Astrophysics and Astronomy Commons^™

Physical Science Day: Design, Implementation, And Assessment, Liang Zeng, Mark A. Cunningham, Steven C. Tidrow, K. Christopher Smith, Jerry Contreras

Physics & Astronomy Faculty Publications

Physical Science Day at The University of Texas–Pan American (UTPA), in collaboration with the Edinburg Consolidated Independent School District, has been designed, developed and implemented to address an identified fundamental shortcoming in our educational process within this primarily (90+%) Hispanic serving border region. Physical Science Day overcomes the lack of knowledge about what physics is by raising youth awareness of physics as the foundation of science, engineering and technology disciplines, through activities including hands-on laboratory experiments, career orientation, and higher educational student and graduated student testimonials. Thus, Physical Science Day encourages, attracts, and enables more Hispanic youth towards science, technology …

Book Review: The International Atlas Of Mars Exploration: From Spirit To Curiosity: V.2: 2004 To 2014, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of The International Atlas of Mars Exploration: from Spirit to Curiosity : V.2: 2004 to 2014 by Philip J. Stooke. 444p bibl index, 9781107030930 $145.00, 9781139344470 LC Call Number: 1000

The Bright End Of The Z~9 And Z~10 Uv Luminosity Functions Using All Five Candels Fields., R. J. Bouwens, P. A. Oesch, I. Labbe, G. D. Illingworth, G. G. Fazio, D. Coe, Benne W. Holwerda, R. Smit, M. Stefanon, P. G. Van Dokkum, M. Trenti, M. L. N. Ashby, J. S. Huang, L. Spitler, C. Straatman, L. Bradley, D. Magee

Faculty and Staff Scholarship

The deep, wide-area (∼800–900 arcmin2 ) near-infrared/WFC3/IR + Spitzer/IRAC observations over the CANDELS fields have been a remarkable resource for constraining the bright end of high-redshift UV luminosity functions. However, the lack of Hubble Space Telescope (HST) 1.05 μm observations over the CANDELS fields has made it difficult to identify z ∼ 9–10 sources robustly, since such data are needed to confirm the presence of an abrupt Lyman break at 1.2 μm. Here, we report on the successful identification of many such z ∼ 9–10 sources from a new HST program (z9-CANDELS) that targets the highest-probability z ∼ 9–10 galaxy …

Evolution Of Cosmic Filaments And Of Their Galaxy Population From Mhd Cosmological Simulations., C. Gheller, F. Vazza, M. Bruggen, M. Alpaslan, Benne W. Holwerda, A. M. Hopkins, J. Liske

Faculty and Staff Scholarship

Despite containing about a half of the total matter in the Universe, at most wavelengths the filamentary structure of the cosmic web is difficult to observe. In this work, we use large unigrid cosmological simulations to investigate how the geometrical, thermodynamical and magnetic properties of cosmological filaments vary with mass and redshift (z ≤ 1). We find that the average temperature, length, volume and magnetic field of filaments scales well with their total mass. This reflects the role of self-gravity in shaping their properties and enables statistical predictions of their observational properties based on their mass. We also focus on …

Galaxy And Mass Assembly (Gama) : M–Re Relations Of Z = 0 Bulges, Discs And Spheroids., Rebecca Lange, Amanda J. Moffett, Simon P. Driver, Aaron S. G. Robotham, Claudia Del P. Lagos, Lee S. Kelvin, Christopher Conselice, Berta Margalef-Bentabol, Mehmet Alpaslan, Ivan K. Baldry, Joss Bland-Hawthorn, Malcolm Bremer, Sarah Brough, Michelle Cluver, Matthew Colless, Luke J. M. Davies, Boris Haußler, Benne W. Holwerda, Andrew M. Hopkins, Prajwal R. Kafle, Rebecca Kennedy, Jochen Liske, Steven Phillipps, Cristina C. Popescu, Edward N. Taylor, Richard Tuffs, Eelco Van Kampen, Angus H. Wright

