Multi-messenger astronomy began when a massive star underwent core collapse in a neighboring dwarf galaxy, whose light and neutrinos reached Earth in 1987. Supernova 1987A was observed optically but was also observed through roughly two dozen neutrinos. Modern instruments have the ability to measure electromagnetic signatures in more wavelengths and detect many more neutrinos from a nearby core-collapse supernova, providing insight into an astrophysical phenomena that is not yet fully understood. In this dissertation, we discuss predictions for future core-collapse supernova signals and the nuclear and particle interactions that produce them. We focus on several different aspects related to both typical and rare supernovae. The diffuse supernova neutrino background (DSNB) - the isotropic background of ~10 MeV neutrinos from all past supernovae - is one such signal that does not rely on a local event for neutrino detection. We update several aspects of theoretical DSNB modeling by (i) using simulation data to better understand neutrino emission spectra as a function of time, (ii) collating recent star formation rate measurements to infer the rate of core collapse in the cosmos, and (iii) performing a signal vs. background analysis of state-of-the-art neutrino experiments. We find that the DSNB is likely to be detected in the next two decades, but large uncertainty on the average neutrino emission spectra combined with unclear treatment of background events prevents a precise timeline. We also discuss the signatures from rare supernovae driven by magnetorotational engines called protomagnetars. We find that outflows from these central engines can produce pions through inelastic np interactions, resulting in ~0.1 - 10 GeV neutrinos that are detectable for galactic supernovae. We also find that these outflows can synthesize heavier nuclei than traditional supernovae through the `weak r-process.' We compare the nucleosynthesis in supernova outflows to that in compact object mergers and find that mergers are more conducive for creating the heaviest nuclei. We also predict the detection rates of another kind of transient called kilonovae that are powered by the decay of unstable nuclei. Finally, these protomagnetar systems may be able to accelerate nuclei in relativistic jets. If these jets are beamed toward us, the gamma ray lines from the decays of unstable nuclei can be boosted to high energies and are detectable from extragalactic distances. / Doctor of Philosophy / Supernovae are one of the most well studied astronomical phenomena because of how broadly they connect to different fields of physics. This kind of event can be bright enough to be seen visually and has been observed and documented for centuries. Its name derives from nova stella - Latin for `new star' - but supernovae occur as the final stages of a star's life. Core-collapse supernovae are an important subclass that occur for stars several times more massive than our own sun. There is a long history of core-collapse supernova observation - from the naked eye to modern optical telescopes - but only one has ever been observed using a particle other than light. SN1987A was a nearby core-collapse supernova that occurred in 1987 and emitted a large burst of rarely interacting particles known as neutrinos along with its usual optical emission. Only two dozen neutrinos were detected during this event, but nearby core-collapse supernovae are rare and astronomers have been eager for another one. With today's modern neutrino detectors, a nearby core-collapse supernova would yield thousands of neutrino events which would help astronomers learn about the internal physics occurring during the collapse, which an optical signal cannot do. In this dissertation, we study the ways in which light and neutrinos can teach us more about core-collapse supernovae. We cover another way to observe supernova neutrinos without waiting for one nearby to occur by predicting the signal from the `diffuse supernova neutrino background.' This is a background of supernova neutrinos that constantly surrounds us, but interacts extremely infrequently, so kiloton-mass detectors are needed to detect this background. Measuring this will also shed light on how stars evolve over a galaxy's history. There are additional subclasses of core-collapse supernovae that give rise to the usual optical and neutrino signal but may also populate the universe with heavy elements, produce higher energy light, and emit higher energy neutrinos. This class is even rarer but are systematically more energetic and are powered internally by objects called `protomagnetars.' We study models of these rare, energetic supernovae and make predictions for each of these signals - heavy elements, high energy light, and high energy neutrinos - to help answer outstanding questions in astrophysics and make predictions for events not yet seen.

