Subjects -> ASTRONOMY (Total: 94 journals)
Showing 1 - 46 of 46 Journals sorted alphabetically
Advances in Astronomy     Open Access   (Followers: 51)
Annual Review of Astronomy and Astrophysics     Full-text available via subscription   (Followers: 39)
Annual Review of Earth and Planetary Sciences     Full-text available via subscription   (Followers: 63)
Artificial Satellites     Open Access   (Followers: 23)
Astrobiology     Hybrid Journal   (Followers: 14)
Astronomical & Astrophysical Transactions: The Journal of the Eurasian Astronomical Society     Hybrid Journal   (Followers: 6)
Astronomical Journal     Full-text available via subscription   (Followers: 8)
Astronomical Review     Open Access   (Followers: 4)
Astronomische Nachrichten     Hybrid Journal   (Followers: 4)
Astronomy & Geophysics     Hybrid Journal   (Followers: 48)
Astronomy and Astrophysics     Full-text available via subscription   (Followers: 60)
Astronomy and Astrophysics     Open Access   (Followers: 32)
Astronomy and Computing     Hybrid Journal   (Followers: 2)
Astronomy Letters     Hybrid Journal   (Followers: 22)
Astronomy Reports     Hybrid Journal   (Followers: 15)
Astronomy Studies Development     Open Access   (Followers: 12)
Astroparticle Physics     Hybrid Journal   (Followers: 8)
Astrophysical Bulletin     Hybrid Journal   (Followers: 3)
Astrophysical Journal     Full-text available via subscription   (Followers: 19)
Astrophysical Journal Letters     Full-text available via subscription   (Followers: 14)
Astrophysical Journal Supplement Series     Full-text available via subscription   (Followers: 14)
Astrophysics     Hybrid Journal   (Followers: 29)
Astrophysics and Space Science     Hybrid Journal   (Followers: 46)
Astrophysics and Space Sciences Transactions (ASTRA)     Open Access   (Followers: 56)
Astropolitics: The International Journal of Space Politics & Policy     Hybrid Journal   (Followers: 12)
Celestial Mechanics and Dynamical Astronomy     Hybrid Journal   (Followers: 11)
Chinese Astronomy and Astrophysics     Full-text available via subscription   (Followers: 24)
Colloid Journal     Hybrid Journal   (Followers: 3)
Comptes Rendus Physique     Full-text available via subscription   (Followers: 2)
Computational Astrophysics and Cosmology     Open Access   (Followers: 3)
COSPAR Colloquia Series     Full-text available via subscription   (Followers: 11)
Earth, Moon, and Planets     Hybrid Journal   (Followers: 55)
Earth, Planets and Space     Open Access   (Followers: 74)
EAS Publications Series     Full-text available via subscription   (Followers: 8)
EPL Europhysics Letters     Partially Free   (Followers: 8)
Experimental Astronomy     Hybrid Journal   (Followers: 39)
Expert Opinion on Astronomy and Astrophysics     Open Access   (Followers: 7)
Extreme Life, Biospeology & Astrobiology - International Journal of the Bioflux Society     Full-text available via subscription   (Followers: 6)
Few-Body Systems     Hybrid Journal   (Followers: 1)
Foundations of Physics     Hybrid Journal   (Followers: 41)
Frontiers in Astronomy and Space Sciences     Open Access   (Followers: 12)
Galaxies     Open Access   (Followers: 6)
Globe, The     Full-text available via subscription   (Followers: 4)
Gravitation and Cosmology     Hybrid Journal   (Followers: 4)
Icarus     Hybrid Journal   (Followers: 75)
International Journal of Advanced Astronomy     Open Access   (Followers: 28)
International Journal of Astrobiology     Hybrid Journal   (Followers: 4)
International Journal of Astronomy     Open Access   (Followers: 19)