Faculty and Staff Scholarship

We perform automated bulge + disc decomposition on a sample of ∼7500 galaxies from the Galaxy And Mass Assembly (GAMA) survey in the redshift range of 0.002 < z < 0.06 using Structural Investigation of Galaxies via Model Analysis, a wrapper around GALFIT3. To achieve robust profile measurements, we use a novel approach of repeatedly fitting the galaxies, varying the input parameters to sample a large fraction of the input parameter space. Using this method, we reduce the catastrophic failure rate significantly and verify the confidence in the fit independently of χ2. Additionally, using the median of the final fitting values and the 16th and 84th percentile produces more realistic error estimates than those provided by GALFIT, which are known to be underestimated. We use the results of our decompositions to analyse the stellar mass – half-light radius relations of bulges, discs and spheroids. We further investigate the association of components with a parent disc or elliptical relation to provide definite z = 0 disc and spheroid M–Re relations. We conclude by comparing our local disc and spheroid M–Re to simulated data from EAGLE and high-redshift data from Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey-Ultra Deep Survey. We show the potential of using the M–Re relation to study galaxy evolution in both cases but caution that for a fair comparison, all data sets need to be processed and analysed in the same manner.

Infrared Polarimetry Of Mrk 231: Scattering Off Hot Dust Grains In The Central Core, E. Lopez-Rodriguez, C. Packham, T. J. Jones, R. Siebenmorgen, P. F. Roche, N. A. Levenson, A. Alonso-Herrero, E. Perlman, K. Ichikawa, C. Ramos Almeida, O. Gonzalez-Martin, R. Nikutta, M. Martinez-Paredez, D. Shenoy, M. S. Gordon, C. M. Telesco

Aerospace, Physics, and Space Science Faculty Publications

We present high-angular (0.17–0.35 arcsec) resolution imaging polarimetric observations of Mrk 231 in the 3.1 μm filter using MMT-Pol on the 6.5-m MMT, and in the 8.7, 10.3, and 11.6 μm filters using CanariCam on the 10.4-m Gran Telescopio CANARIAS. In combination with already published observations, we compile the 1–12 μm total and polarized nuclear spectral energy distribution (SED). The total flux SED in the central 400 pc is explained as the combination of (1) a hot (731 4 K) dusty structure, directly irradiated by the central engine, which is at 1.6 0.1 pc away and attributed to be in …

Comprehensive Mass Balance Isotope Schematics For Determining The Provenance Of The Moon Forming Impactor., John C. Wolbeck

Dissertations, Theses, and Capstone Projects

The goal of this research was to identify areas where deviations from the canonic Moon forming impact scenario (an impactor approximately 12% of the mass of the Earth merging with 100% accretion efficiency with a proto-Earth each of which has a differentiated homologous anatomy of 30% iron and 70% silicates) may greatly reduce the efficacy of the impact mass balance analytics used to determine the provenance of the impactor based on isotope data from terrestrial and lunar samples and physical data from high resolution SPH computer simulations.

Modeling the giant Moon forming impact is complicated by a lack of knowledge …

Fundamental Parameters Of The Lowest Mass Stars To The Highest Mass Planets, Joseph C. Filippazzo

Dissertations, Theses, and Capstone Projects

The physical and atmospheric properties of ultracool dwarfs are deeply entangled due to the degenerate effects of mass, age, metallicity, clouds and dust, activity, rotation, and possibly formation mechanism on their observed properties. Accurate fundamental parameters for a wide range of substellar objects are crucial to testing stellar and planetary formation theories. To determine these quantities, we construct flux-calibrated spectral energy distributions (SEDs) for 234 M, L, T, and Y dwarfs and calculate bolometric luminosity (L_bol), effective temperature (T_eff), mass, surface gravity, radius, spectral indexes, synthetic photometry, and bolometric corrections (BCs) for each object. We use …

"Blinded By The Lines: Mid-Ir Spectra Of Mira Variables Taken With Spitzer", Dana Baylis-Aguirre, Michelle J. Creech-Eakman, Donald G. Luttermoser, Tina Gueth

ETSU Faculty Works

We present preliminary analysis of mid-infrared spectra of M-type and C-type Mira variables. Due to the brightness of this sample, it is straightforward to monitor changes with phase in the infrared spectral features of these regular pulsators. We have spectra of 25 Mira variables, taken with phase, using the Spitzer Infrared Spectrograph (IRS) high-resolution module. Each star has multiple spectra obtained over a one-year period from 2008-09. This is a rich, unique data set due to multiple observations of each star and the high signal-to-noise ratio from quick exposure times to prevent saturation of the IRS instrument. This paper focuses …

