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

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)

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

BC-SIM-TR-007 STC Delta-NECP REPORT Issue 1.0

The present document has been issued to describe the Delta – Near Earth Commissioning Phase (dNECP) Tests of STC Stereo Camera ,Channel Of SIMBIO-SYS (Spectrometers and Imagers for MPO BepiColombo Integrated Observatory SYStem)

BC-SIM-TN-013 STC Inflight Dark Calibration

In this document, we reported the history of the tests performed on the STC detector in the first two years of the BepiColombo’s cruise phase. The scope of these tests was to monitor the dark current behavior of the STC channel’s detector. A detailed description is provided for each test phase: data acquired, the deducted results and conclusions. The STC Channel is part of SIMBIO-SYS, a scientific payload of the BepiColombo ESA-JAXA mission to Mercury. During the NECP (Near-Earth Commissioning Phase ), all the initial commissioning activities were completed and the three channels of SIMBIO-SYS have operated properly demonstrating that all the channels and subsystems worked nominally. Since then, every six months different instrument checkouts have been carried-out to check the performance of the three SIMBIO-SYS channels and improve their calibration. This document reports the conclusion on the Dark calibration of STC Channel due to the analysis of the ICOs tests

SIMBIO-Sim: a performance simulator for the SIMBIO-SYS suite on board the BepiColombo mission

The SIMBIO-SYS simulator is a useful tool to test the instrument performance and to predict the instrument behaviour during the whole scientific mission. It has been developed with Interactive Data Language (IDL), and it give three groups of output data: i) the geometrical quantities related to the spacecraft and the channels, which include both the general information about the spacecraft and the information for each filter; ii) the radiometric outputs, which include the planet reflectance, the radiance and the expected signal measured by the detector; iii) the quantities related to the channel performance, which are for example the integration time (IT), which has to be defined to avoid the detector saturation, the expected dark current of the detector

Development of a simulator of the SIMBIOSYS suite onboard the BepiColombo mission

BepiColombo is the fifth cornerstone mission of the European Space Agency (ESA) dedicated to study the Mercury planet. The BepiColombo spacecraft comprises two science modules: the Mercury Planetary Orbiter (MPO) realized by ESA and the Mercury Magnetospheric Orbiter provided by the Japan Aerospace Exploration Agency. The MPO is composed by 11 instruments, including the 'Spectrometer and Imagers for MPO BepiColombo Integrated Observatory System' (SIMBIOSYS). The SIMBIOSYS suite includes three optical channels: a Stereoscopic Imaging Channel, a High Resolution Imaging Channel, and a Visible and near Infrared Hyperspectral Imager. SIMBIOSYS will characterize the hermean surface in terms of surface morphology, volcanism, global tectonics, and chemical composition. The aim of this work is to describe a tool for the radiometric response prediction of the three SIMBIOSYS channels. Given the spectral properties of the surface, the instrument characteristics, and the geometrical conditions of the observation, the realized SIMBIOSYS simulator is capable of estimating the expected signal and integration times for the entire mission lifetime. In the simulator the spectral radiance entering the instrument optical apertures has been modelled using a Hapke reflectance model implementing the parameters expected for the hermean surface. The instrument performances are simulated by means of calibrated optical and detectors responses. The simulator employs the SPICE (Spacecraft, Planet, Instrument, C-matrix, Environment) toolkit software, which allows us to know for each epoch the exact position of the MPO with respect to the planet surface and the Sun

BC-SIM-TR-013 - STC ICO1 REPORT Issue 1.0

The present document has been issued to describe the Instrument Check Out Phase (ICO#1) Tests of STC, channel of the Spectrometers and Imagers for MPO BepiColombo Integrated Observatory SYStem (SIMBIO-SYS)

BC‐SIM‐TR‐026 STC ICO3 REPORT

The present document has been issued to describe the ICO#3 (Third Instrument Check Out Phase) Tests of STC, channel of the Spectrometers and Imagers for MPO BepiColombo Integrated Observatory SYStem (SIMBIO-SYS)