Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Keyword
-
- Astronautics (4)
- Astronomy (4)
- Science (4)
- Technology (4)
- Magnetic reconnection (3)
-
- Gravitation (2)
- Kelvin-Helmholtz instability (2)
- Photometry (2)
- Southward IMF (2)
- Standard-Model Extension (2)
- Star clusters (2)
- Turbulence (2)
- White dwarfs (2)
- Airglow (1)
- Astrometry (1)
- BASE-9 (1)
- Bayesian software (1)
- Bow shock (1)
- Catalogs (1)
- Collisionless plasmas (1)
- Color figures (1)
- Exosphere (1)
- Galaxy: kinematics and dynamics (1)
- Gravity Probe B (1)
- Lorentz symmetry (1)
- Lorentz violation (1)
- MHD shock (1)
- Magnetic field reconnection (1)
- Magnetic fluctuations (1)
- Magnetopause (1)
Articles 1 - 18 of 18
Full-Text Articles in Physical Sciences and Mathematics
A Deep Proper Motion Catalog Within The Sloan Digital Sky Survey Footprint, Jeffrey A. Munn, Hugh C. Harris, Ted Von Hippel, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Steven Degenarro, Elizabeth Jeffery, Trudy M. Tilleman
A Deep Proper Motion Catalog Within The Sloan Digital Sky Survey Footprint, Jeffrey A. Munn, Hugh C. Harris, Ted Von Hippel, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Steven Degenarro, Elizabeth Jeffery, Trudy M. Tilleman
Publications
A new proper motion catalog is presented, combining the Sloan Digital Sky Survey (SDSS) with second epoch observations in the r band within a portion of the SDSS imaging footprint. The new observations were obtained with the 90prime camera on the Steward Observatory Bok 90 inch telescope, and the Array Camera on the U.S. Naval Observatory, Flagstaff Station, 1.3 m telescope. The catalog covers 1098 square degrees to r = 22.0, an additional 1521 square degrees to r = 20.9, plus a further 488 square degrees of lesser quality data. Statistical errors in the proper motions range from 5 mas …
The Power Of Principled Bayesian Methods In The Study Of Stellar Evolution, Ted Von Hippel, David Van Dyk, David Stenning, Elliot Robinson, Elizabeth Jeffery, Nathan Stein, William Jefferys, Erin M. O'Malley
The Power Of Principled Bayesian Methods In The Study Of Stellar Evolution, Ted Von Hippel, David Van Dyk, David Stenning, Elliot Robinson, Elizabeth Jeffery, Nathan Stein, William Jefferys, Erin M. O'Malley
Publications
It takes years of effort employing the best telescopes and in- struments to obtain high-quality stellar photometry, astrometry, and spectroscopy. Stellar evolution models contain the experience of life- times of theoretical calculations and testing. Yet most astronomers fit these valuable models to these precious datasets by eye. We show that a principled Bayesian approach to fitting models to stellar data yields substantially more information over a range of stellar astrophysics. We highlight advances in determining the ages of star clusters, mass ratios of binary stars, limitations in the accuracy of stellar models, post-main-sequence mass loss, and the ages of individual …
Bayesian Analysis For Stellar Evolution With Nine Parameters (Base-9): User's Manual, Ted Von Hippel, Elliot Robinson, Elizabeth Jeffery, Rachel Wagner-Kaiser, Steven Degennaro, Nathan Stein, David Stenning, William H. Jefferys, David Van Dyk
Bayesian Analysis For Stellar Evolution With Nine Parameters (Base-9): User's Manual, Ted Von Hippel, Elliot Robinson, Elizabeth Jeffery, Rachel Wagner-Kaiser, Steven Degennaro, Nathan Stein, David Stenning, William H. Jefferys, David Van Dyk
Publications
BASE-9 is a Bayesian software suite that recovers star cluster and stellar parameters from photometry. BASE-9 is useful for analyzing single-age, single-metallicity star clusters, binaries, or single stars, and for simulating such systems. BASE-9 uses Markov chain Monte Carlo and brute-force numerical integration techniques to estimate the posterior probability distributions for the age, metallicity, helium abundance, distance modulus, and line-of-sight absorption for a cluster, and the mass, binary mass ratio, and cluster membership probability for every stellar object. BASE-9 is provided as open source code on a version-controlled web server. The executables are also available as Amazon Elastic Compute Cloud …
Book Review: Planetary Rings: A Post-Equinox View 2nd Ed, T. D. Oswalt
Book Review: Planetary Rings: A Post-Equinox View 2nd Ed, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Planetary Rings : a Post-Equinox View 2nd Ed. by Larry W. Esposito, Cambridge, 2014 246p bibl index, 9781107028821 $120.00
The Geocoronal H Α Cascade Component Determined From Geocoronal H Β Intensity Measurements, F. L. Roesler, E. J. Mierkiewicz, S. M. Nossal
The Geocoronal H Α Cascade Component Determined From Geocoronal H Β Intensity Measurements, F. L. Roesler, E. J. Mierkiewicz, S. M. Nossal
Publications
"Geocoronal H α and H β intensity measurements using the Wisconsin H α Mapper Fabry-Perot are used to determine the intensity of the H α cascade component. From basic atomic physics and the work of Meier (1995), we show that the total cascade in geocoronal H α emission is 0.52 ± 0.03 times the geocoronal H β intensity, I(H β), for solar Lyman series excitation of geocoronal hydrogen. The results are consistent with the H α cascade measurements of Mierkiewicz et al. (2012), which were determined directly from the analysis of H α line profile measurements, and significantly narrow the …
