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Physics and Astronomy

Research Presentation Video

Watch Claire Dickey '14 discuss her research project.

KAPAO PRIME: III Telescope Integration and First Light Imaging

Dalton Bolger (2014); Student Collaborator(s): Jonathan Wong (2015); Fernando Ortega (2015); Christian Guerrero (2016 HMC); Katie Badham (2013 Sonoma State University); Additional Collaborator(s): Scott Severson (Sonoma State College); Mentor(s): Phil Choi

Abstract: We present preliminary on-sky results from the first-light observations of the Pomona College Adaptive Optics (AO) instrument, KAPAO Prime. KAPAO Prime underwent assembly and lab calibration throughout the majority of the summer. The summer concluded with installation onto the Table Mountain Observatory (TMO) 1-meter telescope during a three-night engineering run which began on July 30, 2013. We present details of the instrument mounting and alignment; characterization of atmospheric observing conditions; initial low-order, tip-tilt, corrections; and the final high-order, on-sky loop closure using reference stars, Beta Pegasi and Alpha Lyrae. On-sky results are compared to in-lab performance tests as well as discussion of further hardware development as part of an upcoming senior thesis.
Funding Provided by: National Science Foundation #AST-0960343; Sherman Fairchild Foundation (JW, FO)

The World of Extragalactic 33GHz radio emission: Star Formation, Active Galactic Nuclei, Anomalous Dust and more

Dillon Dong (2015); Additional Collaborator(s): Eric Murphy (Caltech -IPAC); Mentor(s): Phil Choi

Abstract: One of the central questions of astronomy involves explaining how the universe became the diverse space we observe around us today. Charting the history of star formation by observing star forming regions in other galaxies at varying distances (and therefore varying times in the universe's life) helps fill in that puzzle. Our project, the Star Formation in Radio Survey uses the Jansky Very Large Array to target 118 galaxy nuclei and extranuclear star-forming regions in 56 nearby (d < 30Mpc) galaxies, each of which have infrared spectral mappings from the SINGS and KINGFISH surveys. These new 33GHz data probe free-free emission, providing a sensitive, extinction-unbiased measure of the current star formation activity in each complex. Thus, these data can accurately calibrate other empirical star formation rate diagnostics that are easier to measure for high redshift studies. Our initial investigation includes an extranuclear region in NGC 6946 that has shown a large excess of radiation at 33GHz relative to what is expected given lower frequency radio data. This has been identified as the first extragalactic detection of “anomalous dust" emission, likely from electric dipole radiation from rapidly rotating ultrasmall (a < 10^-6 cm) dust grains. This resolved ~2'' source is detected at >70σ at 33GHz, but has no detected counterpart at 8μm. We are also preparing a radio spectral index map of the massive (~13 Msun/yr) molecular outflow from an AGN with no apparent partner: NGC1266. This map will help model the gas's diffusion and probe its underlying physics.
Funding Provided by: Paul K. Richter and Evelyn E. Cook Richter Memorial Fund

High-Mass Star Formation in NGC6822: The Ultraviolet as a Tool for Identification

Anne Hedlund (2014); Additional Collaborator(s): Barry Madore (Carnegie Institute for Science); Mentor(s): Phil Choi

Abstract: One of the challenges involved in studying star formation rates is the inability to distinguish young, hot blue stars from generally older, cooler red stars based only on observations from the red part of their optical spectra. Since the blue part of the spectrum is difficult to obtain from ground, we will use the Galaxy Evolution Explorer (GALEX) space telescope to obtain UV data. We gathered photometric data from a GALEX mosaic of NGC6822 and matched around 1000 of theses sources with a ground-based, optical catalog, Massey. By matching GALEX data with Massey, we were able to create spectral energy distributions (SEDs) for the matched stars from the far ultraviolet to the near-infrared. We have begun examining the numerous ways to characterize the SED of an O and B star such as modeling O and B stars as blackbody sources and creating SEDs for stars of known spectral types from literature. In the future, we will be able to use the varying luminosities in the UV part of the spectrum of my cataloged SED’s to identify O and B stars and hence explore topics related to star formation by comparing H-alpha maps from TYPHOON and gas distributions with the spatial distributions of O and B stars that we find.
Funding Provided by: Kenneth T. and Eileen L. Norris Foundation; National Science Foundation #AST-0960343

