The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory
The first director of the Crimean Astrophysical Observatory academician G. A. Shajn actively studied the interstellar medium in the Galaxy and galaxies in the 1950s. He and his followers showed first that the interstellar medium consisting of gas and dust is important component of galaxies. Observat...
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irk-123456789-796522015-04-04T03:01:53Z The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory Pronik, I.I. MS3: Physics of Stars and Galaxies The first director of the Crimean Astrophysical Observatory academician G. A. Shajn actively studied the interstellar medium in the Galaxy and galaxies in the 1950s. He and his followers showed first that the interstellar medium consisting of gas and dust is important component of galaxies. Observational evidence in favour of the star formation from interstellar clouds were obtained. 2005 Article The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory / I.I. Pronik // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 250-258. — Бібліогр.: 57 назв. — англ. 0233-7665 http://dspace.nbuv.gov.ua/handle/123456789/79652 en Кинематика и физика небесных тел Головна астрономічна обсерваторія НАН України |
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MS3: Physics of Stars and Galaxies MS3: Physics of Stars and Galaxies Pronik, I.I. The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory Кинематика и физика небесных тел |
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The first director of the Crimean Astrophysical Observatory academician G. A. Shajn actively studied the interstellar medium in the Galaxy and galaxies in the 1950s. He and his followers showed first that the interstellar medium consisting of gas and dust is important component of galaxies. Observational evidence in favour of the star formation from interstellar clouds were obtained. |
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Pronik, I.I. |
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The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory |
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The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory |
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The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory |
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The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory |
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astronomical school on galaxies founded by academician g. shajn at the crimean observatory |
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Головна астрономічна обсерваторія НАН України |
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MS3: Physics of Stars and Galaxies |
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The astronomical school on galaxies founded by academician G. Shajn at the Crimean Observatory / I.I. Pronik // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 250-258. — Бібліогр.: 57 назв. — англ. |
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Кинематика и физика небесных тел |
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AT pronikii theastronomicalschoolongalaxiesfoundedbyacademiciangshajnatthecrimeanobservatory AT pronikii astronomicalschoolongalaxiesfoundedbyacademiciangshajnatthecrimeanobservatory |
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2025-07-06T03:40:38Z |
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2025-07-06T03:40:38Z |
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1836867376209985536 |
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THE ASTRONOMICAL SCHOOL ON GALAXIES FOUNDED
BY ACADEMICIAN G. SHAJN AT THE CRIMEAN OBSERVATORY
I. I. Pronik
Scientific-Research Institute “Crimean Astrophysical Observatory”
Nauchny, 98409 Crimea, Ukraine
e-mail: ipronik@crao.crimea.ua
The first director of the Crimean Astrophysical Observatory academician G. A. Shajn actively
studied the interstellar medium in the Galaxy and galaxies in the 1950s. He and his followers
showed first that the interstellar medium consisting of gas and dust is important component of
galaxies. Observational evidence in favour of the star formation from interstellar clouds were
obtained.
INTRODUCTION
The first director of the Crimean Astrophysical Observatory (CrAO) academician Grigory Abtamovich Shajn
at the end of his life in the 1950s actively studied the interstellar medium of the Galaxy. This work initiated
studies under his leadership of the Galaxy and galaxies using data on gaseous nebulae, dust clouds, and stars.
Observations were carried out near the settlement Simeiz – one of the resorts of the Great Yalta. At the beginning
of the 1950s, G. Shajn and V. Gase fulfilled an imaging survey of the Milky Way in the hydrogen Hα emission
line. Their program was published in [40, 45]. Before this survey, only about 80 emission nebulae were known.
The Simeiz catalogue by V. Gase, G. Shajn [10] has listed 301 objects, the majority of which were new diffuse
emission nebulae. Their “Atlas of diffuse gaseous nebulae” [47] was one of the most popular surveys at the time
before the completion of the Palomar Sky Survey.
