2017
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Bridget Andersen (University of Virginia) ADVISOR: Dr. Ian Stephens (RG Division) PROJECT TITLE: The Mass Evolution of Protostellar Disks and Envelopes in the Perseus Molecular Cloud Abstract: In the typical model for low-mass star formation, a dense molecular cloud of gas and dust undergoes gravitational collapse to form a protostellar system consisting of a new central star, a circumstellar disk, and a surrounding envelope of remaining material. In this basic model, the mass distribution of the system evolves as matter accretes from the large scale envelope through the disk and onto the protostar. While this general picture is supported by simulations and indirect observational measurements, the specific timescales related to disk growth and envelope dissipation remain poorly constrained. The goal of our study is to conduct a rigorous test of a method introduced by Jørgensen et al. (2009) that uses data from the Submillimeter Array to obtain observational mass measurements of disks and envelopes around embedded protostars. Using data from the recent Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey, we derive disk and envelope mass estimates for 59 protostellar systems in the Perseus molecular cloud. We compare our results to independent disk mass measurements from the VLA Nascent Disk and Multiplicity (VANDAM) survey and find a strong linear correlation, validating the efficacy of the Jørgensen et al. method. Then, leveraging the unprecedented size and uniformity of our sample, we find no significant trend in protostellar mass distribution as a function of age, as approximated from bolometric temperatures. These results may indicate that the disk mass of a protostar is set near the onset of the Class 0 protostellar stage and remains relatively constant throughout the Class I protostellar stage.
Aliza Beverage (University of Minnesota) ADVISOR: Dr. Howard Smith (OIR Division) PROJECT TITLE: A Multiwavelength Analysis of AGN and Star Formation in Colliding Galaxies Abstract: Galaxy mergers are key components in galaxy evolution, generally causing massive starbursts and AGN. We have gathered photometry for a sample 103 merging galaxies outlined in Brassington et al. 2015 that span wavebands from the UV to the FIR. We will review the data for these galaxies to complete their SEDs and then model their key characteristics including: star formation rate, specific star formation rate, dust mass and temperatures, and AGN contribution. The study will also address how well the simulations are able to reproduce the observed behaviors of these systems.
Jane Bright (Denison University) ADVISOR: Dr. Guillermo Torres (SSP Division) PROJECT TITLE: Accurate Stellar Parameters for Eclipsing Binaries, and Tests of Stellar Evolution Theory Abstract: Eclipsing binary star systems are the best source of accurate measurements of masses and radii of stars. We use spectroscopic and photometric data from the eclipsing binary V2154 Cyg to derive the best stellar parameters for the system. These parameters can then be compared to stellar evolution models. V2154 Cyg is of particular interest because the smaller of the two stars is of the size where models often predict radii that are too small, which is thought to be caused by stellar activity not present in the models. Our accurate measurements of the stellar parameters of the stars in V2154 Cyg will allow us to test models of stellar structure and evolution.
Jenny Calahan (University of Arizona) ADVISOR: Dr. Joseph Hora (OIR Division) PROJECT TITLE: Clusters of Young Stellar Objects in the Cygnus-X Infrared Dark Clouds Abstract: The Cygnus-X region is a vast star formation environment, filled with every stage of star formation from dense molecular clouds to evolved protostars. We hope to further understand the process of star formation by observing clustering patterns and masses of molecular clouds as compared to later stage young stellar objects (YSOs). In order to identify clusters of dense clouds, we will write a python script to automatically sort regions of smaller dense clouds into larger groups across the entire Cygnus-X complex. We will also utilize SED information of YSOs as found in Cygnus-X by the IRAC and MIPS instruments on Spitzer in combination with Herschel data. Using the observed SEDs we will use SEDfitter to find predictions of the mass and luminosity of each YSO which we can then compare to previously calculated molecular cloud masses.
Yijia Li (Nanjing University) ADVISOR: Dr. Christine Jones (HEAD) PROJECT TITLE: Characterizing recent outbursts from Active Galactic Nuclei (AGN) in early-type galaxies Abstract: We have used Chandra X-ray observations of relatively nearby early-type galaxies (those within about 50 Mpc of our Milky Way), to select galaxies that show evidence of an outburst from a supermasssive black hole at the galaxy's center. Usually the outburst generates cavities that we can see in the galaxies' hot X-ray-emitting coronae. By measuring the size of the cavities and the distance of the cavities from the galaxy center, we can determine the amount of energy released from the supermassive balck hole to produce the cavities and can measure when the outburst began. This project will require first "cleaning" and "merging" individual Chandra observations, then identifying any "point" sources that need to be omitted from the analysis, measuring the spatial distribution of gas in the hot halo, by first generating a surface brightness profile of the gas, measuring the gas temperature, and then measuring the sizes of cavities in the hot halos and their distances from the galaxy center which will be used to calculate when the supermassive blackhole outburst occurred and how much energy was released.
Gautam Nagaraj (North Carolina State University) ADVISOR: Dr. Francesca Fornasini (HEAD) PROJECT TITLE: Measuring Black Hole Masses for Active Galactic Nuclei (AGN) in the Chandra Cosmos Legacy Survey Abstract: In recent decades, a strong correlation between supermassive black hole (SMBH) masses and the masses, luminosities, and velocity dispersions of the host galaxies has been established for the local universe. One of the most important questions in extragalactic astronomy is whether the correlation extends to higher redshifts (back in time): was the coevolution of black holes and galaxies constant or a complex function of time, environmental conditions, and AGN feedback mechanisms? While quasars, the highest-luminosity AGN, have been studied extensively at a large range of redshifts, faint AGN, which are at least 20 times more common in the universe, have not, and we still do not know if they have similar histories to quasars. The Chandra Cosmos Legacy Survey observed 4016 X-ray sources, mostly faint AGN. Marchesi et al. (2016) identified optical/IR counterparts to 97% of these sources, and with spectra from large optical surveys such as the Sloan Digital Sky Survey, we are using the technique of reverberation mapping to determine the masses of hundreds of SMBHs in Broad-Line AGN.