International Journal of Astronomy and Astrophysics     Open Access   (Followers: 29)
International Journal of Satellite Communications Policy and Management     Hybrid Journal   (Followers: 13)
International Letters of Chemistry, Physics and Astronomy     Open Access   (Followers: 12)
ISRN Astronomy and Astrophysics     Open Access   (Followers: 7)
Journal for the History of Astronomy     Full-text available via subscription   (Followers: 19)
Journal of Astrobiology & Outreach     Open Access   (Followers: 3)
Journal of Astronomical Instrumentation     Open Access   (Followers: 3)
Journal of Astronomical Telescopes, Instruments, and Systems     Hybrid Journal   (Followers: 5)
Journal of Astrophysics     Open Access   (Followers: 26)
Journal of Astrophysics and Astronomy     Open Access   (Followers: 52)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 199)
Journal of Cosmology and Astroparticle Physics     Hybrid Journal   (Followers: 38)
Journal of Geophysical Research : Planets     Full-text available via subscription   (Followers: 178)
Journal of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 178)
Journal of High Energy Astrophysics     Full-text available via subscription   (Followers: 22)
Kinematics and Physics of Celestial Bodies     Hybrid Journal   (Followers: 10)
KronoScope     Hybrid Journal   (Followers: 1)
Macalester Journal of Physics and Astronomy     Open Access   (Followers: 4)
MNASSA : Monthly Notes of the Astronomical Society of South Africa     Full-text available via subscription   (Followers: 1)
Molecular Astrophysics     Full-text available via subscription   (Followers: 1)
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 14)
Monthly Notices of the Royal Astronomical Society : Letters     Hybrid Journal  
Nature Astronomy     Hybrid Journal   (Followers: 8)
New Astronomy     Hybrid Journal   (Followers: 27)
New Astronomy Reviews     Full-text available via subscription   (Followers: 17)
Nonlinear Dynamics     Hybrid Journal   (Followers: 19)
NRIAG Journal of Astronomy and Geophysics     Open Access   (Followers: 5)
Open Astronomy     Open Access   (Followers: 2)
Physics of the Dark Universe     Open Access   (Followers: 4)
Planetary and Space Science     Hybrid Journal   (Followers: 101)
Planetary Science     Open Access   (Followers: 52)
Proceedings of the International Astronomical Union     Full-text available via subscription   (Followers: 2)
Publications of the Astronomical Society of Australia     Hybrid Journal   (Followers: 2)
Publications of the Astronomical Society of Japan     Hybrid Journal   (Followers: 3)
Publications of the Astronomical Society of the Pacific     Full-text available via subscription   (Followers: 4)
Research & Reviews : Journal of Space Science & Technology     Full-text available via subscription   (Followers: 17)
Research in Astronomy and Astrophysics     Full-text available via subscription   (Followers: 29)
Revista Mexicana de AstronomĂ­a y AstrofĂ­sica     Open Access   (Followers: 2)
Science China Physics, Mechanics & Astronomy     Hybrid Journal   (Followers: 4)
Solar Physics     Hybrid Journal   (Followers: 34)
Solar System Research     Hybrid Journal   (Followers: 14)
Space Science International     Open Access   (Followers: 192)
Space Science Reviews     Hybrid Journal   (Followers: 97)
Space Weather     Full-text available via subscription   (Followers: 24)
Transport and Aerospace Engineering     Open Access   (Followers: 13)
Universe     Open Access   (Followers: 5)
Similar Journals
Journal Cover
Macalester Journal of Physics and Astronomy
Number of Followers: 4  

