Very-long Term Research Articles

Simultaneous H$\mathsf{\alpha}$ and photometric observations of P Cygni

For the first time an extensive set of (quasi-) simultaneous photometric ( UBV ) and spectroscopic (H α line profiles) observations of P Cygni, covering a period from May, 1990 to June, 1994 was analyzed in terms of time variability. It is found that the H α equivalent width ( EW ) exhibits two different patterns of variability: a slower one, called Long-Term (LT) variability, with an amplitude of about 30 Aand a characteristic duration of about 600 days and a faster one, called Short-Term (ST) variability, with an amplitude up to 10 Aand duration of 40 to 60 days. Suggestive evidence for EW variation on a longer time scale (about few years) also exists. The variations in the H α luminosity are not solely due to changes in the underlying continuum but also reflect variations in the physical properties of the wind. We find, in terms of a simplified spherically-symmetric wind model, that the LT variation of the line can be successfully explained in terms of a 26% alteration of the mass-loss rate, possibly accompanied by variations in the velocity field. From the analysis of the photometric behaviour of the star we find evidence for a very slow variation in the stellar brightness with an amplitude of about 0.13 mag and a duration of about 2600 days, i.e. about 7 years. During this variation, i.e. when the star brightens, the effective temperature decreases (by about 10% ) and the radius increases (by about 7% ). The properties of this Very Long Term (VLT) variation suggest that P Cygni has probably experienced a normal S Dor-type variation with a minimum phase around 1988 and a maximum phase in 1992. Some hints for a positive correlation between mass loss variations and changes in the stellar radius, due to the normal SD variability, do exist implying that the behaviour of P Cygni is more likely similar to that of R71 and S Dor but different from e.g. AG Car, R127 and HD 160529. Superimposed on the VLT component in the photometric variability of P Cygni, we observe ST brightness variations with an amplitude between 0.1 and 0.2 mag which appears to recur on a time scale of three to four months. The colour behaviour of these microvariations, at least of those which appear near the maximum phase of the VLT variation, is redder in $B-V$ and bluer in $U-B$ when the star brightens in V . The properties of this ST photometric variability are similar to the properties of the so-called 100 d-type micro-variations, recognized in other LBVs by van Genderen et al. ([CITE],b). Based on time-scale evidences we suggest that the microvariabilities observed are rather due to relaxation oscillations(Stothers & Chin [CITE]) than to strange-mode oscillations in the stellar interior. Evidence for a close relationship between ST variations in H α and changes in the stellar brightness and temperature is found. From other results about P Cygni's spectral variations (Markova [CITE]), we conclude that the ST variability of the wind is most likely connected with processes in the stellar photosphere.

Synergistic use of debris environment models for flexible, very-long term projections

Long-term debris environment projections are of great importance for assessing the necessity and effectiveness of debris mitigation measures. Two types of models have been developed to predict these environments. Environment evolution models like the EVOLVE code are using detailed mission model data to input spacecraft, upper stages, and operational debris into specific orbits at specific times; debris from fragmentations are placed in orbits defined by the state vector of the fragmenting object(s) and the breakup model. The second type, typified by the CHAIN program, uses a particle-in-box model that bins the environment in size and altitude rather than following the orbit evolution of individual debris fragments. A 3-Step approach using both the EVOLVE and CHAIN model in a synergistic way was used to increase the reliability of long term environment projections. EVOLVE historical projections 1957–1995 could be validated by comparison to measurements. The comparison of 100 year projection runs of EVOLVE and CHAIN for different traffic scenarios showed a good agreement. In this paper, for the first time, CHAIN projections up to 10,000 years, based on validated boundary conditions derived by EVOLVE are presented, indicating clearly the need of early implementation of effective mitigation measures to prevent exponential population growth by collisional cascading effects.

Metabolic changes in fed rats caused by chronic administration of ethyl 2{5(4-chlorophenyl) pentyl}oxirane-2-carboxylate, a new hypoglycaemic compound

Ethyl 2{5(4-chlorophenyl)pentyl}oxirane-2-carboxylate (POCA) is strongly hypoglycaemic in fasted normal and diabetic rats [H. P. O. Wolf, K. Eistetter and G. Ludwig, Diabetologia 22, 456 (1982)]. POCA was fed for 12 weeks to rats on a standard low-fat (3%) diet at levels of 0.05% and 0.2% to give daily intakes of about 50 and 200 mg/per kg body-wt respectively. This is much more than effective hypoglycaemic doses in fasted rats (5–10 mg/kg body-wt). The animals appeared healthy but they had slightly decreased rates of weight gain compared with the controls. POCA caused a 15% increase in the weight of the myocardium and accumulation of lipid in the liver. Chronic administration of POCA did not cause any large changes in water-soluble blood metabolite concentrations, although VLDL-triacylglycerol and both VLDL and HDL cholesterol concentrations were lowered. There were only small changes in some metabolites of the glycolytic and gluconeogenic pathways and the citrate cycle in liver and skeletal muscle. ATP concentrations were maintained in all groups. There were 2-to 3-fold increases in the total content of CoA and of carnitine and their acylated forms. POCA-feeding caused small decreases in LPL activities in heart and had variable effects in adipose tissue. POCA was also fed to a few rats on a high fat (30%) diet for 4 weeks. Only small changes in blood, liver and muscle metabolite concentrations were found, except for large increases in the liver CoA and carnitine contents. It was concluded that POCA does not cause large perturbations of glucose homeostasis, or acute toxic effects, during 12 weeks administration to normal animals at high dose levels. The very-long term importance of accumulation of lipid in liver: increase in myocardial weight; and also of hepatic peroxisomal proliferation [A. J. Bone, H. S. A. Sherratt, D. M. Turnbull and H. Osmundsen, Biochem. biophys. Res. Commun. 104, 708 (1982)] cannot yet be determined. The possible use of POCA and related compounds in the chemotherapy of diabetes merits further investigation.