Constraining the Low-Mass Luminosity Function

Claire Dickey (2014); Mentor(s): Philip Choi

Abstract: We present a novel technique for self-consistently constraining the full luminosity function of globular clusters by measuring the cumulative fraction of light from resolved stars as a function of the total integrated cluster light. Using HST WFPC2 observations of a sample of six metal-poor clusters in the Large Magellanic Clouds (NGC 1754, 1835, 1898, 1916, 2006, and 2019), we have resolved stars down to the main sequence turn-off. Color-magnitude diagrams for each cluster show well-developed horizontal branches, and the luminosity functions fit the expected power law slope of 0.3 along the red giant branch. Using the ratio of resolved to unresolved light, we then smoothly extrapolate the luminosity function below the (currently unresolved) main sequence turn-off. This technique allows for new and independent constraints on the initial mass function for globular clusters.
Funding Provided by: Paul K. Richter and Evelyn E. Cook Richter Memorial Fund; National Science Foundation #AST-0960343

KAPAO Prime: II Wavefront Sensing and Loop Performance Optimization

Fernando Ortega (2015); Student Collaborator(s): Jonathan Wong (2015); Dalton Bolger (2014); Christian Guerrero (2016 HMC); Katherine Badham (2013 Sonoma State University); Additional Collaborator(s): Scott Severson (Sonoma State University); Mentor(s): Philip Choi

Abstract: Adaptive Optics (AO) systems allow astronomers to counteract the light-distorting effects of the atmosphere, providing for a superior telescope image quality. A Wavefront Sensor (WFS) is essentially the eyes of an AO system, allowing the system to measure and correct the aberration of an incoming light beam in real time. KAPAO Prime, the AO system for use on Pomona College’s 1-meter telescope at the Table Mountain Observatory, uses a Shack-Hartmann style WFS. This type of WFS divides the wavefront into compartments and measures the compartments’ individual tilt in order to determine the total wavefront error. The system then corrects for the wavefront error using a deformable mirror. Careful alignment of the system’s WFS leg is essential for understanding and optimizing the performance of the AO feedback loop. Furthermore, with the use of various programs written in Interactive Data Language (IDL), we were better able to align KAPAO Prime’s WFS camera and visualize the telemetry of a working AO loop.
Funding Provided by: Sherman Fairchild Foundation (JW, FO); Paul K. Richter and Evelyn E. Cook Richter Memorial Fund (DB); National Science Foundation #AST¬0960343

KAPAO Prime I: Design and Assembly of an Adaptive Optics instrument

Jonathan Wong (2015); Student Collaborator(s): Dalton Bolger (2014); Fernando Ortega (2015); Christian Guerrero (2016 HMC); Katie Badham (2013 Sonoma State University); Additional Collaborator(s): Scott Severson (Sonoma State University); Mentor(s): Philip Choi

Abstract: KAPAO Prime is Pomona's permanent natural guide star Adaptive Optics instrument for the college's 1-meter telescope at Table Mountain Observatory (TMO). KAPAO Prime includes significant upgrades to improve the performance and robustness of the system compared to the prototype. Such upgrades include custom optics to improve image quality, dichroic optics instead of beam splitters for significantly better throughput, and a larger pickoff mirror to significantly widen the field of view. One of many processes this summer included aligning the static system up to the wavefront sensor (WFS) leg. The tolerances of specific optics while mounted to the telescope were also examined. KAPAO Prime was assembled and successfully operated both in a laboratory setting and on a live star during this summer. The system will be optimized and fully automated in the future.
Funding Provided by: Sherman Fairchild Foundation (JW, FO); Paul K. Richter and Evelyn E. Cook Richter Memorial Fund (DB); National Science Foundation #AST¬0960343

An Automated Photodiode Frequency Response Measurement System for LIGO

Alexander Cole (2015); Mentor(s): Eric Gustafson (Caltech)

Abstract: LIGO will detect gravitational waves using laser interferometers that will be quantum noise limited over most of the apparatus's operating frequency range. To build an interferometric gravitational wave detector that works at the limits set by quantum mechanics, one must ensure that the detector can be controlled and read out optically. In the LIGO interferometers, several photodiodes are used to sense various degrees of freedom and provide feedback signals so that the cavities are in optical resonance. In addition, the main interferometric gravitational wave signal is read out with a photodiode. It is thus necessary to treat the photodiode and its readout electronics as systems whose performances, including frequency response, can change over time and with changing operating conditions. This project’s purpose was to build an automatic frequency response measurement system for the interferometer’s photodiodes. We use a modulated diode laser coupled through a fiber optic distribution system to illuminate the photodiodes, and then automatically and quickly measure the frequency response of each photoreceiver using a network analyzer and an RF switch to select the photodiodes one after another. The experiment was carried out at Caltech on the LIGO 40m prototype interferometer and designed with Advanced LIGO scalability in mind.
Funding Provided by: National Science Foundation (Caltech)

Total Internal Reflection Microscopy of Lipid Bylayers on a Fused Silica Substrate

