Astrophysics and Astronomy Commons^™

Models Of Time Travel And Their Consequences, Antonio M. Mantica

Oglethorpe Journal of Undergraduate Research

How do we travel through time? We know that we can move forward in it (we have no choice), but can we jump forward in time? Can we go backward in time? It also gives rise to other troubling questions: is time measurable in distinct increments, or does it flow continuously? In "Models of Time Travel and their Consequences," Antonio Mantica walks the reader through current understandings of how time functions in Einstein's universe and proposes three distinct models to explain it. Following that, he provides a list of experiments to credit or discredit the models. Appropriate for audiences of …

Update On Radiation Dose From Galactic And Solar Protons At The Moon Using The Lro/Crater Microdosimeter, J. E. Mazur, Cary Zeitlin, Nathan A. Schwadron, M. D. Looper, Lawrence W. Townsend, J. B. Blake, Harlan E. Spence

Physics & Astronomy

The NASA Lunar Reconnaissance Orbiter (LRO) has been exploring the lunar surface and radiation environment since June 2009. In Mazur et al. [2011] we discussed the first 6 months of mission data from a microdosimeter that is housed within the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument onboard LRO. The CRaTER microdosimeter is an early version of what is now a commercially available hybrid that accurately measures total ionizing radiation dose in a silicon target (http://www.teledynemicro.com/product/radiation-dosimeter). This brief report updates the transition from a deep solar minimum radiation environment to the current …

Variable Hard-X-Ray Emission From The Candidate Accreting Black Hole In Dwarf Galaxy Henize 2–10, Thomas J. Whalen, Ryan C. Hickox, Amy E. Reines, Jenny E. Greene

Dartmouth Scholarship

We present an analysis of the X-ray spectrum and long-term variability of the nearby dwarf starburst galaxy Henize 2–10. Recent observations suggest that this galaxy hosts an actively accreting black hole (BH) with mass ~10⁶ . The presence of an active galactic nucleus (AGN) in a low-mass starburst galaxy marks a new environment for AGNs, with implications for the processes by which "seed" BHs may form in the early universe. In this paper, we analyze four epochs of X-ray observations of Henize 2–10, to characterize the long-term behavior of its hard nuclear emission. We analyze observations with Chandra from …

Symmetry And The Arrow Of Time In Theoretical Black Hole Astrophysics, David Garofalo

Faculty Articles

While the basic laws of physics seem time-reversal invariant, our understanding of the apparent irreversibility of the macroscopic world is well grounded in the notion of entropy. Because astrophysics deals with the largest structures in the Universe, one expects evidence there for the most pronounced entropic arrow of time. However, in recent theoretical astrophysics work it appears possible to identify constructs with time-reversal symmetry, which is puzzling in the large-scale realm especially because it involves the engines of powerful outflows in active galactic nuclei which deal with macroscopic constituents such as accretion disks, magnetic fields, and black holes. Nonetheless, the …

Butterfly Pitch-Angle Distribution Of Relativistic Electrons In The Outer Radiation Belt: Evidence Of Nonadiabatic Scattering, Nikolai O. Artemyev, O. V. Agapitov, F. S. Mozer, Harlan E. Spence

Physics & Astronomy

In this paper we investigate the scattering of relativistic electrons in the nightside outer radiation belt (around the geostationary orbit). We consider the particular case of low geomagnetic activity (|Dst|<20 nT), quiet conditions in the solar wind, and absence of whistler wave emissions. For such conditions we find several events of Van Allen probe observations of butterfly pitch angle distributions of relativistic electrons (energies about 1–3 MeV). Many previous publications have described such pitch angle distributions over a wide energy range as due to the combined effect of outward radial diffusion and magnetopause shadowing. In this paper we discuss another mechanism that produces butterfly distributions over a limited range of electron energies. We suggest that such distributions can be shaped due to relativistic electron scattering in the equatorial plane of magnetic field lines that are locally deformed by currents of hot ions injected into the inner magnetosphere. Analytical estimates, test particle simulations, and observations of the AE index support this scenario. We conclude that even in the rather quiet magnetosphere, small scale (magnetic local time (MLT)-localized) injection of hot ions from the magnetotail can likely influence the relativistic electron scattering. Thus, observations of butterfly pitch angle distributions can serve as an indicator of magnetic field deformations in the nightside inner magnetosphere. We briefly discuss possible theoretical approaches and problems for modeling such nonadiabatic electron scattering.