Hannah Richstein (Texas Christian University) ADVISOR: Dr. Yuanyuan Su (HEAD) PROJECT TITLE: Chandra Mapping of a Non-Cool-Core Cluster out to the Virial Radius Abstract: Galaxy clusters are the largest known gravitationally bound structures in the Universe, often containing thousands of galaxies. These clusters can be classified as either cool cores (CC) or non-cool cores (NCC), depending on their temperature profiles, cuspiness, and other properties of their intracluster media (ICM). A growing number of clusters are found to be NCC clusters, but it is unclear how they are formed. We have been awarded deep Chandra X-Ray observation to probe the ICM properties of a massive NCC cluster, Abell 586, to the virial radius. With these data we aim to examine how NCC clusters are produced, and specifically what role major mergers could play in the process.
Jasmine Sinanan-Singh (Harvard University) ADVISOR: Dr. Francesca Civano (HEAD) PROJECT TITLE: Investigating Black Hole Spins at High Redshift Abstract: Supermassive black hole (SMBH) spin encodes vital information about the history of SMBH growth. Examining spin over different redshifts will help us understand SMBH growth over cosmic time, an important part of understanding how SMBHs and their host galaxies evolved over time. We average the X-ray spectra of AGN from the Chandra-COSMOS Legacy Survey in different redshift bins and compute the average Fe K-alpha emission line at rest frame. We derive our method from Corral et al. (2008) to compute the rest-frame averaged X-ray spectrum and test this method on the two brightest sources in the Chandra-COSMOS Legacy Survey. We do not fit complex models to individual spectra, but rather increase the signal-to-noise ratio by averaging the spectra and then fitting to a model. For the redshift bin z=0.8-0.9, we detect an average Fe K-alpha iron emission line around 6.52 keV with a width of 220 eV and an equivalent width of 310 eV. We have tested and applied our method to a subsample of the Chandra-COSMOS Legacy Survey. Our results are in agreement with results found in Corral et al. (2008). The next step is to compute the average iron lines for the other redshift bins out to z~6.
Jamie Sullivan (University of Texas at Austin) ADVISOR: Dr. Alex Wiegand (TA Division) PROJECT TITLE: Minkowski Functional Analysis of the Completed Sloan Digital Sky Survey III Galaxy Map to Further Constrain Non-linear Structure Formation Abstract: Galaxy correlation functions are one of the primary statistical tools used to extract a characterization of the large-scale structure of the universe. The higher-order correlation functions reveal the strongly non-Gaussian nature of the galaxy distribution, but are quite difficult to compute. Through the use of Minkowski functionals we exploit both the topology and geometry of the distribution to efficiently compute the higher-order functions. By applying this analysis to the full SDSS-III Luminous Red Galaxy dataset, we will produce an unprecedented accuracy in the Minkowski Functionals. Results of this analysis will be used to probe the redshift evolution of these galaxies, and possibly to constrain cosmological model parameters.
Abygail Waggoner (Ball State University) ADVISOR: Dr. Ilse Cleeves (AMP Division) PROJECT TITLE: Chemical Processes in Protoplanetary Disks Abstract: Protoplanetary disks are a natural outcome of the formation of a young star, with the star at the center of the disk. In its young age, the star emits strong flares of X-ray radiation whose strength depends on the mass of the star and the strength of the stellar magnetic fields. The X-rays penetrate the disk, especially in the surface layers. These layers are composed of dust grains, atoms, molecules, ions, and some ices, which chemically respond to the flare. This project aims to understand 1) which molecules and atoms respond most strongly to X-ray flares emitted from a T Tauri star, 2) what are the long term (Myr) and short term (days to years) effects on chemical abundances in the disk, and 3) how do the chemicals react in different vertical layers and at varying distances from the star. The results of this theoretical exploration will provide testable predictions for future ALMA observations of time-domain chemistry.
David Zegeye (Haverford College) ADVISOR:Dr. Raffaele D'Abrusco (HEAD) PROJECT TITLE: The Evolution of Galaxies through the Spatial Distribution of Their Globular Clusters: the Brightest Galaxies in Fornax Abstract: Globular Clusters (GCs) are compact objects that possess 104 to 106 gravitationally bound stars. GCs are ideal proxies to reconstruct the evolution of their host galaxies because many properties of the population of GCs are determined by the host galaxy growth. Measurements of GC distributions reveal spatial, overly dense structures in their host galaxy that may have resulted from major mergers or satellite galaxy accretion. In recent years, significant research on the spatial distribution of GCs has been performed for galaxies found in galaxy clusters. D'Abrusco et al. (2016) investigated the large-scale structure of the spatial distribution of intracluster GCs in the core of the Fornax Cluster, using ground-based data. This project will continue the study of globular cluster distribution for galaxies in the Fornax Cluster, by using data produced by the Advanced Camera for Surveys on the Hubble Space Telescope in order to provide more insight into the evolutionary history of their host galaxies.
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