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Abstract

In this thesis, I investigate the nature of circumstellar material around massive young stellar objects (MYSOs). I make extensive use of spatially-resolved observations, and examine spatial structure at scales ranging from tens of astronomical units up to nearly a parsec. In the first of three scientific studies presented in this thesis, I present the results of a survey to observe MYSO candidates with the Very Large Telescope Interferometer at mid-infrared wavelengths, using the MIDI instrument. I consider the properties of this sample of 20 objects as a whole, and address the sources individually. In the second study, I focus on the well-known MYSO IRAS 13481-6124. By combining interferometric data from both near- and mid-infrared wavelengths, I derive a temperature profile for the circumstellar disk around this object, which I discuss in the context of theoretical disk models. In the third study, I examine the high-luminosity source AFGL 4176 at wavelengths of 1 mkm–1 mm. I construct one-dimensional radiative transfer models of the envelope, and interpret the interferometric observations in terms of a parameterized disk model. The observations and results presented in this thesis will be of use to future studies of MYSOs, both theoretical and observational, and provide an important groundwork for observations of such objects with the next generation of interferometric instruments at the Very Large Telescope.