G. Shajn and V. Gase [48, 49] showed that the interslellar matter is important component of the Galaxy.
It was thought before the 1950s that emission nebulae are stable objects with the irregular morphology. G. Shajn
and V. Gase [45, 46, 51] found emission nebulae with different morphological properties. They discovered
a principally new class of nebulae – supernova remnants, which are not excited by stars. An example is
the Cygnus Loop. They found a filamentary nebula of such type, S 151 in Auriga [50]. S. Pikelner [20] proposed
that an excitation mechanism of the supernova remnant is the collision of the intersected shocks.
G. Shajn and V. Gase suggested first the idea that the expansion and directed motion in diffuse nebulae are
influenced by the Galactic interstellar magnetic field. G. Shajn [41–43] has shown first from the observations
that the interstellar matter, consisting of gas and dust with a frozen magnetic field, is an important component
of the Galaxy.
G. Shajn and V. Gase [48, 49] found first that diffuse gaseous nebulae have masses of hundreds and thousands
solar masses and that nebulae are not ejected from the stars.
A wealth of data on the emission nebulae allowed Shajn to suggest the idea about their evolution [41, 42].
He found that gaseous nebulae are linked with the groups of young stars [43, 52]. Their evolution proceeds
on different discrete spatial scales: about 10 pc, 100 pc, and several hundred pc [38, 43, 52]. In particular,
G. Shajn [44] studied a large region in the spiral arm near the Sun. This region of 1000 pc in size, contains
diffuse matter with the frozen magnetic field and can represent a place for future star formation.
Short reviews of the emission nebulae studies by G. Shajn and V. Gase are made by S. Pikelner [21, 22] and
V. Pronik [34].
STRUCTURE OF THE GALAXY
Using the data of more than 300 diffuse gaseous nebulae with their exciting stars, V. Gase [9] first prepared
the sketch of patches of the three nearest to the Sun spiral arms of the Galaxy in Orion, Perseus, and Sagittarius.
A general picture of her sketch remains valid up to now.
To search for exciting stars of emission nebulae new catalogues of stars of early spectral type were needed.
G. Shajn [40] described the research plan for this study: “Partly for that purpose spectroscopic observations of
stars brighter than 12.2m, by means of a 400 mm camera equipped with a 410 mm prism (6.9◦) are being carried
c© I. I. Pronik, 2004
250
out at the Simeiz Observatory. Star magnitudes, colour indices, and colour excesses are also being determined,
mainly in the regions with emission nebulae.” A short summary of the Shajn’s Plan was given by G. Shajn and
V. Gase [45]. This plan was later transformed to the Plan of the Galaxy structure studies.
The Shajn’s Plan was fulfilled by 12 researchers. Seven researchers worked at the Crimean Astrophysical
Observatory: E. Brodskaja, R. Ikhsanov, I. Kopilov, L. Metik, I. Pronik, P. Shajn, G. Sharapova. The remaining
researchers were from various regions of the Soviet Union: A. Alksnis from Riga, N. Grigoreva from Moscow,
A. Numerova from Leningrad, R. Raznik from Uljanovsk, V. Straizys from Vilnius. Stars of different spectral
types were studied in 13 sky regions of 10◦×10◦ along the Milky Way. The observational data for those regions
were obtained in the Crimea. The galactic longitudes of the regions are shown at the bottom of Fig. 1 by thick
horizontal bars. The general characteristics of the regions, authors, and years of publishing of results are shown
in Table 1, where column 1 is a number of the region; columns 2 and 3 are right ascension α and declination
δ at the epoch 1950.0; columns 4 and 5 are galactic longitude l ′ and galactic latitude b ′ in the old coordinate
system; column 6 is the size of the region in square degrees; column 7 is the number of studied stars N ; column 8
is the number of the O–B stars n; column 9 is the authors and years of publishing of the paper. The detailed
references may be found in the reviews by I. Pronik [25] and by I. Pronik, L. Sharipova [33].