Torsional Oscillations And Observed Rotational Period Variations In Early-Type Stars, Jiří Krtička, Zdeněk Mikulášek, Gregory W. Henry, Petr Kurfürst, Marian Karlický

Information Systems and Engineering Management Research Publications

Some chemically peculiar stars in the upper main sequence show rotational period variations of unknown origin. We propose that these variations are a consequence of the propagation of internal waves in magnetic rotating stars that lead to the torsional oscillations of the star. We simulate the magnetohydrodynamic waves and calculate resonant frequencies for two stars that show rotational variations: CU Vir and HD 37776. We provide updated analyses of rotational period variations in these stars and compare our results with numerical models. For CU Vir, the length of the observed rotational period cycle, | $\mathit {\Pi }=67.6(5)$ | yr, can …

The Baryon Cycle At High Redshifts: Effects Of Galactic Winds On Galaxy Evolution In Overdense And Average Regions, Raphael Sadoun, Isaac Shlosman, Jun-Hwan Choi, Emilio Romano-Díaz

Physics and Astronomy Faculty Publications

We employ high-resolution cosmological zoom-in simulations focusing on a high-sigma peak and an average cosmological field at z ~ 6–12 in order to investigate the influence of environment and baryonic feedback on galaxy evolution in the reionization epoch. Strong feedback, e.g., galactic winds, caused by elevated star formation rates (SFRs) is expected to play an important role in this evolution. We compare different outflow prescriptions: (i) constant wind velocity (CW), (ii) variable wind scaling with galaxy properties (VW), and (iii) no outflows (NW). The overdensity leads to accelerated evolution of dark matter and baryonic structures, absent from the "normal" region, …

Hubble Space Telescopeconstraints On The Winds And Astrospheres Of Red Giant Stars, Brian E. Wood, Hans-Reinhard Müller, Graham M. Harper

Dartmouth Scholarship

We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope, focusing on spectra of the Mg ii h and k lines near 2800 Å in order to study stellar chromospheric emission, winds, and astrospheric absorption. We focus on spectral types between K2 III and M5 III, a spectral type range with stars that are noncoronal, but possessing strong, chromospheric winds. We find a very tight relation between Mg ii surface flux and photospheric temperature, supporting the notion that all K2-M5 III stars are emitting at a basal flux level. Wind velocities (V …

On The Composition Of Young, Directly Imaged Giant Planets, Julianne I. Moses, Mark S. Marley, K. Zahnle, M. R. Line, Jonathan J. Fortney, T. S. Barman, Channon Visscher, Nikole K. Lewis, M. J. Wolff

Faculty Work Comprehensive List

The past decade has seen significant progress on the direct detection and characterization of young, self-luminous giant planets at wide orbital separations from their host stars. Some of these planets show evidence for disequilibrium processes like transport-induced quenching in their atmospheres; photochemistry may also be important, despite the large orbital distances. These disequilibrium chemical processes can alter the expected composition, spectral behavior, thermal structure, and cooling history of the planets, and can potentially confuse determinations of bulk elemental ratios, which provide important insights into planet-formation mechanisms. Using a thermo/photochemical kinetics and transport model, we investigate the extent to which disequilibrium …

Investigating The Impact Of Unsupervised Feature-Extraction From Multi-Wavelength Image Data For Photometric Classification Of Stars, Galaxies And Qsos, Annika Lindh

Dissertations

This thesis reviews the current state of photometric classification in Astronomy and identifies two main gaps: a dependence on handcrafted rules, and a lack of interpretability in the more successful classifiers. To address this, Deep Learning and Computer Vision were used to create a more interpretable model, using unsupervised training to reduce human bias.

The main contribution is the investigation into the impact of using unsupervised feature-extraction from multi-wavelength image data for the classification task. The feature-extraction is achieved by implementing an unsupervised Deep Belief Network to extract lower-dimensionality features from the multi-wavelength image data captured by the Sloan Digital …

Anisotropic Cubic Curvature Couplings, Quentin G. Bailey

Publications

To complement recent work on tests of spacetime symmetry in gravity, cubic curvature couplings are studied using an effective field theory description of spacetime-symmetry breaking. The associated mass-dimension-eight coefficients for Lorentz violation studied do not result in any linearized gravity modifications and instead are revealed in the first nonlinear terms in an expansion of spacetime around a flat background. We consider effects on gravitational radiation through the energy loss of a binary system and we study two-body orbital perturbations using the post-Newtonian metric. Some effects depend on the internal structure of the source and test bodies, thereby breaking the weak …