A Statistical Study Of Magnetic Field Fluctuations In The Dayside Magnetosheath And Their Dependence On Upstream Solar Wind Conditions, A. P. Dimmock, K. Nykyri, T. I. Pulkkinen
A Statistical Study Of Magnetic Field Fluctuations In The Dayside Magnetosheath And Their Dependence On Upstream Solar Wind Conditions, A. P. Dimmock, K. Nykyri, T. I. Pulkkinen
Publications
The magnetosheath functions as a natural interface connecting the interplanetary and magnetospheric plasma. Since the magnetosheath houses the shocked solar wind, it is populated with abundant magnetic field turbulence which are generated both locally and externally. Although the steady state magnetosheath is to date relatively well understood, the same cannot be said of transient magnetic perturbations due to their kinetic nature and often complex and numerous generation mechanisms. The current manuscript presents a statistical study of magnetic field fluctuations in the dayside magnetosheath as a function of upstream solar wind conditions. We concentrate on the ambient higher-frequency fluctuations in the …
Nonadiabatic Heating In Magnetic Reconnection, Xuanye Ma, Antonius Otto
Nonadiabatic Heating In Magnetic Reconnection, Xuanye Ma, Antonius Otto
Publications
Plasma transport process as a fundamental problem in magnetospheric physics is often associated with strong nonadiabatic heating. At the magnetopause, observations show an increase of specific entropy (i.e., S = p/ργ) by 2 orders of magnitude from the magnetosheath into the magnetosphere. In the near‐Earth magnetotail, particle injection requires strongly entropy depleted plasma bubbles, and their evolution can be strongly modified in the presence of nonadiabatic heating. In this study, one of the critical plasma transport mechanisms, magnetic reconnection, is investigated as a nonadiabatic process in the framework of MHD. It is important to examine whether magnetic reconnection can provide …
High-Resolution Spectroscopy Of The Lunar Sodium Exosphere, E. J. Mierkiewicz, R. J. Oliversen, F. L. Roesler, O. L. Lupie
High-Resolution Spectroscopy Of The Lunar Sodium Exosphere, E. J. Mierkiewicz, R. J. Oliversen, F. L. Roesler, O. L. Lupie
Publications
"We have applied high-resolution Fabry-Perot spectroscopy to the study of the lunar sodium exosphere for the study of exospheric effective temperature and velocity variations. Observing from the National Solar Observatory McMath-Pierce Telescope, we used a dual-etalon Fabry-Perot spectrometer with a resolving power of 180,000 to measure line widths and Doppler shifts of the sodium D2 (5889.95 Å) emission line. Our field of view was 360 km, and measurements were made in equatorial and polar regions from 500 km to 3500 km off the limb. Data were obtained from full moon to 3 days following full moon (waning phase) in March …
Three Moving Groups Detected In The Lamost Dr1 Archive, Zhao J. K., Zhao G., Y. Q. Chen, T. D. Oswalt, K. F. Tan, Y. Zhang
Three Moving Groups Detected In The Lamost Dr1 Archive, Zhao J. K., Zhao G., Y. Q. Chen, T. D. Oswalt, K. F. Tan, Y. Zhang
Publications
We analyze the kinematics of thick disk and halo stars observed by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope. We have constructed a sample of 7993 F, G, and K nearby main-sequence stars (d < 2 kpc) with estimates of position (x, y, z) and space velocity (U, V, W) based on color and proper motion from the Sloan Digital Sky Survey DR9 catalog. Three “phase-space overdensities” are identified in (V,√U2 + 2V 2) with significance levels of σ > 3. Two of them (the Hyades–Pleiades stream …
The White Dwarfs Within 25 Pc Of The Sun: Kinematics And Spectroscopic Subtypes, Edward M. Sion, J. B. Holberg, Terry D. Oswalt, George P. Mccook, Richard Wasatonic, Janine Myszka
The White Dwarfs Within 25 Pc Of The Sun: Kinematics And Spectroscopic Subtypes, Edward M. Sion, J. B. Holberg, Terry D. Oswalt, George P. Mccook, Richard Wasatonic, Janine Myszka
Publications
We present the fractional distribution of spectroscopic subtypes, range and distribution of surface temperatures, and kinematical properties of the white dwarfs (WDs) within 25 pc of the Sun. There is no convincing evidence of halo WDs in the total 25 pc sample of 224 WDs. There is also little to suggest the presence of genuine thick disk subcomponent members within 25 pc. It appears that the entire 25 pc sample likely belongs to the thin disk. We also find no significant kinematic differences with respect to spectroscopic subtypes. The total DA to non-DA ratio of the 25 pc sample is …
The Link Between Shocks, Turbulence And Magnetic Reconnection In Collisionless Plasmas, H. Karimabadi, V. Roytershteyn, H. X. Vu, Y. Omelchenko, J. Scudder, W. Daughton, A. Dimmock, Katariina (Heidi) Nykyri, Et Al.
The Link Between Shocks, Turbulence And Magnetic Reconnection In Collisionless Plasmas, H. Karimabadi, V. Roytershteyn, H. X. Vu, Y. Omelchenko, J. Scudder, W. Daughton, A. Dimmock, