2016

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ADVISOR:Dr. Saku Vrtilek (HEA Division) 
CO-ADVISORS/MENTORS: Dr. Mike McCollough (OIR Division)

PROJECT TITLE: The Structure of Cygnus X-3

Abstract: 
We have infrared data of Cygnus X-3 obtained with the Gemini North telescope in Hawaii. The student will help reduce and analyze the data. We will construct Doppler tomograms (a method similar to medical cat scans) to image the structure of the system. We also have scheduled observations this summer of a Fermi source recently identified as an XRB using a Magellan telescope in Chile. 
What the student will learn: About optical telescopes, and how astronomical data are obtained and reduced, as well as sSome physics and mathematics related to binary stars and tomography. There will be a paper on which the student will be listed at least as co-author.

ADVISOR:Dr. Howard Smith (OIR Division) 
MENTORS: Drs. Rafael Martinez-Galarza, Matthew Ashby (OIR Division)

PROJECT TITLE: SEDs of Interacting Galaxies

Abstract: 
Colliding galaxies are not only dramatic events, they are vital evolutionary processes in the cosmic order, facilitating the production of stars and their essential by-products. Observations suggest that the most luminous galaxies during the cosmic epoch of peak star formation are powered by the energetics of star formation, and are apparently the result of galaxy mergers. Because they are bright, these luminous galaxies are becoming increasingly important to understand as new telescopes find more of them, stretching back to the epoch of reionization. In the past decade, space missions from the ultraviolet to the far-infrared have enabled the measurement of the full spectrum of merging galaxies from the ultraviolet radiation of hot young stars to the submillimeter light emitted by dust heated by absorbed UV. We are in the midst of a detailed accounting of the spectral energy distribution (SED) of nearby merging galaxies to improve our understanding of merger processes. We study a range of merger stages, and model the SED shapes to retrieve key parameters such as the star formation rates and dust properties. We have simultaneously undertaken a series of merger simulations and applied the models to the simulated SEDs to test the credibility of the analysis method while improving the simulation inputs. Four important issues are highlighted: the role of a black hole nucleus in contributing to a galaxy's luminosity, the accurate accounting of the mass in cold dust, the reliability of simple-minded star formation metrics like the Schmidt-Kennicut relation, and the reality of the so-called galaxy main sequence which correlates a galaxy's star formation rate with its mass. In this project, the student, building on our prior analysis of 31 merging systems, will extend to sample to include many more dramatic, late-stage mergers, and then work to assemble the largest complete sample of merger SEDs available. The student will work on state-of-the-art computer systems to analyze data from recent space missions from GALEX to Herschel, with some emphasis on the infrared datasets. The results will likely lead to one or more publications.

Callie Hood (University of North Carolina)

ADVISOR: Dr. Jayne Birkby (SSP Division) 
CO-ADVISORS/MENTOR: Dr Mercedes Lopez-Morales (SSP Division)

PROJECT TITLE: Exoplanets in high resolution: hunting for molecules in the atmospheres of hot giant exoplanets

Abstract: 
High-resolution spectroscopy enables the direct detection of the spectra of exoplanet atmospheres. From this, we can learn about their chemical make-up, study their structure including clouds and stratospheres, and measure their global wind patterns along with the length of their exo-days. In this project, we will analyze spectra from a program observed at the Very Large Telescope in Chile, using the high-resolution spectrograph ARIES, to study the atmospheric properties of large hot exoplanets. This technique is a forerunner for detecting biomarker gases in the atmospheres of Earth-like planets with the giant segmented mirror telescopes which will be commissioned in the 2020s. This project will give the student experience in i) the processing of high-resolution infrared echelle spectra, ii) coding algorithms to detect very faint exoplanet signals via cross-correlation with laboratory models of molecular spectra, iii) an insight into the exciting and rapidly evolving field of exoplanet atmospheres, and iv) the opportunity to propose new and exciting targets for upcoming observations for a new high-resolution program with ARIES at the MMT in Tucson.

Luan Luan (Nanjing University)

ADVISOR: Dr. Christine Jones (HEA Division) 
CO-ADVISOR: Dr. Akos Bogdan (HEA Division) 
PROJECT TITLE: The X-ray Point Source Population in M87

Abstract: 
The giant elliptical galaxy M87 lies at the center of the Virgo galaxy cluster. Very deep Chandra X-ray observations show a large population of point sources in M87, most of which are likely to be low-mass X-ray binaries, although some will be background AGN. With the Chandra observations, we will be able to measure the luminosity function of the X-ray sources in M87, compare Chandra observations taken at different times to look for X-ray transients, and identify X-ray sources associated with globular clusters. We will compare the results for M87 with studies done for less massive galaxies, particularly the Sombrero galaxy and Centaurus A.

