Department Library


Derek Sean Felli (PhD Dissertation, December 2017, Advisor: Victor Migenes Gaetan )


Even though low mass stars (< 8 solar masses) vastly outnumber high mass stars (< 8 solar masses), the more massive stars drive the chemical evolution of galaxies from which the next generation of stars and planets can form. Understanding mass loss of asymptotic giant branch stars contributes to our understanding of the chemical evolution of the galaxy, stellar populations, and star formation history. Stars with mass < 8 solar masses form planetary nebulae, while those with mass < 8 solar masses go supernova. In both cases, these stars enrich their environments with elements heavier than simple hydrogen and helium molecules. While some general info about how stars die and form planetary nebulae are known, specific details are missing due to a lack of high-resolution observations and analysis of the intermediate stages. For example, we know that mass loss in stars creates morphologically diverse planetary nebulae, but we do not know the uniformity of these processes, and therefore lack detailed models to better predict how spherically symmetric stars form asymmetric nebulae. We have selected a specific group of late-stage stars and observed them at different scales to reveal the uniformity of mass loss through different layers close to the star. This includes observing nearby masers that trace the molecular shell structure around these stars. This study revealed detailed structure that was analyzed for uniformity to place constraints on how the mass loss processes behave in models. These results will feed into our ability to create more detailed models to better predict the chemical evolution of the next generation of stars and planets.


Adam K Johanson (PhD Dissertation, April 2015, Advisor: Victor Migenes Gaetan )


Four regions of massive star formation in the Large Magellanic Cloud (LMC) were observed for water and methanol maser emission and radio continuum emission. A total of 42 radio detections were made including 27 new radio sources, four water masers, and eight compact HII regions. The lobes of a radio galaxy were resolved for the first time, and the host galaxy identified. Seven sources were associated with known massive young stellar objects (YSOs). A multi-wavelength analysis using both the infrared and radio spectrum was used to characterize the sources. Mid-infrared color-magnitude selection criteria for ultracompact HII (UCHII) regions in the LMC are presented, yielding 136 UCHII region candidates throughout that galaxy. New maser detections identified two previously unknown massive YSOs. No methanol masers were detected, consistent with previous studies and supporting the hypothesis that the LMC may be deficient in these molecules. These discoveries contribute to the history of star formation in the LMC, which will lead to a better understanding of star formation in the Milky Way and throughout the universe.


Daniel Robert Blakley (Masters Thesis, July 2014, Advisor: Victor Migenes Gaetan )


The intent of this project was founded upon the need to train students in the techniques of radio astronomy with the purpose of establishing a radio telescope in order to teach the principles and practice of radio astronomy.This document describes the theory, research, to establish the 1st generation radio telescope system within the Department of Physics and Astronomy at Brigham Young University. Included are introductions to: (1) The nature of star forming regions in the spiral arm structure of the galaxy, H I (the hydrogen spin-flip transition) and OH MASERS, (2) The of terminology used with the system components and their measurements, (3) The characteristics of the imaging system and its limitations, and (4) Future work and plans. Within the body of this work, I also present an introduction to the purpose, architectural design, as well as a brief description of some of the system level functions and associated equipment that constitute the development infrastructure for the 2nd generation radio astronomy system.The major work accomplished includes history, some of the fundamental theory behind radio astronomy, significant aspects of the theory behind the system, building of the system, its calibration and characteristics as well as next steps

Chuck Honick (Senior Thesis, May 2014, Advisor: Victor Migenes Gaetan )


We present the status and future plans of the radio astronomy observatory at Brigham Young University. The Physics and Astronomy department and the West Mountain Observatory already have optical facilities that offer students the opportunity to observe in the optical and NIR, but not in any other wavelengths. An array is being built for students to obtain data in the radio spectrum. The array is being built around the operational 4 meter dish on top of the Eyring Science Center and will eventually contain baselines up to 20 km and a 10 m dish. We currently have four sites for additional baselines. The array initially will be ready to observe HI at 1420 MHz and the OH MASER lines at 1665 MHz and 1667 MHz. We present preliminary spectra in L-band (21cm-18cm) with the 4 meter dish. The system will be using LNA's for signal amplification and will have digital correlation and spectral analysis through CASPER. The system is locked to a rubidium clock with a GPS master. In the future, we hope to extend the frequency coverage to C-band (5 GHz).


Dino Munoz (Senior Thesis, April 2013, Advisor: Victor Migenes Gaetan )


The research project in which I have been working for my senior thesis at BYU was about the study of the environment circumstances in which masers are found. There are multiple known astrophysical settings where masers are produced. Such regions include star-forming regions, evolved atmospheres of late type stars, interstellar medium in other galaxies and supernova remnants. From all these options, I took on the job to study the masers which are found in galaxies other than Milky-way (i.e. extragalactic masers). These masers have the strongest intensities and are therefore called mega-masers (often 10 million times more luminous than masers found in the Milky-way galaxy).

