Ju Hu

Spectral analysis and the two-dimensional distribution of physical parameters in a quiescent prominence

The profiles of Hα and Ca ii K lines of a arch quiescent prominence on April 1, 1971 have been analyzed and the two-dimensional distributions of electron temperature Te, micro-turbulence velocity vt and the column number density of hydrogen along the line-of-sight NH have been obtained. Te, υt, and NH are found to be 7500 K, 6 km s−1 and 2.2 × 1018 cm−2 on an average, respectively. The electron temperature at the central part of the prominence and along the two arcades are greater than that at the edges, while the distribution of the micro-turbulence velocity in these regions is opposite. There is no systematic variation in Te and vt, from the center to the periphery as described by Hirayama (1971). The column number density in the central region is lower than that at the two edges.The contour lines of Te, υt, and NH are predominantly vertical rather than horizontal. This implies that the height-variation of physical parameters in filamentary structure is small. The arrangement of this structure in the prominence is likely to be arched and is probably in the direction of magnetic field lines.

A CCD imaging spectrograph in the improved solar tower of Nanjing University

Since 1992 the solar tower telescope of Nanjing University (118°51′ E, 32°03′ N) as well as its multichannel solar spectrograph, originally established in 1982, have been reconstructed and a two-channel imaging spectrograph has been operated successfully. The apertures of the coelostat and the secondary mirror are both 60 cm. The spherical objective mirror, having an aperture of 43 cm and a focal length of 2170 cm, produces a solar image of 20 cm diameter. Two auxiliary telescopes using a small fraction of the coelostats aperture were set up for guiding and Hα monochromatic monitoring. A multichannel spectrograph can be operated in six wavebands simultaneously. A CCD imaging spectrograph can be used for data acquisition at Hα and Caii K line wavebands automatically and simultaneously. The instrument consists of two CCD cameras, an image processor (SR-151), a personal computer, and a mechanical scanning device. The principal characteristics of the instruments are described. Some observational results are presented as examples.

Spectral analysis of H?, H?, and H? lines of a white-light flare (3B/X6.1) on October 27, 1991

We have analyzed time series of Hα, Hβ, and Hγ line profiles taken from a 3B/X6.1 flare which occurred on October 27, 1991 in active region NOAA 6891. Each set of the spectra was taken simultaneously for the first 10 min of the flare event with a low and non-uniform time resolution of 10–40 s. A total of 22 sets of Hα, Hβ, and Hγ were scanned by a PDS with absolute intensity calibration to derive the dynamics and energetics of material in the flare region. Our results are as follows: (1) The Balmer line emitting region is accelerated downward to about 50 km s-1 for the first 50 s and then is decelerated to about 10 km s-1 for the next 150 s. (2) The radial velocity peak precedes the Balmer line intensity peak by about 40 s. (3) The total energy radiated from these Balmer lines is estimated to be 4.9 × 1029 erg.

Simultaneous monochromatic and spectral observations of two large loop prominence groups

Abstract Using the solar tower telescope of Nanjing University, we observed the two large loop prominence groups of 1982 Dec. 20 and 1983 Feb. 9. Hα photographs and spectra around the Hα and H and K lines were obtained simultaneously. From these data, we derived a line of sight velocity distribution, which agrees perfectly with the distribution for matter falling freely without viscosity. From the widths of the Hα and the K lines, we found the loop material to have a uniform kinetic temperature and a turbulent velocity that increases with height. From the central intensities of the lines we derived a density of n(H) ≅ 1.3 − 2.6 × 1010 cm−3. A possible mechanism of the formation of loop prominence groups and their relation with flares are discussed.

A study of the white light flare of 1974 September 10

Abstract We have made a detailed analysis of the spectral data of the white light flare of 1974 September 10. Using a non-LTE theory we have calculated a semi-empirical atmosphere model and its radiation loss. From the spectra we found (1) a Balmer jump amounting to 11% at the flare maximum, (2) strong and broad Balmer line emission, the width of the higher order terms reaching a minimum between main quantum number 8 and 9, and (3) the continuum emission peaking at about the same time as the microwave emission, a few minutes before the H α flare maximum. These features may be common to all white light flares. Analysis shows that the heating in the photosphere and lower chromosphere is probably produced by backwarming of the enhanced emission in the upper chromosphere, while the heating of the upper chromosphere is probably due to bombardment by high-energy electron beams.

The solar surge of 1982-12-30☆

Abstract We describe the morphology of the flare-accompanying solar surge of 1982-12-30 at S10W20 on the solar disk and give the time evolution of its velocity field. Observations of the spectrum show that there was rotating motion of 20–30 km/s during the ascent, which decreased in the course of time.

Analysis of high time resolution spectra of the 1991-10-24 white-light flare

Abstract This paper analyzes the spectrum of a Class 2N/X2.1 white-light flare obtained by the Nanjing University Solar Tower Multi-Wavelength Spectrograph on 1991-10-24 with a high time resolution (5s). A systematic comparison of the line profiles and continuum strength with the X-ray and radio burst data shows that the flare is a Type-I white-light flare with the following characteristics: 1) During the flare impulsive phase the central intensities of lines in different wavelengths, the continuum, the line half-widths, the red asymmetry of the wings and the hard X-ray burst at the high energy portion all reached maximum at the same time. 2) The Hα line had a half-width of 10 A when the continuum emission reached maximum, and showed strong line reversal at the center. Hβ and Hγ also showed line reversal. 3) The five lines observed all showed clear red asymmetry, which lasted some 1 min. Based on these results, we find electron-beam bombardment, combined with chromospheric evaporation and condensation can provide a good qualitative interpretation of the energy storage and release of this white-light flare.

Are White-Light Flares Related to High-Energy Particles?

Solar white-light flares (WLFs) are defined as those flares which are visible in optical continuum. Up to now, only less than 100 WLFs have been reported. WLFs are of great importance because they present the most extreme conditions in solar flares and provide a severe challenge to energy transport mechanisms and atmospheric models.

Spectral analysis of the 1984 October 18 solar prominence

Abstract On the basis of [11], we calculated the various physical parameters of the solar prominence of 1984 October 18, using further the method of complete linearization and a semi-empirical model on the N-LTE theory. Our conclusions are: 1. When finding the doppler width of prominence lines δλD, the method of complete linearization is more accurate than the classical method. 2. Our semi-empirical model based on the N-LTE computer program of [9] gave a central temperature of the prominence of ∼ 5900 K, the temperature increasing from the centre outwards, a turbulence velocity of 5.5 ∼ 6.5 km/s, and a mean hydrogen density n H = 3.8 × 10 11 cm −3 . Calcium was found to be mainly as CaII and CaIII, with n (CaIII) ⪢ n (Call). 3. Our calculated distribution of the column density of hydrogen over energy levels showed that the lower energy levels are in N-LTE, the higher ones, in LTE.