2,194 research outputs found
La composizione chimica degli ammassi aperti molto giovani
No full textGli ammassi aperti (OC) sono eccellenti traccianti delle proprietà chimiche e della loro evoluzione del disco Galattico.
Questi sistemi rappresentano bene il concetto di popolazione stellare singola, cioè un gruppo di stelle coeve, (inizialmente) chimicamente omogenee. Essi coprono un'ampia gamma di metallicità e di età; soprattutto sono quasi onnipresenti nel disco Galattico. Pertanto, gli OC ci permettono di indagare diversi aspetti, come ad esempio l'evoluzione stellare e i modelli di nucleosintesi, l'evoluzione chimica galattica, i gradienti, i processi di migrazione e le connessioni stella-pianeta.
Tuttavia, in contrasto con gli ammassi aperti di età intermedia e vecchia, per i quali è ora disponibile un numero significativo di studi, gli ammassi più giovani delle Iadi (~600 Myr) sono stati per lo più trascurati in termini di composizione chimica (con poche eccezioni). Le indagini precedenti sembrano indicare un comportamento anomalo dei sistemi più giovani (ammassi aperti, associazioni e gruppi), e sono stati identificati tre principali problemi osservativi. (i) C'è una mancanza di sistemi di metallicità super-solare nel vicinato solare, in contrasto con le previsioni dei modelli di evoluzione Galattica.
(ii) Le stelle giovani e relativamente fredde (sotto 5400 K) mostrano una sovrabbondanza di diverse specie atomiche, derivate da righe spettrali di ionizzate e/o ad alta eccitazione. Infine, (iii) abbiamo rilevato il (in-)famoso puzzle del bario (Ba): estremi, inaspettatamente alti potenziamenti di Ba si trovano a giovani età, con valori fino a +0.7 dex a 30 Myr. Per quanto riguarda il comportamento degli altri elementi del processo s come ittrio (Y), zirconio (Zr), lantanio (La) e cerio (Ce), c'è un disaccordo generale in letteratura. Diversi autori sostengono che seguono la stessa tendenza del Ba, mentre altri trovano abbondanze solari a tutte le età. Ultimamente, diversi studi concordano sul fatto che l'attività stellare (più forte nelle giovani età che per gli OC più vecchi di 600 Myr) può alterare la formazione di righe spettrali moderate e forti (e/o può influenzare la struttura dell'atmosfera stellare). Di conseguenza, le righe che si formano negli strati superiori della fotosfera sono sistematicamente più forti nelle stelle giovani che in quelle vecchie (assumendo che le stelle abbiano parametri fondamentali simili).
La nostra ipotesi di lavoro è che l'anemia locale, la sovrabbondanza di atomi ionizzati e l'enigma del Ba potrebbero essere dovuti alle limitazioni dell'analisi di abbondanza standard quando applicata a stelle giovani e attive.
L'obiettivo della mia Tesi è di espandere la nostra comprensione di questo argomento da un punto di vista osservativo. Durante i 3 anni del mio dottorato, ho analizzato spettri ad alta risoluzione e alto S/N di stelle di tipo solare osservate dalla Gaia-ESO survey e dal consorzio Global Architecture of Planetary Systems -GAPS- e appartenenti a diversi sistemi stellari giovani (ammassi aperti, gruppi e associazioni). La mia indagine indica la necessità di rivedere le tecniche spettroscopiche applicate alle stelle molto giovani.
In attesa di una spiegazione teorica, possiamo superare questi problemi adottando nuovi approcci o con scelte strategiche delle righe spettrali da utilizzare. Ho sviluppato un nuovo metodo spettroscopico che si basa principalmente sull'uso di righe del Ti: con questo, la distribuzione della metallicità galattica nell'ambiente solare viene ripristinata e non dobbiamo ricorrere a complesse spiegazioni ad hoc. Viene anche esplorata la correlazione del parametro stellare con l'attività, così come la dipendenza delle sovrabbondanze. Infine, il puzzle del Ba sembra essere molto più complesso di quanto ci aspettassimo. Sia da un punto di vista spettrale che di nucleosintesi, manca ancora una soluzione. Questa Tesi si occupa delle questioni spettroscopiche dell'analisi dell'abbondanza di stelle molto giovani.Open clusters (OCs) are excellent tracers of the chemical properties and their evolution of the Galactic disc.
These systems represent the concept of single stellar population well, that is, a group of coeval, (initially) chemically homogeneous stars. They cover a wide range in metallicity and age; crucially they are almost ubiquitous in the Galactic disc. Therefore, OCs allow us to investigate several aspects, such as e.g., stellar evolution and nucleosynthesis models, galactic chemical evolution, gradients, migration processes, and star-planet connections.
