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Dissertations / Theses on the topic 'Nucleosynthesis'

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Published: 4 June 2021

Last updated: 31 July 2024

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1

Izzard, R. G. "Nucleosynthesis in binary stars." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604980.

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Galactic chemical evolution models require stellar nucleosynthesis yields as input data. Stellar evolution models are used to calculate such yields but do not take into account the fact that many stars are in binaries. The computing time required to explore the binary star parameter space is usually considered to be prohibitively large. Therefore binaries, except for type Ia supernovae and novae which are included in an ad hoc way, are ignored in most galactic chemical evolution models. In this dissertation synthetic nucleosynthesis models are developed which approximate full stellar evolution models. Cunning methods are employed to model shell burning in low- and intermediate-mass stars while high-mass stars have their surface abundances fitted to their mass. Explosive yields are fitted to published results. The synthetic nucleosynthesis model, with the addition of algorithms to deal with mass transfer in binaries, is coupled to a rapid binary star evolution code. The use of a synthetic model speeds up the calculation of stellar yields by a factor of about 10⁷ and extends the analysis to binary stars. Single- and binary-star yields are calculated for a range of initial mass and separation distributions. A change in the primary or single-star mass distribution is most significant. Changing the secondary mass or separation distribution has a smaller effect. Consideration is then given to variation of the input physics to determine which free parameters are important for the calculation of yields from single and binary stars. It is found that certain parameters are important for some isotopes. Future prospects are then briefly discussed.

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2

Leonard, Richard Edward. "Variations in Primordial Nucleosynthesis /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487932351056492.

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3

Smith, Christel Johanna. "Primordial nucleosynthesis and neutrino physics." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3354965.

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Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed June 16, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

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4

Joseph, Craig L. "Q-nucleosynthesis : implications for stellar evolution /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487260531956577.

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5

Moreno, Guzmán Fermín. "Accretion onto Neutron Stars: Hydrodynamics and Nucleosynthesis." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/6594.

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In the middle of the 70s, some authors suggested that accretion of hydrogen and helium rich material by a neutron star in a binary system, where the companion star would have low mass, could explain thermonuclear bursts observed by the first satellites launched to the space in order to analyze the Xray band of the electromagnetic spectrum. This phenomenon, known as type I X-ray bursts (XRB), is a thermonuclear runaway produced by the themonuclear fusion of the accreted material in degenerated conditions. This kind of explosion from stellar source is the most frequent in our galaxy (and the third, after supernovae and classical novae, in terms of total output energy), because his short recurrence period. Due to the extreme gravitational field of a neutron star it is known that produced nucleosynthesis is not ejected to the interstellar medium but forming part of the neutron star crust.
In this work we have tried, first, to study the effects of nuclear uncertainties, related to nuclear reaction rates, in the nucleosynthesis produced during a X-ray burst, and second, to simulate physical properties and associated nucleosynthesis to this kind of events, through hydrodynamical models.
In order to analyze the impact of uncertainties of the nuclear reaction rates in the nucleosynthesis, and due to the prohibitive calculation time with an hydrodinamical code, we have used a post-processing code which we have coupled, for a given set of 10 temperatures and densities profiles, an extensive nuclear reactions network formed by 606 isotopes and 3551 nuclear reactions, whose reaction rates have been modified using to alternative methods. In the first one, every rate has been individually modified, multiplying it by 0.1 and 10, calculating the final nucleosynthesis. This way, it is possible to evaluate the impact in final nucleosynthesis individual variations in the nuclear reaction rates. Also we have analyzed the effects in final nucleosynthesis by modifying the energy associated to each reaction (Q-value). In the second method, nuclear reaction rates have been modified simultaneously, multiplying each one by a random factor which follow a log-normal distribution with a probability of 95.5% of being in the interval [0.1,10]. In order to analyzed this method from an statistically point of view, the nucelosynthesis has been calculated up to 10,000 times, with a Monte Carlo code specifically built to this Thesis, for different set of random numbers. Obtained results with both methods are coincidents and show that for a network formed by 3,500 reactions approximately, only about 60 reactions have an impact in final yields greater than a factor of 2.Finally, we have used an hydrodynamical code, one-dimensional (spherically symmetric), Lagrangian and multi-shell, to which we have coupled a nuclear reactions network formed by 324 isotopes and 1392 reactions with the aim of reproduce physical parameters and nucleosynthesis produced during X-ray bursts. To do that, we have applied this code to different models, analyzing the effect of spatial resolution in the accreted shell, the metallicity of the transferred material as well as the mass of the neutron star, in the final result. For each model, we have simulated different bursts, with energies, luminosities and recurrence times coincidents with observations and, together with the nucleosynthesis, similar to the results obtained by other authors.
A mediados de los años 70, varios autores sugirieron que la acreción de material rico en hidrógeno y helio por parte de una estrella de neutrones, integrante de un sistema binario donde la masa de la estrella compañera fuese pequeña, podría explicar las erupciones termonucleares observadas por los primeros satélites lanzados al espacio para analizar la banda X del espectro electromagnético. Dicho fenómeno, conocido como erupciones de rayos X de tipo I (en inglés, type I X-ray bursts, XRB), consiste en el alud termonuclear producido por la fusión termonuclear del material acretado, en condiciones degeneradas. Este tipo de explosión termonuclear de origen estelar es el más frecuente en nuestra galaxia (y el tercero, tras las supernovas y las novas clásicas, en términos de energía total liberada), debido a su corto periodo de recurrencia. Como consecuencia del extremo campo gravitatorio de una estrella de neutrones, se cree que la nucleosíntesis producida durante este tipo de eventos no es expulsada al medio interestelar, pasando a formar parte de la corteza de la estrella.
En este trabajo hemos intentado, por un lado, estudiar los efectos de las incertidumbres de origen nuclear, asociadas a los ritmos de las reacciones nucleares, en la nucleosíntesis producida durante un X-ray burst; y por otro lado, simular las propiedades físicas y la nucleosíntesis asociada a este tipo de eventos, mediante modelos hidrodinámicos.
Para estudiar el impacto de las incertidumbres de los ritmos de las reacciones nucleares en la nucleosíntesis, y debido a que el tiempo de cálculo con un código hidrodinámico resultaría prohibitivo, hemos utilizado un código de post-procesado al que se ha acoplado, para un conjunto determinado de 10 perfiles de temperatura y densidad, una extensa red de reacciones nucleares, formada por 606 isótopos y 3551 reacciones nucleares, cuyos ritmos de reacción han sido modificados utilizando dos métodos alternativos. En el primero, cada ritmo ha sido modificado individualmente, multiplicándolo por 0.1 y 10, calculándose la nucleosíntesis final. De esta manera, puede evaluarse el impacto que tienen en las abundancias finales las variaciones individuales de los ritmos de las reacciones nucleares.
Así mismo, también se ha analizado el efecto que produce en las abundancias finales el hecho de modificar la energía asociada a cada reacción (Q-value). En el segundo método, los ritmos nucleares se han modificado simultáneamente, multiplicando cada uno de ellos por un factor aleatorio según una distribución log-normal, y cuya probabilidad de encontrarse en el intervalo [0.1,10] es del 95,5%. Para poder hacer una estimación estadística de este último método, se ha calculado la nucleosíntesis hasta 10.000 veces, con un código Monte Carlo específicamente construido para esta Tesis, para diferentes conjuntos de números aleatorios. Los resultados obtenidos con ambos métodos son coincidentes y demuestran que, para una red formada por unas 3500 reacciones nucleares, sólo unas 60 reacciones tienen un impacto en las abundancias finales mayor que un factor 2.
Por último, hemos utilizado un código hidrodinámico, unidimensional (en simetría esférica), Lagrangiano y multicapa, al que se ha acoplado una red de reacciones nucleares formada por 324 isótopos y 1392 reacciones nucleares, con el objetivo de reproducir los parámetros físicos y la nucleosíntesis producida en los X-ray bursts. Para ello, hemos aplicado este código a diferentes modelos, analizando el efecto de la resolución espacial de la capa acretada, la metalicidad del material transferido, así como la masa de la estrella de neutrones, en el resultado final. Para cada modelo, hemos simulado diferentes erupciones, con energías, luminosidades, y periodos de recurrencia, coincidentes con las observaciones y, junto con la nucleosíntesis, similares a los resultados obtenidos por otros autores.

