Constraining the properties of the Eta Carinae system via three-dimensional smoothed particle hydrodynamics models of ground- and space-based observations

The first chapter introduces Eta Carinae, highlighting why it is so interesting and worth studying, while Chapter 2 reviews the theory of radiation-driven winds from hot, massive (> 10 M&odot ) stars, before outlining the key observational signatures and physics of colliding wind binary systems. Chapter 3 focuses on the observational diagnostics implying binarity and colliding stellar winds in Eta Carinae, concluding with a summary of past numerical hydrodynamical modeling efforts, and showing that with the exception of X-rays, very little work has been done on the numerical simulation and interpretation of observations in other wavebands. Chapter 4 explains the 3D SPH method and visualization program used in this thesis.Chapter 5 presents a detailed 3D dynamical model for the high-ionization forbidden line emission observed by the Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) in Eta Carinae. Large scale (&sim 1500 AU) 3D SPH simulations and radiative transfer calculations are used to generate synthetic position versus velocity spectrograms at various orbital phases and STIS slit Position Angles (PAs). When compared to the available observations, these model spectro-images provide important details about the physical mechanisms responsible for the emission, as well as the location and orientation of the observed emitting structures. This 3D dynamical model constrains, for the first time, the absolute orientation of the binary orbit on the sky.Chapter 6 introduces a 3D "bore-hole" model for the periodic eclipse-like events seen in ground-based photometric observations of Eta Carinae. 3D SPH simulations, together with the CMFGEN and SPLASH radiative transfer codes, are used to generate synthetic light curves in the optical BVRI and NIR JHKL wavebands. The synthetic light curves reproduce the observed steep rise and drop before periastron, and give roughly the same peak-to-peak change in magnitude and "eclipse" duration. Several key trends with wavelength are also reproduced. The bore-hole model further constrains the argument of periapsis of the system to values of o &sime 210°--240°.Chapter 7 presents definitive evidence for the detection of high velocity material (up to &sim 1900 km s-1) in the Eta Carinae system during the 2009.0 periastron passage. The observations imply direct detection of high-velocity material flowing from the wind-wind collision zone. Detailed 3D SPH simulations constrain the longitude of periastron to values of 240° &lsim o &lsim 270°, and the orbital inclination to 40° &lsim i &lsim 60°, as these are the only orientations for which dense, high-velocity gas is in line-of-sight to the primary star at the appropriate orbital phases (0.047--0.102). The simulations further show that the high-velocity absorbing material is likely located at distances of 15 to 45 AU from Eta Car A (in line-of-sight).In Chapter 8, the published K-band continuum interferometric data of Eta Carinae is analyzed with the goal of constraining the rotational velocity and spatial orientation of the rotation axis of Eta Car A. The influence of Eta Car B on the inner wind of Eta Car A is also investigated. Synthetic interferometric observables computed from radiative transfer models show that both single-star prolate- and oblate-winds are able to explain the available measurements. Moderately fast rotation and high inclination angles are required to simultaneously fit the two available data sets, with W = 0.77--0.92 and i = 60°--90° for the best prolate-wind models, and W = 0.73--0.90 and i = 80°--90° for the best oblate-wind models ( W is defined as the ratio of the rotational velocity of Eta Car A to its critical velocity). The results of Chapter 8 further show that, assuming the standard orbital and wind parameters, the inner density structure of Eta Car A's wind can be sufficiently disturbed by Eta Car B at certain orbital phases, mimicking the effects of a prolate/oblate latitude-dependent wind in the available interferometric observables in the K-band continuum. (Abstract shortened by UMI.)...