Session E2: Poster Session I and Welcome Reception (5:45 - 7:15pm)

The shape of the $^{66}$Ga$\rightarrow ^{66}$Zn ground state beta decay spectrum

The ground state branch of the beta decay of $^{66}$Ga is a $0^+\rightarrow0^+$ transition with a relatively high {\it ft} value. Because of this large {\it ft}, the shape of the beta spectrum of this branch has been of interest historically for investigating higher order contributions to the decay. Previous measurements of the spectrum shape indicate that there are significant non-statistical components, but disagree on their sign and magnitude. As a test of the new Wisconsin iron-free superconducting beta spectrometer, we have made a precise measurement of the shape of the ground state branch of the $^{66}$Ga beta spectrum. We obtain a shape that is in better agreement with a statistical shape than are previous measurements.   

Isobaric analog states in odd-odd nuclei

We calculate the excitation energies of Isobaric Analog states in selected odd-odd nuclei. We use the formula for e.g. $^{96}$Ag E{*}(J=0$^{+}T=2)$= BE($^{96}$Ag) - BE( $^{96}$Pd) +V$_{C}$ where V$_{C}$=E$_{1}$ Z / A$^{(1/3)}$ + E$_{2}$ ; E$_{1}$ =1.441 MeV ; E$_{2}$ =-1.06 MeV. We list the following in MeV. ( $\Delta(BE),$V$_{C},$E{*}(calc), E{*}(single j),E{*} (multij shell model), Experiment) $^{44}$Sc (4.435, 7.308, 2.873, 3.047, 3.418, 2.779) $^{46}$Sc (2.160, 7.148, 5.024 , 4.949, 5.250, 5.022 ) $^{52}$Mn (5..494, 8.399, 2.905, 2.774, 2.731, 2.926) $^{60}$Cu ( 6.910, 9.430, 2.520, 2.235, 2.726 2.536 ) $^{94}$Rh (10.386, 13.043, 2.657, 1.990 , 3.266,.........) $^{96}$Ag (12.342, 13.574, 1.142, 0.900, 1.9172,........) The experimental energies of the isobaric analog states are known for the lighter nuclei but not for $^{94}$Rh or $^{96}$Ag. If we use the semi-empirical mass formula of Wapstra (2003) one gets the excitation energy in $^{96}$Ag to be 0.367 MeV.   

Selective photo-activation analysis with laser-driven x-rays

We discuss a technique for the identification of nuclear isotopes by \textit{selective} photo-activation analysis. A narrow divergence beam of high-energy photons is produced when a laser driven electron beam Compton backscatters off a counter-propagating high-intensity laser pulse. The x-rays from this compact laser-driven synchrotron light source are MeV energy, narrow-bandwidth, tunable, polarized, and bright (10$^{\mathrm{8}}$ photons s$^{\mathrm{-1}})$. Such characteristics make these x-rays well-suited for nuclear interrogation by means of triggering ($\gamma $,f) and ($\gamma $,xn) reactions. The narrow bandwidth of the x-ray light can be exploited to selectively activate nuclei with isotopic sensitivity, without causing unwanted background from collateral activation. Additionally, the polarized nature of the x-rays can be used to study anisotropy of neutron emission, for precise identification of isotopes. Activation by laser-driven synchrotron x-rays will be compared with activation by bremsstrahlung.   

Meson condensation analogs in ultracold atomic and molecular dipolar gases

We show how an analog of meson condensation in dense nuclear matter can be realized in an ultracold gas of fermionic atoms, or molecules, with large magnetic dipole moments. We construct an antiferrrosmectic-C phase that at high densities has lower energy than the Fermi gas or ferronematic phases. The antiferrrosmectic-C phase is a one-dimensional periodic structure in which the fermions localize in layers with their pseudospin direction aligned parallel to the layers, and staggered layer by layer.   

