There is no abstract available for this thesis. / Department of Physics and Astronomy

We have obtained broad-band NIR-photometry for six Galactic star clusters, M92,M15,M13, NGC1851, M71 and NGC6791, as observed with the WIRCam wide-field imager on the Canada-France-Hawaii Telescope; supplemented by images taken with HAWK-I on VLT. From the resultant (V − J)-V and (V − K)-V colour-magnitude diagrams, fiducial sequences spanning the range in metallicity, −2.4 ≤ [Fe/H] ≤+0.3, have been defined which extend from the tip of the red-giant branch to ∼ 2.5 magnitudes below the main-sequence turnoff. These fiducials provide a valuable set of empirical isochrones for the interpretation of stellar population data in the 2MASS system. From the NIR data, the reddenings of M15, M71 and NGC6791 — which have been subject to considerable controversy — were found to be E(B−V)=0.075, 0.22 and 0.155 mag respectively. Comparisons of our CMDs to Victoria isochrones that have been transformed using the MARCS model colour-Teff relations reveal that the models reproduce the giant branches of clusters more metal-rich than [Fe/H] ≈ −1.3, but they become systematically redder than the observed RGBs as the cluster metallicity decreases. These discrepancies are seen consistently in the two colours and therefore may indicate that the temperature scale of the stellar evolutionary models for giant stars at low metallicity is too cool.MARCS colour transformations were also tested using the classic Population II subdwarfs. The MARCS colours show redward offsets of ∼ 0.03 mag when compared with the observed (V − K) and (J − K) colours (assuming best estimates of Teff, log g, and [Fe/H]), and a systematic blue offset relative to the isochrone temperatures. Together with the indications from the cluster (V − K) and (V − J) CMDs, these results suggest that there is a problem with the MARCS colour transformations involving J.

The common envelope (CE) interaction is a still poorly understood, yet critical phase of evolution in binary systems that is responsible for various astrophysical classes and phenomena. In this thesis, we use various approaches and techniques to investigate different aspects of this interaction, and compare our models to observations. We start with a semi-empirical analysis of post-CE systems to predict the outcome of a CE interaction. Using detailed stellar evolutionary models, we revise the α equation and calculate the ejection efficiency, α, both from observations and simulations consistently. We find a possible anti-correlation between α and the secondary-to- primary mass ratio, suggesting that the response of the donor star might be important for the envelope ejection. Secondly, we present a survey of three-dimensional hydrodynamical simulations of the CE evolution using two different numerical techniques, and find very good agreement overall. However, most of the envelope of the donor is still bound at the end of the simulations and the final orbital separations are larger than the ones of young observed post-CE systems. Despite these two investigations, questions remain about the nature of the extra mechanism required to eject the envelope. In order to study the dynamical response of the donor, we perform one-dimensional stellar evolution simulations of stars evolving with mass loss rates from 0.001 up to a few M⊙/yr. For mass-losing giant stars, the evolution is dynamical and not adiabatic, and we find no significant radius increase in any case. Finally, we investigate whether the substellar companions recently observed in close orbits around evolved stars could have survived the CE interaction, and whether they might have been more massive prior to their engulfment. Using an analytical prescription for the disruption of gravitationally bound objects by ram pressure stripping, we find that the Earth-mass planets around KIC 05807616 could be the remnants of a Jovian-mass planet, and that the other substellar objects are unlikely to have lost significant mass during the CE interaction. / Graduate

