Massive young stars dynamically modify their surroundings, altering their stellar nurseries and the gas that exists between stars. With my research, I assess the modification of the Galactic magnetic field within HII regions and stellar bubbles associated with OB stars. Because HII regions are plasmas, magnetic fields should be important to the dynamics of the region. Understanding how the magnetic field is modified in these structures is critical for inputs to simulations and for assessing stellar feedback. To obtain information on the properties of the magnetic field, I measure the Faraday rotation of linearly polarized radio waves that pass through the plasma of the HII region. In this thesis, I present results of Faraday rotation studies of two Galactic \HII regions. The first is the Rosette Nebula (l = 206 deg, b = -1.2 deg), and the second is IC 1805 (l = 135 deg, b = 0.9 deg), which is associated with the W4 Superbubble. I measure positive rotation measure (RM) values in excess of +40 to +1200 rad m^-2 due to the shell of the Rosette nebula and a background RM of +147 rad m^-2 due to the general interstellar medium in this area of the Galactic plane. In the area of IC 1805, I measure negative RM values between +600 and --800 rad m^-2 due to the HII region. The sign of the RM across each HII region is consistent with the expected polarity of the large-scale Galactic magnetic field that follows the Perseus spiral arm in the clockwise direction, as suggested by Van Eck et al. (2011, ApJ, 728, 14). I find that the Rosette Nebula and IC 1805 constitute a "Faraday rotation anomaly", or a region of increased RM relative to the general Galactic background value. Although the RM observed on lines of sight through the region vary substantially, the |RM| due to the nebula is commonly 100 -- 1000 rad m^-2. In spite of this, the observed RMs are not as large as simple, analytic models of magnetic field amplification in HII regions (such as by magnetic flux conservation in a swept-up shell) might indicate. This suggests that the Galactic field is not increased by a substantial factor within the ionized gas in an HII region. Finally, these results show intriguing indications that some of the largest values of |RM| occur for lines of sight that pass outside the fully ionized shell of the IC 1805 HII region, but pass through the Photodissociation Region (PDR) associated with IC 1805.

The Bok globule B335 is a small molecular cloud in the solar neighbourhood near the galactic plane. The aim for this three-paper-study is to construct and analyze the extinction for this globule. The method we apply is to use the light from field stars behind the cloud in broadband filters ranging from UV to the mid-infrared. We have observations performed at the ESO telescopes at La Silla and Paranal as well as at the Nordic 2.5 m telescope at La Palma. Together with images and spectra from 2MASS-, ISO- and Spitzer-archives we are able to cover the wavelength range from 0.35 to 24 μm. An important tool to analyze these observations results in order to get the extinction is the grid of synthetic stellar atmospheric spectra provided by Hauschildt (2005). The extinction so received is a result in itself. From the analysis of the extinction wavelength dependence we derive properties of the dust, especially its composition and grain size distribution. By modeling the grain size distribution we are able to find the extinction from the reddening of the stars. We find that the extinction in the optical wavelength 0.35 to 2 μm range nicely follows the functional form described by Cardelli et al. (1989). Our result from the wavelength range redward of 2 μm show an extinction dependent on the part of the cloud examined. For the rim of the cloud we get an extinction similar to that reported earlier for the diffuse interstellar medium. From the central parts of the cloud, however, a higher extinction was found. Our grain size model contains a carbonaceous particle distribution and a silicate one. The result can be explained by depletion of carbon onto carbonaceous grains and also by carbon onto all grains including the silicates. Our modeling of the extinction and our classification of the background stars allow us to - determine the distance to the globule - estimate the gas column density ratio - estimate the mass of globule - get a handle on the dust conversion processes through the grain size distribution   From the water- and CO-ice spectra we are able to estimate the ice column densities. We find similar ice column densities for the two ices. The estimates differ, when calculated from band strengths or from Lorenz-Mie calculations of ice mantles on the grain size distribution, by a factor of two.