Gravitational Wave–Gauge Field Oscillations, R. R. Caldwell, C. Devulder, N. A. Maksimova

Dartmouth Scholarship

Gravitational waves propagating through a stationary gauge field transform into gauge field waves and back again. When multiple families of flavor-space locked gauge fields are present, the gravitational and gauge field waves exhibit novel dynamics. At high frequencies, the system behaves like coupled oscillators in which the gravitational wave is the central pacemaker. Due to energy conservation and exchange among the oscillators, the wave amplitudes lie on a multidimensional sphere, reminiscent of neutrino flavor oscillations. This phenomenon has implications for cosmological scenarios based on flavor-space locked gauge fields.

High-Velocity Bipolar Molecular Emission From An Agn Torus, Jack F. Gallimore, Moshe Elitzur, Robert Maiolino, Alessandro Marconi, Christopher P. O'Dea, Dieter Lutz, Stefi A. Baum, Robert Nikutta, C. M. V. Impellizzeri, Richard Davies, Amy E. Kimball, Eleonora Sani

Physics and Astronomy Faculty Publications

We have detected in ALMA observations CO J = 6 → 5 emission from the nucleus of the Seyfert galaxy NGC 1068. The low-velocity (up to ±70 km s⁻¹ relative to systemic) CO emission resolves into a 12 × 7 pc structure, roughly aligned with the nuclear radio source. Higher-velocity emission (up to ±400 km s⁻¹) is consistent with a bipolar outflow in a direction nearly perpendicular (≃80°) to the nuclear disk. The position–velocity diagram shows that in addition to the outflow, the velocity field may also contain rotation about the disk axis. These observations provide compelling …

Directly Comparing Gw150914 With Numerical Solutions Of Einstein's Equations For Binary Black Hole Coalescence, B. P. Abbott, K. Gill, B. Hughey, M. J. Szczepańczyk, M. Zanolin, Et Al.

Publications

We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic models, because for all simulations—including sources with two independent, precessing spins—we perform comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported by Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)] (at the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing simulations. Follow-up simulations performed …

Directly Comparing Gw150914 With Numerical Solutions Of Einstein's Equations For Binary Black Hole Coalescence, B. P. Abbott, R. Abbott, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Darkhan Tuyenbayev

Physics & Astronomy Faculty Publications

We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic models, because for all simulations - including sources with two independent, precessing spins - we perform comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported by Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)] (at the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing …

H-, He-Like Recombination Spectra ‒ Ii. L-Changing Collisions For He Rydberg States, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland

Physics and Astronomy Faculty Publications

Cosmological models can be constrained by determining primordial abundances. Accurate predictions of the He i spectrum are needed to determine the primordial helium abundance to a precision of < 1 per cent in order to constrain big bang nucleosynthesis models. Theoretical line emissivities at least this accurate are needed if this precision is to be achieved. In the first paper of this series, which focused on H ι, we showed that differences in l-changing collisional rate coefficients predicted by three different theories can translate into 10 per cent changes in predictions for H ι spectra. Here, we consider the more complicated case of He atoms, where low-l subshells are not energy degenerate. A criterion for deciding when the energy separation between l subshells is small enough to apply energy-degenerate collisional theories is given. Moreover, for certain conditions, the Bethe approximation originally proposed by …

The Data Reduction Pipeline For The Sdss-Iv Manga Ifu Galaxy Survey, David R. Law, Brian Cherinka, Renbin Yan, Brett H. Andrews, Matthew A. Bershady, Dmitry Bizyaev, Guillermo A. Blanc, Michael R. Blanton, Adam S. Bolton, Joel R. Brownstein, Kevin Bundy, Yanmei Chen, Niv Drory, Richard D'Souza, Hai Fu, Amy Jones, Guinevere Kauffmann, Nicholas Macdonald, Karen L. Masters, Jeffrey A. Newman, John K. Parejko, José R. Sánchez-Gallego, Sebastian F. Sánchez, David J. Schlegel, Daniel Thomas, David A. Wake, Anne-Marie Weijmans, Kyle B. Westfall, Kai Zhang