  This is an Open Access Journal Open Access journal
ISSN (Print) 2332-7669
Published by Macalester College Homepage  [7 journals]
  • Tensile Bending Behavior of PVA Fiber and Crumb Rubber Modified Hot
           Mixture Asphalt

    • Authors: Elena J. Youngdale et al.
      Abstract: High performance hot mixture asphalt has been tested and utilized to improve total life cycle costs on high traffic roads. This study sought to test three variables and find the optimum dosages of each. First, was the synthetic polyvinyl alcohol (PVA) fibers. Second, a dosage of fine shredded rubber tire (crumb rubber). Third, varying dosages of coarse and fine crumb rubber. A total of 14 mixtures with varying amounts of PVA fiber, coarse, and fine rubber were created and tested for maximum bending stress and fracture energy in a semi-circular bending beam test (SCB test). Both coarse rubber and PVA fibers were found to decrease maximum bending stress and fracture energy. Both tested mechanical properties increased slightly with the optimum dosage of 1% fine rubber.
      PubDate: Wed, 13 May 2020 05:18:10 PDT
  • SuperCDMS: Energy Calibration of a Ge HV Particle Detector

    • Authors: Salamong Xiong et al.
      Abstract: The goal of the SuperCDMS collaboration is to directly detect dark matter. Weakly Interacting Massive Particles (WIMPs) are potential candidates. To detect WIMPs, it is important to be able to predict how a Ge/Si particle detector will respond to a dark matter signal. In particular, it is necessary to calibrate the recoil energy measured by these detectors. This paper presents evidence for dark matter, a description of the detector operation, and procedures used to analyze measured data from a SuperCDMS-HV Ge particle detector using Am-241 and a PuBe neutron source. Due to high event rate, criteria were developed to remove low-quality data arising from particle interactions that occur too soon after a previous interaction. Peaks in histograms of pulse amplitudes were identified as energy peaks from the various radioactive sources, and fits of these peaks formed the basis for generating an energy calibration function. The calibration function was used to generate the calibrated energy spectrum.
      PubDate: Wed, 13 May 2020 05:17:54 PDT
  • Calculating centrality variables and geometric quantities associated with
           high energy Pb+Pb and Au+Au collisions using a Monte Carlo Glauber model

    • Authors: Anya Wolterman
      Abstract: The Glauber model provides insight into the initial state of nuclear collisions by treating them in terms of the interactions between their constituent nucleons, in accordance with theories about the scattering of composite particles. These phenomenological techniques are commonly used to determine various geometric quantities associated with such complex, femtoscopic many-body systems. The Monte Carlo Glauber approach uses a random impact parameter and measured nuclear densities to investigate quantifiable properties like particle multiplicity and average geometric eccentricity for heavy ion collisions. The former involves incorporating a particle production model to plot the total transverse energy or the number of particles produced at mid-rapidity, both being measures of centrality. The latter delves into the eccentricity of different event classes, which can be used to characterize various collision shapes for measurements of elliptic flow of heavy mesons. The results of both applications are then compared with analyses from CMS and STAR as part of efforts to study the properties of the ultra-hot, super-dense phase of matter known as the Quark-Gluon Plasma.
      PubDate: Wed, 13 May 2020 05:17:44 PDT
  • Fabrication of Nanoscale Columnar Diodes by Glancing Angle Deposition

    • Authors: Jacob D. Weightman
      Abstract: Glancing angle deposition (GLAD) is a process in which thin films are deposited onto a substrate with obliquely incident vapor together with precisely controlled azimuthal substrate rotation. Ballistic shadowing effects due to the oblique incidence produce nanoscale structures, and a variety of feature shapes, including tilted columns, helices, and vertical columns can be achieved by varying the azimuthal rotation during the deposition process. Due to this control of morphology and the compatibility of the process with a wide variety of materials, GLAD films have found applications in a variety of fields including sensing, photonics, photovoltaics, and catalysis, where they are predominantly used as coatings with tunable optical, mechanical, and chemical properties. However, there has been little work regarding its use for the fabrication of electronic devices. GLAD films are interesting in this respect because it would enable nanoscale devices to be made without lithography. We propose a method for fabricating vertically-aligned, columnar Schottky diodes by GLAD. We then fabricate these devices using electron beam evaporation of chromium onto a silicon substrate, with chromium and aluminum contacts, and characterize these devices by SEM and I-V curve measurements.
      PubDate: Wed, 13 May 2020 05:17:33 PDT
  • Nitrogen Vacancy Center Optical Magnetometry of a Barium-Iron-Cobalt

