Interns and Projects: Summer 2019
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1 Jea Adams (Amherst College) ADVISOR: Dr. Nimesh Patel (R&G) PROJECT TITLE: Triggered star-formation in the globules of IC 1396 Abstract: The bright-rimmed globules at interfaces of ionized hydrogen (HII regions) and dense molecular clouds have long been studied as potential sites of star-formation. These edges are compressed to densities high enough to trigger star formation, due to shock fronts caused by UV radiation from the OB stars in the HII region. But direct evidence of this triggering effect on star-formation is difficult to establish observationally, and obtaining a fuller understanding is challenging because it requires observations at multiple wavelengths, on large angular scales, and which also have the high angular resolution characteristic of molecular line emission from high density tracers, as well as continuum emission from dust. We have recently published our results on a newly discovered protostar using Herschel and IRAM 30m observations of the IC 1396 globule A. (Sicilia-Aguilar et al., 2019, A&A 622,A118). We have also obtained SMA observations of this protostar, as well as another new source in the same globule. In this project, we will analyze the dust continuum emission in this source, and CO 2-1 emission from the bipolar outflow, to further improve our understanding of the phenomenon of triggered star-formation. 2 Amanda Ash (University of North Georgia) ADVISOR: Dr. Stephanie Douglas (SSP; NSF Fellow) PROJECT TITLE: Magnetic activity variability in the Praesepe open cluster Abstract: Stellar rotation and magnetic activity operate in a feedback loop where a rotationally powered dynamo produces magnetic fields, and then stellar winds carry mass and angular momentum away, slowing the star and weakening the dynamo. To measure rotation, we look for periodic brightening and dimming caused by starspots rotating into and out of view. To trace the magnetic field, we use indirect measurements like H-alpha and X-ray emission. Most surveys that compare rotation and activity don't account for potential activity variability, however, even though it's been shown that a single star's H-alpha measurement can vary significantly. Last winter, I carried out a survey of stars in the Praesepe cluster (M44) that tracked H-alpha simultaneously with photometric variability, in an attempt to correlate H-alpha active regions with starspots. The student will measure H-alpha emission from reduced MDM data and correlate H-alpha time-series with light curves from K2.
3 Zoe de Beurs (University of Texas at Austin) ADVISOR: Dr. Saeqa (Saku) Vrtilek (HEA) PROJECT TITLE: Revealing the Structure of Sco X-1, the Brightest Source in the X-ray Sky (except the Sun) Abstract: The student will reduce and analyze Doppler tomography observations of binary system Sco X-1 taken with the Magellan 6.5 m telescope in 2019 May. Specifically, the student will construct Doppler tomograms (a diagnostic technique similar to medical CAT scans) to image the structure of this system. The student will learn about optical telescopes, and about how these unusual data are obtained, reduced, and interpreted to understand the physics of this binary system. It is expected that the work will result in co-authorship of a refereed publication. 4 Frederick Dauphin (Carnegie Mellon University) ADVISOR: Dr. Griffin Hosseinzadeh (OIR) PROJECT TITLE: Selecting Superluminous Supernovae from Transient Surveys with Machine Learning Abstract: Superluminous supernovae are a rare type of stellar explosion whose power source is poorly understood. In order to characterize the observational properties of the class and compare them to models, we need to significantly increase the sample size of well observed events. Today's transient surveys (e.g., the Zwicky Transient Facility) produce hundreds of supernova candidates per night, but only a small fraction of these can be classified spectroscopically. This means we need a way to predict which candidates will be superluminous supernovae based only on information available at discovery: how bright they are and where they happened in the sky. Previous work has shown that superluminous supernovae preferentially occur in dwarf galaxies, whereas other types of supernovae are more likely to be found in more massive galaxies. Although the correlation is not perfect, this type of contextual information can be used to sift through the stream of transient discoveries to produce a much smaller sample of events for spectroscopic classification that are highly likely to be superluminous supernovae. We propose to use supervised machine learning to carry out this filtering, which most astronomers currently do by hand. The intern would explore various machine learning algorithms and train them on the set of all previously classified supernovae. The resulting classifier would then be used on new discoveries to determine which candidates we should observe spectroscopically. If this method is more efficient than human filtering, it will have wide-reaching implications for the Large Synoptic Survey Telescope, which will discover transients at an even more unmanageable rate.