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6

Alvelid, Jonatan. "r-Process Simulation and Heavy-Element Nucleosynthesis." Thesis, KTH, Fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-150101.

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r-process, short for rapid neutron capture process, is a nucleosynthesis process taking place on short time scales. Rapid neutron captures produce less and less stable neutron-rich nuclei which in turn beta minus decays when the probability for beta decay is higher than the probability for neutron captures, upon which more neutrons are captured and the process repeats itself, creating r-process paths. Very neutron-rich heavy elements are the product of this process taking place at explosive astrophysical sites with high neutron flux. Simulations of r-processes are important for finding out the exact sites, something that is yet not known. To get more accurate simulation results leading to a better understanding of r-processes, the initial parameter dependence of the simulations is important to understand. This report discusses the dependence on three important initial parameters; temperature, density and electron fraction. Furthermore, the dependence on nuclear masses is covered, which is important since no exact model for nuclear masses exists for the neutron-rich nuclei involved. Finally, different stopping criteria are simulated, representing different physical environments in which r-processes may occur. Results from the simulations, carried out using r-Java 2.0, show that r-process simulations are sensitive to all parameters discussed; further research can tell to which extent. A better understanding of the dependence on the parameters will hopefully extend our knowledge of r-processes and where in the universe they occur.
r-process, rapid neutron capture process, är en snabb nukleosyntesprocess. Snabba neutroninfångningar producerar allt mer instabila neutronrika atomkärnor som slutligen betaminussönderfaller när sannolikheten för betasönderfall blir högre än sannolikheten för en ny neutroninfångning. Därefeter fångas fler neutroner och processen upprepar sig själv i r-processkedjor. Väldigt neutronrika tunga ämnen bildas under denna process som kräver explosiva astrofysikaliska platser med höga neutronflux. Då det ännu är okänt exakt var dessa platser är så hjälper r-processsimulationer att förstå detta. För att förbättra simuleringsresultaten och därmed förståelsen av r-processer så är det viktigt att förstå hur initiala parametrar påverkar simuleringarna. Temperatur, densitet och förhållandet mellan fria elektroner och nukleoner är tre parametrar som denna rapport behandlar. Påverkan av kärrnmassor diskuteras också, vilket är viktigt då ingen exakt modell för kärnmassor existerar. Slutligen behandlas även olika stoppkriterium vilket representerar olika fysikaliska miljöer där r-processer eventuellt förekommer. Resultat från simuleringar, gjorda i r-Java 2.0, visar på att r-processimuleringar är känsliga för alla parametrar som har behandlats men där vidare forskning får visa till vilken grad. En bättre förståelse för hur simuleringarna påverkas av parametrar kommer förhoppningsvis öka förståelsen för r-processer och var i universum de förekommer.

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7

Karlsson, Daniel. "Nuclear density functional theory calculations for the r-process nucleosynthesis : Nuclear density functional theory calculations for the r-process nucleosynthesis." Thesis, KTH, Fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-250775.

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8

Erni, Peter. "Early nucleosynthesis studies with quasar absorption line spectroscopy." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983739854.

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9

Kifonidis, Konstantinos. "Nucleosynthesis and hydrodynamic instabilities in core collapse supernovae." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962128457.

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10

Lau, Ho Bun. "Evolution and nucleosynthesis of zero-metallicity AGB stars." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612023.

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11

Young, Patrick Allen. "Hydrodynamics, nucleosynthesis, and mass loss in massive stars." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280579.

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I test the predictive power of the stellar evolution code TYCHO. Systematic errors are present in the predictions for double-lined eclipsing binary stars when only standard physics common to the majority of stellar evolution codes is included. A mechanism for driving slow circulation and mixing in the radiative regions of stars is identified in numerical simulations of convection and a physical theory developed. Mixing is caused by dissipation of inertial waves driven by the interaction of convective fluid motions with the boundary of the convection zone. Evolutionary calculations incorporating this physics are tested in several observational regimes. Light element depletion in young clusters, turnoff ages of young clusters with brown dwarf Li depletion ages, and evolution of carbon stars on the asymptotic giant branch are all predicted satisfactorily. Tests of solar models yield good agreement with surface observables, chemical abundances, helioseismological data, and neutrino fluxes. The predictive accuracy of a non-calibrated, state-of-the-art stellar evolution code is ∼7% for surface observables. The main sequence sun is relatively easy to model, so this gives an estimate of our minimum predictive error. The solar models also highlight problems with uniqueness of evolutionary tracks converging on a given point and the potential for avoiding the effects of missing physics by calibration. A reanalysis of the binary sample with the more complete physics shows a dramatic improvement in the accuracy of the models. The potential for avoiding the effects of missing physics by calibration is explored. A TYCHO model for a late AGB star is used for the boundary conditions on a hydrodynamic simulation of proto-planetary nebula evolution as an illustration of the unified technique. NaCl and NaCn are observed at large radii in the Egg Nebula. These molecules require high densities to form, which are difficult to explain at large distances from the star. The 2-D simulation of a fast wind interacting with earlier mass loss produces clumps of material through a thermal instability with the necessary conditions for formation of the molecules. In conclusion, the effects of the more complete physics on the core size and abundance profiles of a massive star during core Si burning are examined as an example of future developments.