    • Authors: William Setterberg
      Abstract: Experimentally probing the intrinsic properties of superconductors—such as the London penetration depth λ and the critical fields Hc1 and Hc2—poses a difficult task. Various sample- and measurement-related factors can impact the efficacy of results obtained for λ or Hc1, such as perturbations to the magnetic properties of a superconducting sample or crystalline defects. One measurement technique that can minimize the impact of both of these issues is known as Nitrogen Vacancy (NV) center magnetometry. In this work, we use NV center magnetometry to perform minimally-invasive measurements of the lower critical field Hc1 and the London penetration depth λ on a sample of Ba(Fe1−xCox)2As2, x = 7.4% (BaCo122).
      PubDate: Wed, 13 May 2020 05:17:26 PDT
  • The Leoncino Dwarf: A Neutral Hydrogen Analysis of AGC 198691 and its
           Extremely Metal-Poor Environment

    • Authors: Tylyn Page
      Abstract: Studies of low-mass galaxies are important for populating the low-mass ends of funda- mental physical relations. Extremely metal-poor (XMP) galaxies are low-mass galaxies with gas-phase oxygen abundances of 12+log(O/H) ≤ 7.35 ( 1/20 Z⊙), and are especially interesting as proxies for studying the distant past, as their chemical makeup resembles those of galaxies in the early universe. AGC 198691, referred to as the Leoncino Dwarf, was discovered through the Arecibo Legacy Fast ALFA (ALFALFA) survey and found to have an oxygen abundance of less than 3% Z⊙. Presented here are the results of recent Karl G. Jansky Very Large Array (VLA) HI observations of Leoncino, with discussion of its apparently dispersion-dominated kinematics, level of agreement with mass-metallicity (MZ) and luminosity-metallicity (LZ) relations, current star formation, and theories regarding its extremely low metal content.
      PubDate: Wed, 13 May 2020 05:17:15 PDT
  • Large Scale Grid Integration of Wind and Solar Power with Storage

    • Authors: Nicholas Moore
      Abstract: The current energy grid in the United States is dominated by carbon intense energy generation methods that are based on production when and where it is required. However, solar and wind power have proved themselves as the most promising carbon free energy generation sources. Due to the unpredictable and uncontrollable nature of energy production from solar and wind, large scale integration of these resources into the electric grid will require robust storage capacity. In this project, we model the energy grid of the Midcontinent Independent System Operator (MISO) energy region with high concentrations of solar and wind power to analyze the impacts on storage, over-generation, base load and cost. Historical load data was taken from the MISO region, while solar and wind data was from the National Renewable Energy Laboratory Solar and Wind Integration Data Sets, all for the year 2007. Our findings show that the necessary storage capacity is significantly reduced when there is over-generation of energy, either from solar and wind or base load. Despite this, due to the falling price of solar, wind and storage technologies, the most cost efficient means of shifting to a carbon neutral energy grid is through the over-generation of wind, solar and storage, without base load.
      PubDate: Wed, 13 May 2020 05:17:05 PDT
  • Probing the Magnetic Fields in Cosmic Web Filaments

    • Authors: Andrew L. Mizener
      Abstract: We present a project to constrain the properties of magnetic fields in Cosmic Web filaments. We first perform rotation measure (RM) synthesis on 24 S-band Karl G Jansky Very Large Array (VLA) observations of moderate-redshift active galactic nuclei (AGN). These observations are combined with an existing catalog of Cosmic Web filaments in order to determine the number of filaments a given sight-line passes near or through. By tracking how observables such as rotation measure and polarization fraction change as a function of the number of intervening cosmic web filaments, we take the first steps towards providing observational constraints on the magnetic field strength within these structures. We find that the dispersion in RM increases as the distance between a line of sight and the filament closest to that line of sight decreases, suggesting that we are detecting a signal from magnetic fields within these structures.
      PubDate: Wed, 13 May 2020 05:16:57 PDT
  • Shape Model of Potentially Hazardous Asteroid 1981 Midas from Radar and
           Lightcurve Observations

