© 1999-2004 Astronomical Institute of Kharkov University. Department of Solar, Lunar and Planetary Physics

CHROMOSPHERIC D3 HELIUM EMISSION OBSERVED AT THE TOTAL SOLAR ECLIPSE OF JULY 31, 1981

Akimov L.A., Beletsky S.A. , Dyatel N.P.

Investigations of the Sun at the solar eclipces are carried out at the Kharkov Astronomical observatory.

Abstract: The digital images of 350 eclipse chromospheric spectra obtained with a special automatic photometer have been used to construct the image of the D3 HeI chromosphere over the range of 36°N - 42°S in latitude. The chromospheric emission comes from two very irregular layers with peaks of the intensities at the heights of 1100 - 1700 km for the layer with the dominant emission, and at the height of around 300 km for the lower layer. The distribution of the surface brightness averaged over all measured latitudes (36°N - 42°S) versus height also reveals two peaks. The energy emitted by the upper layer is determined to be 7 times larger than that emitted by the lower one. The chromospheric D3 emission is well correlated with the emission of the green corona (503.3 nm) at low heights. The correlation disappears at heights more than 1500 km. The chromosphere above active regions and spots is lowered. It is supposed that such behaviour is affected by large scale magnetic fields of the Sun and by structural elements, such as spicules and fibrils.

Key words: Sun, chromosphere, eclipse, helium emission

Spectrogfram movies of the flash spectra with D3 HeI and D1,D2 NaI were obtained during the total solar eclipse of September 22, 1968, July 10, 1972, and July 31, 1981. The conventional method of processing was used for the eclipse of the 1968 and 1972 to obtain the intensities of the D3 helium emission at different heights over the limb for the selected points corresponding to Baily beads (Belkina, Dyatel, 1972; Livshits et al.,1976). The measurements of 350 spectra near the third contact of the 1981 eclipse were performed with a special automatic photometer to obtain the digital image of spectra. From this digital images, using the developed algorithms and software we constructed the image of the D3 chromosphere for the west limb (Fig.1). Here we see two very irregular emission belts with peaks of intensities at the heights of 1100-1700km and about 300km for the upper and lower belts respectively. The dominant emission above the active regions at the equatorial zone. Three bright prominences can be also seen there. It is possible to estimate the contribution of the energy emitted by each of the layers using the altitudinal distribution of the surface brightness averaged over all measured latitudes (36°N-42°S) (Fig.2).

Approximating the altitudinal energy distribution by normal distribution with reasonable coefficients we obtain that the energy emitted by the upper layer is 7 times larger than that of the lower one. From Fig.3.

which shows the variation of the helium emission integrated over all heights we obtain that the total energy of the emission above the active regions is 1.5-2 times of that for the normal chromosphere outside the equatorial zone. The comparison of the D3 integral brightness distribution for H=0,1500,3000km with similar distribution of the emission of the green corona (SGD, 1981) is shown in Fig.4.

We see that the D3 emission follows the intensity of the corona with dominant emission in the zone of active latitudes up to h=1500km. After h=1500km the behavior of the D3 emission changes. At the height of 3000km we do not see the dominant emission in D3 (excluding prominences) above the bright active region (0-25°S), moreover it is less than that of the normal chromosphere. Here the chromosphere lowers. We see the explanation of such distributions at different heights in both the large-scale magnetic fields of the Sun and chromospheric structure such as spicules and fibrils at heights more than 1500km. The results of the paper are in good agreement with those obtained from the 1968 and 1972 eclipses (Akimov et al., 1997)

R e f e r e n c e s
1. Akimov, L.A., Belkina, I.L. and Dyatel, N.P.,1997. Izv. Krymea Ast. Obs. in press.
2. Belkina, I.L. and Dyatel, N.P.,1972. Astron. Zh., 49, 588.
3. Livshits M.A., Akimov, L.A., Belkina, I.L. and Dyatel, N.P.,1976. Solar Phys. 49, 315.

2002/06/08