Thesis (M.S.)--University of Toledo, 2009. / Typescript. " As partial fulfillment of the requirements for the Master of Science in Physics." "A thesis entitled"--at head of title. Bibliography: leaves 21-22.

The effect of dust/gas heating and cooling is shown to have a significant effect on the process of clustered star formation. Compared to an isothermal simulation, a simulation with a more accurate description of the equation of state produces an order of magnitude fewer stars as well as stars of much greater mass. The energetics algorithm used to calculate the dust and gas temperature includes the radiative heating of dust, dust-gas collisional heating/cooling, cosmic-ray heating, and molecular cooling. It uses DUSTY, a spherical continuum radiative transfer code, to model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. The gas temperature is then determined by assuming energy balance. Before the complete energetics algorithm is included in a simulation, first only the dust heating component is included. The gas temperature is then set solely by the dust temperature. The resultant mass functions of our simulations which include heating are compared to those which assume an isothermal equation of state. We find that including dust heating severely limits star formation; we form at least an order of magnitude fewer objects when we include dust heating compared to an isothermal simulation. The mass functions from our simulations which include heating are much more similar than the mass functions from our isothermal simulations to the observed mass functions, in that they are able to form high-mass stars (M [> subscript tilde] 10M[solar mass]). The distribution of the high-mass objects is well-approximated by the Salpeter initial mass function. Including the complete energetics algorithm in a simulation produces results similar to a simulation with only dust heating. Both simulations have similar density profile parameters. The mass accretion, mass, and luminosity evolution of the sinks is also similar. The average temperature, however, is cooler than the simulation with only dust heating. We form fewer objects comparatively and are still unable to form enough low and intermediate-mass objects to replicate the observed mass function. This may be an effect of small number statistics, or possibly physical processes that are not considered in this work. / text

No description available.

No description available.

The distributions of physical properties, such as the temperature, mass, or density of the dust grains in molecular clouds near Galactic massive star forming regions are relatively poorly understood. These properties are significant in characterizing the early stages of high-mass star formation. The major goal of this thesis is to study the dust properties using continuum emission to learn about the effect on the dust of the extreme environments around high-mass star formation. For this we estimate mass, temperature and luminosity of the hot (??? 100 K), cool (20-40 K) and cold (??? 20 K) dust in the environs of Galactic H??? regions using Infrared Astronomy Satellite (IRAS) and James Clerk Maxwell (JCMT) Submillimeter Common User Bolometer Arrays (SCUBA & SCUBA-2) data.??????A total of 83 clouds has been examined using IRAS data. A two-component model Spectral Energy Distribution (SED) of hot and cool dust is used to fit the IRAS data. A three-component model SED is fitted to combined SCUBA and IRAS data for 15 clouds near H??? regions to measure the cold dust component. Surprisingly, the ratio of the bolometric luminosity of the cool dust to the hot dust appears to have the same value 2.8 in virtually all objects. The cool dust has typically four to five orders of magnitude greater mass than the hot dust. However, the mass in cold dust is much greater than the mass in cool and hot dust. These results may prove useful for using IR observations for estimating gas masses in extragalactic systems with active high-mass star formation.??? ???The clouds in the environments of H??? regions are modelled assuming a thermal equilibrium in large grains, ignoring small grains and polycyclic aromatic hydrocarbons (PAHs). A number of different models having varying density distributions and external stellar radiation are compared to the IRAS SEDs. The model results suggest that the assumptions are not valid. We need a larger amount of dust at 30 K than the models produced and in this thesis we propose a solution to this problem, which we have not yet tested. ??????The JCMT Submillimeter Common User Bolometer Array-2 (SCUBA-2) data of six complexes is used to analyze the cold dust near Galactic H??? regions. Dust physical property maps such as the temperature, optical depth, column density and visual extinction are constructed from the SCUBA-2 data at 450 and 850 ??m wavelengths. All of the molecular cloud cores are found to be at very low temperatures, down to 6 K at the centres, with increasing values toward the periphery. This is surprising because we expected some internal heating at the centre. The column densities at the centres of the clouds exceed 10???? cm????? and the derived peak visual extinction values of most of the cloud cores are above 100, indicating a highly opaque cloud centre. The observed clouds are massive with gas masses ranging from 10?? to over 10??? M???. All of these properties together suggest that the cores are high-mass starless cores (HMSCs), which are not hosting any massive stars at the centre. Note that there are only a few such observations, on these potential precursors of high-mass proto-stellar objects, by others. From the derived physical properties such as high column densities, high visual extinction and the cold temperatures toward the centres of the cores, we speculate that the all the sample cores are in a state of collapse. Note that the Jeans masses of the clouds are much less than their real cloud masses and the free fall times range from 10?? to 10??? years, confirming the potential state of the cores.