5 John Della Costa (University of Florida) ADVISOR: Dr. Howard Smith (OIR) PROJECT TITLE: Colliding Galaxies, Star Formation, and Black Holes Abstract: Collisions between galaxies are ubiquitous, and drive massive bursts of star formation and the growth of supermassive black holes / active nuclei (AGN). Over cosmic time, these cataclysms help to build up the populations of stars and AGN seen today, and during their most active phases they light up the galaxies, turning them in to ultra- or even hyper luminous monsters that are detectable across billions of parsecs and deep into the cosmic past. We have a ongoing project that has compiled the largest, most reliable, and most complete spectral energy distributions (SED) of hundreds of mergers and luminous galaxies using newly reprocessed photometry from space missions and ground programs extending the ultraviolet to the far infrared (about 33 wavelength bands). Using new modeling codes, we have extracted from these SEDs dozens of key physical parameters from star formation rates, AGN fraction, dust temperature, stellar mass, to the dust mass and character; we also have complimentary spectroscopic datasets. This unique sample has enough objects to offer excellent statistical analyses, we believe for the first time. The results so far have spotted important trends - including for example (1) the star formation rate versus the AGN fraction, and Significantly, we have extensive computational simulations of merging galaxies that can be used to test the modeling. First comparisons confirm the reliability of the modeling codes, but much more remains to be done. Key issues include the role of AGN feedback to stimulate or suppress star formation, the nature of the ionized interstellar medium, and the existence of a previously underestimated (but massive) cold dust component. Another key question is whether or not luminous galaxies in the early universe (whose morphology is not known) follow the same star formation processes we find in the local universe. This REU internship will emphasize work in all these areas. The intern will simultaneously gain familiarity with multiple datasets and with computational modeling. The student will work with our team to prepare one or more papers for publication about black holes, star formation, and luminous galaxies. Some emphasis will be given to improving the SED modeling with modules to enable more accurate retrieval of key physics.
6 Hannah Gulick (University of Iowa) ADVISOR: Dr. Sarah Sadavoy (R&G; Hubble Fellow) PROJECT TITLE: ALMA Observations of Protostellar Disks Abstract: Planets form in dense, flat disks around young stars. The seeds for planet formation are small particles of dust within these disks that must grow from micron sizes to pebbles and boulders. The timescales for this formation process are not well understood, and recent theoretical models suggest that a good metric to study the onset of dust grain growth is through polarized scattering. This project will explore why some disks around young stars show evidence of polarized dust scattering (and hence grain growth) whereas other disks do not show this detection. One explanation could be that the masses and densities of these disks are too low for substantial dust grain growth at early stages. Another explanation could be that the undetected disks have poor geometry to detect dust scattering. Either explanation is critical to use this new technique to study how disks form planets at early (< 1 Myr) stages. For this project, the student will use observations of disks from an unbiased survey with the ALMA interferometer. The student will measure the mass, size, density, and inclination of these disks using a simple radiative transfer code to determine if the disk properties or disk geometry affects the detection rate of dust scattering.
7 Caleb Harada (University of Maryland, College Park) ADVISOR: Dr. Antonijia Oklopcic (TA) PROJECT TITLE: Atmospheric escape in exoplanets Abstract: A significant fraction of exoplanets discovered to date orbit their host stars at much closer separations than any of the Solar System planets. These close-in exoplanets are subject to intense stellar radiation, which can have dramatic effects on their atmospheres. The upper layers of a planetary atmosphere can get heated by stellar X-ray and UV radiation to temperatures of several thousand degrees, creating pressure gradients that drive a supersonic planetary outflow. Recently, the helium line at 1083 nm has been identified as an excellent probe of extended exoplanet atmospheres which contain evidence of atmospheric escape. The goal of this theoretical project is to establish what information about the uppermost layers of planetary atmospheres can be extracted from observations, particularly from transit light curves in the helium line at 1083 nm. The student will use a set of pre-generated models of escaping exoplanet atmospheres to produce synthetic transit light curves and investigate how the shape of the transit light curve depends on various properties of the planet and/or its host star.
