2018
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1 Courtney Bishop (College of William and Mary) ADVISOR: Dr. Anna Rosen (RG) PROJECT TITLE: Producing Synthetic ALMA Observations of Massive Star Forming Molecular Cores Abstract: Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium with their intense radiation fields dwarfs the contribution by their vastly more numerous low-mass cousins. Massive star forming regions in our galaxy are rare, distant, and highly obscured making the earliest moments of their formation difficult to capture. However, large-scale high- resolution radio interferometers such as ALMA are now making it possible to capture these early phases with molecular line observations (e.g., molecular lines like 13CO and SiO). In this project, we would like to have an REU student produce mock molecular line observations from 3D adaptive mesh refinement (AMR) radiation hydrodynamic simulations of the collapse of massive pre-stellar cores into massive stellar systems. These simulations include stellar feedback - the injection of momentum and energy into the interstellar medium by young stars - from the stellar radiation field and collimated protostellar outflows. These processes shape the gas dynamics of the collapsing core. The student will use python, yt (a visualization software for AMR simulations), RADMC-3D (a radiative-transfer calculation code), and CASA (a data post-processing code for sub-mm and radio observations) to make synthetic molecular line maps from our simulation outputs. The student will then analyze their post-processed images to determine morphological features of the entrained gas in the outflows and the accretion disk properties, and also develop new diagnostics to analyze molecular line data for massive star forming regions.
2 Jacqueline Blaum (Iowa State University) ADVISOR: Dr. Rafael Martinez-Galarza (HEAD) PROJECT TITLE: Constraining Star Formation in the Milky Way with Machine Learning Abstract: A comprehensive picture of star formation in the Milky Way requires an accurate census of all young stellar objects (YSOs) in star-forming molecular clouds. However, current infrared YSO catalogs are built from images where sources are spatially blended together, while their identification as young stars is ambiguous, which translates into incomplete catalogs. There are two primary causes for this incompleteness: 1) the loci of YSOs in widely used infrared color-color or color-magnitude diagrams often overlap with other kinds of sources leading to ambiguous classifications, and 2) the clustering of sources makes it difficult to identify them individually within large beams. The goal of this summer project is to more accurately reclassify a sample of intrinsically red young stellar object (YSO) sources in the Spitzer, WISE, and Herschel catalogs and to produce a new census of young stellar sources using modern techniques of astrostatistics and machine learning. The student will work with Drs. Rafael Martinez-Galarza and Matthew Ashby to select a suitable sample of infrared sources and perform an improved classification using two new algorithms that we developed 1) a machine-learning (ML) algorithm for supervised classification and unsupervised outlier detection, and 2) a deblending method for spatially clustered sources. Using the results from this analysis, the student will produce multi-wavelength SEDs of individual young stars in clustered environments and physically characterize these objects. This will allow us to construct the YSO luminosity function in the Galaxy and reveal environmental dependencies of the star formation properties, and also to test competing theories of star formation by comparing their predictions with our derived set of properties (mass, age, optical extinction, etc.). A new picture of star formation in the Milky Way will emerge from this summer experience.
3 Thomas Boudreaux (High Point University) ADVISOR: Dr. Idan Ginsburg (TA Division) PROJECT TITLE: Exploring the Dynamics of Globular Clusters Abstract: Despite over 150 confirmed globular clusters around the Milky Way, a generalized model of cluster expansion and mass evaporation rates has yet to be developed. Numerical studies have focused on the affects of external tidal fields and stellar evolution, two properties which models now suggest play important roles in shaping the long term evolution of a cluster. Moreover, a link has been suggested between the primordial binary fraction and a cluster's core radius expansion rate. While there are hints this link may exist, there has yet to be a firm quantitative relation discovered. Using the publicly available Nbody6++GPU code, we directly integrate a cluster core consisting of 1000 bodies (total mass of 516 Solar) over 500 Myr in order to find such a relation.
