5,554 research outputs found
The effects of different Type Ia SN yields on Milky Way chemical evolution
We study the effect of different Type Ia SN nucleosynthesis prescriptions on the Milky Way chemical evolution. To this aim, we run detailed one-infall and two-infall chemical evolution models, adopting a large compilation of yield sets corresponding to different white dwarf progenitors (near-Chandrasekar and sub-Chandrasekar) taken from the literature. We adopt a fixed delay time distribution function for Type Ia SNe, in order to avoid degeneracies in the analysis of the different nucleosynthesis channels. We also combine yields for different Type Ia SN progenitors in order to test the contribution to chemical evolution of different Type Ia SN channels. The results of the models are compared with recent LTE and NLTE observational data. We find that 'classical' W7 and WDD2 models produce Fe masses and [\u3b1/Fe] abundance patterns similar to more recent and physical near-Chandrasekar and sub-Chandrasekar models. For Fe-peak elements, we find that the results strongly depend either on the white dwarf explosion mechanism (deflagration-to-detonation, pure deflagration, double detonation) or on the initial white dwarf conditions (central density, explosion pattern). The comparison of chemical evolution model results with observations suggests that a combination of near-Chandrasekar and sub-Chandrasekar yields is necessary to reproduce the data of V, Cr, Mn and Ni, with different fractions depending on the adopted massive stars stellar yields. This comparison also suggests that NLTE and singly ionized abundances should be definitely preferred when dealing with most of Fe-peak elements at low metallicity
Dinamica di dischi di accrescimento eccentrici e legame con i fenomeni di 'superhump'
This thesis investigates the dynamics of accretion disk of SU Ursae Majoris systems and their correlation with the superhump phenomena.
The various aspects of the disk eccentricity will be described through a 2D model, which considers the contribution of binary potential, the presence of a Linblad resonance and the viscosity of the disk.
After the derivation of the final equation for eccentricity in 2D disks, the computational results will be analysed, these will be compared with the superhump observational evidences and the pros and cons of the model developed will be highlighted.ope
[Mg/Fe] ratios in the solar neighbourhood: stellar yields and chemical evolution scenarios
Context. The [Mg/Fe] abundance ratios are a fundamental fossil signature to
trace the chemical evolution of the disc. Despite of the huge observational and
theoretical effort, discrepancies between models and data are still present and
several explanations have been put forward to explain the [/Fe]
bimodality. Aims. In this work, we take advantage of a new AMBRE:HARPS dataset,
which provides new and more precise [Mg/Fe] estimations, as well as reliable
stellar ages for a subsample of stars, to study the evolution of the solar
neighbourhood. Methods. The above data are compared with detailed chemical
evolution models for the Milky Way, exploring the most used prescriptions for
stellar yields and different formation scenarios for the Galactic disc, i.e.
the delayed two-infall and the parallel model, also including prescriptions for
stellar radial migration. Results. We see that most of the stellar yields
struggle to reproduce the observed trend of the data and that semi-empirical
yields are still the best to describe the [Mg/Fe] evolution in the thick and
thin discs. In particular, most of the yields still predict a steeper decrease
of the [Mg/Fe] ratio at high metallicity than what is shown by the data. The
bulk of the data are well reproduced by the parallel and two-infall scenarios,
but both scenarios have problems in explaining the most metal-rich and
metal-poor tails of the low- data. These tails can be explained in
light of radial migration from inner and outer disc regions, respectively.
Conclusions. Despite of the evidence of stellar migration, it is difficult to
estimate the actual contribution of stars from other parts of the disc to the
solar vicinity. However, the comparison between data and models suggests that
peculiar histories of star formation, such as that of the two-infall model, are
still needed to reproduce the observed distribution of stars.Comment: 16 pages, 16 figures. Accepted for publication in Astronomy and
Astrophysics (A&A
Monitoring Biological Damage on Paper-based Documents in the Historical Archive of the Palermo Astronomical Observatory
Libraries and archives house a wide variety of documents made of materials of vegetal and animal origin: unbound papers and books, manuscripts and printed books, photographs (negative and positive), prints, maps, available to the public for reading needs, study and information. These materials are often subject to fluctuations in environmental and micro-environmental parameters. For this reason, it is essential to implement constant monitoring and control of environmental conditions and potential deteriogens in order to slow down deterioration processes.The monitoring of the microbial degradation of paper documents in the Historical Archives of Palermo Astronomical Observatory has revealed microorganisms (bacteria and fungi) that may be considered responsible for damaging the items examined, thus enabling an evaluation of the real risks and the proper methodologies to use to avoid future recolonization.Gli archivi e le biblioteche custodiscono diverse tipologie di documenti composti da materiali di origine vegetale e animale: carte sciolte e volumi, sia manoscritti che a stampa, fotografi e (negativi e positivi), mappe, stampe, a disposizione del pubblico per esigenze di lettura, studio e informazione. Questa varietà di materiali sono spesso sottoposti a parametri ambientali e micro-ambientali non costanti. Per questo motivo è fondamentale operare sia un controllo costante delle condizioni ambientali sia un campionamento microbiologico sulla superficie, al fine di rallentare i processi di deterioramento.Il monitoraggio del degrado microbiologico di documenti presenti nell’Archivio Storico dell’Osservatorio Astronomico di Palermo ha permesso di rilevare diversi microrganismi (batteri e funghi) che possono essere considerati responsabili del degrado dei documenti analizzati, valutando il reale rischio e le metodologie più idonee per impedire la ricolonizzazione futura
Microbially-enhanced composting of olive mill solid waste (wet husk): Bacterial and fungal community dynamics at industrial pilot and farm level.