8 Maryam Hussaini (University of Texas at Austin) ADVISOR: Dr. Andra Stroe (OIR; Clay Fellow) PROJECT TITLE: Unraveling the physics of shock cluster galaxies Abstract: Nearby clusters usually contain many old galaxies, with characteristic red colors indicating they stopped forming new stars long ago. Unlike peaceful nearby clusters, distant galaxy clusters undergo frequent cosmic collisions with other clusters. These collisions were commonplace in the early Universe, but astronomers recently realized they are just as prevalent in the nearby Universe. Studying far away galaxy clusters is difficult, but we can use nearby colliding clusters as probes of the early Universe. Cluster collisions drive dangerous cosmic `weather': giant shock waves and turbulence which travel through galaxies like enormous tsunamis and tornadoes. As the shock passes through them, the typical old, dormant cluster galaxies can actually be awoken to start forming new stars. Capitalizing on unique optical data from the Gemini telescope in Hawaii, the student will be the first to unveil the spatially resolved physics of 'shocked' cluster galaxies. The student will measure the star-formation rate, the presence of black hole activity and the nature and strength of the ionizing radiation and how these vary within the galaxies. The student will learn how to reduce and analyze integral-field unit spectroscopic data and will become familiar with concepts of cluster formation, galaxy evolution, star formation and emission line physics. For either project led by Dr. Stroe, the student should have some knowledge of the Linux operating system, and with scripting and programming in general. Some knowledge of Python in particular would be useful but is not required.
9 Kenneth Lin (Univ. of Massachusetts Amherst) ADVISOR: Dr. Dong-Woo Kim (HEA) PROJECT TITLE: The X-Ray Galaxy Atlas Abstract: Over the past 20 years, X-ray observations have changed our understanding of the galaxy population by allowing us to study in depth their high energy content. In particular, we are here interested in the hot interstellar medium, which is the dominant gas phase in galaxies otherwise lacking a significant gaseous component. This has a large impact in our understanding of their properties (e.g. total mass) and of their formation and evolution, hence on the history of the Universe. For this reason, we have built an X-ray Galaxy atlas consisting of a large number of galaxies using the high-resolution Chandra data and wide field XMM-Newton data. We have published the first version of the Atlas (see arXiv/1812.02718, GalaxyAtlas ) with Chandra data alone. We intend to add archival XMM-Newton data which cover the outer regions in order to have a complete view of the entire galaxy. Our main goal is to produce large-scale 2D maps of surface brightness, projected temperature, pressure and entropy as well as 3D temperature, density and mass profiles. We will then use these products to address the important issues of galaxy formation and evolution, including AGN/stellar feedback, interactions with nearby galaxies and the hotter ambient medium. We will make use of the Smithsonian high-performance computing super-cluster (Hydra) to optimally process a large number of repeated computing tasks. The student may involve one or more sub-projects:
10 Serena Moseley (Carleton College) ADVISOR: Dr. Chelsea MacLeod (HEA) PROJECT TITLE: Long-Term Variability of Nearby Quasars Abstract: The Time Domain Spectroscopic Survey (TDSS) is accumulating approximately 2600 high-S/N spectra of nearby quasars that were observed before by the Sloan Digital Sky Survey about a decade ago. These spectra will be used to study the long-term variability of the broad Balmer emission lines on rest-frame time scales of several years, which corresponds to the dynamical time of the broad-line region. The variability patterns will be used to test models for the dynamics of the gas in the quasar broad-line regions. The student's work will be to examine the variations in the available spectra and identify and classify the variability patterns. The inspection and classification will first be done by eye and then by making measurements of the Balmer emission lines. This work will give the student the opportunity to learn about manipulation of optical spectra, programming, and the basics of the physics of the gas in quasar broad-line regions.
11 Lily Whitler (Arizona State University) ADVISOR: Dr. Charlotte Mason (OIR; Hubble & CfA Fellow) PROJECT TITLE: Measuring the Timeline of Cosmic Reionization Abstract: We cannot see the first galaxies which formed in the universe, but we can observe the impact they had on their surroundings. In the universe's first billion years the majority of hydrogen transitioned from neutral to ionized. This process, `Reionization', was probably caused by photons from the first galaxies, and is an exciting frontier of observational and theoretical astrophysics. The Hubble Space Telescope and biggest telescopes on the ground can observe galaxies at the end of Reionization. By studying these galaxies and how they are affected by Reionization we can learn how Reionization started and about the nature of the very first galaxies. This project combines theoretical modeling and analysis of observations. The student will use a theoretical model of Reionization which predicts the properties of galaxies at our observational frontiers, using a combination of analytical techniques and large-scale simulations. The student will update the model using Python code to explore how the connections between dark matter and galaxies impact Reionization. The model will then be compared with existing observations of galaxies using statistical techniques to measure the timeline of Reionization. These results will be be pivotal in understanding how Reionization took place, and thus the properties of the first galaxies.
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