Three Super-Earths Orbiting Hd 7924, Benjamin J. Fulton, Lauren M. Weiss, Evan Sinukoff, Howard Isaacson, Andrew W. Howard, Geoffrey W. Marcy, Gregory W. Henry, Bradford P. Holden, Robert I. Kibrick

Information Systems and Engineering Management Research Publications

We report the discovery of two super-Earth-mass planets orbiting the nearby K0.5 dwarf HD 7924, which was previously known to host one small planet. The new companions have masses of 7.9 and 6.4 ${{M}_{\oplus }}$, and orbital periods of 15.3 and 24.5 days. We perform a joint analysis of high-precision radial velocity data from Keck/HIRES and the new Automated Planet Finder Telescope (APF) to robustly detect three total planets in the system. We refine the ephemeris of the previously known planet using 5 yr of new Keck data and high-cadence observations over the last 1.3 yr with the APF. With …

Gps Phase Scintillation At High Latitudes During Geomagnetic Storms Of 7–17 March 2012 – Part 1: The North American Sector, P. Prikryl, R. Ghoddousi-Fard, E. G. Thomas, J. M. Ruohoniemi, S. G. Shepherd

Dartmouth Scholarship

During the ascending phase of solar cycle 24, a series of interplanetary coronal mass ejections (ICMEs) in the period 7–17 March 2012 caused geomagnetic storms that strongly affected high-latitude ionosphere in the Northern and Southern Hemisphere. GPS phase scintillation was observed at northern and southern high latitudes by arrays of GPS ionospheric scintillation and TEC monitors (GISTMs) and geodetic-quality GPS receivers sampling at 1 Hz. Mapped as a function of magnetic latitude and magnetic local time, regions of enhanced scintillation are identified in the context of coupling processes between the solar wind and the magnetosphere–ionosphere system. Large southward IMF and …

Search For Life, John W. Delano Phd

Atmospheric and Environmental Science Faculty Scholarship

NASA's Astrobiology program seeks to determine the origin and distribution of life in the Milky Way galaxy using scientific expertise from many disciplines (e.g., astronomy, biochemistry, geochemistry). This presentation, which provides an overview of the progress that has been made in this effort, was delivered on 23 June 2015 at the Green Mountain Academy for Lifelong Learning in Manchester, VT. With NASA's development of the Space Launch System (SLS), vigorous multi-disciplinary scientific research, and additional spacecraft (e.g., TESS) for finding and analyzing planets orbiting other stars, exciting discoveries will continue.

A Sluggs And Gemini/Gmos Combined Study Of The Elliptical Galaxy M60: Wide-Field Photometry And Kinematics Of The Globular Cluster System, Vincenzo Pota, Jean Brodie, Terry Bridges, Jay Strader, Aaron Romanowsky, Alexa Villaume, Zach Jennings, Favio Faifer, Nicola Pastorello, Duncan Forbes, Ainsley Campbell, Christopher Usher, Caroline Foster, Lee Spitler, Nelson Caldwell, Juan Forte, Mark Norris, Stephen Zepf, Michael Beasley, Karl Gebhardt, David Hanes, Ray Sharples, Jacob Arnold

Faculty Publications

We present new wide-field photometry and spectroscopy of the globular clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo cluster. Imaging of NGC 4649 was assembled from a recently obtained Hubble Space Telescope/Advanced Camera for Surveys mosaic, and new Subaru/Suprime-Cam and archival Canada–France–Hawaii Telescope/MegaCam data. About 1200 sources were followed up spectroscopically using combined observations from three multi-object spectrographs: Keck/Deep Imaging Multi-Object Spectrograph, Gemini/Gemini Multi-Object Spectrograph and Multiple Mirror Telescope/Hectospec. We confirm 431 unique GCs belonging to NGC 4649, a factor of 3.5 larger than previous data sets and with a factor of 3 improvement in …

Spectropolarimetry Of Epsilon Aurigae: Probing Stellar And Disk Atmospheres, Kathleen M. Geise

Electronic Theses and Dissertations

The bright eclipsing binary system epsilon Aurigae offers a unique opportunity to uncover physical mechanisms contributing to disk formation and evolution and to explore the relationship between photospheric anisotropies, stellar pulsation and mass loss. This research contributes to our understanding of stellar evolution in the context of binary stars. The research also offers the opportunity to investigate disk formation and evolution significant to our understanding of protoplanetary disks now seen in many star systems. Lastly, the project considers radiative transfer of polarized light that contributes to diverse fields such as atmospheric studies of exoplanets.