Drake Ranquist (Senior Thesis, April 2013, Advisor: Victor Migenes Gaetan )


Magnetic reconnection is the leading mechanism for energy release in solar eruptions. The coronal magnetic field cannot be measured remotely or in situ, which makes modeling difficult. Using NIMROD, an extended magnetohydrodynamics simulation code, we have developed an indirect method to obtain the asymmetry of the magnetic field during observed solar eruptions. We analyzed the eruptions on 6/7 Dec 2010 and 7 Mar 2011 with the Atmospheric Imaging Assembly. We traced post-flare loops and found the asymmetric reconnection models that best fit the observations using rotation and chi-squared algorithms. To further constrain the results, we rotated these fits onto the observations from the Solar Terrestrial Relations Observatory. We estimated that the 2010 event had a magnetic field asymmetry of 4:1 and the 2011 event an asymmetry of 1.5:1. In combination with other signatures of asymmetric magnetic reconnection, this can yield a method for determining the upstream magnetic field ratios during solar eruptions.


Stephen Clouse (Senior Thesis, July 2012, Advisor: Victor Migenes Gaetan )


In this study we present a map of the water maser emission from the nucleus of the Seyfert 2 galaxy Mrk 1210, as observed with the Very Long Baseline Array. We detect red-shifted and blue-shifted masers but detect none at the systemic recession velocity of the galaxy. Observations by the Green Bank Telescope (GBT) show a spectral profile of the megamasers that is somewhat unlike the characteristic triple-peaked profiles of classic water megamasers in AGN accretion disks. However, our map shows that the masers are aligned roughly perpendicular to extended radio continuum structures in the nucleus, suggesting the masers come from the accretion disk. We find that we can fit the megamaser distribution with a flat, inclined disk, with two of the maser loci falling near the midline of the disk and a third coming from an azimuthal angle of 47 degrees on the near side of the disk. We also find them all to have accelerations less than 0.25 km/s/yr, which is consistent with the flat disk model. With this scenario, we can estimate the mass of the central black hole to be approximately 1.3*10^7 solar masses .

Andrea Munyan (Senior Thesis, April 2012, Advisor: Victor Migenes Gaetan )


Starburst galaxies are those that show a very high rate of star formation, and most of these galaxies are actually two or more galaxies colliding to form a merging galaxy system with extremely complicated morphology. The evolution of these merging galaxies are not well known, and MASER emission has been used to indirectly observe the mechanics within a merging system, such as the location and proper motion of a star forming region. However, it has been proposed that MASERs we believed to originate from star forming regions could instead be related to the presence of an Active Galactic Nuclei (AGN). Differentiating between a star forming region and an AGN as the origin of MASER emission would allow us to determine the nature and evolution of the merging galaxy environment. We studied the OH megamaser emission within IIZw096 at high radio resolutions and compared our results to data taken previously to study the nature of this merging galaxy system.

Blake Stauffer (Senior Thesis, April 2012, Advisor: Victor Migenes Gaetan )


Evolutionary processes of late type stars can be studied by using their maser emission as probes. Current models show that the environment inside a planetary nebula cannot support maser emission. The target, planetary nebula PN K3-35, has maser emission that is unexplained. The mechanics of radio interferometry and data reduction using the Astronomy Image Processing System are explained to show how the conclusions are obtained. Observation of the nebula does not reveal the mechanism for maser radiation, but results in a kinematic model of the maser regions in PN K3-35. Two 22 GHz water maser regions are present with a flux of 14 Jy above the continuum flux of 6 Jy.


Kerianna Butler (Capstone, December 2011, Advisor: Victor Migenes Gaetan, David Kieda, Stephan LeBohec )


The BL Lacertae object Markarian 421 is a variable gamma ray source and can flare to many times that of the Crab Nebula. This source is observed by VERITAS, the Very Energetic Radiation Imaging Telescope Array System, which consists of four imaging atmospheric Cherenkov telescopes and is located in southern Arizona. During the 2007/2008 observing season we observed the source for over 30 hours and report the statistical significance of gamma rays to be 235 standard deviations. We correlate our results with x ray data and summarize the mechanisms which are thought to cause gamma ray emission.