Figure 1. Distribution of the stars W–R, O, B0, B1 (dots) and emission nebulae (circles) in the Galaxy superposed by
the grid with the old galactic coordinates (G. Shajn, V. Gase [52]). Thick horizontal bars and numbers at the bottom
show longitudes of the Shajn’s Plan regions
Table 1. The characteristics of the studied Shajn’s Plan regions in the Milky Way
No. α δ l ′ b ′ Area N n, type Authors,
1950 1950 sq. degr. years of publishing
1 2 3 4 5 6 7 8 9
1. 0h00m +66◦30′ 86◦ +5.0◦ 15 605 44, O–B5 Raznik, 1963–1967
2. 0 30 +62 00 89 0.0 45 2816 500, O–B5 Brodskaja and Grigoreva, 1964;
Grigoreva, 1964–1967
3. 1 25 +61 50 95 +0.5 85 3206 731, O–B5 Kopilov, 1953; Brodskaja, 1960–1961
4. 2 30 +58 00 104 −1.0 48 3340 835, O–B5 Brodskaja and Shajn, 1958; Brodskaja, 1961
5. 5 32 +22 00 153 −3.6 4 86 6, O–B5 Brodskaja, 1963
6. 5 32 −05 30 177 −17.6 56 1572 57, O–B6 Kopilov and Straizys, 1963; Straizys, 1963
7. 18 10 −15 00 343 −0.6 68 3914 276, O–B3 Pronik, 1958–1963
8. 18 54 +05 00 6.1 −0.7 36 1492 79, O–B3 Pronik, 1960–1961; Grigoreva et al., 1971;
Pronik and Sharapova, 1971
9. 20 05 +36 00 41.0 +1.1 36 5000 120, B0–B5 Numerova, 1958–1961
10. 20 16 +42 30 47.6 +3.0 30 952 952, O–A Ikhsanov, 1959–1960
11. 20 44 +45 00 53 +0.6 42 3404 60, O–B2 Metik, 1960–1963
12. 21 24 +58 30 67 +5.6 25 2060 67, O–B5 Alksnis, 1958–1961
13. 23 25 +61 30 81 +0.8 64 5752 400, O–B5 Brodskaja, 1953–1956
More than 35 000 stars were studied and more than 4 000 stars among them were classified as the new
O–B stars. The regions with the extinction in the optical range as high as 25m per kpc were found in these
studies. These data could be used to study the structure of dark matter, composition of clusters and associations
of O–B stars in spiral arms in Orion, Perseus, and Sagittarius.
251
The Crimean archives include several hundred plates obtained with the Hα filter, more than 400 plates of
10◦×10◦ regions with objective prism spectra of stars brighter than 13m, and more than 100 plates of 10◦×10◦
regions with the direct images of stars brighter than 18m.
Reviews of the results on the Galaxy structure obtained in the course of the Shajn’s Plan were made by
I. Kolesnik [12], I. Pronik [25], and by I. Pronik and L. Sharipova [33].
A review of studies on the distribution of the interstellar extinction in the Galaxy in the wavelength range
0.1 – 5 μm and the discussion on the shape of the reddening curve was made by V. I. Burnashev [4].
THE PROBLEM OF STAR FORMATION
The Shajn’s Plan included also the star formation studies. G. Shajn and V. Gase [45] wrote: “It is very much
possible that the role of the interstellar matter will also appear very considerable in the just outlining hypothesis
on so-called protostars.”
The interest to star formation was increased in 1940s–1950s. The question was whether stars are forming
in the recent epoch or they were formed simultaneously with the Universe. If yet, how they are formed and
whether it is possible to look at protostars. V. Ambartsumyan [1] showed that star associations are unstable,
star formation is taking place in them continuously “almost on our eyes”. It means that the age of luminous
stars is by a factor 10 less than the age of the Universe.
B. Bok and E. Reilly [2] suggested that small dark objects, globulae, can represent an evolution stage
preceding of star formation. A minimum extinction in globulae was estimated to be equal to 2m–5m.
B. Vorontsov-Velyaminov [56] wrote that the matter, from which young hot supergiants were formed, was
beforehand disposed in spiral arms and thus there is a chance to reveal it.
