Observations of relative intensities of HgI and NaI emission lines

The mercury line HgI 5460A shows very large temporal variability, as seen in Fig. 3. The central intensity of this line varies in the ranges between 1.7 and 42.2 per cent relative to intensity of [OI] 5577A line, i.e. by 25 times. Generally, the variations if this line strength have seasonal nature. The lowest levels of intensity are observed in the summer time. But in several nights, the high level of light illumination up to 28 per cent is seen in summer time, too. Probably, these spectra were exposed at bad air transparency, through cirry or thin clouds with the essential amount of scattered city light. In the winter time, the intensity of mercury line increases on average by 4 or 5 times relative to summer time even at the clear cloudless sky, and reaches 10 per cent relative to [OI] line. In 2008 winter, since January 20 the open und unprotected mercury glow-discharge lamps were installed in the Nizhnyj Arkhyz, village of astronomers, and as a result, the level of relative intensity was no longer less than 20 per cent relative to [OI]. Additionally, the dispersion is increasing each winter. In one of winter nights, 2007 February 2007, in its second half, the changes of the HgI line intensity were detected dependent on the object location in the sky and ranged from 15 per cent near the southern horizon to 35 per cent near the northern horizon, that is by two times. Note that the basic sources of light pollution are located to the North of BTA.

Figure 3. Variations of HgI 5460A to [OI] 5577A line relative intensity depending on time. Annual levels of intensities for clear sky in the winter time are shown by the horizontal line sections.

The seasonal variations of HgI 5460A line relative intensity are shown in Fig. 4. The period of increasing pollution is marked here with a light background band. The increasing light pollution is seen since middle December till end of March. This is the time when the snow cover appears in Nizhnyj Arkhyz and surrounding highland villages. One can note that the midline of this period is shifted relative to December 22, the date of winter solstice. This means that the maximum of HgI/OI ratio is not connected with the seasonal weakening of [OI] line due to deep location of the Sun under horizon, but namely with the mercury emission and with the reflection of city lights from snow cover. Additionally sky pollution increases due to absence of leaves on the trees.

Figure 4. Variations of HgI 5460A to [OI] 5577A intensity ratio depending on season. Phase of 1-year period is calculated with the initial date of January 1. Date of observation marked with the color of the sign, the scale in years is shown to the right of the figure. Old observations are red and orange points, new ones are light and dark blue. Light background band is the time of a year when the snow cover in the asronomers' village of Nizhnyj Arkhys becomes settled.

The temporal variations of NaI/[OI] intensity ratio are shown in Fig.5. NaI line is a blend of two components 6A distant by wavelength. They are resolved in some spectrograms. As the central intensity of lines was measured, these few measurements are referred to brighter short-wave component, so the intensity of the blend is underestimated. The behaviour of NaI line resembles this one of HgI line. Total range of this line variation is twice as large as HgI range. Its ratio varies between 2 and 91 per cent, i.e. 45 times. The increasing of pollution level in winter due to snow cover is notable, too. In the season of 2008, minimum level of this ratio is 42 per cent, what is twice larger than in the previous season. The growth of the light pollution by this line from season to season is sharper than in HgI line.

Figure 5. Variation of NaI 5890+5896A to [OI] 5577A intensity ratio on time. Annual levels of the ratio taken for clear sky in winter are drawn by segments of horizontal line.

The seasonal variations of of sodium line relative intensity are shown in the Fig. 6. High light pollution was observed not only in winter, but in Summer and Autumn seasons, too. The record value of 91 per cent was reached on the night of 2006 November 30 during the observations of CI Cam, the 12 mag star. There is a record in the journal of observations that the observations were done with clouds on the sky. This is a prime evidence that the light pollution by mercury and sodium emission increases due to scattering city lights on the aerosol and nebulosity in the lower layers of the atmosphere.

Figure 6. Variations of NaI 5890+5896A to [OI] 5577A intensity ratio depending on season. Phase of 1-year period is calculated with the initial date of January 1. As in the Figure 4, date of observation marked with the color of the sign, the scale in years is shown to the right of the figure. Old observation are red and orange points, new are light and dark blue ones. Light background band is the time of a year when the snow cover in the asronomers village of Nizhnyj Arkhys becomes settled.

The dependence between relative intensities of mercury and sodium is shown in the Fig. 7. This was drawn including only those spectrograms where both lines, HgI and NaI are visible. This is a weak dependence. For example, when the intensity of HgI is 5 per cent of [OI], the relative intensity of NaI varies in the range between 6 and 37 per cent. Newertheless, as mean at the low level, HgI line intensity increases so as NaI with the proportion 1 : 1. This means that the artificial component of NaI contributes about the same light amount as this one of HgI emission.

Figure 7. Dependence between the relative intensities of HgI 5460A line and NaI 5890+5896A line.

Continue:
Night sky spectrum of the Special Astrophysical Observatory.
Observations of relative intensities of HgI and NaI emission lines
Characteristics of interference due to light pollution at the SAO observational sight.
Light pollution sources-1.
Light pollution sources-2.
Results and conclusions.
Continued. Monitoring the situation.
THE WATER-BOTTLING PLANT IS STARTED-UP IN THE CENTER OF LIGHT-PROTECTED ZONE OF 6-METER TELESCOPE.