We have used broad-band near infrared photometry in combination with optical Johnson-Cousins photometry to study the dust properties in the line of sight to the Galactic globular cluster M4. These data have been used to investigate the reddening effects in terms of absolute strength, distribution and variations across the cluster field, as well as the shape of the reddening law defined by the type of dust. All three aspects were poorly defined for this system and therefore there has been controversy about the absolute distance to the globular cluster which is closest to the sun. Here, we introduce a new method to determine the ratio of absolute to selective extinction (RV ) in the line of sight toward resolved stellar populations, which is known to be a useful indicator for the type of dust and therefore characterizes the applicable reddening law. This method is independent of age assumptions and appears to be significantly more precise and accurate than existing approaches. In a first application, we determine AV /E(B − V ) = 3.76 ± 0.07 (random error) for the dust in the line of sight to M4 for our set of filters. That corresponds to a dust-type parameter RV = 3.62 ± 0.07 in the Cardelli, Clayton & Mathis (1989) reddening law. With this value, the distance to M4 is found to be d = 1.80 ± 0.05 kpc, corresponding to a true distance modulus of (m − M)0 = 11.28 ± 0.06. These uncertainties do not include possible systematic errors in the theoretical isochrones. A reddening map for M4 has been created which reveals a spatial differential reddening of δE(B − V ) ≥ 0.2 mag across the field within 10′ around the cluster centre; this is about 50% of the total mean reddening, which has been determined to be E(B − V ) = 0.37 ± 0.01. In order to provide accurate zero points for the extinction coefficients of our photometric filters, a computer code has been written to investigate the impact of stellar parameters such as temperature, surface gravity and metallicity on the extinction properties and the necessary corrections in different bandpasses. Using both synthetic ATLAS9 spectra and observed spectral energy distributions, we found similar sized effects for the range of temperature and surface gravity typical of globular cluster stars: both cause a change of about 3% in the necessary correction factor for each filter combination. Interestingly, variations in the metallicity cause effects of the same order when the assumed value is changed from the solar metallicity ([Fe/H] = 0.0) to [Fe/H]=-2.5. Our analysis showed that the systematic differences between the flux of a typical main-sequence turnoff star in a metal poor globular cluster and a Vega-like star are even stronger (∼ 5%). We compared the results from synthetic spectra to those obtained with observed spectral energy distributions and found significant differences in detail for temperatures lower than 5 000 K. We have attributed these discrepancies to the inadequate treatment of molecular bands in the B filter within the ATLAS9 models. Accordingly, for those cooler temperatures we obtained corrections for temperature, gravity and metallicity primarily from the observed spectra. Fortunately, these differences do not affect our principal astrophysical conclusions in this study, which are based on stars hotter than 5 000 K. / Graduate

Typescript. / Includes bibliographies. / Photocopy. / Microfilm. / xi, 175 leaves, bound ill. 29 cm

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references. / xviii, 406 leaves, bound ill. 29 cm