The Shajn’s Plan was fulfilled in the 1950s, 49 papers were published, 47 of them – before 1966. One of
the important results of these studies were evidence for a link of early type stars and dark matter. The comp-
lexes of emission nebulae, young stellar clusters, and luminous stars were found to show the enhanced dust
extinction. The distribution of O–B5 stars and dark clouds in the Galaxy were studied by E. Brodskaja [3]
and I. Kopilov [13]. These are the two first papers in the frame of the Shajn’s Plan. Figure 2 displays one of
the striking examples of the dust extinction as high as ΔAv = 5m in the region No. 1 observed by R. Raznik [35].
R. Ikhsanov [11] studied 22 young stellar clusters connected with emission nebulae and showed that the pre-
sence of a large amount of dust is one of the important characteristics of very young nebulae. In particular,
the extinction in the Orion nebula is found to be as high as Av ∼ 9m–10m.
Figure 2. Dependence of the extinction Av on the distance modulus v0–Mv for five parts of the region No. 1 studied by
R. Raznik [35]. Figures at the top show number of the part of the region No. 1
252
Table 2. A hierarchy of sizes of star forming regions and complexes of young stars and emission nebulae
Star forming regions Emission regions
(P. Solomon et al. [54]) (Shain’s Plan)
object size, pc object size, pc
clusters 10–15 separate nebulae 8–50
associations 30–200 groups of nebulae 100
superassociations 500 large groups of nebulae to 300
complexes of detail of the regular magnetic
star formation 1000 field near the Sun 1000
R. Raznik [36, 37] studied the reddening of O5–B3 stars in 31 young open clusters and found that many of
them exhibit anomalously high colour excesses.
It is believed now that a progress in understanding of star formation processes was achieved after the dis-
covery in 1963 of the hydroxyl radio line at the wavelength of 18 cm [57], and later discoveries of the lines
of other molecules. “Only in 1970, it turned out finally that cold molecular gas is collected in massive clouds
which serve as the “maternity hospitals” of stars” [55]. All molecules exist in the dense clouds connected with
the dust, which protect molecules from the destruction by interstellar ultraviolet radiation.
However, a genetic link of gas nebulae, dust clouds, and clusters of young stars was observationally established
one decade before the discovery of the hydroxyl radio line. It was justified in all papers by G. Shajn and V. Gase
(for example [53]) and by those who fulfilled the Shajn’s Plan. A basic view on the star formation remains
unchanged since those studies and can be summarized as follows:
1. Stars are formed by groups in the regions of accumulation of gas nebulae [52].
2. Clouds, from which stars are formed, are essentially more massive than the star clusters [48, 49, 52].
3. A hierarchy of the characteristic sizes for star forming regions [54] is similar to a hierarchy of the sizes
discovered by G. Shajn [39] for the gas–star groups (Table 2).
4. Stars are formed in the cocoons consisting of very dense interstellar matter. It was shown that the O–B
stars in young star clusters are often surrounded by more dense dust clouds, than the stars of the later
spectral types.
5. Clusters of giant clouds with Hα emission and young clusters associated with them are located in the spiral
arms of galaxies [39, 43, 48, 52].
Thus, it is possible to express a confidence that the observational evidence for genetic connection of young
stars, emission diffuse, and dark nebulae obtained by G. Shajn and other astronomers under his leadership will
be assessed at its true value in the history of star formation studies.
INDIVIDUAL GALAXIES
Studies of individual galaxies have been begun by G. Shajn at the Crimean Astrophysical Observatory in
the 1950s. He revealed 82 diffuse nebulae and more than 200 luminous clumps of stellar nature in spiral arms of
the galaxy NGC 598 (M33) [39]. The clumps were brighter than 16m or absolute magnitude −5.5m. G. Shajn
showed that the population I stars in M33 are numerous.
It was shown that the masses of 13 gaseous nebulae in the galaxy M33 and of three nebulae in the galaxy
M31 are in the range from 0.5 · 104 M� to 3 · 105 M� [49]. G. Shajn concluded first that interstellar matter in
galaxies is dominant component by mass inside the complexes of gaseous nebulae and young stars.