4 Ivalu Christensen (Lund University; self-funded) ADVISOR: Dr. Nimesh Patel (RG) PROJECT TITLE: Probing the chemistry in low- and high-mass protostars with the SMA Abstract: Studying the chemical composition of star forming sites can further develop our understanding of the physics of star formation. For this project, a low mass protostellar system, IRAS 16293-2422, and a hot core in high mass star-forming region G35.20-0.74N are studied. SMA data obtained in 2009 and 2011 of these objects will be imaged and the spectra will be analyzed using the Cassis software with the purpose of identifying the organic composition of both star-forming regions and comparing them. Furthermore, the LTE column densities and excitation temperatures will be characterized for selected lines.
5 Sierra Dodd (University of Washington) ADVISOR: Dr. Paul Green (HEAD) PROJECT TITLE: Characterizing Stellar Variables in the Time Domain Spectroscopic Survey Abstract: The Time Domain Spectroscopic Survey (a subprogram of SDSS-IV eBOSS) obtains classification/discovery spectra of photometric variables selected from PanSTARRS and SDSS multi-color lightcurves. Tens of thousands of TDSS spectra are already available, and classified both via pipeline and by visual inspection. About half are quasars, and half stars. Variable star types include RR Lyr, close eclipsing binaries, CVs, pulsating white dwarfs and other exotic systems, but spectral class is usually insufficient to determine the cause of variability. The REU student will obtain richer public multi-epoch lightcurves for brighter (r<19.5) stars from the Catalina Sky Survey and Palomar Transit Factory Surveys, and run a variety of lightcurve analyses to constrain variable type, both for broad statistics relevant to future variability surveys like LSST, and to characterize the variable stars in TDSS for future classification.
6 Tenley Hutchinson (Spelman College) ADVISOR: Dr. Rosanne Di Stefano (HEAD) PROJECT TITLE: Identifying the precursors of compact-object mergers Note: Ms. Hutchinson's poster describing this work won the Chambliss award at the Seattle AAS meeting. Abstract: One of the most exciting developments in astronomy and astrophysics during the past century has been the discovery of gravitational-wave-induced mergers of double black holes and double neutron stars. These discoveries have validated important features of general relativity. As more events are detected we will learn a great deal about stellar remnants and the properties of matter in extreme environments. Such signatures are expected if at least one of the compact objects slated for merger is bright during part of the pre-merger evolution. The compact objects could be luminous at early times due to a fallback disk, for example. Or they could be bright because they are accreting matter, perhaps from a companion in a wider orbit. In either case, we expect distinctive features at X-ray wavelengths which include gravitational lensing effects, where one compact object lenses its companion, that produce short-lived, repeated spikes in the X-ray emission. Dozens of already-observed X-ray sources in each of several external galaxies, and up to 1000 in the Local Group (1500 to 2000 sources in total) are bright enough that these signals are potentially detectable. This number is large enough that detections are expected and, if we do not discover systems fitting the predicted profiles, null results would be meaningful. The goal for a student working on this project would adopt is to examine archival data from the Chandra X-ray Observatory, XMM-Newton, and several other missions to search for evidence of double-compact-object binaries in which one or both components are bright at X-ray wavelengths. The student would have the opportunity to work directly with the data, and also to assess the significance of any detected signals or null results. Skills that would become part of the student's repertoire are familiarity with accessing large archived data sets, and signal processing. The student would become comfortable with the physics of accretion, X-ray emission, and gravitational lensing. We anticipate at least one publication would come from this work.
7 Amalya Johnson (Columbia University) ADVISOR: Dr. Paul Nulsen (HEAD) PROJECT TITLE: AGN Feedback in Brightest Cluster Galaxies Note: Ms. Johnson described this work in a press briefing at the Seattle AAS meeting. You can watch it at the 17:10 mark of the Black Holes and Galaxies Near & Far session. Abstract: Powerful radio sources at the centers of galaxy clusters play a key role in regulating star formation in the very massive galaxies that host them. Jets from the central supermassive black (SMBH) hole heat surrounding gas, while gas that cools from the hot cluster atmosphere can form stars and feed the SMBH. Cooled gas that falls into the SMBH boosts the jet power, leading to more heating. In this way, jet heating is linked to cooling and star formation in a feedback loop. To understand this process, we must understand how a central radio source interacts with it cluster atmosphere. Cygnus A is by far the most powerful radio galaxy in the local Universe and it is hosted by a cluster central galaxy. Each radio lobe of Cygnus contains a compact primary hotspot and a brighter secondary hotspot, where the radio jets impact the cluster atmosphere. A very deep X-ray image of Cygnus A has revealed an almost circular "hole" surrounding the primary hotspot in the eastern radio lobe. The aim of the project is to determine the properties of this hole in order to understand how it was formed and what it tells us about the interaction between the radio source and its environment. This will involve analyzing X-ray data and applying theory to interpret the results.