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12

Sawada, Ryo. "Nucleosynthesis Constraints on the Energy Growth Timescale of a Core-collapse Supernova Explosion." Kyoto University, 2020. http://hdl.handle.net/2433/253085.

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13

Arcones, Segovia Almudena. "On nucleosynthesis relevant conditions in neutrino-driven supernova outflows." [S.l.] : [s.n.], 2007. http://mediatum2.ub.tum.de/doc/619019/document.pdf.

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14

Wylie, Elizabeth Claire. "Nucleosynthesis and s-process element formation in giant stars." Thesis, University of Canterbury. Physics and Astronomy, 2006. http://hdl.handle.net/10092/1346.

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A thorough understanding of nucleosynthesis and element formation in stars of all evolutionary phases is of vital importance in stellar astrophysics. It provides information about internal structure, conditions and nuclear processes occurring in the stellar interior. The heavy elements formed in a star throughout its life are returned to the interstellar medium through mass loss processes. New populations of stars are then formed from this previously enriched material. This continues the cycle of element recycling in the Universe and has great consequence for galactic chemical evolution. As both modelling and observing techniques advance, more surveys are required to ensure there is agreement between the two. It is hoped that when a thorough understanding of the internal processes in giant stars is reached, the evolutionary models will reproduce the observed elemental yields. This work provides an internally self-consistent analysis of the element abundances produced via nucleosynthesis and s-process element formation occurring in giant stars in different stellar environments. High resolution spectroscopic observations have been taken of Asymptotic Giant Branch (AGB) and Red Giant Branch (RGB) stars in three different stellar environments. Spectrum synthesis has been used to determine s-process element abundances for RGB stars in the Hyades open cluster, RGB and AGB stars in the globular cluster, 47 Tucanae, and AGB stars in the galactic field. It was found that the two Hyades giant studied showed solar, or near-solar, abundances of s-process elements. Enhancements in the light s-process elements, Y and Zr, of +0.02 to +0.11 were observed, while enhancements in the heavy s-process elements, La, Pr and Nd, ranged from +0.06 to +0.16. These results are consistent with previous findings of enhancements in Y of ~+0.12, and of ~+0.15 for the heavy s-process elements. The results from 47 Tucanae suggest a genuine star-to-star scatter in the s-process element abundances in the giant stars of this globular cluster. This is unexpected due to the fact that stars in a globular cluster are thought to have the same formation and chemical history. However, spreads in s-process element abundances of as much as +-0.7 dex are observed between this study and three other studies of similar stars in the same cluster. A range of field stars along the AGB phase, ranging from M to MS to S to SC, have been analysed for s-process enrichment. The observed element abundances are compared with those predicted by recent modelling of the AGB phase of evolution. Enhancements in s-process element abundances range from [s/Fe]~0.00 for M stars, to ~+0.50 for MS stars, through to ~+0.95 for S stars. The comparison of these enhancements with those predicted by modelling provides an indication of the success of these models and will enable theoreticians to further refine their understanding of the internal nucleosynthetic processes present in giant stars.

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15

Alves, Cruz Monique. "Nucleosynthesis in extremely metal-poor and zero metallicity stars." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-153061.

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16

Goriely, Stephane. "Some nuclear physics aspects of the r-process nucleosynthesis." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293481.

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17

Rath, Dipti Prakash. "The ?Li(³He,p)?Be reaction and primordial nucleosynthesis /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487672245903636.

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18

Angell, Christopher T. Karwowski Hugon J. "The effect of pygmy resonances on p-process nucleosynthesis." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2008. http://dc.lib.unc.edu/u?/etd,2062.

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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2008.
Title from electronic title page (viewed Feb. 17, 2009). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics and Astronomy." Discipline: Physics and Astronomy; Department/School: Physics and Astronomy.

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19

Lara, Juan Felipe. "Neutrino heating and baryon inhomogeneity in big bang nucleosynthesis /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004313.

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20

VESCOVI, DIEGO. "Nucleosynthesis of light and heavy elements across the Galaxy." Doctoral thesis, Gran Sasso Science Institute, 2021. http://hdl.handle.net/20.500.12571/15915.