In the 1960s, the observations of normal and active galaxies at the Crimean Astrophysical Observatory have
been carried out under the leadership of A. Severny, V. Nikonov, and K. Chuvaev [5] using the imagetube and
5–9 filters in the spectral region 3700–7100 Å in the prime focus of the 2.6-m Shajn telescope. Several thousand
plates were obtained for more than 200 extragalactic objects and are collected in the archive of the Crimean
Astrophysical Observatory. Some of the results obtained using these observational data are outlined in this
section.
K. Chuvaev and I. Pronik [6] studied more than 200 clumps consisting of blue star forming regions and
gaseous nebulae inside spiral arms of the Sc galaxies NGC 628, NGC 4254, and of the galaxy pair NGC 5194/5195.
Figure 3 shows spiral arm patches revealed in the interacting pair NGC 5194/5195. Sizes, luminosities, masses,
and colour–colour diagrams of the clumps in all galaxies were obtained in this study.
I. Pronik [23] showed that a star population of bars in SB galaxies is younger in comparison with that of
the central regions of normal galaxies of the same morphological types. It was interpreted that current star
formation processes in bars are more active.
253
Figure 3. Spiral arm patches in the NGC 5194/5195 system (K. Chuvaev and I. Pronik [6]). The image was obtained
with the filter centered on the Hα line. The underlined figures correspond to the blue patches without Hα emission
It was shown that for each galaxy the larger the distance of the spiral arm clump from the galaxy center is
the bluer this clump is in the colour–colour diagram. The galaxies with the bluest central regions contain also
the bluest patches of spiral arms [26].
The multicolour photometry of 31 superassociations with gaseous nebulae in the peculiar pair of galaxies
NGC 4038/4039 (the “Antennae”) was carried out by O. Dobrodij and I. Pronik [7]. It was shown that the super-
associations of the Antennae differ from star forming regions in normal galaxies by their higher sizes, higher
masses of neutral hydrogen, and higher masses of young star populations. The properties of superassociations
of NGC 4038/4039 are close to those of blue dwarf galaxies which have the excess of blue hot stars.
L. Metik and I. Pronik [14–19] carried out the multicolour photometry of nine elliptical (E) galaxies con-
taining Seyfert nuclei: Mkn 34, Mkn 42, Mkn 69, Mkn 205, Mkn 279, Mkn 290, Mkn 298, NGC 1275, and
NGC 7469. It was shown that the rate of current star formation in the central regions of galaxies with Seyfert
nuclei is appreciably higher compared to that of normal galaxies of the same morphological types.
Star-like objects near the nuclei of the Seyfert galaxies NGC 1275, NGC 7469, Mrk 290, Mrk 298, 3C 120,
and 3C 390.3 having signs of interaction with the nuclei were revealed (see Fig. 4). Absolute magnitudes
of these objects are about −16m–17m, and their masses are about 108 M�. Spectral energy distributions of
some of the revealed objects is similar to that of quasars or galaxies with the ultraviolet excess in spectra.
254
Figure 4. Star-like objects which were revealed by I. Pronik and L. Metik [30] near the active galactic nuclei; a – nucleus
of a galaxy, b – a star-like object
Analysis of the 6-m telescope spectra of some compact objects supported the results of the multicolour studies
[14–16, 18, 19, 30].
I. Pronik, V. Prokof’eva, and L. Sharipova [31] performed the BVR photometry of compact objects near
the nuclei of Seyfert galaxies revealed by L. Metik and I. Pronik (Fig. 4) using the TV-complex of the 0.5-m tele-
scope of the Crimean Astrophysical Observatory. It was shown that these objects consist of both early-type
and late-type stars.
L. Metik and I. Pronik [17] studied physical and kinematic characteristics of components of 47 galaxy pairs
of different morphological types. Three groups of pairs were revealed. They differ by relations of radial velocity
differences and colour indices of pair members. It was concluded that there is a difference in the origin and/or
evolutionary phase of these groups.