John Horne (2014); Mentor(s): Alfred Kwok

Abstract: Unavailable at press time.
Funding Provided by: Pomona College SURP

BOB YbF & RbF: Isotope Invariant Data Analysis

Zachary Glassman (2014); Additional Collaborator(s): Jens-Uwe Grabow (Leibnitz University, Hannover); Timothy Steimle (Arizona State University); Mentor(s): Richard Mawhorter

Abstract: Determining the electric dipole moment (eEDM, or “shape”) of the electron could unlock a path to physics beyond the standard model, which predicts a value less than 10-40 e•cm, while most other theories predict a much larger value. The current limiting measurement is ~10-27 e•cm, made by an Imperial College team on open shell molecule YbF. Observing the nuclear electric hyperfine structure (eQq) for YbF will help constrain the wave functions used to quantify the eEDM. There is also a very small but nonzero probability for electrons to be near and even inside the nucleus, resulting in a slight perturbation of the nuclear quadrupole moment Q for closed shell molecules like RbF, as well as in parity-violating (PV) shifts due to the relativistic electron-nucleus interaction in molecules like YbF and PbF. These include the larger spin-dependent anapole moment as well as the tiny spin-independent eEDM. We use Fourier transform microwave spectroscopy with sub-kHz resolution to explore these senistivities, and have also utilized isotope invariant data analysis techniques. This allows us to couple together data from different isotopes to determine more robust fit parameters and to predict spectra for unobserved molecules, as well as to see effects of the breakdown of the Born-Oppenheimer approximation, i.e. the complete separation of the nuclear and electronic wave functions. We have determined BOB values for several different diatomic molecules including KF, RbF and YbF.
Funding Provided by: Pomona College SURP; Sontag Facutly Fellowship

Efficiency and Durability of P3HT:PCBM Inverted Organic Photovoltaics

Madeline McGaughey (2016); Mentor(s): David Tanenbaum

Abstract: Organic photovoltaics (OPVs) have been an area of increasing interest in the scientific community due primarily to their ability to be manufactured under ambient conditions and significantly lower production cost (compared with conventional silicon-based photovoltaics). To become a commercially viable alternative, however, their stability and efficiency must be improved. Further, a replacement must be found for indium tin oxide (ITO), which serves as a transparent electrode, but which is both brittle and expensive. Inverted poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) photovoltaic cells were fabricated and characterized for efficiency and decay/stability. Two different variants of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were added in some cells as an electron hole conducting layer. It was observed that cells with the less conductive PEDOT:PSS layer yielded a lower initial power conversion efficiency (PCE) than cells with no PEDOT:PSS layer (average 0.28% versus 0.75%s), while cells with the more conductive PEDOT:PSS layer yielded a higher average initial PCE (0.85%). Several samples with the more conductive PEDOT:PSS layer were encapsulated under ambient conditions using a piece of indented glass sealed with a UV-cure epoxy. Though the short-circuit current, a key factor in overall PCE degradation, was stabilized, the average initial PCE was lower than in the unencapsulated cells (0.47%). Further, the overall PCE stability was not noticeably improved due to a more rapid decay in open-circuit voltage.
Funding Provided by: Pomona College SURP; National Science Foundation #DMR-1126080

An Assessment of Organic Solar Cell Performance

Charles Owens (2014); Mentor(s): David Tanenbaum

Abstract: The maximum power output and degradation of 20 organic solar cells were measured over five months in both an inside and outside environment. These organic cells are state of the art, and came from eight different international collaborators. The degradation of each cell was measured by observing the power conversion efficiency (PCE) and normalized conversion efficiency (NPCE) of each cell. Multiple programs were written using Microsoft Excel 2010 VBA in order to locate each cell’s daily maximum power value along with graphing the maximum power’s corresponding current vs. voltage (I-V) curve. Since 12 cells were used in both the indoor and outdoor setups, the performances of these cells were able to be compared and evaluated with one another. For the outdoor setup, IAPP cells experienced complete degradation within the first ten days of measurement; one Heliatek cell and two IMEC cells experienced a sudden drop in performance after the first thirty-five and fifty-five days of measurement, respectively; all other cells are currently still active and producing positive PCE values.
Funding Provided by: Rose Hills Foundation

Deposition of Ultra-Thin Semiconductor Nanocrystal Films for use in Novel Photovoltaics

Eric Puma (2014); Additional Collaborator(s): Nanditha Dissanayake (Brookhaven National Laboratory); Matthew Eisaman (Brookhaven National Laboratory); Mentor(s): David Tanenbaum