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The synthesis of elements mostly takes place in stars. Elements up to iron peak are a by-product of thermonuclear fusion reactions sustaining the stellar structure itself. This is the case of the Sun, whose energy generation is provided by the pp chain and (to a lesser extent) by the CNO cycle. However, a precise evaluation of their relative contributions is still lacking. On the other hand, elements heavier than iron are almost entirely produced via the slow (s) and rapid (r) neutron capture processes. Low-mass stars during their Asymptotic Giant Branch (AGB) phase are the site of the so-called main component of the s-process. In those objects a 13C n-source (the 13C pocket), formed due to partial mixing of hydrogen from the convective envelope, operates. The physical mechanism responsible for such mixing is still a matter of debate. Binary neutron star mergers are instead primary sites for the production of heavy elements through the r-process. This was recently confirmed by the detection of the kilonova AT2017gfo as the electromagnetic counterpart of the gravitational wave signal GW170817. Interestingly, the production of r-process elements can be accompanied by the synthesis of light elements, which could be detected during the early kilonova emission. With a multi-messenger approach, we investigate the nucleosynthesis occurring in these astrophysical scenarios by comparing results not only to stellar spectra, but also other observables: i.e. emission of neutrinos, isotopic measurements in primitive meteorites, and electromagnetic radiation emissions. Regarding the Sun, we use solar models to study the impact of a different 7Be electron-capture rate on the solar structure. We compare the results with the measured 7Be and 8B solar neutrino fluxes and find that the agreement with the Sudbury Neutrino Observatory measurements of the neutral current component of the 8B neutrino flux is improved. We then revise and generalize the relation connecting the measured solar photon luminosity and the total solar neutrino fluxes, namely the luminosity constraint. In particular, we study and determine the energy contributions due to non-equilibrium burning of 3He and 14N and due to solar expansion/contraction. We finally show the importance of such a relation for the search of CNO neutrinos by providing a specific relation that links CNO and pp neutrino fluxes. For what concerns the nucleosynthesis in AGB stars, we examine the origins of now-extinct radioactivities that were alive in the solar nebula, as testified by meteoritic measurements, in the light of most updated stellar models for intermediate-mass stars and massive stars. We find that, while the Galactic inheritance broadly explains most of the isotopes involved with lifetime τ ≳ 5 Myr, shorter-lived isotopes require nucleosynthesis events close in time to the solar formation. We investigate the possibility that an Asymptotic Giant Branch or a Massive star could have contaminated the solar nebula. We find that both scenarios meet serious problems to reproduce the presence of isotopic anomalies measured in early solar system solids of the solar system. In another work, we perform the first numerical simulations of the formation of a magnetically-induced 13C pocket in a stellar evolutionary code with fully coupled nucleosynthesis. We find that magnetic fields of the order 10^5 G can induce the formation and the buoyant rise of magnetic flux tubes in the He-intershell of AGB stars. The ensuing mixing can account for the downward penetration of poorly magnetized H-rich material, necessary for the formation of the 13C pocket. By adopting a single magnetic field configuration, new magnetic models provide a consistent explanation to the majority of the heavy-element isotope data detected in presolar SiC grains from AGB stars. Finally, we study the production of light elements in the ejecta of binary neutron star mergers. The outcome of numerical relativity merger simulations is combined with detailed r-process nucleosynthesis calculations performed with the Skynet nuclear reaction network. We find that hydrogen and helium are the most abundant light elements. However, despite their high abundance, the possibility of detecting hydrogen and helium features in kilonova spectra is very unlikely.

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21

Rehm, Jan Bernhard. "The Influence of Matter-Antimatter Domains on Big Bang Nucleosynthesis." Diss., lmu, 2000. http://nbn-resolving.de/urn:nbn:de:bvb:19-4206.

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22

Matei, Catalin. "Nucleosynthesis of ¹⁶O Under Quiescent Helium Burning." Ohio : Ohio University, 2006. http://www.ohiolink.edu/etd/view.cgi?ohiou1159463892.

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23

Sihvola, Elina. "Big bang nucleosynthesis with inhomogeneous baryon density and antimatter regions." Helsinki : University of Helsinki, 2001. http://ethesis.helsinki.fi/julkaisut/mat/fysii/vk/sihvola/.

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24

Milam, Stefanie Nicole. "Following Carbon's Evolutionary Path: From Nucleosynthesis to the Solar System." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/194067.

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Studies of carbon's evolutionary path have been conducted via millimeter and submillimeter observations of circumstellar envelopes (CSEs), planetary nebulae (PNe), molecular clouds and comets. The 12C/13C isotope ratio was measured in Galactic molecular clouds using the CN isotopologs. A gradient of 12CN/13CN was determined to be 12C/13C = 6.01 DGC +12.28, where DGC is distance from the Galactic center. The results of CN are in agreement with those of CO and H2CO indicating a true ratio not influenced by fractionation effects or isotope-selective photodissociation. The 12C/13C isotope ratios in the envelopes of various types of stars were also measured from both CO and CN isotopologs. Such objects as carbon and oxygen-rich asymptotic giant branch (AGB) stars, supergiants, planetary nebulae, and S-type stars were observed. Results from this study indicate 12C/13C values for supergiants ~ 10 and AGB stars 12C/13C ~ 20- 76. Theory would suggest a lower ratio for objects undergoing third dredge-up, though this is seemingly not the case. Multiple carbon-bearing species including CO, HCN, HNC, CN, CS, and HCO+ have also been observed towards the oxygen-rich supergiant, VY CMa. This object has recently revealed a unique chemistry where carbon is not solely contained in CO, and may play a more important role in the chemical network of oxygen-rich circumstellar envelopes. Additionally, observations of species with carbon- carbon bonds, such as CCH and c-C3H2, have been conducted towards evolved planetary nebulae, such as the Helix and Ring nebulae. There is a close agreement in the inventories of species found in PNe and diffuse clouds, suggesting a potential molecular precursor to the interstellar medium. Observations of carbon-bearing species (H2CO and CO) in comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT), and C/2002 T7 (LINEAR) have been conducted. Formaldehyde is known to have an extended distribution in these objects, likely arising from silicate-organic grains. Evidence of cometary fragmentation was also obtained for H2CO in comet T7 LINEAR as well as for HNC and HCO+ in Hale-Bopp. Such events could contribute to planetary distribution of organics.

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25

Fenner, Yeshe, and yfenner@astro swin edu au. "Chemical evolution of galactic systems." Swinburne University of Technology. Centre for Astrophysics and Supercomputing, 2005. http://adt.lib.swin.edu.au./public/adt-VSWT20050804.161449.

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This thesis explores the chemical signatures of galaxy formation and evolution using a software package designed specifically for this investigation. We describe the development of this multi-zone chemical evolution code, which simulates the spacetime evolution of stars, gas and a vast array of chemical elements within galactic systems. We use this tool to analyse observations of a wide range of astrophysical systems. The chemical evolution code is first calibrated using empirical constraints from the Milky Way. These simulations help shed light on the nature of the gas accretion processes that fueled the formation of our Galaxy. We demonstrate the importance of low- and intermediate-mass stars in explaining the elemental and isotopic abundance patterns measured in Galactic stars. An intriguing question in astrophysics is whether pollution from intermediate-mass stellar winds is responsible for anomalous abundances in globular cluster stars. We test this scenario by modelling the formation and chemical evolution of a globular cluster. Recently, the most detailed abundance pattern ever measured beyond the local universe was obtained for a high-redshift quasar absorption cloud, providing an exciting opportunity to explore early conditions of galaxy formation. We compare the chemical abundances in this distant object with predictions from a series of models, in order to gain insight into the protogalaxy's age and star formation history. We continue investigating the high-redshift universe, turning our attention to the issue of space-time variations in the fine-structure constant, as suggested by quasar absorption-line constraints. An excess abundance of heavy Mg isotopes in the absorbing clouds could partly account for the data, without needing to invoke variations in fundamental constants of nature. An enhanced early population of intermediate-mass stars could lead to such extreme Mg isotopic ratios, but we show that additional chemical consequences of this scenario conflict with observations.