The study of the emission regions in galaxies was performed using not only multicolour photometry but
also the spectra obtained with the high speed spectrograph at the prime focus of the 2.6-m Shajn telescope.
Emission regions and stellar populations of the central regions of 17 E, S, and Irr normal galaxies were studied by
I. Pronik [24]. Figure 5 shows the dependence of equivalent widths of the Hα line on the colour indices (U −B)
for normal and Seyfert galaxies. One can see that the dependence for the normal galaxies is continuously
prolonged by Seyfert galaxies. It was concluded that the brightness of the Hα emission of each central region is
caused by the colour index of the star population rather than by the morphological type of the galaxy. Thus,
the main mechanism of Hα emission in central regions of normal galaxies is recombination of hydrogen which
is ionized by ultraviolet radiation of blue stars.
In the 1960s, V. Pronik with E. Dibay from the Crimean Laboratory of the Sternberg Astronomical Institute
(Moscow), just after the identification in 1963 by M. Schmidt of emission lines in the spectrum of the star-like
high-redshift object (QSO) 3C 273, began a new page in the study of galaxies in the Crimea – a study of
active galactic nuclei (AGNs) with the brilliant star-like nuclei and very broad emission lines in their spectra.
The history of the AGN study at the Crimean Astrophysical Observatory is described by Yu. Efimov et al. [8].
I. Pronik, N. Merkulova, L. Metik, and V. Pronik [27] studied stellar populations in central regions with
sizes of 0.2 – 20 kpc of 20 normal galaxies of morphological types from Irr to E using the spectra in the range
1800–3400 Å. These data were obtained with the space telescope “Astron”. The analysis of the observed line and
continuous spectra permits one to conclude that the main contribution into the near UV spectrum of the central
regions of Sc and Irr galaxies and extragalactic H II regions with O–B associations is caused by O, B, and A main
sequence stars. It was shown that the near UV spectrum of the central regions of early morphological type
255
Figure 5. Dependence of equivalent widths of the Hα emission line on the colour indices (U −B) for the central regions
of normal and Seyfert galaxies according to the paper by I. Pronik [24]. Small letters indicate the classes after Morgan
galaxies is caused mainly by stars of the horizontal and post-asymptotic branches of the Hertzsprung–Russell
diagram. Spectra of two Markarian galaxies and two extragalactic H II regions with O–B associations were
interpreted as showing the regions of current star formation [28, 29].
A review on the star formation characteristics of central parts of normal and peculiar galaxies was published
by I. Pronik and V. Pronik in 1988 [32]. A classification of these regions according to the level of current star
formation (the weak, moderate, and intense types) was proposed:
1. Central regions with weak star formation are observed almost in normal E and S galaxies. Their surface
brightness decreases from the center to periphery according to the power law B ∼ r−1/4 and colour index
decreases too. The colour variation gradient decreases from E to the lenses of S galaxies. The main
photometric and spectroscopic parameters vary smoothly along the sequence of morphological types,
reflecting smooth variations of star contents.
2. Centers of moderate star formation cannot be revealed from the structure inhomogeneities of the central
regions, but only from the spectroscopic and photometric characteristics. In general, they differ from
the characteristics of central regions of normal galaxies. Bars of SB galaxies, members of interacting
galaxies, and most of Markarian galaxies which are, in general, bluer than the central regions of normal
galaxies show examples of centers of moderate star formation. Bluer colours in all these cases favour
a higher stellar content of earlier spectral types compared to the normal galaxies.
3. The regions of intense star formation are observed as large H II regions named “hot spots”. Short intense
episodes of star formation are present in M82, in the pair of interacting galaxies NGC 4038/4039, and in
galaxies with high infrared emission. Observations showed that more than 40% of nearly normal galaxies
have high emission at 10 μm. Stellar populations of all these galaxies can be interpreted in the frame of
models including the bursts of star formation.
Acknowledgements. I thank V. Pronik and L. Sharipova for the helpful discussions; N. Petrova, M. Smirnova,
and L. Filatova for the preparing of figures.
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