However, at variance with intermediate-age and old OCs, for which a significant number of studies is now available, clusters younger than the Hyades (~600 Myr) have been mostly overlooked in terms of their chemical composition (with few exceptions). Previous investigations seem to indicate an anomalous behaviour of the youngest systems (open clusters, associations, and moving groups), and three main observational issues have been identified. (i) There is a lack of super-solar composition systems in the solar neighbourhood, at odds with predictions of the Galactic evolution models.
(ii) Young and relatively cool (temperatures lower than 5400 K) stars exhibit over-abundance of different atomic species, derived either from ionised and/or from high-excitation potential lines. Finally, (iii) we detected the (in-)famous barium (Ba) puzzle: extreme, unexpectedly high Ba enhancements are found at young ages, with values up to +0.7 dex at 30 Myr. Regarding the behaviour of the other s-process elements like yttrium (Y), zirconium (Zr), lanthanum (La), and cerium (Ce), there is general disagreement in the literature. Several authors claim that they follow the same trend as Ba, while others find solar abundances at all ages. Lately, different studies agree that stellar activity (stronger at young ages than for OCs older than 600 Myr) can alter the formation of moderate and strong spectral lines (and/or it can influence the structure of the stellar atmosphere). As a consequence, lines forming in the upper layers of the photosphere are systematically stronger in young stars than in old ones (assuming the stars to have similar fundamental parameters).
Our working hypothesis is that the local anaemia, the over-abundance of ionised atoms, and the Ba puzzle could be due to limitations of the standard abundance analysis when applied to young, active stars.
The goal of my Thesis is to expand our understanding of this topic from an observational point of view. During the 3 years of my Ph.D., I have analysed high-resolution, high S/N spectra of solar-type stars observed by the Gaia-ESO survey and by the Global Architecture of Planetary Systems -GAPS- consortium and belonging to several young stellar systems (open clusters, moving groups and associations). My investigation points to the need to revising the spectroscopic techniques when applied to very young stars.
While waiting for a theoretical explanation, we can overcome these issues by adopting new approaches or with strategic choices of the spectral lines to use. In particular, I developed a new spectroscopic method that is based mostly on the use of Ti lines: with this, the Galactic metallicity distribution in the solar surroundings is restored and we don't have to call for complex, ad hoc explanations. The correlation of the stellar parameter with activity is also explored, as well as the dependency of over-abundances. Finally, the Ba puzzle seems to be far more complex than we expected. Both form a spectral and a nucleosynthesis point of view, a solution is still missing. This Thesis deals with the spectroscopic issues of the abundance analysis of very young stars
Radial Velocity and Chemical Composition of Evolved Stars in the Open Clusters NGC 6940 and Tombaugh 5
No full textWe present and discuss medium resolution (R ∼ 13000), high signal-to-noise ({{S}}/{{N}}∼ 100), spectroscopic observations in the field of the open clusters NGC 6940 and Tombaugh 5. Spectra were recorded for seven candidate red giant stars in both clusters. For the latter, we present the very first chemical abundance analysis. We derive radial velocities for all the stars in NGC 6940, confirming membership to the cluster for all of them, while on the same ground, we exclude two stars in To 5. We perform a chemical abundance analysis of different atomic species, in particular Fe I, Si I, Ca I, Ti I, and Ni I. The mean metallicity of NGC 6940 is [Fe/H] = +0.09 ± 0.06 dex, in good agreement with previous works, while for To 5 is [Fe/H] = +0.06 ± 0.11 dex. Therefore, both clusters exhibit a chemical composition close to the solar value and do not deviate from the [Fe/H] Galactic radial abundance gradient. With these new values, we estimate the fundamental cluster parameters, after having derived clusters’ distances from the Gaia DR2 database. By adopting these distances, we derive updated estimated for the clusters ages: 1.0 ± 0.1 Gyr of NGC 6940 and 0.25 ± 0.05 Gyr for Tombaugh 5
Martina Drijverová and her literary works for children (author´s portrait)
No full textThis thesis Martina Drijverova and her literatur for children (the author´s portrait) is engaged in work of writer and screenwriter Martina Drijeverová. She is an excellent writer of literature for children. In the first part of this work her story writing is mentioned and the second part deals with her fairy-tale writing. The other author´s work written for children is in the third part. The conclusion of this thesis appreciates the author´s credit in literature for chidlren. Analysis of some books are available. The supplementary part is composed of autor´s biography and her photograph, some book covers, list of the autor´s work {--} televiews, radio plays and serials, audio tapes and CDs, stage plays, books written in Braille
HERStory Makers 2022: Martina Čagalj
No full textMartina Čagalj is a PhD candidate at the University of Split studying seaweeds as a potential source of bioactive compounds. She took part in HERStory Makers 2022.What is HERStory Makers?HERStory Makers is a social media competition for female-identifying early career researchers to share their research, their career journeys, and to inspire the next generation. Winners are selected by public vote. HERStory Makers is also part of EXPLORATHON, Scotland's contribution to European Researchers' Night.In 2022-23, EXPLORATHON was supported by the Engineering & Physical Sciences Research Council [grant number EP/X020894/1].Author contributions to contentMartina Čagalj conceived, planned, and recorded the video content. Kirsty Ross edited the video content to insert HERStory Maker credits, add subtitles, and maintain video length below Twitter/X limit of 2 mins and 20 secs, prior to scheduling the social media posts.</p