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26

Samyn, Mathieu. "Improved nuclear predictions of relevance to the r-process of nucleosynthesis." Doctoral thesis, Universite Libre de Bruxelles, 2004. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211170.

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Glorius, Jan [Verfasser]. "Experimental studies of optical potentials for p-process nucleosynthesis / Jan Glorius." München : Verlag Dr. Hut, 2013. http://d-nb.info/1042308144/34.

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Scholz, Philipp [Verfasser]. "Exploring statistical properties of nuclei for explosive stellar nucleosynthesis / Philipp Scholz." München : Verlag Dr. Hut, 2018. http://d-nb.info/1170473377/34.

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29

Margerin, Vincent. "Transfer reaction measurements and the stellar nucleosynthesis of 26A1 and 44Ti." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/25428.

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Progress in the description of stellar evolution is driven by the collaborative effort of nuclear physics, astrophysics and astronomy. Using those developments, the theory of the origin of elements in the Universe is challenged. This thesis addresses the problem behind the abundance of 44Ti and the origin of 26Al. The mismatch between the predicted abundance of 44Ti as produced by the only sites known to be able to create 44Ti, core collapse supernovae (CCSNe), and the observations, highlight the current uncertainty that exists in the physics of these stars. Several satellite based γ-ray observations of the isotope 44Ti have been reported in recent times and confirm the disagreement. As the amount of this isotope in stellar ejecta is thought to critically depend on the explosion mechanism, the ability to accurately model the observed abundance would be a pivotal step towards validating that theory. The most influential reaction to the amount of 44Ti in supernovae is 44Ti(α, p)47V. Here we report on a direct study of this reaction conducted at the REX-ISOLDE facility, CERN. The experiment was performed at a centre of mass energy 4.15±0.23 MeV, which is, for the first time, well within the Gamow window for core collapse supernovae. The experiment employed a beam of 44Ti extracted from highly irradiated components of the SINQ spallation neutron source of the Paul Scherrer Institute. No yield above background was observed, enabling an upper limit for the rate of this reaction to be determined. This result is below expectation, suggesting that the 44Ti(α, p)47V reaction proceeds more slowly than previously thought. Implications for astrophysical events, and remnant age, are discussed. In Wolf-Rayet and asymptotic giant branch (AGB) stars, the 26gAl(p,γ)27Si reaction is expected to govern the destruction of the cosmic γ-ray emitting nucleus 26Al. The rate of this reaction, however, is highly uncertain due to the unknown properties of several resonances in the temperature regime of hydrogen burning. We present a high-resolution inverse kinematic study of the 26gAl(d, p)27Al reaction as a method for constraining the strengths of key astrophysical resonances in the 26gAl(p,γ)27Si reaction. In particular, the results indicate that the resonance at Er = 127 keV in 27Si determines the entire 26gAl(p, γ)27Si reaction rate over almost the complete temperature range of Wolf-Rayet stars and AGB stars. The measurements of spectroscopic factors for many states in 27Al and a shell model calculation of nuclear properties of rp-resonant states in 27Si also allow for testing the structure model.

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Stancliffe, Richard James. "The evolution and nucleosynthesis of thermally pulsing asymptotic giant branch stars." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615303.

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GNECH, ALEX. "Theoretical calculation of nuclear reactions of interest for Big Bang Nucleosynthesis." Doctoral thesis, Gran Sasso Science Institute, 2020. http://hdl.handle.net/20.500.12571/14971.

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Standard Big Bang Nucleosynthesis (BBN) predicts the abundances of the light elements in the early universe. Even if the overall agreement with the experimental data is good, still some discrepancies exist on the relic abundances of ${}^7$Li and ${}^6$Li. In order to exclude or confirm these scenarios, the BBN model needs precise input parameters, in particular the cross-sections of the BBN nuclear reaction network. However, the suppression of the cross-sections due to the Coulomb barrier makes the measurement very difficult and so affected by large systematic errors. Therefore, reliable theoretical calculations result fundamental in order to reduce the uncertainties. In this work we present a theoretical study of two nuclear reactions connected to ${}^6$Li abundance and recently the $alpha$+d$ ightarrow$ ${}^6$Li + $gamma$ and the p+${}^6$Li$ ightarrow$${}^7$Be+$gamma$ radiative captures. For the first reaction we use a so-called ab-initio approach in which we solve the full six-body problem by using realistic nuclear potentials to describe the nucleon interactions. In particular we concentrate on the calculation and characterization of the final state of the reaction, the ${}^6$Li ground state, focusing on the electromagnetic static structure and the quantities relevant from the astrophysical point of view such as the asymptotic normalization coefficient. For doing this we use the Hyperspherical Harmonic approach developed by the Pisa group providing for the first time the possibility of using this approach beyond A = 4 nuclear systems. The second reaction is instead studied by using a two-body cluster approach where the proton and ${}^6$Li are considered as structureless particles. The angular distribution of the emitted photon obtained in this work were used by the LUNA Collaboration to determine the efficiency of the detector used in the measurement of the reaction.

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Deboer, Richard J. "Measurement of cross sections for 65Cu([alpha],p) 68Zn nuclear reaction at low energy with comparison to Hauser-Feshbach statistical model." Virtual Press, 2005. http://liblink.bsu.edu/uhtbin/catkey/1319221.

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Where did the elements come from? Why are they found in the abundance that they are? These are two of the fundamental questions that the field of astrophysics has sought to answer. The first major studies of elemental synthesis were done in the 1950's and 1960's. Most notable among them was the Burbidge, Burbidge, Fowler, and Hoyle paper [Clayton 73]. This paper set forth the general theory of elemental synthesis in stars and supernovae by means of nuclear reactions. It remains the leading theory for elemental abundance today.As with most theories, the picture of elemental synthesis remains incomplete. While it is thought that the overall theory is correct, there are still many mysteries in the details. There are several kinds of nuclear reactions that occur in stars and supernova that create the elements heavier than iron. They include the r-process, s-process, and p-process, along with several others. However, there are some elements whose creation is not fully understood. There are a variety of reasons for this, which will be discussed.In our experiment we studied the nuclear reaction properties of an isotope of Copper (65Cu). It is theorized that it is produced by the p-process during a supernova explosion. The p-process can be described simply as the collision of an alpha particle with a large atomic nucleus with a proton byproduct. Little actual experimental data has been taken involving the p-process, which is why we chose this reaction. The experiment was done using the Tandem Van de Graaff Accelerator at Ohio University.
Department of Physics and Astronomy

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Wijekumar, Vythilingam. "Proton threshold states in ²⁶A1 and their role in astrophysics /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487262825074605.

