Stellar dynamics

This review attempts to place stellar dynamics in relation to other dynamical fields and to describe some of its important techniques and present-day problems. Stellar dynamics has some parallels, in increasing order of closeness, with celestial mechanics, statistical mechanics, kinetic theory, and plasma theory; but even in the last case the parallels are not very close. Stellar dynamics describes, usually through distribution functions, the motions of a large number of bodies as they all act on each other gravitationally. To a good approximation each star can be considered to move in the smoothed-out field of all the others, with random encounters between pairs of stars adding a slow statistical change to these smooth motions. Smooth-field dynamics has a well-developed theory, and the state of smooth stellar systems can be described in some detail. The ‘third integral’ presents an outstanding problem, however. Stellar encounters also have a well-developed theory, but close encounters and encounters of a single star with a binary pose serious problems for the statistical treatment. Star-cluster dynamics can be approached through a theory of smooth-field dynamics plus changes due to encounters, or alternatively through numerical simulations. The relation between the two methods is not yet close enough. The dynamical evolution of star clusters is still not fully understood.     

The standstill luminosity in Z Cam systems

We consider accretion discs in close binary systems. We show that the heating of a disc at the impact point of the accretion stream contributes significantly to the local energy budget at its outer edge. As a result, the thermal balance relation between local accretion rate and surface density (the 'S-curve') changes; the critical mass transfer rate above which no dwarf nova outbursts occur can be up to 40 per cent smaller than without impact heating. Standstills in Z Cam systems thus occur at smaller mass transfer rates than otherwise expected, and are fainter than the peak luminosity during the dwarf nova phase as a result.     

Organic matter diagenesis in the anoxic sediments of saanich inlet,British Columbia,Canada: a case for highly evolved community interactions

Cytochrome c and ferricyanide reducing activities are measured in a Desulfovibrio desulfuricans (strain ATCC No. 17990) that indicate that the APS reductase activity is constitutive. This enzymatic activity is also measured in a Saanich Inlet isolate identified as Desulfovibrio salexigens (Saanich). Successful measurement of the Cytochrome c reducing activity was also made in the sediment extracts from Saanich Inlet, and this activity was found to be present in sediments as deep as 50 cm. Bacterial biomass distributions were estimated using measurements of ATP in the Saanich Inlet sediments. ETS activity measurements correlated well with the in situ [³⁵S]-SO₄^2? reduction rate measurements; both of the methods showing a subsurface maximum in activity at a depth of about 10 cm. However, some differences between the results obtained from these two procedures were also found, e.g., the in situ [³⁵S]-SO₄^2? reduction activity approximated zero values at or near 25 cm depth, while 5–10% of the surface ETS activity was present at a depth of as much as 50 cm. The hypothesis presented is that the subsurface maximum may be due to the anaerobic oxidation of methane by [³⁵S]-SO₄^2? ions as mediated by the sulfate-reducing bacteria. A discussion of the strong interactive relationships between a variety of organisms in an ecosystems context, so necessary in bringing about organic matter diagenesis in anoxic marine environments, is also presented.