Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [201]-212).

This study presented the light variation mechanism along with temperature, distance, and changes in projected surface area of the dwarf nova CN Orionis. Modeling the disk and hot spot as blackbodies produced graphs of flux, temperature, and projected surface area over time, making it possible to deduce the cause for the light variation. This is a valid approximation, since the disk is considered to be opaque in nature. The orbital period of CN Orionis was in phase with the above parameters, which affirm projected surface area of the hot spot is heavily responsible for the flux variations, and not temperature variations. Further determinations of these parameters and more data collection would be quite beneficial for confirmation and further study of accretion disk physics. / Department of Physics and Astronomy

Thesis (Ph. D.)--Open University. BLDSC no. DXN046358.

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The magnetic rotator model has long been the favored explanation for coherent photometric modulations in the DQ Herculis class of cataclysmic variables. However, to date, all evidence supporting this model has been of the indirect variety. Unlike their synchronously rotating cousins, the AM Herculis objects, DQ Herculis stars have not yet been discovered to emit polarized radiation. Therefore, in light of this crucial lack, the evidence used to place these objects in the magnetic cataclysmic variable category has been strictly circumstantial, based primarily on the coherence of the photometric periodicities. In this work, time-resolved spectroscopy of four long-period DQ Herculis stars is performed. In addition, two of the same objects are observed with a new, sensitive circular polarimeter. Chapters II and III describe these observations and the results of each. To summarize, coherent variations in the wavelength of emission lines were found with the spectroscopic observations. A model is put forth, explaining this phenomenon as being due to varying illumination from a bright spot on the primary. This, of course, adds strength to the magnetic rotator model. Secondly, circular polarization was definitely found in one object studied, and possibly in a second. Therefore, for the first time, there is direct evidence of the magnetic nature of these binaries. In Chapter IV, the model of the rotating bright spot illuminating the disk is explored in further detail, including modeling with a minicomputer. Afterward, a problem brought out by the low polarization coupled with large amplitude photometric variations and a cool spectrum is investigated, namely, is it possible to produce large amounts of cyclotron radiation without producing large amounts of circular polarization? The results tend to show that, for a large emitting area, the answer is yes. Chapter V is a summary of the rest of the work.

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Bibliography: pages 155-165. / The unusual spectra of the spatially-resolved nova shells of DQ Her, T Aur and CP Pup are reviewed. Because calculations for these conditions have not been made, recombination models of HI, HeI and CNO from a neutral to a doubly ionized state were constructed. The models are described and the results presented for densities at various temperatures. A photoionization model is also described. The effects of non-uniform density distributions in nova shells have been investigated and the observational consequences discussed. A model of the CP Pup shell is described and the evolution of this plasma during the nova's constant luminosity phase traced. The properties of neon novae are summarized and compared with the features seen in the optical spectra of old classical novae. Enhanced neon abundances are used in the model of the CP Pup Shell to investigate its effect on the evolution of the shell. Finally, the results of some near-infrared observations made on the shells of CP Pup, RR Pic and T Pyx are reported.

An explanation of the emission line behavior in cataclysmic variables has been among the most important and elusive problems in eruptive star research. This work expands accretion disk chromosphere models of line emission to predict line behavior qualitatively. A search for UX UMa-like thick disk cataclysmics in the Palomar Green survey sample gave space densities consistent only with luminous high accretion rate disks: Ṁ ≥ 10⁻⁷·⁰Mₒ/yr. Instead, 20 composites whose combined energy distributions were "flat", Fᵥ α ν⁰, were discovered. These typically were early K dwarfs paired with 30,000K subdwarf O stars. The study also showed that a substantial fraction of subdwarf O and B stars are binary. The detached eclipsing binary BE UMa showed a reflection effect emission line spectrum due to the close 7Rₒ separation between an EUV-emitting subdwarf O star and an M1-5 dwarf. Analysis gave the hot star physical parameters as: 80,000K ≤ T(p)(K) ≤ 100,000, 7.0 ≤ log g(p) ≤ 8.0, and log (He/H) = 1.0 ± 1.0. The BE UMa optical emission line spectrum was modeled using a quantitative photoionization-recombination stellar atmosphere-like code. A rich high excitation continuum fluorescence and recombinational spectrum including HeII λ4686 and CIII λ4650 was formed at lower optical depths corresponding to nₑ ≤ 10¹³·⁵ cm⁻³ and Tₑ = 20,000K. The model suggests that T(p) = 100,000K. Cataclysmic variables too have a central source due to loss of half the accretion energy at the white dwarf surface. This temperature is no higher than the innermost disk regions; hence, mass accretion rates determine the character of the EUV radiation. Observations of 13 cataclysmics representing most types were obtained. From these data, the H, HeI, HeII, CaII, and high excitation metal emission line behavior in cataclysmics were analyzed. Cataclysmic variable accretion rates were shown to follow a sequence; from the low excitation dwarf novae [10⁻⁹·⁵ ≤ Ṁ (Mₒ/yr) ≤ 10⁻⁸·⁵] to the high excitation novae and nova-like systems [10⁻⁸·⁵ < Ṁ(Mₒ/yr) ≤ 10⁻⁶·⁵]. Predicted line profiles were consistent with observations. Thus, the model accounts well for the considered observations.