    • Authors: Riley McGlasson
      Abstract: We report observations of potentially hazardous, Apollo-class asteroid 1981 Midas, which passed 0.090 au from Earth (35 lunar distances) on March 21, 2018. During this close approach, Midas was observed by radar both from the Arecibo Observatory on March 21 through 25 (five nights), and from NASA's Goldstone Deep Space Communications Complex on March 19 and 21. These radar observations yielded one-dimensional continuous-wave spectra and two-dimensional delay-Doppler images. In addition, there have been optical lightcurve observations of Midas during four apparitions (1987, 1992, 2004, and 2018), which showed a rotation period of 5.22 hours. Midas has an absolute magnitude of H = 15.2. By combining the lightcurves and radar data, we have constructed a shape model for Midas. This model shows that Midas has two lobes separated by a neck which, at its thinnest point, is about 60% of the width of the lobes. From our model, we also confirm the lightcurve-derived rotation period and show that Midas has dimensions of 3.33 x 1.99 x 1.85 km +/- 10% and a pole position within 6 degrees of (370,-610) in ecliptic longitude and latitude.
      PubDate: Wed, 13 May 2020 05:16:52 PDT
  • Deposition of TiN for Battery and Supercapacitor Electrodes for Energy

    • Authors: Kieran M. Liming
      Abstract: Titanium Nitride (TiN) can be sputtered into a thin film, and is a promising component for battery and supercapacitor electrodes. This research explored the relationship between Nitride partial pressure and film characteristics. We sputtered TiN into thin films in a low vacuum environment at tempuratures of approximately 70o C. Most films were deposited over the course of one hour including a five minute presputtering period where the substrate was covered. We found that film thickness, system voltage, and film restivitiy to be a function of N2 partial pressure.
      PubDate: Wed, 13 May 2020 05:16:40 PDT
  • Searching for Doublet Vectorlike Leptons Using the ATLAS Particle Detector

    • Authors: Brynn Keller
      Abstract: Vectorlike leptons are a simple extension of the standard model, akin to a fourth family of leptons. This paper describes aspects of the preparation for a search for VLLs at an ATLAS particle collider. During this research, signal and control regions were determined with use of a Monte Carlo simulation in order to best estimate where to measure different kinds of background and where to search for a potential signal. These signal and control regions were optimized with respect to MET, LT, and number of light and heavy leptons with a goal of a 95\% confidence limit.
      PubDate: Wed, 13 May 2020 05:16:29 PDT
  • Crumpling of graphene optimizes graphene field effect transistors (GFETs)
           as ultrasensitive biosensors

    • Authors: Hannah E. Gilbonio et al.
      Abstract: Biosensors are devices that translate biological responses into electrical signals. They have many applications in various fields, however biosensors are especially useful for early detection of diseases such as cancer and other genetic disorders. This could be done, for example, via detection of specific proteins or nucleic acids in body fluids. For the case of DNA and RNA, detection of genetic mutations or specific sequences in DNA can be indicative of the state of a disease. Biosensors with high sensitivity and specificity are essential to the future of the aforementioned fields, however current biosensor technology does not meet the demands of high sensitivity, low cost, and ease of use by the patients. Graphene field effect transistors (GFETs) provide a refreshing alternative to biosensing with benefits including easy integration as biomolecular sensors, low fabrication costs,and most notably they have the ability to lower the biomarker detection limit to the femto-molar range. In this paper, we present a prototype for the new class of GFETs where the channel consists of a layer of crumpled graphene that yields extreme sensitivity for detection of DNA in the sub-atto-molar range. Furthermore, we find that increasing the crumpling ratio of the graphene increases the device’s sensitivity for nucleic acid detection. We hypothesize this is due to two main mechanisms:formation of ’electrical hot spots’ due to variations in the Debye length above the sensor layer and the presence of a more significant band gap for the deformed graphene channel which in turn affects its conductivity. Continuing the work of this project would take the form of further increasing the sensitivity to be able to detect historically scarce molecules that can then lead to more effective biosensing tools in medicine.
      PubDate: Wed, 13 May 2020 05:16:17 PDT
  • A Search for Pulsars Towards the Galactic Center