Bacterial and fungal community dynamics during microbially-enhanced composting of olive mill solid
waste (wet husk), used as a sole raw material, were analysed in a process carried out at industrial pilot
and at farm level by the PCR-DGGE profiling of the 16 and 26S rRNA genes. The use of microbial starters
enhanced the biotransformation process leading to an earlier and increased level of bacterial diversity.
The bacterial community showed a change within 15 days during the first phases of composting. Without
microbial starters bacterial biodiversity increased within 60 days. Moreover, the thermophilic phase was
characterized by the highest bacterial biodiversity. By contrast, the biodiversity of fungal communities in
the piles composted with the starters decreased during the thermophilic phase. The biodiversity of the
microbial populations, along with physico-chemical traits, evolved similarly at industrial pilot and farm
level, showing different maturation times
Composition of health-promoting phenolic compounds in two extra-virgin olive oils and diversity of associated yeasts
Extra virgin olive oil (EVOO), a basic component of the Mediterranean diet, is an important functional food, for its content in health-promoting compounds, showing antioxidant, antiinflammatory and antiproliferative activities. Here, two Tuscan EVOOs were analyzed for the occurrence and concentrations of health-promoting phenols, such as tyrosol and hydroxytyrosol and the secoiridoid derivatives, oleocanthal and oleacein. Independently of the milling period, the two EVOOs showed different contents of oleocanthal and oleacein. During storage, the contents of oleocanthal and oleacein decreased, while those of simple phenols increased. In all oil samples oleacein displayed a higher rate of reduction than oleocanthal. Multivariate analyses of the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) profiles, revealed the occurrence and diversity of oil-borne yeast communities, which differed in the two EVOOs. Sequences of excised DGGE bands identified Candida adriatica, Eremothecium coryli and Lachancea fermentati as the main components of the oil-borne yeast community. Our work detected, for the first time, differences in the content of tyrosol, hydroxytyrosol, oleocanthal and
oleacein between the two Tuscan EVOOs analyzed, consistent with the differences found in yeast community composition. Further studies could confirm whether oil-borne yeasts may affect the composition of health-promoting oil phenolic compounds
Origin of neutron capture elements with the Gaia-ESO survey: the evolution of s- and r-process elements across the Milky Way
We study the abundance patterns and the radial gradients of s-process
elements (Y, Zr, Ba, La and Ce), r-process elements (Eu) and mixed-process
elements (Mo, Nd and Pr) in the Galactic thin disc by means of a detailed
two-infall chemical evolution model for the Milky Way with state-of-the-art
nucleosynthesis prescriptions. We consider r-process nucleosynthesis from
merging neutron stars (MNS), magneto-rotational supernovae (MR-SNe) and
s-process synthesis from low- and intermediate- mass stars (LIMS) and rotating
massive stars. The predictions of our model are compared with data from the
sixth data release of the Gaia-ESO survey, from which we consider 62 open
clusters with age > 0.1 Gyr and 1300 Milky Way disc field stars. We conclude
that: i) the [Eu/Fe] vs. [Fe/H] is reproduced by both a prompt and a delayed
source, but the quick source completely dominates the Eu production; ii)
rotation in massive stars contribute substantially to the s-process elements of
the first peak, but MNS and MR-SNe are necessary in order to reproduce the
observations; iii) due to the adopted yields, our model overpredicts Pr and
underpredicts Nd, while the [Mo/Fe] vs. [Fe/H] is nicely reproduced. For the
radial gradients, we conclude that: i) our predicted slope of the [Fe/H]
gradient is in agreement with the one observed in open clusters by Gaia-ESO and
other high-resolution spectroscopic surveys. ii) The predicted slope of the
[Eu/H] radial gradient is steeper than the observed one, independently on how
quick the production of Eu is. We discuss the possible causes of this
discrepancy in terms of both different Galaxy formation scenarios and stellar
radial migration effects. iii) For all the elements belonging to the second
s-process peak (Ba, La, Ce) as well as for Pr, we predict a plateau at low
Galactocentric distances, which is probably due to the enhanced enrichment from
LIMS in the inner regions.Comment: 17 pages, 11 figures. Submitted to MNRA
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