41,840 research outputs found
Lithium and age of pre-main sequence stars: The case of Parenago 1802
No full textWith the aim to test the present capability of the stellar surface lithium abundance in providing an estimation for the age of PMS stars, we analyze the case of the detached, double-lined, eclipsing binary system PAR 1802. For this system, the lithium age has been compared with the theoretical one, as estimated by applying a Bayesian analysis method on a large grid of stellar evolutionary models. The models have been computed for several values of chemical composition and mixing length, by means of the code FRANEC updated with the Trojan Horse reaction rates involving lithium burning
Fluvial dynamics in the Castel di Sangro plain: morphological changes and human impact from 1875 to 1992.
No full textIn recent years, morphology and hydrogeology of the Castel di Sangro plain have undergone significant man-made changes. The plain is located in a very complex geological area where the Latium-Abruzzi carbonate platform, the Morrone-Rotella-Pizzone carbonate platform and the Molise nappe meet. Hydrology, hydrogeology, morphology and neotectonics of the area are conditioned by interlocking and overlapping of such palaeogeographic units. Some of them can be clearly recognised in the upper and middle Sangro area.
After outlining the geological, structural and geomorphological features of the area, the authors discuss the morphological changes which occurred in the Sangro River pattern and its alluvial plain from 1875 to 1992 as a result of construction of major hydraulic structures (dams, river bed cementation, urbanisation of flood plain and spring areas, wells). Elements inferred from comparison of maps and aerial photographs were also considered. The study provides a concise description of objective observations on both natural and man-induced fluvial processes and groundwater flows
High stability of AnchoisOil extracted with limonene from anchovy fillet leftovers
No full textTo investigate the vitamin content in an AnchoisOil sample stored at − 20 °C under N2 for more than four years, we have developed a new HPLC method for simultaneous identification and quantification of vitamins in anchovy fish oil that is efficient and applicable in practice. Coupled to full retention of the original visual appearance (orange color and transparency), the relatively high concentrations of lipid-soluble vitamin Q (coenzyme Q10) and vitamin A (retinol) in AnchoisOil extracted with d-limonene from European anchovy fillet leftovers more than four years after extraction point to remarkable chemical stability of this marine oil. These findings further support the practical use of the “LimoFish” process to extract valued fish oil from the leftovers of the world’s most caught fish species. Graphical Abstract: (Figure presented.
19F(p, α)16O and 19F(α,p)22Ne Reaction Rate Measured via THM and Fluorine Nucleosynthesis in AGB stars
No full textAsymptotic Giant Branch (AGB) stars have been proven to be sites of F production through spectroscopy observations by several authors, but it is not clear whether these stars might account for the total fluorine abundance of the Galaxy. Recently the two main channels for 19F destruction in AGB stars, namely the 19F(α,p)22Ne and 19F(p,α)16O reactions, have been studied via the Trojan Horse Method in the energy range of interest for astrophysics. In both cases experimental results have shown the presence of resonant structures below 500 keV, hinting to an enhancements in efficiency of fluorine destruction by stellar H- and He- burning. In particular the 19F(p, α)16O reaction rate at T 9 ≤ 0.2K turns out to be increased up to a factor of 1.7 while the 19F(p, α)16O is enhanced more than a factor of 4 at 0.1 ≤ T 9 ≤ 0.25. We present here a re-analysis of the role of AGB stars as fluorine galactic source by comparing stellar observations with predictions of AGB nucleosynthesis (for stellar masses from 1.5 to 5Mo) computed by employing in state-of-the-art models the THM reaction rates for 19F destruction
Indirect investigations on fusion reactions
No full textStellar evolution and element nucleosynthesis involve a wide range of interacting physical processes whose knowledge is fundamental to understand the astrophysical phenomena. Several nuclear processes hold the keys to many of the most intriguing problems. However, their studies can be challenging and a number of issues can be better understood by means of “indirect methods”, which are alternative and complementary to direct measurements. Among them, the Trojan Horse Method (THM) gives powerful hints to neutron or charged-particle-induced reactions while the Asymptotic Normalisation Coefficient (ANC) is effective to study particle capture reactions. We will review a couple of cases which were recently studied with those methods and define the importance of those reactions in the framework of stellar physics
ASTROPHYSICAL IMPACT of the UPDATED 9Be(p,)6Li and 10B(p,)7Be REACTION RATES AS DEDUCED by THM
No full textThe complete understanding of the stellar abundances of lithium, beryllium, and boron represents one of the most interesting open problems in astrophysics. These elements are largely used to probe stellar structure and mixing phenomena in different astrophysical scenarios, such as pre-main-sequence or main-sequence stars. Their different fragility against (p,) burning reactions allows one to investigate different depths of the stellar interior. Such fusion mechanisms are triggered at temperatures between T ≈ (2-5) × K, thus defining a corresponding Gamow energy between ≈ 3-10 keV, where S(E)-factor measurements need to be performed to get reliable reaction rate evaluations. The Trojan Horse Method is a well defined procedure to measure cross sections at Gamow energies overcoming the uncertainties due to low-energy S(E)-factor extrapolation as well as electron screening effects. Taking advantage of the measure of the 9Be(p,)6Li and 10B(p,)7Be cross sections, the corresponding reaction rates have been calculated and compared with the evaluations by the NACRE collaboration, widely used in the literature. The impact on surface abundances of the updated 9Be and 10B (p,) burning rates is discussed for pre-MS stars
On the introduction of 17O+p reaction rates evaluated through the THM in AGB nucleosynthesis calculations
No full textThe effect of the recent
No full textThe Trojan Horse Method (THM) has been used to investigate the low-energy cross sections of the 17O(p,α)14N and 18O(p,α)15N fusion reactions and to extract the strengths of the resonances that more contribute to the reaction rates at astrophysical energies. Moreover, the strength of the 65 keV resonance in the 17O(p,α)14N reaction, measured by means of the THM, has been used to renormalize the corresponding resonance strength in the 17O + p radiative capture channel. Since, proton-induced fusion reactions on 17O and 18O belong to the CNO cycle network for H-burning in stars, the new estimates of the cross sections have been introduced into calculations of Asymptotic giant branch (AGB) star nucleosynthesis to determine their impact on astrophysical environments. Results of nucleosynthesis calculations have been compared with geochemical analysis of ”presolar” grains. These solids form in the cold and dusty envelopes that surround AGB stars and once that have been ejected by stellar winds, come to us as inclusions in meteorites providing invaluable benchmarks and constraints for our knowledge of fusion reactions in astrophysical environments
The dialogue between the author and the hero in the “Notes” of G. R. Derzhavin
No full textВ центре внимания автора статьи «Записки» Г. Р. Державина, представляющие по своей сути его автобиографию. Труд этот был создан на закате жизни, он включает все важнейшие события жизни Г. Р. Державина, поэта и государственного деятеля. Рассказ ведется от третьего лица, что придает особую атмосферу повествованию, выстраивается своеобразный диалог между автором и героем, все это и является предметом исследования автора статьи.The focus of the author of the article “Notes” G. R. Derzhavin, representing in essence his autobiography. This work was created at the end of his life; it includes all the most important events in the life of G. R. Derzhavin, poet and statesman. The story is told in a third person, which gives a special atmosphere to the story, a certain dialogue emerges between the author and the hero, all this is the subject of the author's research
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