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Rayson, Di
The Structure, Dynamics and Evolution of the Magellanic System
(1990-06) Wayte, Simon; Catholic Theological College
The Magellanic System is probed with a focus on the interactions in the System giving insight into the structure, dynamics and evolution of the Magellanic System. The past orbits of the Magellanic Clouds are modelled. A tidal encounter between the LMC and SMC has almost certainly occurred within the last 10^9 years. The observed structure of the Magellanic System supports this hypothesis and so it is accepted. This encounter event is found to be crucial to the understanding of the Magellanic System. Ca II absorption spectra of 25 Magellanic Cloud supergiants have been obtained at a resolution of 5 km s^-1 using the Anglo-Australian Telescope. They are used with new H I observations from the Parkes radio telescope to reveal the three-dimensional structure of the Large and Small Magellanic Clouds. Radio continuum polarization maps of the LMC and SMC have been obtained at 2.3, 4.75 and 8.55 GHz using the Parkes telescope. They complement the optical polarization measurements in revelation of the magnetic field structure of the Magellanic Clouds. The gas in both Magellanic Clouds is seen to have a distance-velocity association. This breaks down south of 30 Doradus where the gas structure is complex. The radio and optical polarization measurements are seen to agree, indicating no significant line-of-sight structure to the aligned magnetic field visible in either the LMC or SMC. The pan-Magellanic field originally proposed by Mathewson and Ford finds support, and a clearly revealed spiral field centred on 30 Doradus merges smoothly with it. The Parkes telescope has been used to obtain finely gridded H I measurements of the Magellanic Stream and the high velocity H I around the Magellanic System. The origin of the intermediate velocity gas components seen in the direction of the LMC is finally determined. The Magellanic Stream is found to be bifurcated along its entire length with many anomalous velocity H I clouds alongside. A two component profile is discovered in the tip of the Stream indicating that nearby the extreme velocity clouds are part of the Stream. The high velocity clouds (HVCs) ahead of the Magellanic Stream are found to be part of a halo HVC population. The diffuse ram pressure origin of the Magellanic Stream is modelled. The origin of the Magellanic Stream is found to be the collision of a multi-phase halo (made up of the halo HVCs and diffuse corona) with the Inter-Cloud region. The popular tidal model for the origin of the Magellanic Stream fails to satisfy some of the important observational features and is thus rejected.
Review: the Interacting Magellanic System
(Kluwer Academic (merged with Springer-Verlag), 1991) Wayte, Simon; Haynes, Raymond; Milne, Douglas; Catholic Theological College
The Magellanic System is viewed focusing on the global interactions in the System. These give insight into its history and structure. The past orbits of the Magellanic Clouds (MCs) are examined. A tidal encounter between the Large and Small Magellanic Clouds (LMC, SMC) has almost certainly occurred within the last 10^9 yrs. This hypothesis is supported by the observed structure of the Magellanic System, and so is accepted. The Magellanic Stream is an indirect result of the tidal encounter which is crucial to understanding the Magellanic System. It is a complex interacting gas feature, bifurcated along its entire length with many anomalous velocity H I clouds alongside. The possible models for the Magellanic Stream are examined and here I propose that its origin is due to the collision of a multi-phase halo with the vast region of gas between the LMC and the SMC. In this respect the polar subsystem around our Galaxy is seen to be particularly important. The popular tidal model for the origin of the Magellanic Stream fails to satisfy key observational features, and is thus rejected.
Structure of the Interstellar Medium in the Magellanic Clouds
(1990-06-01) Wayte, Simon; Catholic Theological College
Ca II absorption spectra of 25 early-type Magellanic Cloud supergiants, presented here, have been obtained at a resolution of 5 km s^-1^ using the newly commissioned coude echelle spectrograph of the AAT. They are used in conjunction with H I observations from the Parkes 64 m radio telescope and polarization observations to reveal the three-dimensional structure of the Large and Small Magellanic Clouds. A large-scale grid map of H I in and around the Magellanic System shows that the intermediate-velocity gas components seen in the direction of the LMC have differing origins; the 60 km s^-1^ component is galactic, the 130 km s^-1^ component is galactic (or possibly tidally torn Magellanic gas), and the 170 km s^-1^ component is LMC gas. The gas in both Magellanic Clouds is seen to have a distance-velocity association also seen in the stellar component of the SMC (Mathewson et al.). This relation breaks down south of 30 Doradus, where the gas structure is complex. Radio and optical polarization measurements are shown to agree, indicating that there is no significant line-of-sight structure to the aligned magnetic field visible in either the LMC or SMC. The pan-Magellanic field originally proposed by Mathewson and Ford finds support from a reanalysis of past optical polarization measurements, and a spiral field centered on 30 Doradus is clearly revealed. The spiral field merges smoothly with the pan-Magellanic field in the LMC, suggesting a common cause for both phenomena, a collision of the SMC with the LMC. The idea of a collision of the LMC and SMC as put forward in the models of Murai and Fujimoto and Mathewson et al. is supported by the new observations.
The Magellanic Stream; New Observations
(1989) Wayte, Simon; Catholic Theological College
New H I observations of the Magellanic Stream have been made using the Parkes 64 m telescope. These observations highlight in detail its complicated structure and uncover new features of the Stream. The extreme velocity clouds (EVCs) are morphologically linked to the Stream indicating that these H I clouds are very truly part of the Stream. Also it is suggested that many of the high velocity clouds seen around the Stream are indeed part of the Magellanic Stream itself, and that the stream consists of many different velocity components in bulk motion.