My objective is to understand the …

Precise Mass And Radius Measurements For The Components Of The Bright Solar-Type Eclipsing Binary Star V1094 Tauri, P. F.L. Maxted, R. J. Hutcheon, G. Torres, C. H.S. Lacy, J. Southworth, B. Smalley, K. Pavlovski, Laurence A. Marschall, J. V. Clausen

Physics and Astronomy Faculty Publications

Context. V1094 Tau is a bright eclipsing binary star with an orbital period close to nine days that contains two stars similar to the Sun.

Aims. Our aim is to test models of Sun-like stars using precise and accurate mass and radius measurements for both stars in V1094 Tau.

Methods. We present new spectroscopy of V1094 Tau, which we use to estimate the effective temperatures of both stars and to refine their spectroscopic orbits. We also present new, high-quality photometry covering both eclipses of V1094 Tau in the Strömgren uvby system and in the Johnson V-band.

Results. The masses, …

A Disk-Based Dynamical Mass Estimate For The Young Binary Ak Sco, I. Czekala, S. M. Andrews, Eric L.N. Jensen, K. G. Stassun, G. Torres, D. J. Wilner

Physics & Astronomy Faculty Works

We present spatially and spectrally resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of gas and dust in the disk orbiting the pre-main sequence (pre-MS) binary AK Sco. By forward-modeling the disk velocity field traced by CO J = 2-1 line emission, we infer the mass of the central binary, {M}_*=2.49+/- 0.10 {M}_☉ , a new dynamical measurement that is independent of stellar evolutionary models. Assuming the disk and binary are co-planar within ̃2°, this disk-based binary mass measurement is in excellent agreement with constraints from radial velocity monitoring of the combined stellar spectra. These ALMA results are …

Faint Agns At Z > 4 In The Candels Goods-S Field: Looking For Contributors To The Reionization Of The Universe, E. Giallongo, A. Grazian, F. Fiore, A. Fontana, L. Pentericci, E. Vanzella, M. Dickinson, Dale D. Kocevski, M. Castellano, S. Christiani, H. Ferguson, S. Finkelstein, N. Grogin, N. Hathi, A. M. Koekemoer, J. A. Newman, M. Salvato

Physics and Astronomy Faculty Publications

Context. Establishing the number of faint active galactic nuclei (AGNs) at z = 4−6 is crucial to understanding their cosmological importance as main contributors to the reionization of the Universe.

Aims. In order to derive the AGN contribution to the cosmological ionizing emissivity we have selected faint AGN candidates at z> 4 in the CANDELS GOODS-South field, which is one of the deepest fields with extensive multiwavelength coverage from Chandra, HST, Spitzer, and various ground-based telescopes.

Methods. We have adopted a relatively novel criterion. As a first step, high redshift galaxies are selected in the NIR H band …

A Feasibility Study Of Photometric Reverberation Mapping With Meter-Class Telescopes, Carla June Carroll

Theses and Dissertations

For the past several decades, mass estimates for supermassive black holes hosted by active galactic nuclei (AGN) have been made with the reverberation mapping (RM) technique. This methodology has produced consistent results and has been used to establish several relations that link the characteristics of the host galaxy to the mass of the central black hole. Despite this success, there are less than 50 AGN with black hole masses derived from RM. This low number is generally attributed to the difficulties in coordinating large blocks of telescope time for making simultaneous photometric and spectroscopic observations. Spectroscopic observations also generally require …

Search For Vector-Like T Quarks Decaying To Top Quarks And Higgs Bosons In The All-Hadronic Channel Using Jet Substructure, Cms Collaboration, V. Khachatryan, A. M. Sirunyan, Marc M. Baarmand, Marcus Hohlmann, Himali Kalakhety, Francisco X. Yumiceva

