Twilight enhancement observation of the infrared helium line 10830 angstrom (nablyudeniye sumerochnoy vspyshki infrakrasnoy linii geliya 10830 angstrom)

N 65 - 22588

NASA TT F-82U5

TWILIGHT ENHANCEMENT OBSERVATION OF THE INFRARED
HELIUM LINE 10830 A

by

P.V. Shcheglov

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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON JUNE 1962

DRAFT TRANSLATION NASA TT F-82 U5

JUN 2 2 1962

TWILIGHT ENHANCEMENT OBSERVATION OF THE INFRARED
HELIUM LINE 10830 A

(Nablyudeniye sumerechnoy vspyshki infrakrasnoy linii

Geliya 10830 A)

Astronomicheskiy Zhurnal by P. V. SHCHEGLOV

Tom 39, vyp.l, 158 - 159,
Izd-vo A. N.SSSR, 1962

The observation of the helium line 10830 A in the night -
and twilight-sky glow is of considerable interest for geophysics.
The mechanism of such glow in aurorae has been studied in detail in
reference p.]. The possibility of observing the twilight enhancement
of the helium line 10830 A, excited by the resonance emission lines
of helium 537 and £81* A in the extreme ultraviolet region of the
solar spectrum is also indicated there.

We made an attempt to observe the line 10830 A in twilight
on February 1961, using an interference monochromator which consisted
of a dielectric light filter at A = 10830 A, behind which a Fabry —
Perot 6talon was disposed. The latter was provided with multi-layer
coverings for that spectral region. The problem of contour determina-
tion of the helium line was not set up ; the 6talon had an instrumental
contour near 2 A, and served only as indicator of the presence of mono-
chromatic emission; that is why the triplet structure of the line
10830 A was not washed away. The whole system's filtration for the

helium line is sufficiently high and apparently nearly eoual to that
of the interfefometer light-filter. The equivalent width of the band of
continuous emission passing through the system did not exceed 5 A.
Therefore, from the standpoint of its effectiveness, the utilized mono-
chromator is superior to the usually applied for similar observations
high-aperture ratio diffraction spectrographs.

The image of the interference pattern was constructed by an
objective f = 90 mm 1 : 2 on the cathode of an electron-optical conver-
ter, which served as image receiver. The etalon was so inclined during
the observations as to register the center-distant interference rings .

The results of observations may be seen from Fig. la, S 9 6.
In Fig.l a, the twilight is still rather bright and the night-sky glow
conceals the interference pattern of the line. The latter is well seen
in Fig. 1l6 where the buildings are outlined against the background in
the lower part of the picture. Finally, a total disappearance of inter-
ference fringes is noted in Fig, 18 . The photographs were obtained by
means of 15 minute exposures directly following one another. The absence

of fringes in the third photo is of particular importance. It attests to

o

the fact that precisely the twilight enhancement of the line 10830 A is

registered, and not the head of the hydroxyl band in the night-sky glow,
whose wavelength is near that of helium line. The disappearance of fringes
in the third photo indicates also that the interference pattern of Fig.l
cannot be explained by light diffusion of street lighting gas-discharge
lamps, where helium is present.

3.

Twilight sky glow in the line 10830 A was observed by us in
April I960 with the aid of the same instrumentation. It was noted that
the decrease in helium line intensity is slower at those observations
than in wintertime, which is explained by a greater twilight duration.
Apparently, the line 10830 A emission may be not only observed in the
twilight enhancement, but also in the night sky. Such observations may
provide indications on helium distribution in the terrestrial atmosphere
and on its temperature. The contour of the line IO83O A may be measured
interferometrically to that effect. Besides, similarly to the fact that
the geocoronal line H* emission is an indication of solar emission in
Lfc J ooservable from the ground, the observation of line IO83O A will
allow to keep track of Sun's activity in the lines 58k and 037 X.

-;hkbh<- END -JHHHBfr

State Astronomical Institute Entered on

in the name of 8 May 196l

P. K. Shterriberg.

REFERENCE

1. N. N. SHEFOV . Issledovaniye novykh emissiy verkhney atmosfery na

Zvenigorodskoy stantsii v period MGG (dissertatsiya) .
(Investigation of new emissions in the upper atmosphe-
re at the Zvenigorod station during the IGY Period.
(Dissertation), Moscow, i960.

Translated by ANDRE L. BRICHANT
for the

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION.

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Pac. 1. CyMepeiiian ucnuuiKa Jiumiii 10830 A
Fig.l. Twilight enhancement of the
line 10830 A

AcTpoHOMH'i.-- -i.ii it wypitaji, N» 1

Astronomicheskiy Zhurnal
No.l, 1962