    • Authors: Jacob W. Hetrick et al.
      Abstract: We present observations from two separate methods for observing the Galactic Center in an attempt to characterize its pulsar and neutron star populations. A persistent puzzle of the past 20 years has been the lack of pulsar detections towards the Galactic Center, specifically within a few parsecs of the central supermassive black hole Sgr A*. This object is bright in the total intensity of its polarized emission, but is very weakly linearly polarized. We take advantage of these circumstances in an experimental search technique where we utilize the Faraday effect in an attempt to detect high rotation measure (RM) point sources towards the Galactic Center, as the few pulsars that have been detected in this region have all been measured at a high RM. We also conduct a wide-field search of the 5◦area around the Galactic Center at low frequencies (230-470MHz) and at multiple epochs in an attempt to detect transient sources and other significant emitters of synchrotron radiation.
      PubDate: Wed, 13 May 2020 05:16:04 PDT
  • Modeling Scavenging for a Hydraulic Free-Piston Engine

    • Authors: Nathan Davies
      Abstract: The hydraulic free-piston engine at the University of Minnesota offers a solution to improve the hydraulic efficiency and reduce emission output of off-road vehicles. We developed a MATLAB Simulink model to track the pressure, temperature, and mass profile of the fuel within the cylinder during operation. By varying different initial conditions of our model, we found that a higher intake manifold pressure and larger bottom dead center location results in higher scavenging efficiency. These results can be used to improve the controller of this engine and better maintain stable operation.
      PubDate: Wed, 13 May 2020 05:15:53 PDT
  • Band Extension and Possible Ridge Compression on Europa

    • Authors: Sarah Chinski
      Abstract: Jupiter's icy moon Europa has captivated and perplexed the scientific community since the discovery of its global liquid water ocean. Over the course of several missions to the Jovian system, high-resolution observations of Europa have determined that there are spreading zones where new crust is created, similar to the mid-ocean spreading tectonic process we observe on Earth. These features, known as bands, have symmetric hills and valleys, indicating brief events of activity where material from the interior is exuded through a central crack, and solidifies on both sides, creating two positive topography. Recently, Europan scientists have been questioning how these features affect the total ice volume of the moon. After all, if ice is being created at these features, then the total volume of ice on Europa would be increasing, unless there was some mechanism in place to balance this net positive change in volume.In this thesis, I begin with a hypothesis: maybe the volume of ice being created through band extension can be compensated by compressional features. To test this hypothesis, we map, measure, and calculate surface area and volume estimates for bands and ridges in four regions across a global mosaic of Europa using moderate resolution images from the Galileo spacecraft. From our results, we may be able to draw important constraints on the thickness of the outer ice shell, which has been highly debated among scientists for decades.Initial results of this study show that the surface area of ridges can compensate for 35-70% of band surface area, with percentages varying greatly by region. Volume ratios of ridges to bands were calculated for several plausible values of shell thickness, ranging from 100 m - 50 km. It appears that in order to compensate for band spreading, the bands would need to propagate to depths of 200 m – 1 km. While these calculations are only indicative of a small percentage (4.62%) of the total surface area of Europa and therefore are not yet conclusive for understanding the surface expression of tectonic activity, they prompt further investigation on a more global scale.
      PubDate: Wed, 13 May 2020 05:15:46 PDT
  • Electrical Measurement of SRAM Cell Variation and Sensitivity to
           Singe-Event Upsets by Low-Energy Protons

    • Authors: James M. Cannon
      Abstract: With the rise of the transistor in the 1970s, electronics shifted from analog circuitry, where values are stored on a continuum, to digital, in which ones and zeros are the law of the land. Transistors, as a class circuit element, can be affected by radiation and cosmic rays which then cause temporary or permanent failures, depending on the specifics of the situation. On Earth, this poses little risk with all electronics shielded by the magnetosphere, however for space bound electronics, the risks from these extraterrestrial particles are not so negligible. The first step in designing a mission to be able to survive upsets from energetic particles is to understand how these particles affect all the devices of a space-bound circuit. While this characterization historically assumes constant behavior across one chip, in this senior honors thesis I present an electrical characterization of cell level variations in upset probability by low-energy protons for a specific class of digital chip: SRAM. This characterization is possible because of random process variation in the manufacturing of the underlying transistors that is then responsible for variation in the critical charge to upset for each cell of an SRAM. The results of the electrical characterization are then related to upset data acquired by irradiating chips at the Vanderbilt University Pelletron. These data are used in conjunction with the cell level electrical characterization to discuss the effects of virtually screening out cells with higher probability to upset.
      PubDate: Wed, 13 May 2020 05:15:37 PDT
  • Design and Modal Analysis of an Ultra-wideband Receiver for Green Bank

