Chemical ejecta and final fates of intermediate-mass and massive stars

In my PhD work I carried out a detailed investigation on the final fates and chemical ejecta produced by intermediate-mass and massive stars. The first part of the thesis is focused on massive and very massive stars. We derive the ejecta for a large number of elemental species (H, He, C, N, O, F, Ne, Na, Mg, Al, Si, S Ar, K, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn) during the pre-supernova evolution and after the explosion or collapse event. We use a set of stellar tracks computed with PAdova and TRieste Stellar Evolution Code (PARSEC), with initial masses in the range between 8 M to 350 M , for thirteen different initial metallicities from Z = 0.0001 to Z = 0.02. Adopting suitable explodability criteria available in the recent literature, for each stellar model we derive the final fate and remnant mass, which critically depend on the initial mass and metallicity. Three main classes of explosion events are considered. Massive stars with initial masses from 8 Msun to 100 Msun , build a degenerate iron core which eventually collapses either generating a successful explosion and a neutron star, or experiencing an inexorable infall with consequent black hole formation (failed supernovae). Very massive objects (VMOs), with initial mass ∼ 100 M , can end their life either as pulsation pair instability supernovae (PPISN), pair instability supernovae (PISN), or directly collapsing to black hole (DBH). For these objects, the fate is mainly determined by the mass of helium-core. From our analysis we derive a general scenario on the fate of massive and very massive stars emerges. It is evident that both the pre-SN evolution and the subsequent SN channel are significantly affected by the initial metallicity, as a consequence of its impact on the efficiency of mass loss and the growth of the stellar core. In particular, we find that suitable conditions for the occurrence of PPISN and PISN events are not limited to extremely low metallicities, as invoked in early studies. Rather, such energetic events may take place already at Z > Zsun /3, hence in the local Universe, in agreement with recent findings in the literature. Once final fates and remnant masses are known, we compute the elemental ejecta for all stars in the grid, accounting for both wind and explosion contributions. The wind ejecta are directly derived from PARSEC stellar evolution models, for all isotopes from 1 H to 28 Si and heavier elements up to Zn. The explosion ejecta are obtained from supernova nucleosynthesis calculations available in the literature, for the three classes here considered(CCSN, PISN or PPISN). Suitable parameters (masses of the CO and He cores) are adopted to link the explosion models to our PARSEC tracks. We also calculate the integrated yields ejected by a simple stellar population with a specified initial mass function in view of comparing the chemical contributions of both winds and explosions from the three classes of stars (CCSNe, PISNe and PPISNe). As a final result of this work, we aim at releasing a large database of chemical ejecta and compact remnants produced by massive and very massive stars over a large range of initial masses and metallicites. These will be a key relevance in the framework of the galaxy chemical evolution studies. In the second part of the thesis we investigate the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience both the third dredge-up and hot-bottom burning. This study was performed in the context of the LUNA (Laboratory Underground Nuclear Astrophysics) collaboration. Nucleosynthesis calculations were carried out adopting the new rate for the key reaction 22 Ne(p, γ) 23 Na, which plays a major role in determining the abundance of sodium. To this aim we used the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range 3.0 Msun 6.0 Msun , and metallicities Z=0.0005, Z=0.006, and Z = 0.014. We find that the new LUNA measurements have much reduced the nuclear uncertainties of the tors of 22Ne and 23Na AGB ejecta, which drop from fac-10 to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of 23Na, the uncertainties that still affect the 22Ne and 23Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge- up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. While best-fitting AGB models can be singled out, the AGB hypothesis still needs to be validated, as various issues still remain

Strengths of the resonances at 436, 479, 639, 661, and 1279 keV in the 22^{22}Ne(p,γ\gamma)23^{23}Na reaction

The $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction is included in the neon-sodium cycle of hydrogen burning. A number of narrow resonances in the Gamow window dominates the thermonuclear reaction rate. Several resonance strengths are only poorly known. As a result, the $^{22}$Ne(p,$\gamma$)$^{23}$Na thermonuclear reaction rate is the most uncertain rate of the cycle. Here, a new experimental study of the strengths of the resonances at 436, 479, 639, 661, and 1279 keV proton beam energy is reported. The data have been obtained using a tantalum target implanted with $^{22}$Ne. The strengths $\omega\gamma$ of the resonances at 436, 639, and 661 keV have been determined with a relative approach, using the 479 and 1279 keV resonances for normalization. Subsequently, the ratio of resonance strengths of the 479 and 1279 keV resonances was determined, improving the precision of these two standards. The new data are consistent with, but more precise than, the literature with the exception of the resonance at 661 keV, which is found to be less intense by one order of magnitude. In addition, improved branching ratios have been determined for the gamma decay of the resonances at 436, 479, and 639 keV.Comment: Final version, now using the Kelly et al. (2015) data [15] for normalization; 10 pages, 7 figures, 3 table