Derek Felli (Senior Thesis, April 2011, Advisor: Victor Migenes Gaetan )


Microwave amplification by stimulated emission of radiation (MASER) originates from molecules which have been pumped to an excited state. Galactic MASER emission originates from dense hot clumps of molecular gas. MASERs are found in star forming regions (SFR), supernova remnants, and late-type stars. There are various very well known MASER species OH, H2O, CH3OH, SiO, and H2CO to name some of the most common. In this work we present the result of studying 41 galactic OH-MASERs using the Very Large Baseline Array (VLBA). Common transitions observed in OH-MASERs are the lines 1612, 1665, 1667, and 1720 MHz. The 1665 and 1667 MHz transitions are more common in SFR and are referred to as ``main lines" in the literature. The 1612 and 1720 MHz transitions are common in late-type stars and are known as ``satellite lines". Generally 1612 and 1720 MHz lines are not found in SFR. We studied these four transitions previously mentioned in OH-MASERs, with very high spatial and spectral resolution. We were the first to obtain high resolution observations for 1612 and 1720 MHz transitions in many OH-MASER sources. From our data we determined that the 1720 MHz line strength is correlated of the star formation processes in high-mass and low-mass SFR. Of the 41 sources 5 (11.4%) showed 1612 MHz lines and 10 (22.7%) showed 1720 MHz line. This correlation between satellite line emission and high-mass SFR is helpful in the study of star formation processes.

Michael DeLoss Joner (PhD Dissertation, March 2011, Advisor: Victor Migenes Gaetan )


Photometric techniques are often used to observe stars and it can be demonstrated that fundamental stellar properties can be observationally determined using calibrated sets of photometric data. Many of the most powerful techniques utilized to calibrate stellar photometry employ the use of stars in clusters since the individual stars are believed to have many common properties such as age, composition, and approximate distance. Broadband photometric Johnson/Cousins BVRI observations are presented for several nearby open clusters. The new photometry has been tested for consistency relative to archival work and shown to be both accurate and precise. The careful use of a regular routine when making photometric observations, along with the monitoring of instrumental systems and the use of various quality control techniques when making observations or performing data reductions, will enhance an observer’s ability to produce high-quality photometric measurements. This work contains a condensed review of the history of photometry, along with a brief description of several popular photometric systems that are often utilized in the field of stellar astrophysics. Publications written by Taylor or produced during the early Taylor and Joner collaboration are deemed especially relevant to the current work. A synopsis of seven archival publications is offered, along with a review of notable reports of VRI photometric observations for the nearby Hyades open star cluster. The body of this present work consists of four publications that appeared between the years 2005 and 2008, along with a soon to be submitted manuscript for a fifth publication. Each of these papers deals specifically with high-quality broadband photometry of open clusters with new data being presented for the Hyades, Coma, NGC 752, Praesepe, and M67. It is concluded that the VRI photometry produced during the Taylor and Joner collaborative investigations forms a high-quality data set that has been: 1) stable for a period of more than 25 years; 2) monitored and tested several times for consistency relative to the broadband Cousins system, and 3) shown to have well-understood transformations to other versions of broadband photometric systems. Further work is suggested for: 1) the transformation relationships for the reddest stars available for use as standards; 2) the standardization of more fields for use with CCD detectors; 3) a further investigation of transformations of blue color indices for observations done using CCD detectors with enhanced UV sensitivity, and 4) a continuation of work on methods to produce high-quality observations of assorted star clusters (both open and globular) with CCDbased instrumentation and intermediate-band photometric systems.


Kirstin Marie Cooprider (Masters Thesis, July 2010, Advisor: Victor Migenes Gaetan )


OH Megamasers (OHMs) generally appear in luminous infrared regions i.e. merging galaxies. In this study we assume that OHMs may not be represented by their association with star formation solely, because of the possibility of a compact AGN source in the merging galaxies. In fact, previously classified starburst galaxies where OHMs are found are now optically observed as AGN. OHMs may also serve as a reasonable criterion for the evolutionary stage of the merger. This project focuses on observations from a multi-frequency analysis of merging regions with known OHMs. Optically, Hα and BVRI filters provided an environmental perspective of the “masing” components. In the radio, 18-cm data was used to determine the structure and position of the OHM. We studied the source IIZw096 and compared our results with two familiar OHM sources. We were able to look at each source at high radio resolutions and compare the structure and classification of each.

Daniel Jibson (Senior Thesis, May 2010, Advisor: Victor Migenes Gaetan )


Using data from MERLIN, we observed the 1665 and 1667 MHz OH maser emissions from the expanding circumstellar envelope of U Orionis, one of the few OH/IR sources known to emit detectable tangential emission. We measured the flux within rings of increasing distance from the optical source to determine both the thickness of the envelope and its radius. We present herein the method of analysis of tangential emissions as a potential method for modeling circumstellar envelopes in three dimensions.