This dissertation describes our efforts to use the assembly of matter on nuclear scales as a probe of the assembly of matter on Galactic scales. To investigate the former, we characterize the detailed abundance patterns of the heaviest elements found in ancient, metal-poor stars in the Galaxy. In particular, we place new constraints on and identify several new correlations among the nuclei produced by the rapid nucleosynthetic process, which we use to refine current models of the physical conditions of this process. To investigate the latter, we apply our knowledge of stellar nucleosynthesis to examine correlations between the space motions of stars and their compositions, which retain a record of the composition of the interstellar medium where they formed many billions of years ago. Using new high quality stellar spectra collected from McDonald Observatory and Las Campanas Observatory, we confirm the relative chemical homogeneity of a well-known stellar stream and identify several chemical differences between the two major components of the stellar halo of the Galaxy. Each of these results has significant implications for our understanding of how the Galactic halo formed, grew, and evolved. More profoundly, these results indicate that we have not yet fully characterized the cosmic origins of the heaviest elements in the universe and that we will likely need to examine large samples of metal-poor stars at great distances from the Sun to potentially do so. / text

The 23Mg(pγ)24Al and 26Al(pγ)27Si astrophysical reactions are expected to be of considerable importance in the nucleosynthesis of A≥20 nuclei in classical novae. Previous studies have indicated that both reactions are dominated by resonant capture to excited states, above the proton-emission thresholds, in the proton-rich nuclei 24Al and 27Si, respectively. Consequently, by determining the nuclear properties of such resonant states it is possible to estimate the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates. In this thesis work, excited states in 24Al and 27Si were populated via the 10B(16O, 2n) and 12C(16O, n) heavy-ion fusion-evaporation reactions, respectively. The beams of 16O ions were produced by the Argonne Tandem Linear Accelerator System and prompt electromagnetic radiation was detected using the GAMMASPHERE detector array, which, in the case of the 24Al experiment, was used in coincidence with recoil selection provided by the Argonne Fragment Mass Analyzer. The two γray spectroscopy studies performed in this work allowed level structure determinations below the respective proton-emission thresholds of 24Al and 27Si nuclei, with improved precision on previous work. In addition to this, these studies also allowed a determination of the nuclear properties of proton-unbound astrophysically important γ decaying states, which, in turn, were used to re-evaluate the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates. The improved precision of the level energies and unambiguous assignments of resonant states has reduced the relative uncertainties in both the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates, constraining the production of A≥20 nuclei in classical novae.

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.

Thesis (Ph.D.)--Ohio University, November, 2006. / Title from PDF t.p. Includes bibliographical references.

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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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<p>In order to determine the parent stellar sites for the presolar grains of potential nova origin, it is crucial to know the rates of the thermonuclear reactions which affect the Si production and destruction in novae. One such reaction is the ²⁹P(p, gamma)³⁰S. This reaction also influences type I X-ray bursts. The energy generation and nucleosynthesis in the burst, along with its duration and light-curve structure, are very sensitive to the reaction flow through a few waiting-point nuclei along the rp- and ap-process paths. In particular, network calculations show that the waiting-point nucleus ³⁰S (t_1/2 = 1175.9(17) ms) is critical.</p> <p>The structure of proton-unbound ³⁰S states strongly determines the thermonuclear ²⁹P(p, gamma)³⁰S reaction rate at temperatures characteristic of explosive hydrogen burning in classical novae and type I X-ray bursts (0.1 ≤ T ≤ 1.3 GK). Specifically, the rate had been previously predicted to be dominated by two low-lying, unobserved, J^pi= 3⁺and 2⁺ levels in the E_x = 4.7 to 4.8 MeV region.</p> <p>The 3⁺resonance was observed a few years ago via a ³²S(p, t)³⁰S measurement. However, the 2⁺resonance remained unobserved. To search for it, we have performed a higher energy resolution charged-particle spectroscopy and an in-beam gamma-ray spectroscopy to investigate the level structure of ³⁰S above the proton threshold via the ³²S(p, t)³⁰S and ²⁸Si(³He, n-gamma)³⁰S reactions, respectively.</p> <p>In this work we provide a description of the experimental setup, data analysis and results of both experiments. Moreover, we have calculated the ²⁹P(p, gamma)³⁰S reaction rate via the state-of-the-art Monte Carlo technique, and have investigated the impact of this updated rate on the abundances of elements synthesized in novae, including those of silicon isotopes.</p> / Doctor of Philosophy (PhD)