and the capability of imaging. It has a mount of Littrow type, records dual bands simultaneously, and uses an Echelle grating as the disperser and performs imaging using a field scanner. We describe its optical design and performance estimation. Software development, construction and integration of each component were completed in Korea Astronomy and Space Science Institute. Through tests, we confirmed that the performance of the spectrograph has come close to our expectation. After FISS was installed on the vertical table on the Coud´e room at Big Bear Solar Observatory, we observed various chromospheric features: active regions, quiet regions, filaments, prominences and so on.
We determined physical parameters of limb prominences observed by FISS. By applying a non-linear least square fitting of a radiative transfer model to the profiles of Hα line and CaII 8542˚A line, we derived physical parameters of the prominences. The ranges of temperature and non-thermal velocity are found to be 7,500 - 13,000K and 5 - 11km/s, respectively. The maximum temperature of prominences is found to be below 20,000 K. It is expected that FISS will contribute to revealing fine structures and the dynamics of the solar chromosphere with high resolution.

목차 (Table of Contents)

• 1. Introduction 11
• 1.1 Background 11
• 1.2 New Solar Telescope 13
• 1.3 Adaptive Optics 17
• 1.4 Necessity of a New Instrument 18
• 1.5 Outline 19
• 2. Instrument 21
• 2.1 Introduction 21
• 2.2 Design Concepts 22
• 2.3 Optical design 24
• 2.4 Estimation of spectral parameters 25
• 2.4.1 Theory 25
• 2.4.2 Estimation of parameters 29
• 2.5 Intensity Estimation 29
• 2.6 Components 32
• 2.6.1 Scanner 34
• 2.6.2 Slit 35
• 2.6.3 Collimating/Imaging Mirror 35
• 2.6.4 Disperser 36
• 2.6.5 Filter 37
• 2.6.6 CCD Cameras 39
• 2.7 Integration 39
• 2.7.1 Hardware 40
• 2.7.2 Software 40
• 2.8 Installation 47
• 3. Test 51
• 3.1 Configuration of feed optics 51
• 3.2 Laser Test 52
• 3.3 Sunlight Test 54
• 3.4 Conclusion 63
• 4. Early Observations 65
• 4.1 Data processing 65
• 4.2 Sunspots 67
• 4.3 Filaments 69
• 4.4 Active Regions 69
• 4.5 Quiet Regions 79
• 4.6 Prominence 79
• 4.7 Conclusion 79
• 5. Determination of physical parameters of prominences 83
• 5.1 Introduction 83
• 5.2 Model of Radiative Transfer 85
• 5.3 Data and Analysis 86
• 5.4 Results 87
• 5.5 Conclusion 101
• 6 .Conclusion 103