Method of composing two-dimensional scanned spectra observed by the New Vacuum Solar Telescope

Abstract

In this paper we illustrate the technique used by the New Vacuum Solar Telescope to increase the spatial resolution of two-dimensional (2D) solar spectroscopy observation involving two dimensions of space and one of wavelength. Without an image stabilizer at the NVST, a large scale wobble motion is present during the spatial scanning, whose instantaneous amplitude could reach up to 1.3 ′′ due to the earth's atmosphere and the precision of the telescope guiding system, and seriously decreases the spatial resolution of 2D spatial maps composed with the scanning spectra. We make the following effort to resolve this problem:the imaging system (e.g., the TiO-band) is used to record and detect the displacement vectors of solar image motion during the raster scan, in both the slit and scanning directions. The spectral data (e.g., the Hα line) which are originally obtained in time sequence are corrected and re-arranged in space according to those displacement vectors. Raster scans are carried out in several active regions with different seeing conditions (two rasters are illustrated in this paper). Given a certain spatial sample and temporal resolution, the spatial resolution of the composed 2D map could be close to that of the slit-jaw image. The resulting quality after correction is quantitatively evaluated with two methods. Two-dimensional physical quantity, such as the line-of-sight velocities in multi-layer of the solar atmosphere, is also inferred demonstrating the effect of this technique.

The Co-alignment of Winged Hα Data Observed by the New Vacuum Solar Telescop

“…The MHRIS includes two broad-band interference filter channels (TiO-band and G-band) and three narrow-band Lyot filter channels (Hα, Ca II 3933 Å and He I 10830 Å). The grating spectrometer system (Cai et al 2018a,Cai et al 2018b) consists of the MBS in visible lines and the HDS in near-infrared lines. In this paper, we focus on aligning the winged data of the Hα imaging system.…”

“…However, these spectroscopic images of different wavelength are strict matching in principle, because each spectrum is the performance of a same position on the solar surface within the wavelength range. (Cai et al 2018a). The other method takes monochrome images in different wavelengths based on the narrow-band filtergrams (Bonaccini & Stauffer 1990, Wöhl et al 2002.…”

Research progress based on observations of the New Vacuum Solar Telescope

“…A 316 mm −1 echelle grating is used to obtain the high order spectrum of the He I 10830 nm (the 5th order) and Fe I 1.56 micrometer (the 3rd order). The precise reduction of these spectra observed by the NVST can be seen from Wang et al (2013), and Cai et al (2017Cai et al ( , 2018 [3][4] [9].…”

“…NVST is a vacuum solar telescope with a 985 mm clear aperture located at the Fuxian Solar Observatory of the Yunnan Observatories [1]. The main instruments include the high-resolution multi-channel imaging system [2] and the high dispersion multi-wavelength spectrograph [3] [4]. The two systems have identical focus and are arranged to be perpendicular to each other.…”

The Co-alignment of Winged Hα Data Observed by the New Vacuum Solar Telescope*

“…The advantage of this method is its high spectral resolution and free spectral range, which is capable of investigating the high-speed and multi-atmospheric layer solar features. The 2D spectroscopic images of different wavelengths, which are subsequently synthesized by the scanning spectrograms, are strict matching within a single scan in principle, because each spectrum is the performance of a same position on the solar surface within the wavelength range of a spectrogram (Cai et al 2018b). The other method takes monochrome images in different wavelengths based on the narrow-band filtergrams (Bonaccini & Stauffer 1990;Wöhl et al 2002;Liu et al 2014;Deng et al 2019).…”