We have observed the nearest ultraluminous infrared galaxy Arp 220 with a 13 month near-infrared observing program using the Canada France Hawaii Telescope to search for obscured supernovae in this extreme star forming environment. This monitoring program was aimed as a feasibility study to determine the practicality of a large scale near-IR LIRG/ULIRG imaging survey. Establishing the supernova rate in these dusty galaxies is an important step toward confirming theorized star formation rates and settling the debate between the dominant energy source in LIRGs: star formation or AGN activity. Both the deduced high star formation rate and far-IR luminosity of Arp 220 suggest an atypically high supernova rate of 1-4 per year, two orders of magnitude greater than that of the Milky Way. We attempt the first direct observation of this rate which to date has been probed primarily through radio measurements of supernovae and remnants. Through a point-spread function matching and image subtraction procedure we find no supernovae outside the galactic nucleus, consistent with the paradigm of a strong nuclear-contained starburst. Image subtraction residuals prevent the discovery of supernovae in the central regions of the galaxy. Using differential photometry we find evidence for a statistically significant brightening in the Arp 220 nucleus with a K-band peak of approximately $\Delta m_K=0.16$ magnitudes. To find the true peak magnitude we use Hubble Space Telescope archival data to subtract off the nuclear background and find an absolute magnitude of $M_K = -22.19 \pm 0.16$ (non-absorbed). This exceeds the luminosity of a typical core collapse supernova by roughly 3.5 magnitudes; rather, the observed variations in nuclear brightness are most likely the signature of an active galactic nucleus embedded in the dusty nuclei of Arp 220 or the superposition of light from several supernovae. This method is not sensitive to the detection of individual supernovae and we cannot rule out the occurrence of any nuclear SNe during the observing period. The brightening event is dimmer in the H and J bands, appearing to be affected by extinction. Interpreting this as a supernova-related event we estimate the extinction in the nuclear regions of Arp 220 to lie between $2.01 \le A_K \le 3.40$ or $17.95 \le A_V \le 30.36$ in the optical, in agreement with several other estimates. Improved resolution is required in order to detect supernovae in the extremely bright nuclear environments of LIRGs. Alternatively, infrared spectroscopy would reveal the telltale spectral features of nuclear supernovae. Spectroscopic observations of the Arp 220 nuclei were conducted using Keck in July 2013 for this very purpose; results are pending. We also explore the hypothesis that type Ia supernovae are produced primarily from young stellar populations. We model elliptical galaxies as two component stellar systems using PEGASE stellar templates: a fixed older underlying population coupled with a younger, less massive population. Varying the age and mass ratio of the young component, we examine its effect on I) the colours and II) the supernova rate of the single underlying population. We explore the effect with redshift and employ both theoretical and observational forms of the type Ia delay-time distribution. We then apply our models to the MENeaCS supernova survey and find that the number and distribution of red sequence SN Ia hosts agrees with theoretical expectations. The lack of evidence for a type Ia rate cutoff argues for a continuous delay-time distribution in support of the double degenerate model as the primary SN Ia progenitor channel. We conclude that it is not possible for all type Ia events in ellipticals to originate from a young frosting of stars. / Graduate / 0606 / jkezwer@uvic.ca

I present a detailed study of the behaviour of the exotic X-ray binary Cygnus X-3 at radio, (sub)mm, infrared, red-optical and X-ray wavelengths. Further unusual properties of the system are unearthed and previously expounded models are refined by new observations. In order to address the broader picture, a multiwavelength comparison of Cygnus X-3 with other ‘radio-jet’ X-ray binaries is also undertaken. Infrared observations of Cyg X-3 at high time resolution reveal many rapid flare events superimposed upon the 4.8 hr (presumed) orbital motion. Photometry simultaneously in the H & K-bands allows strong constraints to be placed upon T & N_ε for the flaring component. Dereddening of RI- J-H-K-L-L’ photometry places limits on the likely extinction to Cyg X-3 of 4.5 ≤ A_J ≤ 7.5 mag. Further infrared study, simultaneous with radio monitoring and observations with OSSE/GRO and the INT shed greater light on the source, including possible orbital colour changes and a longterm correlation between radio and infrared flux levels. Deep imaging of the field reveals many previously undiscovered infrared sources within a few arcsec of Cyg X-3. Simultaneous millimetre and radio observations of Cyg X-3 reveal anomalously strong mm fluxes. Interpreting this in terms of significant absorption of the cm fluxes during the passage outwards of the radio-emitting plasmons, strengthens the case for a dense stellar wind in the Cyg X-3 system. Further radio and sub(mm) observations of Cyg X-3 during outburst confirm previously observed phenomena such as quenched radio emission prior to outburst, and establish the importance of radiation loss mechanisms in the decay of radio plasmons ejected from the source. A model describing the qualitative behaviour of the source during outburst is presented.

Stellar population synthesis is a tool for modelling galaxies and their spectral energy distributions. By combining the spectra of every star within a galaxy, it becomes possible to form the spectrum of the galaxy as a whole. This requires a large collection of stellar spectra which, ideally, contains spectra for every kind of star in the model galaxy. To contribute to the development of stellar population synthesis and model atmospheres, I examine two such collections of stars, the MARCS and ATLAS9 theoretical stellar libraries. I compare 18 spectra of model stars for which both libraries have performed calculations. Stars with three different temperatures were chosen (8000K, 4500K and 3500K). For each temperature, three values of metallicity and two values of effective gravity were chosen. I find a mismatch in the spectra of the medium and low temperature model stars (4500K and 3500K), in addition, a difference in molecular features (~7000Å) is found in the 3500K low metallicity models ([Me/H]=-2.5). I conclude that this difference is caused by missing molecular opacities for the calcium hydride (CaH) molecule in the ATLAS9 library. Four possible causes of the overall mismatch are discussed: the temperature structure of the models; the geometry of the models; and partition functions used for the calculation of the models. I conclude that none of these four sources could produce the mismatch. This leaves room for further investigation into the cause of the mismatch.

