Search

The ideal optical system can realize point-to-point imaging, but for an actual observation it is difficult to achieve this ideal phenomenon due to the instrumental effects of imaging system, which is usually described as the instrument profile in the imaging process of a grating spectrometer. The existence of the spectrometer instrument profiles introduces systematic errors in the observed spectral lines, which make the spectrum of the studied objects degenerate and blur. In this paper, we take the spectral data in the $\mbox{H}\upalpha $ band observed by the Multi-Band Spectrometer (MBS) of the New Vacuum Solar Telescope (NVST) as an example; according to the characteristics of its acquired spectral data, we calculate the instrument profiles of the MBS in the spatial and the dispersion direction. The results are, respectively, $0.25''$ and 115 mA, which might reflect the influence of the MBS optical instruments at that time in the $\mbox{H}\upalpha $ band. Then the spectral data is deconvolved separately in the two directions by the corresponding IP to obtain the higher spatial and spectral resolution of the NVST spectral data.

Solar time series analysis is one of the most important topics in statistical astrophysics, which aims at revealing the complex dynamical behavior of long-term solar magnetic activity. In this work, several statistical analysis techniques are combined to study the long-term persistence and phase relationship of monthly filament activity between the low latitudes and the high latitudes during the time period from 1957 April to 2010 June. Based on these advanced analysis approaches, the following remarkable results are found: (1) solar filament activity at the low latitudes lags behind that at the high latitudes with a phase shift of 40 months, and the largest positive coefficient is found to be 0.35; (2) solar filament activity at both the low and the high latitudes exhibits a strong long-term persistence behavior, that is, their nonlinear dynamical behavior could not be regarded as stochastic phenomenon; (3) the relative phase relationships between the low latitudes and the high latitudes are not in phase for the studied periodic scales, but they are coherent in the periods of 10-14 years. To sum up, the analysis results could give more useful information on our understanding the solar and the stellar dynamo theory, and also provide some crucial roles of solar magnetic activity variations.

We present a precise and complete procedure for processing spectral data observed by the one-meter New Vacuum Solar Telescope (NVST). The procedure is suitable for both sit-and-stare and raster-scan spectra. In this work, the geometric distortions of the spectra are first corrected for subsequent processes. Then, considering the temporal changes and the remnants of spectral lines in the flat-field, the original flat-field matrix is split into four independent components to ensure a high-precision flat-fielding correction, consisting of the continuum gradient matrix, slit non-uniform matrix, CCD dust matrix, and interference fringe matrix. Subsequently, the spectral line drifts and intensity fluctuations of the science data are further corrected. After precise reduction with this procedure, the measuring accuracies of the Doppler velocities for different spectral lines and of the oscillation curves of the chromosphere and photosphere are measured. The results show that the highest measuring accuracy of the Doppler velocity is within $100~\mbox{m}\,\mbox{s}^{-1}$ , which indicates that the characteristics of the photosphere and chromosphere can be studied cospatially and cotemporally with the reduced spectra of the NVST.

Magnetic field structures on the solar atmosphere are not symmetric distribution in the northern and southern hemispheres, which is an important aspect of quasi-cyclical evolution of magnetic activity indicators that are related to solar dynamo theories. Three standard analysis techniques are applied to analyze the hemispheric coupling (north-south asymmetry and phase asynchrony) of monthly averaged values of solar Hα flare activity over the past 49 years (from 1966 January to 2014 December). The prominent results are as follows: (1) from a global point of view, solar Hα flare activity on both hemispheres are strongly correlated with each other, but the northern hemisphere precedes the southern one with a phase shift of 7 months; (2) the long-range persistence indeed exists in solar Hα flare activity, but the dynamical complexities in the two hemispheres are not identical; (3) the prominent periodicities of Hα flare activity are 17 years full-disk activity cycle and 11 years Schwabe solar cycle, but the short- and mid-term periodicities cannot determined by monthly time series; (4) by comparing the non-parametric rescaling behavior on a point-by-point basis, the hemispheric asynchrony of solar Hα flare activity are estimated to be ranging from several months to tens of months with an average value of 8.7 months. The analysis results could promote our knowledge on the long-range persistence, the quasi-periodic variation, and the hemispheric asynchrony of solar Hα flare activity on both hemispheres, and possibly provide valuable information for the hemispheric interrelation of solar magnetic activity.

In this paper we illustrate the technique used by the New Vacuum Solar Telescope (NVST) to increase the spatial resolution of two-dimensional (2D) solar spectroscopy observations involving two dimensions of space and one of wavelength. Without an image stabilizer at the NVST, large scale wobble motion is present during the spatial scanning, whose instantaneous amplitude can reach 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 scanned 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 H alpha 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 sampling 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. A physical quantity, such as the line-of-sight velocities in multiple layers of the solar atmosphere, is also inferred from the re-arranged spectrum, demonstrating the advantage of this technique.