ON STAR CHAINS AND DARK FILAMENTS IN GALACTIC NEBULAE BY V.G. FESSENKOV (ASTROPHYSICAL INSTITUTE ALMA ATA)

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• Document Number (FOIA) /ESDN (CREST): CIA-RDP80T00246A003300220003-8
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• Document Creation Date: December 21, 2016
• Document Release Date: November 17, 2008
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ON STAR. CHAINS AND DARK FILAMENTS IN GALACTIC NEBULA;
By V.G.Fessenkov (Ast rophysical Institute, Alma Ata)
When investigating sufficiently dense..sta,r fields one
often finds some short,currents -of s'tgrs oriented with a
certain regularity and in a few cases connected with dark
filaments of the galactic nebulae. Yet it is necessary to
be very cautious in the interpretation of this phenomenon,
because even completely accidental clustering.of some ob-
.jectsscan.sometimes lead to interesting deviations from ho-
mogeneity.
This can be illustrated by the artificial star fields
obtained by us in the following manner. 400-black cards
3,5 x 3,5 cm in size were prepared. Every card was succe-
ssively placed between electrodes of the Rumkorf coil and
perforated during some. time by means of electric dischar
ges. The position of the card may be continually changed
during the exposition, The direction of the spark is deter-
mined by random fluctuations in conductive air layer between
the electrodes. Each card ,becomes perforated owing to this
procedure by nearly 250 extremely small holes:. These cards
were further successively exrposed with.a certain magnifica-
tion on the same photographic plate. Negatives with many
thousands black dots of very minute sizes were obtained.in
this manner; the superposition of several negatives prepa-
red independently permit to obtain an artificial star field
containing 100 000 or even more "stars" on""the area of
10x10 cm.
Another method, perhaps a more trustworthy one, but'
much more slow, consists in denoting the rectangular coordi-
nates obtained by means of registration Of the.positio'n of
small ball in a rotating, wheel (roulette).
.The artificial star fields obtained in 'such a manner
are characterised by noticeable irregularities. Sometimes
short chains containing few stars and even oriented parallel
to other similar chains in their close proximity are present.
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The fluctuations of density, i.e. the fluctuations, in the
number of stars per unit area occur always, as it may be pre
dieted with fair exactness, by the probability theory. Never-
theless these fields: of accidental objects never show any sy -
stematic streaming on a considerable area, as well as chains
with intervals.between the components much smaller than the
mean distance between the stars of a given.field. This artifi-
cial field is represented as an example in Fig.I.. An area of
10 x 10 cm conta,.nsnearly 50 000 small dots distributed qui-
te arbitrarily.
.It may be e;'oncluded that only very close stellar chains
may be considered with high probability as physically conneo-
ted0 But even in this case some additional arguments must be
advanced in favour of this conclusion.
Figure 2 represents an example of a short chain contai-
ning about 7 stars very closely together and apparently of'
the same colour. This object was photographed with the Mak-
sutov telescope of the-Alma Ata Astrophysical Observatory*.,
It is situated in the neighbourhood of the galactic nebula NGC,281
NGC 281 and its coordinates are
c =Oh47:4 5=5603
The scale of the figure is I' in 13.8 mm.
Analogous star chains are present in differ,erit parts of
.the sky, especially near the-dark galactic nebulae. Very oft
ten they are intimately connected with extremely elongated
dark filaments following. them at some length..As'a suffici-
ently conspicuous example the region of the gaseous nebula
McDonald 12 in Cygnus can be indicated. (See Fig.3).
One can easily see numerous dark filaments in the same,
approximately West-East directions The width of these fila-
-ments is nearly P. One of them represents a narrow continua-
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:;ion of a very outstanding; dark lane of the same orientation
in the northern part. of the picture.
In some parts of these filaments and at their border ve-
ry narrow star chains, are located, whose components are near-
ly of the same colour. This can be demonstrated by comparing
the photographs taken in red and blue-light, for instance by
comparing; the=plates of the Palomar. .Atlas of the correspon-
ding;parts of the sky. Figure 4 represents our evaluation of
the stellar magnitudes of five.different star chains in the
region of McDonald 12, using the charts of the Palomar Atlas.
Some of.these chains are indicated in Fig.39 and more clear-
ly in Fig.-5 (scale 201r/mm).
It may be noted that-the colour of all. stars belonging
to the same chain is almost always the same. Moreover.,, it
is stated that bright star chains, namely of 13-14 mg.are
characterised by a small colour index corresponding to type
A, but,the fainter chains are considerably redder in appea-
rance, namely have a colour index equal to one or even one
and a half.
What is the probability that-.these star chains are phy-
sically real?.As it was previously shown this probability
in a very dense.star field is very small from.the statisti-
cal point. of view. But in reality.we have some additional.,
evidence pointing in favour of physioal.oonnections between
the components of the same.chain, namely the similarity in,
colour and the apparent connection with-the dark filaments,.
This was also indicated recently. by Prof.Martynov (I).
Nevertheless, if these systems are ,generally not acciden-
tal agglomerations of stars, then they must be unstable and
consequently very' rare. Purely random{ arrangements of_, diffe--
rent kinds can surely appear in a dense star field.. But
their connection with dark filaments merits further '.tten-
tion.
Nowa few words about the dark filaments, which are,-pre-
sent, in different parts of the sky? usually as so;ne, peculiar-
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rity of gaseous nebulae. It is to be noted that in the
charts of the~Plomar Atlas these filaments are much less
distinguishable, because of numerous faint stars, which
appear in the area of the filaments.
By comparing these features, photographed with- diffe-
rent exposures up to different limitinggstellar.mad"nitudes,
one'can evaluate the, apparent decrease in the number of
stars and consequently the corresponding absorption.. This
absorption is not very,great and generally does not sur-
pass one stellar magnitude:
In the case of the above mentioned dark. filaments in
the region of I Ic Donald 12 in Cygnus their 'width at ?a' dis-
tanc?e of 1000 parsecs corresponds to nearly 0,3 ps. It is
.reasonable to assume that.their thickness in the line of
vision is substantially the same. Adopting now that gene-
ral absorption of light in this region of space i3. some
2-3 mg .per 1000 parsecswhich corresponds to a density of
.the order of 6.10-26 gar/cm3, one can arrive to the conolu
s_i.on that the density of the dust. in the dark filaments
may attain the value as high as 10 22 gr/cm3.or nearly
1000 times greater, than the average for interstellar spa-
ce. The probable presence of gaseous matter must increase
the density still more,
References
I. D.J.trlartynov, Astronomical Circular N 149,1954
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