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Arenson, Joshua. "Studies of r-process nucleosynthesis using r-Java, a GUI based software." Thesis, California State University, Long Beach, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1591590.

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The r-process is a series of nuclear reactions that produce about half of the elements heavier than iron and probably occur during a violent stellar explosion or collision, not regular stellar burning. While the exact astrophysical site of the r-process is still debated in the scientific community, the nuclear physics that make up the r-process are generally known. These nuclear reactions take significant computational resources to calculate in their entirety. r-Java is a computational web-based tool, equipped with a graphical user interface (GUI) designed to calculate abundances produced by the r-process depending on a number of input parameters. In this thesis we will use the latest version of r-Java (v 2.0) to produce abundance curves for a number of initial parameters, as well as vary the initial parameters to obtain a deeper understanding of their influence on the overall production of elements by the r-process. Our main results are the observation of systematic trends between abundance and temperature as well as improved abundance curves obtained through the use of a full network simulation as compared to that of the waiting point approximation (WPA).

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Giri, Rekam. "Cross Section Measurements of the 12C(α, γ)16O Reaction at E_c.m. = 3.7, 4.0, and 4.2 MeV." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1553421450433669.

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Huther, Lutz Verfasser], Gabriel [Akademischer Betreuer] Martínez-Pinedo, and Karlheinz [Akademischer Betreuer] [Langanke. "Nucleosynthesis in neutrino-driven winds / Lutz Huther. Betreuer: Gabriel Martínez-Pinedo ; Karlheinz Langanke." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2014. http://d-nb.info/110809449X/34.

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Sieverding, Andre [Verfasser], Gabriel [Akademischer Betreuer] Martinez-Pinedo, and Karlheinz [Akademischer Betreuer] Langanke. "Neutrinos in Core-Collapse Supernova Nucleosynthesis / Andre Sieverding ; Gabriel Martinez-Pinedo, Karlheinz Langanke." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1163728780/34.

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Huther, Lutz [Verfasser], Gabriel Akademischer Betreuer] Martínez-Pinedo, and Karlheinz [Akademischer Betreuer] [Langanke. "Nucleosynthesis in neutrino-driven winds / Lutz Huther. Betreuer: Gabriel Martínez-Pinedo ; Karlheinz Langanke." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2014. http://nbn-resolving.de/urn:nbn:de:tuda-tuprints-37668.

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39

Nsangu, Tsimba. "Cross section measurements for the nucleosynthesis of heavy nuclei and type Ia supernovae." Thesis, University of York, 2014. http://etheses.whiterose.ac.uk/12626/.

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In this work, two rather different experiments with their respective analysis have been described. The first experiment concerned the 20Ne(d,p)21 Ne transfer reaction and the second the 12 C+12C fusion reaction. An experiment of 20 Ne(d,p)21 Ne transfer reaction was performed in Munich, Germany using the Quadrupole Dipole Dipole Dipole (Q3D) magnetic spectrograph. This experiment has aimed at the investigation of spectroscopic information around the Gamow window of the 17O(α,γ)21 Ne located between Ex = 7.65-8.05 MeV. The stated experiment was performed using an 21Ne implanted target on carbon and covered the excitation energies varying from 6.9 MeV to 8.5 MeV. Sixteen states were identified, three of which, the 8.328(6) MeV, 6.977(17) MeV and 6.960(2) MeV have first been observed in this work. Within the Gamow window however, only one state, the 7.955(2) MeV by correspondence to the 7.9603(10) Mev as recorded in literature, has been identified. Out the sixteen states, this work made eleven firm assignments and two “tentative” assignments. The 12 C+12 C fusion reaction was performed at TRIUMF, Canada using TUDA, the TRIUMF UK Detector Array. The experiment covered the centre of mass located between 3.4 to 4.02 MeV. The aim of this work was the determination of the cross section, which would help, at theses energies, reduce uncertainties observed in present data sets. Analysis such ADCs and TDCs calibrations, different cuts selection necessary for particle identification are presented.

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Arzhanov, Alexander. "Gogny-Hartree-Fock-Bogolyubov Nuclear Mass Models with Application to r-Process Stellar Nucleosynthesis." Thesis, KTH, Kärnfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-139303.

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Hannaske, Roland. "Measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis." Helmholtz-Zentrum Dresden - Rossendorf, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-201284.