Enzyme self-assembly on naked iron oxide nanoparticles for aminoaldehyde biosensing
No full textThe preservation of enzymatic activity is a fundamental requirement for exploiting hybrid nano-bio-conjugates, and the control over protein–nanoparticle interactions, leading to stable and catalytically active hybrids, represents the key for designing new biosensing platforms. In this scenario, surface active maghemite nanoparticles (SAMNs) represent a new class of naked magnetic nanoparticles, displaying peculiar electrocatalytic features and the ability to selectively bind proteins. Recombinant aminoaldehyde dehydrogenase from tomato (SlAMADH1) was used as a model protein, and successfully immobilized by self-assembly on the surface of naked SAMNs, where its enzymatic activity resulted preserved for more than 6 months. The hybrid nanomaterial (SAMN@SlAMADH1) was characterized by UV–Vis spectroscopy, mass spectrometry, and TEM microscopy, and applied for the development of a biosensor for the determination of aminoaldehydes in alcoholic beverages. Measurements were carried out in a low volume electrochemical flow cell comprising a SAMN modified carbon paste electrode for the coulometric determination of the NADH produced during the enzymatic catalysis. The present findings, besides representing the first example of an electrochemical biosensor for aminoaldehydes in an alcoholic matrix, open the door to the use of immobilized enzymes on naked metal oxides nanomaterials for biosensing
The Complex Behaviour of s-Process Element Abundances at Young Ages
No full textOpen clusters appear as simple objects in many respects, with a high degree of homogeneity in their (initial) chemical composition, and the typical solar-scaled abundance pattern that they exhibit for the majority of the chemical species. The striking singularity is represented by heavy elements produced from the slow process of the neutron-capture reactions. In particular, young open clusters (ages less than a few hundred Myr) give rise to the so-called barium puzzle: that is an extreme enhancement in their [Be/Fe] ratios, up to a factor of four of the solar value, which is not followed by other nearby s-process elements (e.g., lanthanum and cerium). The definite explanation for such a peculiar trend is still wanting, as many different solutions have been envisaged. We review the status of this field and present our new results on young open clusters and the pre-main sequence star RZ Piscium
Abundances of neutron-capture elements in selected solar-type stars
No full textAims. The primary objective of this study is to accurately determine the abundances of Cu, Sr, Y, Zr, Ba, La, and Ce in selected solar-type stars. This will allow us to establish observational abundance–metallicity and abundance–age relations and to explore the reasons for the excess of Ba compared to other s-elements in younger solar-type stars. The chosen s-process elements are critical diagnostics for understanding the chemical evolution of our Galaxy.
Methods. We analysed HARPS spectra with a high resolution (R = 115 000) and high signal-to-noise ratio (close to 100) of main-sequence solar-type FGK stars with metallicities from −0.15 to +0.35 dex and ages from 2 to 14 Gyr using one-dimensional (1D) local thermodynamic equilibrium (LTE) synthesis and MARCS atmospheric models. In the procedure of fitting synthetic to observed line profiles, the free parameters included abundance and microturbulent and macroturbulent velocity. The macroturbulent velocity can substantially compensate for non-local thermodynamic equilibrium (NLTE) effects in the line core.
Results. The resulting elemental abundance [X/H] increases with metallicity and age for solar-type stars. The ratio of the abundances of s-process elements [s/Fe] increases with decreasing metallicity and age, while the [Cu/Fe] ratio increases with both metallicity and age. These observed trends agree well with published observational data and with predictions from Galactic chemical evolution (GCE) models. A small [Ba/Fe] enhancement of 0.08 ± 0.08 dex has been detected in seven younger stars with an average age of 2.8 ± 0.6 Gyr. Compared to the abundances of other s-process elements, [Ba/Fe] is 0.07 and 0.08 dex higher than La and Ce on average, respectively. Furthermore, we find that the [Ba/Fe] ratio increases with increasing chromospheric activity. The average [Ba/Fe] for the three most active stars is 0.15 ± 0.10 dex higher than that of the other stars. Chromospheric activity, characterised by stronger magnetic fields found in active regions such as pores, spots, plages, and networks, can significantly alter the physical conditions in the formation layers of the Ba lines. Our primary conclusion is that to account for the observed excess of [Ba/Fe] abundance in younger stars, it is essential to use more complex atmospheric models that incorporate magnetic structures
The role of data science in software development
No full textauthor: Martina WeberMasterarbeit Universität Innsbruck 201
The role of data science in software development
No full textauthor: Martina WeberMasterarbeit Universität Innsbruck 201
The role of data science in software development
No full textauthor: Martina WeberMasterarbeit Universität Innsbruck 201
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