The astronomical relevance of the observations of lithium in the atmospheres of old stars began in the 1982 when Francoise and Monique Spite, of the Meudon Observatory, using the 3.6m FHCT telescope at Mauna Kea, made the unexpected discovery that lithium whas present in the Population II stars even though amounting to only 10% of the "cosmic" value of lx10^-9 . At that time it was generally believed on the bases of the assumed age-lithium relation that lithium should have been destroyed in objects older than the sun, where only traces of 7Li can be found. A second, and even greater surprise, was to find that 7Li in Population II stars was in all the stars studied. This uniformi argue that the 7 Li observed in Population precisely the lithium synthesized in nearly constant lead the Spites to II objects is the primordial nucleosynthesis. This statement had important implications on the stellar structure theory, on the galactic chemical evolution theory and cosmology, most of which are stil a matter of debate and that we will discuss here in some detail. After Dennis Sciama drew my attention on the Spites' work, I undertook some research with the aim to extend the measure 7Li to other population II stars to confirm that 7Li is constant or possibly to find some correlations with stellar properties. The results of this investigation, made in collaboration with J.E. Beckman and R. Rebolo of the Instituto de Astrofisica de Canarias, is given in chapter II, following an introductory chapter on the last views on the origin of the light elements. We know that in the sun lithium is depleted by two orders of magnitude but beryllium and boron are at the "normal" levels suggesting that these last two elements should survive in the surface material of solar-type stars. Thus the unexpected survival of lithium in the atmosphere of old stars raised the hope to find also the other two related light elements, beryllium and boron, enshrined in the atmospheres of these ancient stars. The firsts efforts to assess the quantity of beryllium and boron in the Population II objects are illustrated in chapters 3 and 4, respectively. In the last chapter I report the results of a search for interstellar lines of lithium, beryllium and boron in the Large Magellanic Cloud using spectra of the supernova Shelton, that exploded on the 24th February of this year.
|Titolo:||Determination of the abundances of lithium, beryllium and boron in the population II stars and in the interstellar space of the large magellanic cloud|
|Data di pubblicazione:||10-dic-1987|
|Appare nelle tipologie:||8.1 PhD thesis|