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Zwischen 10 und 1000 s nach dem Urknall bildeten sich während der Big Bang Nukleosynthese (BBN) die ersten leichten Elemente aus Protonen und Neutronen. Die primordialen Häufigkeiten dieser Elemente hingen von denWirkungsquerschnitten der beteiligten Kernreaktionen ab. Vergleiche zwischen den Ergebnissen nuklearer Netzwerkrechnungen mit astronomischen Beobachtungen bieten eine einzigartige Möglichkeit, etwas über das Universum zu dieser Zeit zu erfahren. Da es für die p(n,g)d-Reaktion, die eine Schlüsselreaktion der BBN ist, kaum Messungen im relevanten Energiebereich gibt, beruht deren Reaktionsrate in Netzwerkrechnungen auf theoretischen Berechnungen. Darin fließen auch experimentelle Daten der Nukleon-Nukleon-Streuung, des Einfangquerschnitts für thermische Neutronen sowie (nach Anwendung des Prinzips des detaillierten Gleichgewichts) der d(g,n)p-Reaktion mit ein. Diese Reaktion, die Photodissoziation des Deuterons, ist bei BBN-Energien (Tcm = 20–200 keV) ebenfalls kaum vermessen. Die großen experimentelle Unsicherheiten machen Vergleiche mit den präzisen theoretischen Berechnungen schwierig. In den letzten Jahren wurde die d(g,n)p-Reaktion und insbesondere der M1-Anteil des Wirkungsquerschnitts mit quasi-monoenergetischen g-Strahlen aus Laser-Compton-Streuung oder durch Elektrodesintegration untersucht. Üblicherweise verwendete man für Messungen des d(g,n)p-Wirkungsquerschnitts entweder die auf wenige diskrete Energien beschränkte Strahlung des g-Zerfalls oder Bremsstrahlung, für die aber eine genaue Photonenflussbestimmung sowie der Nachweis von einem der Reaktionsprodukte und dessen Energie nötig ist. Da diese Energie im Bereich der BBN relativ gering ist, gab es bisher noch keine absoluten Messung des d(g,n)p-Wirkungsquerschnitts bei Tcm < 5 MeV mit Bremsstrahlung. Das Ziel dieser Dissertation ist eine solche Messung mit einer Unsicherheit von 5 % im für die BBN relevanten Energiebereich und darüber hinaus bis Tcm ~ 2,5 MeV unter Verwendung gepulster Bremsstrahlung an der Strahlungsquelle ELBE. Dieser supraleitende Elektronenbeschleuniger befindet sich am Helmholtz-Zentrum Dresden-Rossendorf und stellte einen Elektronenstrahl hoher Intensität bereit. Die kinetische Elektronenenergie von 5 MeV wurde mit einem Browne-Buechner-Spektrometer präzise gemessen. Die Energieverteilung der in einer Niob-Folie erzeugten Bremsstrahlungsphotonen wurde berechnet. Die Photonenflussbestimmung nutzte die Kernresonanzstreuung an 27Al, das sich mit deuteriertem Polyethylen in einem mehrschichtigen Target befand. Die 27Al-Abregungen wurden mit abgeschirmten, hochreinen Germanium-Detektoren nachgewiesen, deren Effektivität mit GEANT4 simuliert und durch Quellmessungen normiert wurde. Die Messung der Energie der Neutronen aus der d(g,n)p-Reaktion erfolgte mittels deren Flugzeit in Plastikszintillatoren, die an zwei Seiten von Photoelektronenvervielfachern mit hoher Verstärkung ausgelesen wurden. Die Nachweiseffektivität dieser Detektoren wurde in einem eigenen Experiment in den Referenz-Neutronenfeldern der PTB Braunschweig kalibriert. Die Nachweisschwelle lag bei etwa 10 keV kinetischer Neutronenenergie.Wegen der guten Zeitauflösung der Neutronendetektoren und des ELBE-Beschleunigers genügte eine Flugstrecke von nur 1 m. Die Energieauflösung betrug im d(g,n)p-Experiment 1–2 %. Leider gingen viele Neutronen bereits durch Streuung in dem großen Target verloren oder sie wurden erst durch Teile des kompakten Experimentaufbaus in die Detektoren gestreut. Beide Effekte wurden mit Hilfe von FLUKA simuliert um einen Korrekturfaktor zu bestimmen, der aber bei niedrigen Energien relativ groß war. Der d(g,n)p-Wirkungsquerschnitts wurde daher nur im Bereich 0.7 MeV < Tcm < 2.5 MeV bestimmt. Die Ergebnisse stimmen mit anderen Messungen, Daten-Evaluierungen sowie theoretischen Rechnungen überein. Die Gesamtunsicherheit beträgt circa 6.5 % und kommt zu fast gleichen Teilen von den statistischen und systematischen Unsicherheiten. Die statistische Unsicherheit könnte durch eine längere FLUKA Simulation noch von 3–5 % auf 1 % verringert werden. Die systematische Unsicherheit von 4.5 % ist vorrangig auf die Photonenflussbestimmung, die Neutronen-Nachweiseffektivität und die Target-Zusammensetzung zurückzuführen.

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42

Hencheck, Michael. "Nucleosynthesis during the rapid hydrogen burning process and the abundances of 92Mo and 94Mo /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487856906261345.

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43

Cardall, Christian Y. "Towards limits on neutrino mixing parameters from nucleosynthesis in the big bang and supernovae /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9732712.

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44

Mountford, David James. "Investigations of nuclear reactions relevant to stellar γ-ray emission." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8238.

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The detection of γ-rays from explosive astrophysical scenarios such as novae provides an excellent opportunity for the study of on-going nucleosynthesis in the Universe. Within this context, this work has addressed an uncertainty in the destruction rate of the 18F nucleus, thought to be the primary source of 511 keV γ-rays from novae. A direct measurement of the 18F(p,α )15O cross section has provided the opportunity to extract resonance parameters through the R-Matrix formalism. The inferred parameters of populated states in 19Ne include the observation of a broad 1/2+ state, consistent with a recent theoretical prediction, which will have a significant impact on the rate of destruction of this γ-ray producing radioisotope. The 18O(p,α )15N reaction follows similar nuclear and kinematic processes and is expected to occur in the hydrogen burning layers of AGB stars. Resonance widths have been extracted from a direct measurement in the region around a poorly constrained broad state close to the Gamow window. This has produced a new parameter set for future reference and provides new information on the reaction rate. The complex R-Matrix formalism used in these analyses is a crucial tool in the study of nuclear astrophysics reactions, and many codes have been written to implement the complex mathematics. This thesis presents a comparison of two publicly available codes from the JINA collaboration and a code used extensively by the University of Edinburgh. For this, the recent results of the 18F destruction reaction, presented here, have been used. A minor error was found within one of the codes, and corrected. The final parameters extracted, and the resulting cross sections calculations, are shown to be consistent between the three codes. A further γ-ray line of interest at 1.809 MeV, characteristic of 26Al decay, has been observed throughout the interstellar medium. If, however, this isotope is formed in a known isomeric state, its decay bypasses the emission of this γ-ray, thus complicating the interpretation of observed γ-ray fluxes. To this end, an experiment has been carried out, providing proof of principle of a direct measurement of the 26mAl(p,γ)27Si reaction. The calculation of the isomeric intensity is presented here.

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Malatji, Kgashane Leroy. "Nuclear level densities and gamma-ray strength functions in Ta isotopes and nucleo-synthesis of ¹⁸ᴼTa." University of the Western Cape, 2016. http://hdl.handle.net/11394/5321.