The effects of the initial mass function on Galactic chemical enrichment

Context. We have been seeing mounting evidence that the stellar initial mass function (IMF) might extend far beyond the canonical Mi ∼ 100 M⊙ limit, but the impact of such a hypothesis on the chemical enrichment of galaxies is yet to be clarified. Aims. We aim to address this question by analysing the observed abundances of thin- and thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair instability supernovae. Methods. We built new sets of chemical yields from massive and very massive stars up to Mi ∼ 350 M⊙ by combining the wind ejecta extracted from our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code, we analysed the effects of adopting different yield tables by comparing predictions against observations of stars in the solar vicinity. Results. After several tests, we set our focus on the [O/Fe] ratio that best separates the chemical patterns of the two Milky Way components. We find that with a standard IMF, truncated at Mi ∼ 100 M⊙, we can reproduce various observational constraints for thin-disc stars; however, the same IMF fails to account for the [O/Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi = 350 M⊙, while including the chemical ejecta of very massive stars in the form of winds and pair instability supernova (PISN) explosions. Conclusions. Our study indicates that PISN may have played a significant role in shaping the chemical evolution of the thick disc of the Milky Way. Including their chemical yields makes it easier to reproduce not only the level of the α-enhancement, but also the observed slope of thick-disc stars in the [O/Fe] vs. [Fe/H] diagram. The bottom line is that the contribution of very massive stars to the chemical enrichment of galaxies is potentially quite important and should not be neglected in models of chemical evolution

22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,gamma)23Na

We investigate the impact of the new LUNA rate for the nuclear reaction $^{22}$Ne$(p,\gamma)^{23}$Na on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range $3.0\,M_{\odot} - 6.0\,M_{\odot}$, and metallicities $Z_{\rm i}=0.0005$, $Z_{\rm i}=0.006$, and $Z_{\rm i} = 0.014$. We find that the new LUNA measures have much reduced the nuclear uncertainties of the $^{22}$Ne and $^{23}$Na AGB ejecta, which drop from factors of $\simeq 10$ to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of $^{23}$Na, the uncertainties that still affect the $^{22}$Ne and $^{23}$Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available

The optical head of the EnVisS camera for the Comet Interceptor ESA mission: Phase 0 study

EnVisS (Entire Visible Sky) is an all-sky camera specifically designed to fly on the space mission Comet Interceptor. This mission has been selected in June 2019 as the first European Space Agency (ESA) Fast mission, a modest size mission with fast implementation. Comet Interceptor aims to study a dynamically new comet, or interstellar object, and its launch is scheduled in 2029 as a companion to the ARIEL mission. The mission study phase, called Phase 0, has been completed in December 2019, and then the Phase A study had started. Phase A will last for about two years until mission adoption expected in June 2022. The Comet Interceptor mission is conceived to be composed of three spacecraft: spacecraft A devoted to remote sensing science, and the other two, spacecraft B1 and B2, dedicated to a fly-by with the comet. EnVisS will be mounted on spacecraft B2, which is foreseen to be spin-stabilized. The camera is developed with the scientific task to image, in push-frame mode, the full comet coma in different colors. A set of ad-hoc selected broadband filters and polarizers in the visible range will be used to study the full scale distribution of the coma gas and dust species. The camera configuration is a fish-eye lens system with a FoV of about 180°x45°. This paper will describe the preliminary EnVisS optical head design and analysis carried out during the Phase 0 study of the mission

Impacto de programa fisioterapêutico no desempenho funcional da criança com doença de Charcot-Marie-Tooth tipo 2: estudo de caso

