Solar observation with the Fourier transform spectrometer I : Preliminary results of the visible and near-infrared solar spectrum

Abstract

The Fourier transform spectrometer (FTS) is a core instrument for solar observation with high spectral resolution, especially in the infrared. The Infrared System for the Accurate Measurement of Solar Magnetic Field (AIMS), working at 10–13 μm, will use an FTS to observe the solar spectrum. The Bruker IFS-125HR, which meets the spectral resolution requirement of AIMS but simply equips with a point source detector, is employed to carry out preliminary experiment for AIMS. A sun-light feeding experimental system is further developed. Several experiments are taken with them during 2018 and 2019 to observe the solar spectrum in the visible and near infrared wavelength, respectively. We also proposed an inversion method to retrieve the solar spectrum from the observed interferogram and compared it with the standard solar spectrum atlas. Although there is a wavelength limitation due to the present sun-light feeding system, the results in the wavelength band from 0.45–1.0 μm and 1.0–2.2 μm show a good consistency with the solar spectrum atlas, indicating the validity of our observing configuration, the data analysis method and the potential to work in longer wavelength. The work provided valuable experience for the AIMS not only for the operation of an FTS but also for the development of its scientific data processing software.

Solar Observation with the Fourier Transform Spectrometer. II. Preliminary Results of Solar Spectrum near the CO 4.66 μm and Mg i 12.32 μm

“…The recorded interferogram is presented in Figure 2(a). The inversion algorithm proposed by Bai et al (2021) is employed to invert the spectrum. The inverted CO 2 spectrum in the gas cell from 600 to 2000 cm −1 is shown in Figure 2(b).…”

“…More works should be done so as to obtain an accurate solar spectrum and further derive physical parameters. Bai et al (2021) built an experimental system, consisting of a Newtonian telescope, an optical fiber, and a newly installed FTS, Bruker IFS-125HR, at Huairou Solar Observing Station (HSOS). An inversion algorithm was developed and finally a solar spectrum at 0.4-2.2 μm was obtained from the original interferograms taken by the FTS.…”

“…The maximum wavenumber taken by the sunlight feeding experimental system in Bai et al (2021) is about 4545 cm −1 and the other part of the solar spectrum is cut off by the optical fiber. Moreover, the collecting area of the telescope is small since the diameter of the primary mirror is 10 cm.…”

Nonlinearity Correction of Fourier Transform Spectrometer in Solar Observation Using Simulated Annealing

“…Tens of physical parameters and their variations with the opacity are essential to reconstruct the dynamical threedimensional solar atmosphere, which is a basis for analyzing a variety of quiet or active solar phenomena (Feng et al 2020;Bai et al 2021). Solar spectra obtained by a Fourier transform spectrometer (FTS) provide an effective way to quantitatively analyze the physical parameters because of the FTS ultra-high luminous flux, high spectral resolution, and wide bandpass (Griffiths 1983;Revercomb et al 1988).…”

“…The FTS of AIMS will install a detector array of 64 × 2 to obtain the high-precise solar spectra in the mid-infrared wavelength. The FTS of AIMS spectral resolution reaches 0.6 Å, corresponding to 0.004 cm −1 , in Mg I 12.32 μm that is the working spectral line (Bai et al 2021). But now, we employed the Bruker IFS-125HR FTS with a point source detector as a temporary and simple experimental system at Huairou Solar Observing Station (HSOS), China.…”