Physics and Astronomy Faculty Publications

Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) is an optical fiber-bundle integral-field unit (IFU) spectroscopic survey that is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV). With a spectral coverage of 3622–10354 Å and an average footprint of ~500 arcsec² per IFU the scientific data products derived from MaNGA will permit exploration of the internal structure of a statistically large sample of 10,000 low-redshift galaxies in unprecedented detail. Comprising 174 individually pluggable science and calibration IFUs with a near-constant data stream, MaNGA is expected to obtain ~100 million raw-frame spectra and ~10 million …

Gama/H-Atlas : Common Star Formation Rate Indicators And Their Dependence On Galaxy Physical Parameters., L. Wang, P. Norberg, M. L. P. Gunawardhana, S. Heinis, I. K. Baldry, J. Bland-Hawthorn, N. Bourne, S. Brough, M. J. I. Brown, M. E. Cluver, A. Cooray, E. Da Cunha, S. P. Driver, L. Dunne, S. Dye, S. Eales, M. W. Grootes, Benne W. Holwerda, A. M. Hopkins, E. Ibar, R. Ivison, C. Lacey, M. A. Lara-Lopez, J. Loveday, S. J. Maddox, M. J. Michalowski, I. Oteo, M. S. Owers, C. C. Popescu, D. J. B. Smith, E. N. Taylor, R. J. Tuffs, P. Van Der Werf

Faculty and Staff Scholarship

We compare common star formation rate (SFR) indicators in the local Universe in the Galaxy and Mass Assembly (GAMA) equatorial fields (∼160 deg2), using ultraviolet (UV) photometry from GALEX, far-infrared and sub-millimetre (sub-mm) photometry from Herschel Astrophysical Terahertz Large Area Survey, and Hα spectroscopy from the GAMA survey. With a high-quality sample of 745 galaxies (median redshift z = 0.08), we consider three SFR tracers: UV luminosity corrected for dust attenuation using the UV spectral slope β (SFRUV, corr), Hα line luminosity corrected for dust using the Balmer decrement (BD) (SFRH α, corr), and the combination of UV and infrared …

Detection And Localization Of Continuous Gravitational Waves With Pulsar Timing Arrays: The Role Of Pulsar Terms, X. J. Zhu, L. Wen, J. Xiong, Y. Xu, Y. Wang, S. D. Mohanty, G. Hobbs, R. N. Manchester

Physics & Astronomy Faculty Publications

A pulsar timing array is a Galactic-scale detector of nanohertz gravitational waves (GWs). Its target signals contain two components: the 'Earth term' and the 'pulsar term' corresponding to GWs incident on the Earth and pulsar, respectively. In this work we present a Frequentist method for the detection and localization of continuous waves that takes into account the pulsar term and is significantly faster than existing methods. We investigate the role of pulsar terms by comparing a full-signal search with an Earth-term-only search for non-evolving black hole binaries. By applying the method to synthetic data sets, we find that (i) a …

Jet-Like Correlations With Direct-Photon And Neutral-Pion Triggers At √SNn = 200 Gev, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, D. M. Anderson, A. Aparin, D. Arkhipkin, E. C. Aschenauer, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

Azimuthal correlations of charged hadrons with direct-photon (γ_dir) and neutral-pion (π⁰) trigger particles are analyzed in central Au+Au and minimum-bias p+p collisions at in the STAR experiment. The charged-hadron per-trigger yields at mid-rapidity from central Au+Au collisions are compared with p+p collisions to quantify the suppression in Au+Au collisions. The suppression of the away-side associated-particle yields per γ_dir trigger is independent of the transverse momentum of the trigger particle (p^trig_T), whereas the suppression is smaller at low transverse momentum of the associated charged hadrons ( …

Gw150914: First Search For The Electromagnetic Counterpart Of A Gravitational-Wave Event By The Toros Collaboration, Mario C. Diaz, Martin Beroiz, Tania Peñuela, Lucas M. Macri, Ryan J. Oelkers, Wenlong Yuan, Diego García Lambas, Nicolas A. Pereyra, Soma Mukherjee, Matthew Benacquista, Joey Key