Three body Schr\"odinger equation for the Kratzer pair interaction

Two dimensional solution of the three body Schr\"{o}dinger equation for the Kratzer potential with and without the presence of a constant harmonic confinement is investigated within the using the hyperspherical functions method. For strong confinement the energy eigenvalues are analytically obtained. However, in the presence of a confinement, the energy eigenvalues are calculated numerically using the same method. The results obtained by using different strength of confinement and potential parameters are compared with the results of the absence of the trap ($\omega = 0$). Effect of the confinement on the energy eigenvalues of the Kratzer potential is precisely presented.   

Few-body system of charged fermions in a strong magnetic field

We consider a few-body system of interacting charged fermions in a strong magnetic field. We assume that the charged fermions interact via a Coulomb interaction potential. Additionally, there is a one-particle confining potential term that is superimposed to the two-particle interaction potential. We find out that in the limit of a high magnetic field the behavior of this system resembles that of strongly correlated electronic systems in the quantum Hall regime. Numerical results obtained via diagonalization procedures indicate that the few-body system energy spectrum is quasi-degenerate for a one-particle confining potential resembling a parabolic one.   

Strongly interacting fermions in optical lattices: from few to many particles

We present a general procedure to derive a many-body lattice model for two-component fermions interacting through a Feshbach resonance which is valid for arbitrary scattering length and resonance width. The bare Bloch bands arising from the relevant low-energy scattering channels in free space are strongly coupled for typical broad resonances, and so are an inappropriate basis for describing strongly correlated lattice Fermions. Instead of employing these bare bands, we solve a carefully chosen interacting two-body problem in the lattice and use the two-body eigenstates as an effective closed channel in a many-body resonance model. The use of the full lattice solution for the few-body problem as opposed to a separable approximation such as the harmonic oscillator potential leads not only to significant quantitative differences in parameter values, but also qualitative differences such as tunneling along non-principal axes. Various issues of the two-body lattice problem, such as the renormalization of ultraviolet divergences and the extrapolation to an infinite number of Bloch bands, are addressed.   

Superluminal Particle Hypothesis

Based on Einstein-Podolsky-Rosen Paradox (1935), on a paper by Bohm (1951) and on Bell's Inequalities (1964) we have emitted a hypothesis (1972) that there is no speed barrier in the universe and one can construct any speed smaller or greater than the speed of light. The reason is the following: \begin{itemize} \item suppose a certain physical process produces a pair of entangled particles A and B (having opposite or complementary characteristics), which fly off into space in the opposite direction and, when they are billions of miles apart, one measures particle A; because B is the opposite, the act of measuring A instantaneously tells B what to be; therefore those instructions would somehow have to traveled between A and B faster than the speed of light; hence, one can extend the Einstein-Podolsky-Rosen paradox and Bell's inequalities and assert that the light speed is not a speed barrier in the universe; \item more, one can construct any speed, even greater than the speed of light (c), by measuring particle A at various time intervals; \item also, the information from particles A and B is transmitted instantaneously (thus, there is no speed barrier in the universe). \end{itemize}   

Ratios of hadronic continuum cross sections to deuterium

A recent paper used per-nucleon ratios of continuum electron scattering cross sections from complex nuclei to those for deuterium to examine the role of correlations within those complex nuclei [N. Fomin et al., Phys. Rev. Lett. 108, 092502 (2012)]. These ratios were plotted in terms of the Bjorken x variable at momentum transfers suited to sense short range correlations, Q$^{2}$=2.7 (Gev/c)$^{2}$. Similar ratios for hadron scattering and charge exchange have been created, at much lower Q$^{2}$=0.24 (GeV/c)$^{2}$, using the same idea to examine longer range correlations with a wide range of reactions. The strong interaction limits access to all nucleons, so cross sections for complex nuclei are divided by effective numbers of nucleons struck once and only once. At fixed momentum transfer smooth patterns in x for these ratios are found, much the same for all nuclei. Near x=1 the hadronic and electron ratios agree. The ratios for scattering approach the trends noted by electron scattering as the momentum transfer increases, while those for isovector charge exchange do not. Two cases of the same beam used for both scattering and charge exchange allow a direct comparison for an isospin view of correlations using this ratio method.   

Astrobites: The Astro-ph Reader's Digest For Undergraduates

Astrobites (http://astrobites.com) is a daily blog aimed primarily at undergraduates interested in astrophysical research and written by a team of graduate students located at institutions around the world. Nearly every day we present a journal article recently posted to astro-ph in a brief format that is accessible to anyone with a general background in the physical sciences. In addition to summarizing new work, Astrobites provides valuable context for readers not yet familiar with the some of the background concepts and jargon present in the astrophysical literature. Special posts offer career guidance for undergraduates (e.g. applying for an NSF graduate fellowship) and describe personal experiences (e.g. attending an astronomy summer school). The readership of astrobites has grown dramatically since our founding in fall of 2010, with individuals now accessing the site from 104 countries worldwide. We will discuss the Astrobites format, recent readership statistics, and future planned initiatives.   

Astronomy Education using the Web and a Computer Algebra System

The combination of a web server and a Computer Algebra System to provide students the ability to explore and investigate astronomical concepts presented in a class can help student understanding. This combination of technologies provides a framework to extend the classroom experience with independent student exploration. In this presentation we report on the developmen of this web based material and some initial results of students making use of the computational tools using webMathematica$^{TM}$. The material developed allow the student toanalyze and investigate a variety of astronomical phenomena, including topics such as the Runge-Lenz vector, descriptions of the orbits of some of the exo-planets, Bode' law and other topics related to celestial mechanics. The server based Computer Algebra System system allows for computations without installing software on the student's computer but provides a powerful environment to explore the various concepts. The current system is installed at North Carolina A\&T State University and has been used in several undergraduate classes.   

Case studies approach for an undergraduate astrobiology course

Case studies is a well known and widely used method in law schools, medical schools, and business schools, but relatively little used in physics or astronomy courses. We developed an astrobiology course based strongly on the case studies approach, and after teaching it first at the University of Alabama in Huntsville, we have adapted it and are now teaching it at Alabama A\&M University, a HBCU. The case studies approach uses several well tested and successful teaching methods - including group work, peer instruction, current interest topics, just-in-time teaching, \&c. We have found that certain styles of cases are more popular among students than other styles, and will revise our cases to reflect such student preferences. We chose astrobiology -- an inherently multidisciplinary field -- because of the popularity of the subject matter, its frequent appearance in the popular media (news stories about searches for life in the universe, the discovery of Earth-like exoplanets, etc, in addition to SciFi movies and novels), and the rapid current progress in the field. In this talk we review briefly the case studies method, the styles of cases used in our astrobiology course, and student response to the course as found in our assessment analysis.   

Computational Simulation of MuSun Electronics Response

We have developed a computer program to simulate time projection chamber signals and the subsequent response of the amplifier chain (preamplifier, shaping amplifier, and baseline restorer) used in the MuSun experiment. A SPICE simulation of the amplifier chain was tuned until it agreed with the response to test pulses recorded with an oscilloscope in the laboratory, and the output of the SPICE simulation was then incorporated into the program. The noise model for the simulated output was also improved. Using the AbsRand library, the noise was modeled with a $1/f^{\alpha}$ correlation, based on the noise power spectral density for blank waveforms that were collected in a previous run of the experiment. Additionally, a feature was added to simulate the wire chamber used to detect the position of the muon upon entering, and the speed of the program was improved greatly, making it viable for use in generating significant datasets.   