Abstract: Due to the effects of quantum confinement, semiconductor nanocrystals (SNC) exhibit interesting optoelectronic properties which make them a candidate for use in novel photovoltaic (PV) devices. We believe ultra-thin (i.e. few monolayer) SNC layers can uncover improved optoelectronic properties leading to higher PV efficiencies. We explore dip and drop coating methods to deposit ultra-thin layers of SNCs and characterize these films with atomic force microscopy (AFM) and optical microscopy. Drop coating produces densely packed multilayer films, but offers little thickness control. Alternatively, a custom-built dip coater produces sub-monolayer films with ~30% coverage in one dip, while multiple dips can be used to assemble films of controlled thickness. To understand SNC film performance within a photovoltaic device, we fabricate graphene/SNC/metal-oxide/metal prototype PVs with SNC films and test the optoelectronic behavior. The devices demonstrate photocurrent together with doping-induced charge transport properties in the graphene layer. In future research, these ultra-thin SNC films will be applied in more complex PVs, which we predict can demonstrate hot-carrier based charge extraction leading to higher efficiency PVs from the SNC for the first time.
Funding Provided by: U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists under the Summer Undergraduate Laboratory Internships Program; U.S. Department of Energy, Sustainable Energy Technologies Department

High-resolution spatial mapping of thin-film photovoltaic cells

Emily Yang (2014); Additional Collaborator(s): Ahsan Ashraf (Sustainable Energy Technologies Department, Brookhaven National Laboratory; Department of Physics and Astronomy, Stony Brook University); Matthew Eisaman (Sustainable Energy Technologies Department, Brookhaven National Laboratory; Department of Physics and Astronomy, Stony Brook University); Mentor(s): David Tanenbaum

Abstract: We have developed a high-resolution spatial mapping capability for thin-film photovoltaics (PV) that will lead to improved device performance and lower cost. While PV characteristics such as power conversion efficiency (η) and fill factor are generally extracted by illuminating an entire cell and measuring the current-voltage response, some parameters are often overlooked without further analysis. Using Python, we implemented a lumped circuit model to extract these parameters such as shunt conductance (G) and temperature-dependent performance metrics. Next, in a new approach to the Light-Beam-Induced Current (LBIC) technique, we used a supercontinuum laser to measure the spatial variation in current-voltage response and associated parameters like η and G with a spatial resolution of less than 10 μm. We applied our model to U.S. Photovoltaic Manufacturing Consortium thin-film CIGS (Cu(In1-x,Gax)Se2) solar cells to identify spatial nonuniformities that reduce cell performance, and to connect these to possible improvements in the manufacturing process.
Funding Provided by: U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships Program (SULI); U.S. Department of Energy, Sustainable Energy Technologies Department under contract DE-AC02¬98CH10886

No Longer Retro: A Six Independent Beam MOT

Benjamin Girodias (2015); Student Collaborator(s): Erika Carlson (2015); Mentor(s): Dwight Whitaker

Abstract: Although theoretically predicted almost 90 years ago, Bose-Einstein Condensates (BECs), a state of matter in which macroscopic clouds of ultra-cold atoms display quantum mechanical characteristics, have only been created in the lab since 1995. To produce these BECs, rubidium atoms are initially collected and cooled in a Magneto-Optical Trap (MOT) and then further compressed before being transferred into a shallower magnetic or electric dipole trap where evaporative cooling allows the atoms to form a BEC. This compression process is not well understood, and different groups have had success with wildly different methods. In order to study this compression process as well as improve our existing experimental set-up, we replaced our MOT's three collimated retro-reflected laser beams with six independent diverging beams. By using this diverging beam design, we achieved a larger trapping volume than that was possible with collimated beams, yielding larger numbers of captured atoms despite the loss in beam intensity. Furthermore, this design will give us more degrees of freedom, such as adjustable intensity of each individual beam, to investigate the different compression methods used to form BECs. Initial efforts suggest that this six diverging-beam method would produce larger MOTs and has more parameters to examine, but the set-up has yet to be optimized.
Funding Provided by: Sherman Fairchild Foundation (BG); Paul K. Richter and Evelyn E. Cook Richter Memorial Fund (EC)

A More Efficient Polarimeter Design for the TMO Instrument Package

Chanud Yasanayake (2016); Student Collaborator(s): Vicente Robles (2016); Mentor(s): Alma Zook

Abstract: Pomona College's one-meter telescope is equipped with a CCD camera, Johnson BVRI and Sloan g'r'l' filters, and a Savart-plate polarimeter with a total instrument-package weight of about 100 pounds. A majority of the summer was spent designing and constructing a replacement for this box to provide a more efficient polarimeter as well as to reduce weight to allow adding a newly introduced adaptive optics setup. This replacement is still being built and will hopefully be permanently mounted on the telescope before the 2014 spring semester. In addition, a filter mounting platform and new filter wheel cover were designed to accommodate two Wollaston prisms added to the upper filter wheel. Both the filter mounting platform and the new cover were made on Pomona's 3D printer.
Funding Provided by: Pomona College SURP

Research at Pomona