Chima McGruder (University of Tennessee)

ADVISOR: Dr. Guillermo Torres (SSP Division) 
PROJECT TITLE: Accurate Stellar Parameters for Eclipsing Binaries, and Tests of Stellar Evolution Theory

Abstract: 
The goal of the project is to derive very accurate absolute masses, radii, temperatures, and other parameters for the components of an eclipsing binary for the purpose of using these measurements to test current models of stellar structure and evolution. One possible target for this investigation is V541 Cyg, a high-mass eclipsing system that shows changes in the orbital elements due to apsidal motion. This adds interest to the study because the rate of apsidal motion can be predicted by theory, providing a further test. Another possible target is V2154 Cyg, which is interesting because it is a triple system. While this can complicate the analysis, the fainter component of this triple system is a low-mass star, and as such it provides an important test of models in a regime in which they have shown disagreements with previous observations. These disagreements are not yet well understood, but are possibly related to chromospheric activity. The work will involve analyzing high-resolution spectra to determine the radial velocities of all components of the target system (two for V541 Cyg, or three in the case of V2154 Cyg) as well as the elements of the spectroscopic orbit. This will use sophisticated two- or three-dimensional cross-correlation techniques. The project will also require an analysis of the light curves of the eclipsing binary (already in hand) with specialized software to derive the geometric properties of the system, necessary to compute the sizes of the stars and other characteristics. This investigation will provide an opportunity to learn about stellar astrophysics, stellar evolution models, and how to compare them with the measurements described above.

ADVISOR:Dr. John Johnson (SSP Division) 
PROJECT TITLE: Small Friends of Hot Jupiters

Abstract: 
Hot Jupiters are gas giant exoplanets with periods less than 10 days. These planets have previously been assumed to have formed at several astronomical units, like our own Jupiter, and somehow had their semimajor axes shrunk (the process of migration). However, new theories predict that hot Jupiters can form right next to their host star through the collision of large Earth-sized planetesimals (arxiv:1511.09157). A direct prediction of this new class of models is that hot Jupiters should be accompanied by small planets in similarly short-period orbits. This has been observed in the WASP-47 system (arXiv:1508.02411), which contains a hot Jupiter and two "super-Earths" with periods less than 10 days. Since most hot Jupiters have been detected, or confirmed in the case of transiting planets, using low-precision radial velocities, it is possible that small planets lurk "in the shadows" of known hot Jupiters. The summer student will analyze extant radial velocity data and plan future observations to detect or place limits on these small friends of hot Jupiters.

ADVISOR:Dr. Reinout van Weeren (HEA Division) 
CO-ADVISOR: Dr. Christine Jones (HEA Division)

PROJECT TITLE: A search for lensed X-ray sources behind massive galaxy clusters

Abstract: 
The aim of the project is to search for lensed X-ray AGN behind massive galaxy clusters observed with Chandra and HST. The detection of lensed X-ray sources would enable the study of intrinsically faint and distant objects that would remain undetected without the power of lensing. Even more exciting would be the detection of a multiply lensed X-ray source. If such a source is time variable, it would provide strong constraints on the mass model of the cluster and it would also allow us to study the expansion of the Universe. Only four lensed X-ray AGN are known so far, with relatively modest amplification factors, but no systematic searches have been carried out. A good starting point for a search would be CLASH galaxy cluster sample as HST images, photo-z catalogs, and lensing models are publicly available (https://archive.stsci.edu/prepds/clash/). Chandra has also observed most of the CLASH sample. The X-ray sources in the Chandra images can thus be cross-matched with the HST catalogs to find lensed objects. Chandra's high spatial resolution is essential for this project so that one can locate the optical counterparts and reduce the Poisson noise of the X-ray emitting intracluster medium.

ADVISOR: Dr. Volker Tolls (OIR Division) 
CO-ADVISOR/MENTOR: Dr. Howard Smith (OIR Division)

PROJECT TITLE: Search for Star Formation in Inner Galactic Gas Clouds

Abstract: 
In our Galaxy we have huge reservoirs of dust and gas in the spiral arms fueling star formation. Some of this material eventually falls into the inner regions of the Galaxy, where the bar is located. Here, the gas and dust form large clouds, the inner galactic gas and dust clouds (IGGC), which move along semi-stable x1-orbits and spiral into the center of the Galaxy. Further inward, they will collide with gas and dust clouds on the central 100 pc ring, where they are expected to undergo rapid star formation in regions like Sgr A, B, C, and D. The question is: although the IGGCs are very dense, no HII regions have been found indicating star formation. Why? 
We have mapped several of these clouds in the region called Clump 2 with the Herschel Space Observatory and retrieved additional archival ground-based observations. The goal for this summer project is to determine the basic properties of one of these clouds, IGGC 19/23, which shows several distinct hot cores. This project will combine Herschel spectroscopic and photometric data with observations from the Spitzer Space Telescope and ground-based spectrscopy of molecular lines. The primary part of the project will be to identify individual cloud cores, to extract their physical conditions, to search for signs of star formation activity (e.g., outflows), and to compare the results to findings for similar cores as documented in the literature to understand why these cores might be different.