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>Magister Scientiae - MSc
Most stable and extremely low abundance neutron deficient nuclei with Z ≥ 34 are referred to as p-nuclei. Nearly all p-nuclei with A < 110 are most likely produced in the rp-process while almost all A > 110 are thought to be produced by the photodisintegration of s- and r- process seed nuclei. However, for some nuclear systems, these processes are not sufficient to explain their observed solar abundance. Results from calculations in ¹⁸ᴼTa generally provoke debates since several processes are able, sometimes exclusively, to reproduce the observed ¹⁸ᴼTa abundance in the cosmos, making it a unique case study. Some of the main sources of errors in the predicted reaction rates of ¹⁸ᴼTa arise due to the absence of nuclear data or due to large uncertainties in the nuclear properties such as the nuclear level densities (NLD) and gamma-ray strength functions (γSF) of ¹⁸ᴼ,¹⁸¹Ta. The NLD and γSF are primary ingredients for astrophysical reaction rate calculations based on the Hauser-Feshbach approach. These parameters need to be well understood to improve our understanding of ¹⁸ᴼTa production in astrophysical environments. In this thesis, new experimental data for the low-energy part of the γSF and NLD in ¹⁸ᴼ,¹⁸¹Ta were extracted, using the so-called Oslo method. An experiment was performed and the NaI(Tl) gamma-ray array and silicon particle telescopes at the Oslo cyclotron laboratory were utilized to measure particle-γ coincidence events from which the NLDs and γSFs are extracted below the neutron separation energy threshold Sn. A beam of ³He was used to populate excited states in ¹⁸ᴼ,¹⁸¹Ta through the inelastic scattering (³He,³He’𝛾) and the transfer reaction (³He,𝜶𝛾). Based on results from this measurements, the Maxwellian averaged (n, 𝛾) cross sections for the 179Ta(n, γ) and ¹⁸ᴼTa(n, 𝛾) reactions, at the s-process thermal energy of kT = 30 keV (i.e. a temperature of T = 3.5 × 10⁸ K) and p-process thermal energy of 215 keV (T = 2.5 × 10⁹ K), respectively, were computed with the TALYS reaction code. These results can be used to place the nuclear physics aspects of the large network abundance calculations on a solid footing and have potential to improve our understanding of the astrophysical processes and sites involved in the production of nature’s rarest isotope ¹⁸ᴼTa.
National Research Foundation (NRF)

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Alves, Cruz Monique [Verfasser], and Achim [Akademischer Betreuer] Weiss. "Nucleosynthesis in extremely metal-poor and zero metallicity stars / Monique Alves Cruz. Betreuer: Achim Weiss." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1032131225/34.

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47

Arzhanov, Alexander [Verfasser], Gabriel [Akademischer Betreuer] Martínez-Pinedo, and Robert [Akademischer Betreuer] Roth. "Microscopic nuclear mass model for r-process nucleosynthesis / Alexander Arzhanov ; Gabriel Martínez-Pinedo, Robert Roth." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1166850994/34.

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48

Chornock, R., E. Berger, D. Kasen, P. S. Cowperthwaite, M. Nicholl, V. A. Villar, K. D. Alexander, et al. "The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626063.

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We present a near-infrared spectral sequence of the electromagnetic counterpart to the binary neutron star merger GW170817 detected by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo. Our data set comprises seven epochs of J + H spectra taken with FLAMINGOS-2 on Gemini-South between 1.5 and 10.5 days after the merger. In the initial epoch, the spectrum is dominated by a smooth blue continuum due to a high-velocity, lanthanide-poor blue kilonova component. Starting the following night, all of the subsequent spectra instead show features that are similar to those predicted in model spectra of material with a high concentration of lanthanides, including spectral peaks near 1.07 and 1.55 mu m. Our fiducial model with 0.04 M-circle dot of ejecta, an ejection velocity of v = 0.1c, and a lanthanide concentration of X-lan = 10(-2) provides a good match to the spectra taken in the first five days, although it over-predicts the late-time fluxes. We also explore models with multiple fitting components, in each case finding that a significant abundance of lanthanide elements is necessary to match the broad spectral peaks that we observe starting at 2.5 days after the merger. These data provide direct evidence that binary neutron star mergers are significant production sites of even the heaviest r-process elements.

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Meakin, Casey Adam. "Hydrodynamic Modeling of Massive Star Interiors." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/194035.

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In this thesis, the hydrodynamics of massive star interiors are explored. Our primary theoretical tool is multi-dimensional hydrodynamic simulation using realistic initial conditions calculated with the one-dimensional stellar evolution code, TYCHO. The convective shells accompanying oxygen and carbon burning are examined, including models with single as well as multiple, simultaneously burning shells. A convective core during hydrogen burning is also studied in order to test the generality of the flow characteristics. Two and three dimensional models are calculated. We analyze the properties of turbulent convection, the generation of internal waves in stably stratified layers, and the rate and character of compositional mixing at convective boundaries.

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Eriksen, Kristoffer Albert. "New Observational and Theoretical Insights on Cassiopeia A." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195729.

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Using two techniques not previously applied to Cassiopeia A (Cas A), we measure the reddening toward its expansion center. An estimate of AV from the near-IR [Fe II] lines is hampered by uncertain atomic data, though the spatial variation in their flux ratio allows relative measurement of the extinction in regions without previous optical estimates. We use a second technique based on the broad-band IR shape of the synchrotron emission, and find Aᵥ = 6.2 ± 0.6 for a knot 13" from the expansion center. Assuming a plausible lower limit on the apparent magnitude of the SN in outburst, the ⁵⁶Ni yield was 0.058 < M(Ni) < 0.16M⊙. With the ⁴⁴Ti mass from published gamma-ray observations, this implies a ⁴⁴Ca/ ⁵⁶Fe ratio consistent with the solar abundance. Recently published Spitzer Space Telescope IRS observations detect dust and line emission from cold gas interior to Cas A’s reverse shock. Using simple physical arguments and new hydrodynamic, non-equilibrium photoionization calculations, we infer the physical conditions in this material. We find that the mid-IR bright clumps are photoionized by the SNR shocks, over-dense relative to the expected average in the interior of the remnant, and have abundances consistent with incomplete oxygen burning. The lack of detectable iron lines indicates that any Si-burning material still interior to the reverse shock must be far more tenuous than the clumps of O-burning ashes. Finally, we present calculations from a new multi-dimensional hydrodynamics and non-equilibrium ionization and cooling code designed to model the emission from SNR shocks. Two-dimensional simulations of a shock-cloud interaction in a pure-oxygen plasma, with flow parameters relevant to Cas A, show a wider range of temperatures and ionization states than is typical in single-zone or 1D calculations, indicating that fluid and cooling instabilities play a role in producing the observed spectra of radiative shocks in metal-rich gas.

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