Aerospace, Physics, and Space Science Faculty Publications

A search is performed for a vector-like heavy T quark that is produced in pairs and that decays to a top quark and a Higgs boson. The data analysed correspond to an integrated luminosity of 19.7 fb⁻¹ collected with the CMS detector in proton-proton collisions at s=8" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: normal; word-spacing: normal; overflow-wrap: normal; text-wrap: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">�=8 TeV. For T quarks with large mass values the top quarks and Higgs bosons can have significant Lorentz …

Ruling Out Ic/Cmb X-Rays In Pks 0637-752 And The Implications For Tev Emission From Large-Scale Quasar Jets, Eileen T. Meyer, Markos Georganopoulos, William B. Sparks, Leith E.H. Godfrey, James E.J. Lovell, Eric S. Perlman

Aerospace, Physics, and Space Science Faculty Publications

The Chandra X-ray observatory has discovered dozens of resolved, kiloparsec-scale jets associated with powerful quasars in which the X-ray fluxes are observed to be much higher than the expected level based on the radio-optical synchrotron spectrum. The most popular explanation for the anomalously high and hard X-ray fluxes is that these jets do not decelerate significantly by the kiloparsec scale, but rather remain highly relativistic (Lorentz factors ). By adopting a small angle to the line of sight, the X-rays can thus be explained by inverse Compton upscattering of cosmic microwave background (CMB) photons (IC/CMB), where the observed emission is …

The Event Horizon Of M87, Avery E. Broderick, Ramesh Narayan, John Kormendy, Eric S. Perlman, Marcia J. Rieke, Sheperd S. Doleman

Aerospace, Physics, and Space Science Faculty Publications

The 6 x 10⁹ M⊙ supermassive black hole at the center of the giant elliptical galaxy M87 powers a relativistic jet. Observations at millimeter wavelengths with the Event Horizon Telescope have localized the emission from the base of this jet to angular scales comparable to the putative black hole horizon. The jet might be powered directly by an accretion disk or by electromagnetic extraction of the rotational energy of the black hole. However, even the latter mechanism requires a confining thick accretion disk to maintain the required magnetic flux near the black hole. Therefore, regardless of the jet mechanism, the …

Chiral Imprint Of A Cosmic Gauge Field On Primordial Gravitational Waves, Jannis Bielefeld, Robert R. Caldwell

Dartmouth Scholarship

A cosmological gauge field with isotropic stress-energy introduces parity violation into the behavior of gravitational waves. We show that a primordial spectrum of inflationary gravitational waves develops a preferred handedness, left or right circularly polarized, depending on the abundance and coupling of the gauge field during the radiation era. A modest abundance of the gauge field would induce parity-violating correlations of the cosmic microwave background temperature and polarization patterns that could be detected by current and future experiments.

Determining The Relationship Between The [Oiii] 5007 Å Emission Line Profile And The Stellar Velocity Dispersion In Active Galaxies, Nathaniel Milgram

Physics

The empirical relation between the stellar velocity dispersion (SVD) of the bulge and the mass of the central supermassive black hole (BH) suggests a link between host galaxy and BH evolution. For active galactic nuclei (AGNs), the BH mass (MBH) can be estimated in a straightforward way from the Doppler broadening of the broad emission lines using the so-called virial method. However, the powerful AGN continuum emission often outshines the underlying stellar absorption lines, making it difficult to measure SVD of the host galaxy. Thus, the MBH - SVD relation is difficult to establish for galaxies containing AGNs. As a …

Frequency Of Seyfert Type Transitions In A Sample Of 102 Local Active Galactic Nuclei, Jordan Runco

Physics

A sample of ∼100 type-1 local (0.02 ≤ z ≤ 0.1) active galaxies (AGNs) was selected from the Sloan Digital Sky Survey with black hole masses M_BH > 10⁷ M_ʘ and re-observed using the Keck 10-m telescope to study the local scaling relations between M_BH and the host galaxy properties. As a side product, the data provides insight into any changes of the broad-line region within the 3-9 year time-frame covered by the two sets of spectra. The variability of the broad Hβ emission line is of particular interest to us, not only because it is used …