We present HST spectroscopy for 45 cataclysmic variables (CVs), observed with HST/COS and HST/STIS. For 36 CVs, the white dwarf is recognisable through its broad Ly a absorption profile and we measure the white dwarf effective temperatures (T-eff) by fitting the HST data assuming log g = 8.35, which corresponds to the average mass for CV white dwarfs (similar or equal to 0.8M(circle dot)). Our results nearly double the number of CV white dwarfs with an accurate temperature measurement. We find that CVs above the period gap have, on average, higher temperatures (< T-eff > similar or equal to 23 000 K) and exhibit much more scatter compared to those below the gap (< T-eff >similar or equal to 15 000 K). While this behaviour broadly agrees with theoretical predictions, some discrepancies are present: ( i) all our new measurements above the gap are characterized by lower temperatures (T-eff similar or equal to 16 000-26 000 K) than predicted by the present-day CV population models (T-eff similar or equal to 38 000-43 000 K); (ii) our results below the gap are not clustered in the predicted narrow track and exhibit in particular a relatively large spread near the period minimum, which may point to some shortcomings in the CV evolutionary models. Finally, in the standard model of CV evolution, reaching the minimum period, CVs are expected to evolve back towards longer periods with mean accretion rates. M less than or similar to 2 x 10(-11)M(circle dot)yr(-1), corresponding to T-eff less than or similar to 11 500 K. We do not unambiguously identify any such system in our survey, suggesting that this major component of the predicted CV population still remains elusive to observations.

Nesse trabalho discutimos a formação de componentes estreitas de linhas de emissão observadas em espectros de algumas novas. Nós estudamos as possíveis fontes físicas no sistema binário responsável pela emissão das componentes estreitas de altos fluxos que apresentam velocidade radial, primeiramente identificadas nas linhas de recombinação da nova recorrente U Sco em sua erupção de 2010. Uma busca por novas candidatas a apresentarem o mesmo fenômeno em seus espectros é mostrada, indicando pelo menos 11 outras novas com espectros similares. Nós comparamos a presença dessas componentes com parâmetros básicos das novas e com a classificação espectral na fase inicial permitida da evolução espectral. Modelos de fotoionização mostram que a região emissora de tal radiação não deve ser restrita ao lóbulo de Roche, uma vez que seu volume é insuficiente para reproduzir os fluxos observados. Uma análise comparada também exclui o disco de acreção e a cromosfera da secundária como fontes da radiação. Nós sugerimos a região em torno de L3 como uma possível região emissora, com base nas simulações de fotoionização. / In this paper we discuss the formation of peculiar narrow emission line components observed in the spectra of a few novae. We aim to identify the physical source in the binary system responsible for the emission of transient narrow components that present orbital radial velocity modulations, first observed in the post-outburst recombination lines of Nova U Sco 2010. A search for candidate novae showing similar narrow components is presented, indicating at least 11 other novae with similar spectra. We compared the presence of these components to nova basic parameters and to the spectral classification in the initial permitted phase of the spectral evolution. Photoionization simulations indicate that the forming region cannot be restricted to the primary Roche Lobe, as its volume is not large enough to reproduce the observed fluxes. A detailed analysis also excludes the accretion disk and the the secondary\'s cromosphere as sources of the radiation. We suggest the region around L3 as a possible emitting region, based on photoionization simulations.