8 Megan Masterson (Case Western Reserve) ADVISOR: Dr. Yuanyuan Su (HEAD) PROJECT TITLE: Chandra Observations of a Merging Galaxy Cluster at z>0.5 Note: Ms. Masterson's poster describing this work won the Chambliss award at the Seattle AAS meeting. Abstract: Galaxy clusters are the most massive virialized structures in the Universe. They are the signal peaks in the cosmic density and thus have been appreciated as powerful cosmology tools. In the cold dark matter paradigm, clusters are assembled hierarchically via mergers, the most energetic events in the Universe. For this project, the student will analyze 40 ks Chandra/ACIS observations of the z=0.51 cluster G211.21+38.66, which has an unusual binary structure. The student will also make use of available SDSS data. In combination, the Chandra and SDSS data will constrain the intracluster medium temperature, density, and metallicity, among other properties of this distant system. By comparing these fundamental properties to those of relatively nearby clusters, it will be possible to gain a much better understanding of the growth of galaxy clusters. 9 Evan Nunez (Cal State Polytechnic University Pomona) ADVISOR: Dr. Joel Leja (OIR) PROJECT TITLE: Using Distant Galaxies with Extreme Chemical Conditions as Laboratories for Stellar Theory Abstract: current theoretical models for the evolution of massive stars are very uncertain: specifically, different theoretical models predict outputs of high-energy photons which vary by factors of two or more. It is critical to constrain this ionizing photon budget as this budget is necessary to interpret many important observations, ranging from estimates of galaxy star formation rates to the energy budget for nebular line emission to the reionization rate of the Universe. It's impossible to use nearby stars in the Milky Way to discern between these competing models, because at high metallicities the model predictions converge. However, distant galaxies with low metallicities and recently truncated star formation histories may be provide an ideal testing lab. The student will use multiple cutting-edge stellar evolution codes to identify the ideal candidate galaxies. A successful project will lead to an exciting spectroscopic campaign providing spectroscopic follow-up of these galaxies.
10 Osase Omoruyi (Yale University) ADVISOR: Dr. Elaine Winston (OIR Division) PROJECT TITLE: Studying Star Formation in the Outer Galaxy Abstract: Star formation in the outer Milky Way Galaxy has not been as extensively studied as star formation in the inner Galaxy. Home to low gas density, low metallicity levels, and sparsely distributed molecular clouds, the outer Galaxy's environment contrasts with the gas-rich and high--metallicity environment prevalent in the inner Galaxy. By extending the study of star-forming regions to include sites in the outer Galaxy, we will obtain a more complete understanding of star formation in the Milky Way and how the process depends on environmental factors. Here, we use infrared observations from NASA's Spitzer Space Telescope and the Wide-field Infrared Survey Explorer to examine a so-far marginally-studied star-forming region in the outer Galaxy centered at (l, b) = (92.36, 1.97). Within this region, we search for and classify young stellar objects to provide insights into their parental molecular clouds, including the presence of sub-clustering, the relative ages of those sub-clusters, and whether any external triggering is likely to have occurred. We then use models to estimate the masses of the identified young stars and their disks, and compare our results to star-forming regions in the inner Galaxy.
11 Aldo Sepulveda (University of Texas San Antonio) ADVISOR: Dr. Luca Matra (RG) PROJECT TITLE: Locating exocometary belts around nearby stars Abstract: Belts and rings of exocomets like our Solar System's Kuiper belt (also known as debris disks) are found around at least 20% of nearby stars like the Sun. Their comets are the most untouched relics of the building blocks that went to form planets in planetary systems. Observing where these belts are located in any given planetary system and studying their structure informs us about the presence of planets and their formation conditions.
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