Photometry of the bright stars inside and outside associations in the spiral arm S5 of the andromeda galaxy

Photometry of more than 1000 bright stars of 20 associations and some fields in its vicinity is made, usingUBV plates taken with a 2-m Ritchey-Chrétien telescope of the National Observatory at the Bulgarian Academy of Sciences with limited magnitudes of about 20.6 inU andV, 21.6 inB. The colour-magnitudes of about 20.6 inU andV, 21.6 inB. The colour-magnitude and colour-colour diagrams of 12 associations and 8 fields are constructed and the brightest blue and red stars colour excesses, ages, and integrated luminosities of the associations are determined. The composite diagrams for all association and nonassociation measured stars are constructed too. Inside associations bright stars as well as non-stellar objects occur more often than outside. The brightest stars in S5 are withM _v7 and do not differ considerably from the brightest ones in the spiral arm S4 of M31. Approximately the same are the absolute magnitudes of the brightest stars in our Galaxy and M33. A small difference between the brightest stars of the latter galaxy with those of M31 is possible because the stars in M33 are younger. This is in agreement with the concept that Sc galaxies (for example M33) are younger than Sb ones (for example M31). The same could be the reason for the smaller ratio of blue to red supergiants in M33 than in M31. The age estimations of the associations in S5 together with those in S4 in M31 show that they are older than the associations in M33 which is in agreement with the above mentioned concept.     

A discussion of the Cepheid amplitude behaviour in the instability strip

An analysis is presented which seeks to reveal the possible causes for discrepancy in the results on the dependence of Cepheid amplitudes on star positions in the instability strip noted by different investigators.A comparison of the data used in two of these investigations—that of Yakimova (1970) and that of Sandage and Tammann (1971)—shows that it is most unlikely to be able to explain completely the conflicting results obtained in these studies. But if we analyse the data of Sandage and Tammann following the approach of Yakimova — namely, by considering the Cepheids in only one stellar system and taking into account the stellar colours in maximum light — we obtain Yakimova's result: the light amplitude is the larger, the nearer to the low temperature edge of the instability strip a Cepheid is. Therefore, it appears that differences between the various approaches contribute greatly to the different results of Sandage and Tammann and Yakimova (and the other investigators).     

Period-luminosities relation of classical Cepheids

A new PL-relation (10) — Figure 2 for the Cepheids in the Galaxy, the Magellanic Clouds and M31 has been constructed. On deriving this relation both the period-radius (3) and period-colour relations (7), (8) and (9) are essentially used. The PC-relation (7) determined after the colours of 88 galactic cepheids (Table I), which are obtained from the colour-spectrum relation (6) — Figure 1, common for Cepheids and non-variable supergiants, are used also for the M31 Cepheids, whereas (8) and (9) are for the Large and Small MC Cepheids, respectively, all three PC-relations having a common slope. The comparison of the relations (8) and (9) with (7) shows that the LMC and SMC Cepheids are bluer than the galactic ones with 0^m.04 and 0^m.19, respectively, probably because of their metal-poor abundance. The places of thes-Cepheids in Figure 2 show that these Cepheids possess a dissimilar PL-relation with a different slope. The reason for such a difference is that thes-Cepheids are first harmonic pulsators. The distance moduli of the three galaxies under discussion are obtained from the PL-relation (10). The colour-coefficient of period-colour-luminosity-relation is briefly discussed. The general conclusion based on a comparison of the PL-relation in the present paper with those by other authors (Table V) is that our PL-relation differs in the zero-point by less than 0^m.2; therefore, the manner of constructing the PL-relation by means of PR and PC-relations is reasonable and useful.     

A photometric study of three star fields in the southern region of M33

The 2 m RCC telescope of the Rozhen National Observatory (Bulgaria) was used to obtain the colour-magnitude and colour-colour diagrams of OB110 and OB112 associations which form the largest star grouping in the southern region of M33. The stars withV andU20.4 andB21 were measured. TheV magnitude, the coloursB - V, U - B and the respective identification charts are given. This allowed to construct the luminosity function of OB110+OB112. The group has an integrated magnitudeM _VT=–11.8 which is by 0 ^m .5 fainter than OB78 (M31). The mean absorption and the foreground were examined as well.     

Orbital elements of the eclipsing binary ξ Phe

The elements of the orbit in the cases of elliptic orbit and the nonspherical form of the components were obtained on the basis of the published photoelectric and spectroscopic observations of the eclipsing binary system Phe.     

Epizooic metazoan meiobenthos associated with tubeworm and mussel aggregations from cold seeps of the northern Gulf of Mexico

The abundance and higher taxonomic composition of epizooic metazoan meiobenthic communities associated with mussel and tubeworm aggregations of hydrocarbon seeps at Green Canyon, Atwater Valley, and Alaminos Canyon in depths between 1400 and 2800?m were studied and compared to the infaunal community of non-seep sediments nearby. Epizooic meiofaunal abundances of associated meiobenthos living in tubeworm bushes and mussel beds at seeps were extremely low (usually <100?ind. 10?cm(-2)), similar to epizooic meiofauna at deep-sea hydrothermal vents, and the communities were composed primarily of nematodes, copepods, ostracods, and halacarids. In contrast, epizooic meiobenthic abundance is lower than previous studies have reported for infauna from seep sediments. Interestingly, non-seep sediments contained higher abundances and higher taxonomic diversity than epizooic seep communities, although in situ primary production is restricted to seeps.     

Comparative investigations on Gagate and Vitrain from the Balkan coal basin

Isometamorphous samples of gagate and vitrain from Balkan coal-bearing formations were investigated. Quantitative spectrophotometric, chemical and reflectance measurements were performed. The data obtained from quantitative IR-analysis indicate great differences in the functional composition and structure of the organic matter of the two coal lithotypes. This explains the different properties of the gagate, e.g. lower reflectance, high volatile matter and hydrogene contents, etc. In the case of gagate the aliphatic part predominates in a naphthenic form and hybrid structures bonded to benzene rings as hydroaromatic cycles. Therefore, the number of benzene rings is several times lower than in vitrain, the elemental composition remaining the same. This is why under identical thermobatic conditions and through geological time, the coal molecule of gagate has a lower degree of aromatization.     

GIS-Oriented Database on Seismic Hazard Assessment for Caucasian and Crimean Regions

Izvestiya, Atmospheric and Oceanic Physics - Zones of higher seismic hazard occupy about 20% of Russia’s territory, and 5% are characterized by extremely high hazard. These latter are, in...     

Star complexes and associations in the Andromeda galaxy

Large-scaleU andB plates obtained with the 2 m Ritchey-Chrétien telescope of the Rozhen Observatory (Bulgaria) were searched for new resolved star groups and for independent delineation of the boundaries of the known ones in M31. We detected 210 groups as real O-associations the mean diameter of which is 80 pc. Many of Hodge's open clusters are also reclassified as O-associations. The majority of van den Bergh's OB-associations were recognized as star complexes and their mean diameter is 650 pc. Almost all O-associations are located inside the star complexes. A dozen of new star complexes (mainly around the dark lanes between OB78 and OB22) and numerous groups presumably not containing O-stars were found out. The nature of these groups has to be object of further investigations. Young star groups closer than 3 kpc to the center of M31 were not identified.     

UBV photometry of bright stars in the spiral arm S5 of M31

A photometric study inUBV of about 1000 bright stars outside and inside associations in S5 spiral arm is presented briefly. Characteristics of the associations (such as absorption, age and brightest stars are compared with the same characteristics of the associations in S4 spiral arm of M31, as well as in M33) are discussed.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.