Evaluation of Associated Laguerre Polynomials in Neutrino Induced Pair Creation

Spherically symmetrical models for type II supernovae are attractive due to their relative simplicity, but most fail to produce an actual explosion of the star. One reason may be the inherent anisotropy of the star, but another may be missing sources of energy. A possible energy source could come from the decay of a neutrino into an electron-positron pair while subject to the very large magnetic fields in supernovae. Calculations of the rate of pair production at these large magnetic fields require that we consider electrons and positrons in highly excited energy states, called Landau Levels. At large Landau levels, however, direct computation becomes challenging and prone to error. In this poster I will present how errors arise in direct computation and how I implemented a fourth-order Runge-Kutta scheme that was successful in limiting error without significant increases in computational time.   

A measurement of the K-shell decays in the CoGeNT public dataset

From December 2009 to March 2011 the CoGeNT experiment recorded interactions in their detector with the goal of either detecting dark matter particles or setting stringent limits on the mass and cross-section of these particles, assuming various WIMP (Weakling Interacting Massive Particles) models. The collaboration has made public this datase which contains the energies and time stamp of these interactions. The sensitivity of any dark matter searches will be limited by both statistics and an understanding of the backgrounds coming form naturally occuring radioavtive processes. The energy range where the dark matter should manifest shows a significant background from L-shell processes. This analysis extracts the number of K-shell decays and uses this information to extrapolate down to the lower energy L-shell decays. These measurements will be used in other analyses to gain the greatest sensitivity to possible WIMP interactions in the CoGeNT detector.   

Statistical Data Analysis for the Qweak Experiment

The Qweak experiment utilizes the concept of parity violation in weak interactions to ascertain the weak charge of the proton. Due to parity violation, electron-proton scattering results in an asymmetry of the electron scattering rate which can be discerned from detectors as the helicity of the beam is toggled. This asymmetry allows for the calculation of the weak charge of the proton, which then can be used to establish the value of the weak mixing angle. The weak mixing, or Weinberg, angle is a parameter of the Standard Model, thus any deviation from its predicted value would imply the existence of physics beyond the Standard Model. For this experiment, detector yields and beam parameter values were collected for every helicity state of the beam and from these recorded values asymmetries are calculated. After 2200 hours of data collection taken at the Thomas Jefferson Lab National Accelerator Facility, analysis of the collected data is underway. The data must be scrutinized to assure that it all belongs to the same statistical population. Properties such as the mean and standard deviation were calculated for different subsets of data in order to characterize their sample population. The results from the individual subsets were then compared.   

Organization and Analysis of Data from the Qweak Experiment

The Qweak experiment, which was conducted at the Thomas Jefferson National Accelerator Facility in a collaboration consisting of over twenty institutions, measured the small parity violating asymmetry occurring in elastic e-p scattering at low four-momentum transfer. This asymmetry will be used to calculate a precise value for the proton's weak charge. The Standard Model firmly predicts this weak charge based on the running of the weak mixing angle from the Z0 pole (where it is anchored by precise measurements) down to low energies. Through testing this prediction the Qweak experiment hopes to either constrain or reveal possible new physics beyond the Standard Model. Because of the small size of the predicted asymmetry and the precise nature of the measurement, over 2000 hours of data were taken. In order to help organize and store this data, a database has been implemented containing averages over sets of this data. It must be organized in such a way as to allow the quick and easy retrieval of data by collaborators with minimal knowledge of the database language. Tools for aggregating and expanding parts of this database as well as data analysis will be discussed.   

Monte Carlo Studies of the Hall C Compton Polarimeter

By measuring the scattering asymmetry observed between helicity states in polarized Compton scattering, the Hall C Compton polarimeter at Jefferson National Laboratory gives a precision measurement of the electron beam polarization, a requirement for most parity violation experiments. After updating a Monte Carlo simulation of the Compton polarimeter electron detector and adapting the corresponding analysis scripts, tests were performed to better understand the processes that influence the polarization measurement, assess the validity of the current analysis methods, and gauge the magnitude of various systematic sensitivities. The effects of processes such as secondary particle emission and trigger strictness are now understood more clearly, leading to better analysis methods. Additionally, several basic systematic sensitivities have been quantified, the largest to date estimated at $+$/-0.55 percent polarization. Once all the uncertainties associated with the Compton polarimeter have been determined, an overall systematic error can be assigned to the beam polarization measurement.   

