New Bands and Lines in the Twilight Sky Spectrum

Abstract

AT the Abastumani Astrophysical Observatory we have been making continuous observations of the twilight sky for seventeen years, with the view of studying the features of the Earth's atmosphere¹. In 1957, we began to study the twilight sky spectra by means of a grating spectrograph (grating 135 × 90 mm.², 1,200 lines/mm.; camera, f = 70 mm., dispersion 80 A./mm. in the red region). During the year beginning December 1957, 67 spectrograms were obtained in the region 5400–6800 A., of which 29 belong to the morning and 38 to the evening twilight. The well-known lines of oxygen, λλ6300–6364 A. [O I], 5577 A. [O I] and the sodium D-lines 5890–5896 A., are always present on these spectrograms. In addition, some new lines and bands appear permanently or episodically on them. Two such spectrograms are reproduced in Fig. 1. Table 1 contains the wave-lengths of the lines and bands (λ_obs.), the number of cases of their appearance (n) and the suggested interpretation. This is a preliminary interpretation in so far as in some cases the difference Δλ = λ_obs. − λ (λ is an accurate value of the line or band wave-length for a given atom or molecule) reaches the value of 4–5 A., which exceeds the probable error of measurement of λ_obs. (1–2 A.). Some additional systematic errors in the determination of λ_obs. may have occurred. They may be caused by the high intensity and the complicated structure of the continuous spectrum of the twilight sky, on the background of which one has to study faint lines and bands.