ADVISOR: Dr. Michael Dunham (RG Division)

PROJECT TITLE: Evidence for Episodic Accretion in Protostars

Abstract: 
Stars form from the gravitational collapse of dense molecular cloud cores. The gravitational energy released during this collapse is radiated away as accretion luminosity. A longstanding problem in star formation is that this accretion luminosity is much too low, implying accretion rates much too low to actually form stars. A possible solution to this problem is "episodic accretion", where the accretion rate onto a star is usually much lower than average but occasionally much higher, such that the mean rate remains about the same and a star of a given mass forms in about the same amount of time. 
In this scenario, which represents a paradigm change in our understanding of how stars gain their mass, a forming star (called a protostar) is much more likely to be observed in the low accretion (and thus low luminosity) state. While episodic accretion is capable of resolving the luminosity problem and is supported by indirect evidence, debate over its necessity in matching the observed luminosities of protostars remains. 
In this project the student will use existing observations to calculate and compile new measurements of protostellar luminosities, while also constructing models based on existing accretion theories in order to develop theoretical luminosity predictions. By comparing the two, the student will provide the strongest test yet of both the necessity and ability of episodic accretion in matching the observed luminosities of protostars, and will thus obtain the most definitive results to date on the role of episodic accretion in forming stars.

ADVISOR: Dr. Yuanyuan Su (HEA Division)

PROJECT TITLE: Deep Chandra Observations of NGC 1399: Sloshing fronts and AGN feedback

Abstract: 
The Fornax Cluster is a poor galaxy cluster residing at 19 Mpc (1? = 5.49 kpc) and centered on a bright elliptical galaxy NGC 1399. Such low mass clusters are the main baryon reservoirs in the Universe and are the essential building blocks of the hierarchical formation. Thanks to its proximity, the Fornax Cluster has been a favorite target for many generations of X-ray missions. The cluster center, NGC 1399, displays prominent sloshing cold fronts along the west-east directions. The sloshing was probably induced by off-axis mergers which bring lower entropy gas at the bottom of a cluster potential well into contact with hotter cluster gas outside the center. The second brightest galaxy NGC 1404 is the most likely disturber in this case. NGC 1399 also harbors an active galactic nucleus (AGN) which produced X-ray cavities distributed along the north-south directions and overlapping with the radio emission. Both sloshing and AGN feedback are promising solutions to the cooling catastrophe at centers of cool core clusters. In this case, the sloshing features and that of AGN feedback are in vertical directions, the modeling of which is free from complicated degenerate interpretations of the data. Chandra, with its superb spatial resolution, allows us to study these phenomena in great detail, particularly for such a nearby object. The Fornax Cluster was observed by Chandra for 1 Ms; about 250 ksec was focused on the cluster center. The aim of this project is to quantify the properties of the sloshing fronts, the X-ray cavities, and the cool core in NGC 1399 through the analysis of the existing Chandra observations. We will determine whether sloshing or AGN feedback is more relevant to the regulation of cool cores. We will also constrain the evolution process of low mass clusters through this study.

ADVISOR:Dr. Cara Battersby (RG Division)

CO-ADVISORS/MENTORS: Dr. Eric Keto and Qizhou Zhang (RG Division)

PROJECT TITLE: Extreme Star Formation in the Center of our Galaxy

Abstract: 
We are searching for a summer intern to investigate extreme star formation in the central region of our Galaxy. The center of our Galaxy hosts a supermassive black hole and the densest reservoir of molecular gas in the Galaxy. However, the best measurements to date suggest that this region seems to be breaking star formation laws and under-producing stars by about an order of magnitude. Is there a population of newly formed stars missed by previous observations that explains this discrepancy? Can we explain the dearth of star formation by high turbulence or magnetic fields? The student will collaborate with our Legacy Survey Team working to observe the center of our Galaxy at high resolution and long wavelengths using the Submillimeter Array. Observations from years 1 and 2 of the survey are complete, and the student will work with fully calibrated and reduced data from the survey to investigate the properties and star forming activity of clouds in our Galactic Center. In particular, the student will work with 3-D visualization tools to identify star-forming regions in 3-D. This is a relatively unexplored region of the Galaxy, with many mysteries to solve and discoveries to uncover. Understanding how stars form (or why they don't) in such an extreme environment is key to building a global model for the fundamental process of turning gas into stars.