Integration of the ATLAS FE-I4 Pixel Chip in the Mini Time Projection Chamber

This project deals with development of readout for a Time Projection Chamber (TPC) prototype. This is a type of detector proposed for direct detection of dark matter (WIMPS) with direction information. The TPC is a gaseous charged particle tracking detector composed of a field cage and a gas avalanche detector. The latter is made of two Gas Electron Multipliers in series, illuminating a pixel readout integrated circuit, which measures the distribution in position and time of the output charge. We are testing the TPC prototype, filled with ArCO2 gas, using a Fe-55 x-ray source and cosmic rays. The present prototype uses an FE-I3 chip for readout. This chip was developed about 10 years ago and is presently in use within the ATLAS pixel detector at the LHC. The aim of this work is to upgrade the TPC prototype to use an FE-I4 chip. The FE-I4 has an active area of 336 mm$^2$ and 26880 pixels, over nine times the number of pixels in the FE-I3 chip, and an active area about six times as much. The FE-I4 chip represents the state of the art of pixel detector readout, and is presently being used to build an upgrade of the ATLAS pixel detector.   

Towards Implementing Multi-Pixel Photon Counters as Light Detectors for Cosmic Rays

There has been tremendous effort in recent years to implement multi-pixel photon counters (MPPC) in diverse areas of particle physics and positron emission tomography. The MPPC detectors possess certain favorable properties such as fast response time, high sensitivity to weak light signals, compact size, low operating voltage, and lower cost compared to photomultiplier tubes. However, constructing a working MPPC detector assembly is not a unique process; there are various working setups. In this poster, we present our particular experimental setup for a working MPPC detector assembly. In particular, we describe our efforts to implement the MPPC as a readout detector to be coupled to wavelength shifting fibers that are implanted within plastic scintillators for the measurement of cosmic rays.   

Direct Numerical Simulations of Phytoplankton Blooms

Motivated by observations of phytoplankton blooms in the North Atlantic obtained through satellite imaging, and by the recent developments with objective extractions of flow topologies using Lagrangian Coherent Structures, we studied the Fisher-Kolmogorov equations inside a double-gyre system. We quantified the variabilities in biochemical reaction processes based on a natural coordinate system extracted from the Lagrangian topologies and examined how the initial placement of a biomass in this coordinate system correlated to its growth rate. The Lagrangian topologies are extracted as the extrema of the Finite-Time Lyapunov Exponent (FTLE) field for the flow, and the natural coordinate system used is based on the extracted invariant barriers. We found the dependence of reaction rates on the hyperbolic finite time invariant manifolds highlighting the largest stretching of scalars as well as the reaction rates in the transversal direction from eddy centers to their edges. It was observed that the biological reaction processes are heavily modulated by Coherent Structures in the flow. With initial placement in repelling structures, the biological species is helped to spread out much faster, hence allowing biochemical reactions to take place more quickly. With initial placement in attracting structures, the biological species is brought to be highly concentrated, hence suppressing the overall growth of the biomass.   

Binding and Irradition Study of the Porphyrin-Protein Complex TSPP-HSA

Porphyrins are a class of organic molecules that have found numerous applications in biological physics, such as, for example, photodynamic therapy in the treatment of malignant tumors and serving as fluorescent tags for proteins. In this study, we focus on the porphyryn TSPP and its role as a photoactive ligand to the protein HSA (Human Serum Albumin), capable of mediating conformational changes to the structure of HSA via irradiation. The effect of irradiation on the conformation and binding behavior of HSA in buffer solution at physiological pH will be deduced from a combination of spectroscopy tools including absorption, fluorescence, circular dichroism, and fluorescence lifetime decay spectroscopy. Additionally, computational modeling will be employed to complement experimental data. This work was supported through the grant TWD MARC GM07717.   