This case study aimed at verifying the influence of a physical therapy program on the functional performance of a child with diagnosis of Charcot-Marie-Tooth) disease type 2. The 6 year-old male child presented low and upper limbs affected at both motor and sensitive levels. Before and after the program, the subject was assessed by means of the Pediatric Evaluation Disability Inventory (PEDI), designed for children between 6 months through 7.5 years old. PEDI is divided into three parts – functional skills (involving selfcare, mobility and social function), caregiver assistance, and environment modification – and only the first part was used in this study. Drawing on the difficulties detected at the first evaluation, a physical therapy program was designed, based on the neurodevelopmental concept. The program lasted two months, with two 50-minute sessions per week (a total of 15 sessions). At the post-program evaluation, self-care score raised from 20.8 to 26.7, and mobility scare, from 40 to 54,9, specially in transference and going up and downstairs skills. Thus, the therapy program was effective in improving the subject's functional performance.O estudo visou verificar a influência de um programa fisioterapêutico nodesempenho funcional de uma criança com diagnóstico de Charcot-Marie-Tooth tipo 2. O participante (sexo masculino, 6 anos) apresentava comprometimento motor e sensitivo em membros superiores e inferiores. Antes e após o programa, o participante foi avaliado pelo Pediatric Evaluation Disability Inventory (PEDI), questionário que avalia o desempenho funcional de crianças na faixa de 6 meses a 7 anos e meio. O PEDI divide-se em três partes: habilidades funcionais (envolvendoautocuidado, mobilidade e função social), assistência do cuidador e modificações do ambiente; este estudo limitou-se à parte de habilidades funcionais. A partir das dificuldades detectadas na avaliação inicial, elaborou-se um programa de intervenção fisioterapêutica com base no conceito neuroevolutivo Bobath. O programa foi aplicado por 2 meses, sendo realizadas 2 sessões semanais de 50 minutos cada, totalizando 15 sessões. Na avaliação após a aplicação do programa, aumentou o escore normativo no PEDI, nas áreas de autocuidado (de 20,8 para 26,7) e mobilidade (de 40 para 54,9), especialmente nas habilidades de transferência, subir e descer escadas. Portanto, o programa de intervenção fisioterapêutica mostrou-se eficaz, promovendo melhora no desempenho funcional da criança

STC Observation strategy report

This document contains all the information and concepts necessary to define an observation strategy for STC, the stereocamera channel of SIMBIOSYS, and plan its observations. It first describes the constraints derived from the orbit of Mercury, the planning of BepiColombo mission, and the design of STC detector; then the possibilities offered by the software commanding the instrument are presented. Building on these constraints and possibilities, an observation strategy based on a “segmented orbit” concept is presented and illustrated with some practical examples

BC-SIM-TR-031 STC ICO4 REPORT

The present document has been issued to describe the ICO#4 (Instrument Check Out Phase) Tests of STC, channel of the Spectrometers and Imagers for MPO BepiColombo Integrated Observatory SYStem (SIMBIOSYS)

A Mercury surface radiometric model for SIMBIO-SYS instrument suite on board of BepiColombo mission

The BepiColombo mission represents the cornerstone n.5 of the European Space Agency (ESA) and it is composed of two satellites: the Mercury Planetary Orbiter (MPO) realized by ESA and the Mercury Magnetospheric Orbiter (MMO) provided by the Japan Aerospace Exploration Agency (JAXA). The payload of the MPO is composed by 11 instruments. About half of the entire MPO data volume will be provided by the Spectrometer and Imagers for MPO BepiColombo Integrated Observatory System" (SIMBIO-SYS) instrument suite. The SIMBIO-SYS suite includes three imaging systems, two with stereo and high spatial resolution capabilities, which are the Stereoscopic Imaging Channel (STC) and High Resolution Imaging Channel (HRIC), and a hyper-spectral imager in the Vis-NIR range, named Visible and near Infrared Hyper-spectral Imager (VIHI). In order to test and predict the instrument performances, a radiometric model is needed. It consists in a tool that permits to know what fraction of the incoming light is measured by the detector. The obtained signal depends on the detector properties (such as quantum efficiency and dark current) and the instrument transmission characteristics (transmission of lenses and filter strips, mirrors reflectivity). The radiometric model allows to correlate the radiance of the source and the signal measured by each instrument. We used the Hapke model to obtain the Mercury reflectance, and we included it in the radiometric model applied to the STC, HRIC and VIHI channels. The radiometric model here presented is a useful tool to predict the instruments performance: it permits to calculate the expected optical response of the instrument (the position in latitude and longitude of the filter footprints, the on-ground px dimensions, the on-ground speed, the smearing and the illumination angles of the observed points), and the detector behavior (the expected signal and the integration time to reach a specific SNR). In this work we derive the input flux and the integration times for the three channels of SIMBIO-SYS, using the radiometric model to obtain the source radiance for each Mercury surface area observed