Variable Stars in Galactic Globular Clusters

Based on a search of the literature up to May 2001, the number of known variable stars in Galactic globular clusters is approximately 3000. Of these, more than 2200 have known periods and the majority (approximately 1800) are of the RR Lyrae type. In addition to the RR Lyrae population, there are approximately 100 eclipsing binaries, 120 SX Phe variables, 60 Cepheids (including population II Cepheids, anomalous Cepheids and RV Tauri) and 120 SR/red variables. The mean period of the fundamental mode RR Lyrae variables is 0.585, for the overtone variables it is 0.342 (0.349 for the first-overtone pulsators and 0.296 for the second-overtone pulsators) and approximately 30% are overtone pulsators. These numbers indicate that about 65% of RR Lyrae variables in Galactic globular clusters belong to Oosterhoff type I systems. The mean period of the RR Lyrae variables in the Oosterhoff type I clusters seems to be correlated with metal abundance in the sense that the periods are longer in the more metal poor clusters. Such a correlation does not exist for the Oosterhoff type II clusters. Most of the Cepheids are in clusters with blue horizontal branches.Comment: 45 pages, 10 figures, to be published in AJ November 200

Ecology, life history and distribution of Palingenia longicaudata (Olivier) (Ephemeroptera)

Volume: 130Start Page: 109End Page: 12

Water Biological Sufficiency and Quality of the Bulgarian Danube Stretch (845–375 River Km)

The possibility of categorizing water biological sufficiency and quality through criteria for state biotic standards has been evaluated for 7 sections of the Bulgarian Danube stretch. The results of saprobiological analysis show the relatively stable beta-mesosaprobic level of the entire studied stretch, while indices of the structural organization of the benthic invertebrate communities do not correspond to this and rather correspond to the status of zoobenthos in different types of bottom substrata distributed over the length and width of the stretch. We discuss the necessity of further studies for the precise definition of criteria and norms for the assessment of the water biological sufficiency and quality, corresponding to the specific Danube conditions.</jats:p