Exploring HII Regions and Massive Dusty Stars in the Galactic Center with SOFIA/FORCAST
The center of the Milky Way Galaxy is a rather exotic place. It is home to a supermassive black hole (Sgr A*), 3 massive stellar clusters (the Arches, Central and Quintuplet clusters), and several isolated massive stars which are spread throughout the inner ~100 pc. In this dissertation, I present mid-infrared imaging data of three regions in the Galactic center including the Arches and Quintuplet clusters, and the H HII regions. Observations of these regions were taken with the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, and 37.1 um. These data trace warm dust (~100 K) in the surrounding environment of stars and provide constrains on physical properties of the sources such as luminosity, mass, and temperature. The Arches cluster is surrounded by a grouping of molecular clouds which are heated and ionized by the cluster. Both the clouds (known as the Arched Filaments) and the cluster are named for the arc-like appearance of the clouds which are one of the most striking large scale features in the Galactic center. We examine the distribution of dust temperatures across the clouds in the region and find that they are relatively uniform (70-100 K) even though the filamentary clouds have a large physical size (~25 pc). Equilibrium heating analysis of the dust indicates that the characteristic grain size is smaller (~0.01 um) than typical values for the interstellar medium (~0.1 um). We also find evidence for depleted abundances of polycyclic aromatic hydrocarbons (PAHs). Both the grain size and the PAH depletion indicate processing of material in the clouds and may be explained by shocks or other processes occurring in the region. Adjacent to the Arched Filaments there is a collection of HII regions associated with isolated massive stars known as the H HII regions. Studying these sources provides important information on the prevalence and distribution of massive stars in the region and understanding their origin may provide insights on other field stars which are observed throughout the Galactic center. Observations with SOFIA/FORCAST provide high-angular resolution maps (~4") which allows us to study the detailed morphology of four of the HII regions. Analysis of dust temperatures show that three of the spatially extended objects require multiple heating sources, and we identify potential stellar counterparts. We also compare the size and morphology of the HII regions and argue from this that the properties of H2 are consistent with in situ star formation. Last, we identify 8 new sources that may be part of the H complex and provide initial characterizations of their infrared emission. The Quintuplet Proper Members (QPMs) are a collection of five bright infrared sources for which the Quintuplet cluster is named. These sources are thought to be binary systems with a carbon-rich Wolf-Rayet (WC) star and O/B companion. Dust production by these types of systems are poorly understood and constraining their mass-loss history can provide insight on this process. We produce models of the dust emission associated with the four detected sources using the radiative transfer code DUSTY and show that Q2 and Q3 are best fit by radial density profiles which are consistent with constant mass-loss rates. In contrast, Q1 and Q9 show shallower radial density profiles indicating more vigorous mass loss in the stars' recent past. Q9 is particularly interesting because it has a massive dust reservoir which is significantly larger than the other QPMs. N-band imaging obtained with the Gemini Telescope reveal an extended dusty nebulae associated with the source which suggests the material may have been produced by a recent episode of enhanced mass loss from the star. Such events are atypical of dusty WC stars, and we suggest that the dust may have been produced in an earlier phase of the star.
Galactic Center; Infrared Astronomy; Astronomy; Astrophysics
Herter, Terry Lee
Chernoff, David Fisher; Stacey, Gordon John; Niemack, Michael D.
Astronomy and Space Sciences
Ph. D., Astronomy and Space Sciences
Doctor of Philosophy
Attribution 4.0 International
dissertation or thesis
Except where otherwise noted, this item's license is described as Attribution 4.0 International