    • Authors: Alyssa Bulatek
      Abstract: The next generation of radio receivers for astronomy will be marked by tenfold improvements in sensitivity. These sensitive receivers will be useful for the detection of broadband fast radio bursts and other transients as well as the efficient discovery of radio recombination lines among many other scientific pursuits. One contribution to these improvements is an increase to decade receiver bandwidths. The Green Bank Observatory (GBO) is currently in the process of fabricating a new ultra-wideband (UWB; 0.7 to 4.2 GHz) receiver for the Green Bank Telescope (GBT). The UWB receiver will be used by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) to perform pulsar timing experiments using the GBT with greater sensitivity than before. The design of the receiver features a quad-ridged, flared feed horn and utilizes a corrugated skirt and a quartz spear to extend the receiver's bandwidth to 6:1. Through modeling and performance simulation, we find the predicted efficiency of the receiver to be around 60–70% at lower frequencies and above 50% at higher frequencies. The S11 values for the UWB receiver are better than –10 dB across the entire bandwidth, and performance is only predicted to degrade slightly at 2.8 GHz with the inclusion of a waveguide window.In an effort to determine the potential cause of reduced efficiency as a function of frequency, we perform an analysis of waveguide mode excitation to determine the concentration of higher-order mode excitation in the aperture of the receiver. Preliminary results suggest that higher-order mode (i.e. TM12 and TM13) excitation is present at higher frequencies, but we cannot conclude that it is the sole cause of reduced feed efficiency at those frequencies.
      PubDate: Wed, 13 May 2020 05:15:29 PDT
  • ALFALFA Harvest: HI Imaging and 3D Modeling of Candidate Local Group Dwarf

    • Authors: Lilly Bralts-Kelly et al.
      Abstract: Isolated neutral hydrogen (HI) clouds, or "ultra-compact high-velocity clouds" (UCHVCs), form a small subset of detections by the Arecibo Legacy Fast ALFA (ALFALFA) blind extragalactic survey. These systems, if located within ~1 Mpc, would populate the lowest-mass end of the HI mass function. Subsequent optical imaging has revealed that some of these UCHVCs harbor associated (thought sparse) stellar populations, suggesting that they may be some of the most extreme galaxies known in the Local Volume, with properties akin to ultra-faint dwarf galaxies but with significant neutral gas reservoirs. In this work, we investigate the neutral hydrogen properties of six UCHVC candidate galaxies using deep spectral line imaging from the Karl G. Jansky Very Large Array (VLA). We produce images and discuss the morphological and kinematic properties of six sources: AGC 198606, AGC 215417, AGC 219656, AGC 249525, AGC 258237, and AGC 268069. We also apply the modeling code 3D-Barolo to our deep HI images in order to derive rotation curves and constrain inclination angles for our two most promising galaxy candidates: AGC 198606 and AGC 249525. Successful modeling allows us to determine the dynamical masses of these objects and thus to consider them in the context of various fundamental scaling relations defined by more massive galaxies.
      PubDate: Wed, 13 May 2020 05:15:17 PDT
  • Leoncino and UGC 5186

    • Authors: Josh Bartz
      Abstract: AGC 198691 is commonly known as the Leoncino Dwarf and is one of the most metal poor galax- ies known. An Arecibo observation in 2011 first suggested that Leoncino could be gravitationally interacting with its neighbor UGC 5186. In this paper new VLA data is used to examine the H I com- ponent of both galaxies to determine their gravitational relationship. Although the VLA could not confirm intragalactic gas seen by Aricebo, the H I density and velocity components are strong indirect evidence of gravitational interaction. UGC 5186 has a large gaseous arm reaching in the direction of Leoncino. Additionally both galaxies have nearly identical recessional velocities. This conclusion may help to understand the evolutionary track of these galaxies, and it also sheds light onto Leoncino’s location in the Luminosity-Metallicity relation.
      PubDate: Wed, 13 May 2020 05:15:06 PDT
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