Spectrographic observations of omicron andromedae from 1967 to 1976

The results of qualitative analysis and radial velocity (RV) determinations from 1967 to 1976 are given. These analyses show sometimes the presence of a thin variable shell also in the years 1967–1974, before the appearance of the envelope. Intensity variations of the metallic lines seem to indicate that in the same period changes of temperature and/or electron pressure may occur in the photospheric layers. In the period 1975–76, the considerable range ofRV and the variability of the shell features show that the shell is rather active. Some conspicuousRV variations seem to be correlated to brightness changes. TheRV do not confirm the periods suggested by the photometric observations. A periodogram analysis givesRV curves with a poor evidence of periodicity. However, the periodP=1^d.5845 obtained from this analysis, close to that of Schmidt, seems to confirm Schmidt's hypothesis of a contact binary system. The periodogram analysis of theRV during the years 1900–1976 and some physical arguments, suggest a probable photospheric activity or an invisible companion with the observed shell period of 30 yr. The duplicity, suggested by Kí and Harmanec (1975) for all the Be stars, could be yet questioned foro And.Thesis for the degree of Applied Physics.     

New Development of Eastern Mediterranean Circulation based on Hydrological Observations and Current Measurements

Abstract. A number of recent studies based on hydrographic observations and modelling simulations have dealt with the major climatic shift that occurred in the deep circulation of the Eastern Mediterranean. This work presents hydrographic observations and current measurements conducted from 1997 to 1999, which reveal strong modifications in the dynamics of the upper, intermediate and deep layers, as well as an evolution of the thermohaline characteristics of the deep Aegean outflow since 1995. The reversal of the circulation in the upper layer of the north/central Ionian is worthy of note. The observations indicate a reduction of Atlantic Water in the northern Ionian with an increase on the eastern side of the basin. In the intermediate layer, the dispersal path of the Levantine Intermediate Water (LIW) is altered. Highly saline (>39.0) and well-oxygenated intermediate waters were found near the Western Cretan Arc Straits. They flow out from the Aegean, thus interrupting the traditional path of the LIW, and spread prevalently northwards into the Adriatic Sea. In the deep layer, dense waters, exiting from the Adriatic (σ_ø−29.18 kg · m⁻³), flow against the western continental margin in the Ionian Sea at a depth of between 1000–1500 m. Dense waters of Aegean origin (> 29.20 kg · m⁻³), discharged into the central region of the Eastern Mediterranean during the early stages of the transient, propagate prevalently to the east in the Levantine basin and to the west in the northern Ionian Sea. Near-bottom current measurements conducted in the Ionian Sea reveal unforeseen aspects of deep dynamics, suggesting a new configuration of the internal thermohaline conveyor belt of the Eastern Mediterranean.     

Forced vibrations of rectangular plates subjected to harmonic loading distributed over a rectangular subdomain

Quite frequently naval and ocean structural designers confront the problem of a plate or slab which supports a motor or engine which excites, dynamically, the structural element. Very often the excitation is treated as a concentrated force but, obviously, it acts over a finite area. The present study deals with the title problem for several combinations of boundary conditions by means of a variational approach and also using the finite element method. Dynamic displacement and bending moment amplitudes are determined.     

Fluid circulation in a complex volcano-tectonic setting,inferred from self-potential and soil CO2 flux surveys: The Santa María–Cerro Quemado–Zunil volcanoes and Xela caldera (Northwestern Guatemala)

The region encompassing Santa María, Cerro Quemado, and Zunil volcanoes, close to Quetzaltenango, the second largest city of Guatemala, is volcanically and tectonically complex. In addition, the huge Xela caldera, about 20 km in diameter, crosses this area and links up to the important Zunil fault zone located between the three volcanoes. Two highly active geothermal sites, named Zunil-I and Zunil-II, are also located between these three volcanic edifices at the southeastern boundary of Xela caldera. In order to determine the permeability variations and the main structural discontinuities within this complex volcano-tectonic setting, self-potential and soil CO₂ flux measurements have been coupled, with a step of 20 m, along a 16.880 km-long profile crossing the entire area. Two shallow hydrothermal systems, with maximum lateral extensions of 1.5 km in diameter, are indicated by positive self-potential/elevation gradients below Santa María and Cerro Quemado volcanoes. Such small hydrothermal systems cannot explain the intense geothermal manifestations at Zunil-I and Zunil-II. Another minor hydrothermal system is indicated by self-potential measurements on the flank of Santa María along the edge of the Xela caldera. CO₂ flux measurements display slight variations inside the caldera and decreasing values crossing outside the caldera boundary. We hypothesize the presence of a magmatic body, inside the southeastern border of Xela caldera, to explain the deeper and more intense hydrothermal system manifested by the Zunil-I and the Zunil-II geothermal fields. This magmatic system may be independent from Santa María and Cerro Quemado volcanoes. Alternatively, the hypothesized Xela magmatic system could have a common magmatic origin with the Cerro Quemado dome complex, consistent with previous findings on regional gas emissions. Sectors bordering the Cerro Quemado dome complex also have high amplitude minima-short wavelength anomalies in self-potential, interpreted as preferential rain water infiltration along faults of major permeability, probably related with the most recent stages of Cerro Quemado dome growth.     

The helium abundance and ΔY/ΔZ in lower main-sequence stars

We use nearby K dwarf stars to measure the helium-to-metal enrichment ratio  Δ Y /Δ Z   , a diagnostic of the chemical history of the solar neighbourhood. Our sample of K dwarfs has homogeneously determined effective temperatures, bolometric luminosities and metallicities, allowing us to fit each star to the appropriate stellar isochrone and determine its helium content indirectly. We use a newly computed set of Padova isochrones which cover a wide range of helium and metal content.
Our theoretical isochrones have been checked against a congruous set of main-sequence binaries with accurately measured masses, to discuss and validate their range of applicability. We find that the stellar masses deduced from the isochrones are usually in excellent agreement with empirical measurements. Good agreement is also found with empirical mass-luminosity relations.
Despite fitting the masses of the stars very well, we find that anomalously low helium content (lower than primordial helium) is required to fit the luminosities and temperatures of the metal-poor K dwarfs, while more conventional values of the helium content are derived for the stars around solar metallicity.
We have investigated the effect of diffusion in stellar models and the assumption of local thermodynamic equilibrium (LTE) in deriving metallicities. Neither of these is able to resolve the low-helium problem alone and only marginally if the cumulated effects are included, unless we assume a mixing-length which is strongly decreasing with metallicity. Further work in stellar models is urgently needed.
The helium-to-metal enrichment ratio is found to be  Δ Y /Δ Z = 2.1 ± 0.9  around and above solar metallicity, consistent with previous studies, whereas open problems still remain at the lowest metallicities. Finally, we determine the helium content for a set of planetary host stars.