Lagrange Meshes in Nuclear Physics

We examine different methods of solving the Schr\"{o}dinger equation for two and three-body systems. We begin by constructing variational wave functions, as expansions in a basis of orthogonal polynomials. This method has been found to give accurate results, given a sufficiently large basis. However, computationally this can become very cumbersome, and therefore a Lagrange-mesh calculation is used, leading to a simple calculation of both potential and kinetic matrix elements that is both computationally efficient and results in little to no loss in accuracy. This method has been applied to several problems with well-known analytical solutions, and has given excellent results. We demonstrate the effectiveness of this method in analyzing the structure of light nuclei.   

Microcontact Printing on Gold Nanoparticles with Scanning Probe Assisted Lithographic Methods

We utilize Scanning Probe Assisted Lithographic methods with microcontact printing to fabricate directed assembly of gold nanoparticles. Assembly was achieved either directly or via pre-fabricated templates. The templates were fabricated with weak polyelectrolytes using the mentioned methods. Subsequently, these charged features were utilized in pre-programmed assembly of the nanoparticles. This fabrication strategy can be useful in the construction of novel structures and materials.   

Synoptic Displays for HBESL and the Laser Lab System

This project aimed to produce synoptic displays for two experiments: HBESL, the High Brightness Electron Source Laboratory and NML Laser experiment in order to assist the control of these facilities in the accelerator control network of Fermilab. Both displays were successfully produced and added on the ACNET (Accelerator Control Network) page. Synoptic is a system for graphical representation of real-time data in the accelerator control system of Fermilab. It creates diagrams representing a certain machine or process along with actual reading from the control system indicating its current state as well as supporting the ability to set data back from the control system. In this research, I learned how to use this software, and was able to use it in order to build these two synoptic displays for these two experiments: HBESL, and the laser lab. Both displays for HBESL and the laser experiment were successfully produced and added on the ACNET console under the NML page. Having these displays allow both users and scientists to be able to constantly control their experiments anywhere at any time. Being able to read out and set experimental parameters help users to protect the efficiency of experiments as well as avoiding extreme inaccuracy and inadequate conditions of experiments.   

Comparison of Multi Disk Exponential Gas Distribution vs. Single Disk

In fitting galactic rotation curves to data, most standard theories make use of a single exponential disk approximation of the gas distribution to account for the HI synthesis data observed at various radio telescope facilities. We take a sample of surface brightness profiles from The HI Nearby Galaxy Survey (THINGS), and apply both single disk exponentials and Multi-Disk exponentials, and use these various models to see how the modelling procedure changes the Newtonian prediction of the mass of the galaxy. Since the missing mass problem has not been fully explained in large spiral galaxies, different modelling procedures could account for some of the missing matter.   

Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP) Maps of the Permanently Shaded Regions (PSR) at the Lunar Poles

The Lyman Alpha Mapping Project (LAMP) instrument on-board LRO is a UV spectrograph covering the spectral range of 57-196 nm. We present Lyman-alpha and far-UV albedo maps of the north and south poles. These maps indicate that the coldest, permanently shadowed regions (PSR) in deep polar craters have significantly lower Lyman-alpha albedo than the surrounding regions, which is best explained by a high surface porosity there - possibly related to the accumulation of volatile frosts.   

A Model of Interacting Dark Energy and the Cosmic Coincidence Problem

We will study the behavior of different parts of the cosmic inventory in the presence of interaction between the dark energy and dark matter. Interacting dark energy models have been used primarily to resolve the cosmic coincidence problem. These models still suffer from some stability issues and the degeneracy has to be addressed. However, they can give us a better understanding of the nature of dark energy. In this work we will study the behavior of density parameters for dark energy and dark matter. An interaction will be introduced and the differential equations will be solved numerically. After observing the behavior of the density parameters, we will compare the results of the model with observed data collected by WMAP team. We will also explore the possibility of using our model to describe the history of universe.   