Astrophysical models that address stellar energy generation and nucleosynthesis require a considerable amount of input from nuclear physics and are very sensitive to the detailed structure of nuclei, both stable and unstable. Radioactive nuclei play a dominant role in several stellar environments such as supernovae, X-ray bursts, novae etc. and nuclear data are important in the interpretation of these phenomena. When carbon, nitrogen and oxygen isotopes are present in substantial quantities in a star of sufficient mass, the fusion of four hydrogen nuclei to form a helium nucleus proceeds via the CNO cycles. Energy release in the CNO cycles is limited by the long lifetimes of 14O and 15O. In explosive stellar scenarios such as X-ray bursts, the energy output is very large, suggesting a breakout from the CNO cycles. 15O(α,γ)19Ne is the first reaction that breaks out of the CNO cycle. Nuclear structure information on high lying states in 19Ne is required to calculate the rate of the 15O(α,γ)19Ne reaction. This work focuses on the study of states in 19Ne above 3.53 MeV. The lifetimes of five states in 19Ne above 3.53 MeV were measured in this work. The states in 19Ne were populated via the 3He(20Ne,α)19Ne reaction at a beam energy of 34 MeV. The lifetimes were measured using the Doppler Shift Attenuation Method. The lifetimes of five states were measured and an upper limit was set on the lifetime of a sixth state. Three of the measurements are the most precise thus far. The lifetimes of the other three states agree with the values of the only other measurement of the lifetimes of these states. An upper limit on the rate of the 15O(α,γ)19Ne reaction was calculated at the 90% confidence level using the measured lifetimes. The contributions to the 15O(α,γ)19Ne reaction rate from several states in 19Ne at different stellar temperatures are discussed.

No description available.

Prior to this thesis no serious attempt has been made within binary system population synthesis research to model the selection effects of observational surveys. Conversely, many pulsar population models have accounted for radio survey selection effects but not detailed binary evolution. Such modelling becomes especially important when comparing theory directly to observations. In examining the factors that influence pulsar evolution, both in binary systems and as single stellar objects, we have bridged this existing gap between these two research fields. This thesis populates a model Galaxy with binary systems and evolves the population forward in time. A prediction of the Galactic pulsar population characteristics is produced, at the assumed age of the Galaxy, after we have accounted for detailed changes in stellar and binary evolution and Galactic kinematics. Synthetic observational surveys mimicking a variety of radio pulsar surveys are then performed on this population. The population synthesis synthetic survey (PS3) package is comprised of three components: stellar/binary evolution (binpop), Galactic kinematics (binkin), and survey selection effects (binsfx). The resultant pulsar populations, assuming the magnetic-dipole decay and accretion induced magnetic decay models, can compare well to many of the detected pulsar population characteristics. The comparisons between models and observations have lead to the conclusions described below. The models exclude short (∼ 5 Myr) timescales for standard pulsar exponential field decay and find that ablation of low-mass millisecond pulsar companions can redress both the lack of synthetic isolated pulsars and their excessive distances in height from the Galactic plane. Coalescing double neutron star and collapsar Galactic populations, evolved owing to standard binary evolutionary assumptions, are too centrally concentrated owing to the typical merger timescale of double neutron stars being a few million years. Dwarf galaxy models of coalescing double neutron stars and collapsars produce equally good agreement with long gamma-ray burst projected distances. Therefore our models cannot provide any distinction between which of these populations (coalescing double neutron stars or collapsars) are the progenitor of long gamma-ray bursts. The Galactic birth rate of double neutron star binaries in our model is 8.2 Myr−1 and the merger rate is 6.8 Myr−1. Scintillation is found to be an important aspect in the detection of low flux density pulsars. The assumed pulsar luminosity law is found to require an inverse trend with spin period and our favoured models suggest that there are one million radio active pulsars within the Galaxy.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: D.E. Winget. Vita. Includes bibliographical references. Also available from UMI.