High-Resolution Optical Spectroscopy of the Post-AGB Supergiant V340 Ser ( $${\mathbf{=}}$$ IRAS 17279 $$\mathbf{-}$$ 1119)

Astronomy Letters - Evidence of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser ( $${=}$$ IRAS 17279 $$-$$ 1119)...     

Period variations in BZ Eridani

The O-C diagram of BZ Eri has been presented for the first time, and the period variations present in the system have been analysed. In all, eight period decreases and eight period increases are noticed. Of these, four period decreases and seven period increases are appreciable. The strongest period changes are noticed in the interval 1960 to 1962. The total period change in different portions of the O-C diagram ranges from 1.17×10^–3 d to 3.96×10^–6 d. The trend of the period variation appears to have reversed around the year 1980.     

Precursor heating and acceleration by Langmuir waves: The type II Supernova case

The effect of shock wave propagation is investigated with respect to precursor heating and acceleration, upstream, with the aim of explaining Supernova (SN) observations.A model is presented, where two different sources of Langmuir waves produce upstream heating and acceleration: (1) Langmuir waves excited by resonance beam particles, that are accelerated through the shock front by Bell's mechanism; and (2) Langmuir waves, created in the post-shock turbulent zone.The most important processes considered in the calculations are: (1) the heating efficiency of beam particles of different velocity; (2) Bell's acceleration efficiency; (3) the spectrum of Langmuir waves created in a turbulent regime; (4) the effects of density, and of the density gradient in the medium, where the shock propagates.The calculations are applied to type II SN. The results show that temperatures of 10⁵–10⁶ K, obtained in the preshock region, can explain P-Cygni observed line profiles. Moreover, accelerations of the plasma in front of the shock up tov10⁸ cm s^–1 by momentum exchange, are in good agreement with observations.Partially supported by Conselho Nacional de Desenvolvimento Cientifico e Technológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).     

Einstein-Gleichungen mit Zusatztermen 4. Ordnung und Raum-Zeit-Modelle vom Bianchi-Typ I

In the vacuum case, Einstein's equations generalized by additive terms containing derivatives of the metric up to the 4th order are applied to cosmological Bianchi-type I model space-times.     

On the variational approach to the periodic n-body problem

This expository paper gathers some of the results obtained by the author in recent works in collaboration with Davide Ferrario and Vivina Barutello, focusing on the periodic n-body problem from the perspective of the calculus of variations and minimax theory. These researches were aimed at developing a systematic variational approach to the equivariant periodic n-body problem in the two and three-dimensional space. The purpose of this paper is to expose the main problems and achievements of this approach. The material here was exposed in the talk that given at the Meeting CELMEC IV promoted by SIMCA (Società italiana di Meccanica Celeste).     

Critical inclination in the main problem of a massive satellite

The classical problem of the critical inclination in artificial satellite theory has been extended to the case when a satellite may have an arbitrary, significant mass and the rotation momentum vector is tilted with respect to the symmetry axis of the planet. If the planet’s potential is restricted to the second zonal harmonic, according to the assumptions of the main problem of the satellite theory, two various phenomena can be observed: a critical inclination that asymptotically tends to the well known negligible mass limit, and a critical tilt that can be attributed to the effect of transforming the gravity field harmonics to a different reference frame. Stability of this particular solution of the two rigid bodies problem is studied analytically using a simple pendulum approximation.