Physics & Astronomy Faculty Publications

We present the results of the optical follow-up conducted by the TOROS collaboration of the first gravitational-wave event GW150914. We conducted unfiltered CCD observations (0.35-1 μm) with the 1.5 m telescope at Bosque Alegre starting ∼2.5 days after the alarm. Given our limited field of view (∼100 arcmin2), we targeted 14 nearby galaxies that were observable from the site and were located within the area of higher localization probability. We analyzed the observations using two independent implementations of difference-imaging algorithms, followed by a Random-Forest-based algorithm to discriminate between real and bogus transients. We did not find any bona fide transient …

Bayesian Analysis Of Two Stellar Populations In Galactic Globular Clusters – Iii. Analysis Of 30 Clusters, R. Wagner-Kaiser, D. C. Stenning, A Sarajedini, Ted Von Hippel, D. A. Van Dyk, E. Robinson, W. H. Jefferys

Publications

We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS Treasury observations of 30 Galactic globular clusters to characterize two distinct stellar populations. A sophisticated Bayesian technique is employed to simultaneously sample the joint posterior distribution of age, distance, and extinction for each cluster, as well as unique helium values for two populations within each cluster and the relative proportion of those populations. We find the helium differences among the two populations in the clusters fall in the range of ∼0.04 to 0.11. Because adequate models varying in carbon, nitrogen, and oxygen are not presently available, we …

Metallicity And Age Of The Stellar Stream Around The Disk Galaxy Ngc 5907, Seppo Laine, Carl Grillmair, Peter Capak, Richard Arendt, Aaron Romanowsky, David Martínez-Delgado, Matthew Ashby, James Davies, Stephen Majewski, Jean Brodie, R. Gabany, Jacob Arnold

Faculty Publications

Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby (d = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 μm Spitzer/Infrared Array Camera observations. Combining the near-infrared 3.6 μm data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along an ~60 kpc long segment of the stream. We have fitted the stellar spectral energy distribution with a single-burst …

Determination Of Interstellar O Parameters Using The First Two Years Of Data From The Interstellar Boundary Explorer, N. A. Schwadron, E. Möbius, D. J. Mccomas, P. Bochsler, M. Bzowski, S. A. Fuselier, G. Livadiotis, P. Frisch, H. R. Müller, D. Heirtzler, H. Kucharek, M. A. Lee

Dartmouth Scholarship

The direct measurements of interstellar matter by the Interstellar Boundary Explorer ( IBEX ) mission have opened a new and important chapter in our study of the interactions that control the boundaries of our heliosphere. Here we derive for the quantitative information about interstellar O flow parameters from IBEX low-energy neutral atom data for the first time. Specifically, we derive a relatively narrow four-dimensional parameter tube along which interstellar O flow parameters must lie. Along the parameter tube, we find a large uncertainty in interstellar O flow longitude, 76°.0 ± 3°.4 from χ 2 analysis and 76°.5 ± 6°.2 from …

First-Principles Calculated Decomposition Pathways For Libh4 Nanoclusters, Zhi-Quan Huang, Wei-Chih Chen, Feng-Chuan Chuang, Eric Majzoub, Vidvuds Ozoliņš

Physics Faculty Works

We analyze thermodynamic stability and decomposition pathways of LiBH4 nanoclusters using grand-canonical free-energy minimization based on total energies and vibrational frequencies obtained from density-functional theory (DFT) calculations. We consider (LiBH4)n nanoclusters with n = 2 to 12 as reactants, while the possible products include (Li)n, (B)n, (LiB)n, (LiH)n, and Li2BnHn; off-stoichiometric LinBnHm (m ≤ 4n) clusters were considered for n = 2, 3, and 6. Cluster ground-state configurations have been predicted using prototype electrostatic ground-state (PEGS) and genetic algorithm (GA) based structural optimizations. Free-energy calculations show hydrogen release pathways markedly differ from those in bulk LiBH4. While experiments have found …

A Multi-Wavelength Analysis Of Cold Evolving Interstellar Clouds, Mary Spraggs

Mahurin Honors College Capstone Experience/Thesis Projects

The interstellar medium (ISM) is the dynamic system of gas and dust that fills the space between the stars within galaxies. Due to its integral role in star formation and ga-lactic structure, it is important to understand how the ISM itself evolves over time, in-cluding the process of cooling and condensing required to form new stars. This work aims to constrain and better understand the physical properties of the cold ISM with sev-eral different types of data, including large surveys of neutral atomic hydrogen (HI) 21cm spectral line emission and absorption, carbon monoxide (CO) 2.6mm line emission, and multi-band infrared …