Modeling the Emission from Turbulent Relativistic Jets in Active Galactic Nuclei

Active galactic nuclei (AGN) are characterized by variable emission across all bands; for radio-loud AGN this is mostly synchrotron radiation from relativistic jets of turbulent plasma. We present a numerical model developed to calculate the theoretical observed fluxes of such jets and plot light curves that allow us to analyze the variations over time. We model the jet to contain a Kolmogorov spectrum of turbulent eddies, with varying sizes and velocities. The observed flux of each eddy depends upon its variable Doppler boosting factor, a function of the relativistic sum of the individual eddy and bulk jet velocities, as well as our viewing angle to the jet. The total observed flux is found by integrating the radiation from the eddies over the turbulent spectrum. We examine theoretical light curves for a range of viewing angles, bulk jet velocities, and maximum turbulent velocities. The flux variations produced in the simulations for sensible values of the parameters tested are consistent with the types of variations observed in AGN systems. Structure functions and power spectral densities of these theoretical light curves were computed and are compared with those of observed light curves, including those of radio-loud AGN measured with the Kepler satellite.   

The Outbursts of the Cataclysmic Variable V425 Cassiopeiae

We report time-resolved photometry of the cataclysmic variable V425 Cassiopeiae, taken over several weeks in 2010, 2011, and 2012 at Fresno State's station at Sierra Remote Observatories. We measure a long-term period of 4.24 $\pm$ 0.71 days and a 1.0 magnitude amplitude. This is separate from the orbital period of 0.1496 days (Shafter 1983). Our period value is in direct contrast with a period measured by Kato et al. (2001) of 2.65 days for the same system. As a result of this long-term variability, Kato et al. proposed that V425 Cas is a VY Scl-type system, which is characterized by periods of high mass transfer rate and periods of very low mass transfer rates. We argue that, based on our extended observations, V425 Cas is instead a Z Cam-type system, characterized by standstills, between dwarf nova outbursts that recur rapidly. Observations from Kato et al. (2001) are included for comparison. Further evidence of near-infrared magnitudes of V425 Cas from the 2MASS survey and its absolute magnitudes at outburst maximum, standstill, and minimum are included to support our argument.   

Self-Consistent Simulations of Accretion-Induced Collapse of White Dwarfs

Accreting white dwarfs and white dwarf mergers are commonly thought to end in thermonuclear explosions that produce Type Ia supernovae (SNe Ia). However, there is an alternative outcome for these systems that has not been theoretically explored as thoroughly, nor has it been securely identified observationally. Some white dwarfs, rather than exploding, should undergo electron capture and collapse to neutron stars. This accretion-induced collapse (AIC) scenario is expected to be intrinsically rare compared to SNe Ia, and past studies indicate that the associated optical transient would be faint and short-lived, near the detection limits of current surveys. However, until now there have not been self-consistent numerical studies of AIC that examine the explosion dynamics, subsequent evolution, and all resulting observables. We use GR1D, a one-dimensional general-relativistic hydrodynamics code, to follow AIC through collapse, core bounce, explosion, and shock breakout and to present new results on its neutrino signature and nucleosynthetic yields. This study is preliminary to the goal of developing fully self-consistent three-dimensional models that will yield predictions for electromagnetic, neutrino, and gravitational-wave signals form AIC events.   

Progress in the Study of ALFALFA Galaxy Groups

The Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project is a collaborative undertaking of faculty and students at 11 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey. The survey covers 7,000 square degrees and is expected to include more than 30,000 extragalactic sources when completed. Here we present analysis of HI spectra taken at the National Astronomy and Ionosphere Center and report on progress made with developing analysis software tools as part of the UAT study. These tools will be implemented with follow up observations of targeted sources generated from the original blind survey. This work has been supported by NSF grants AST-0724918, AST-0725267 and AST-0725380.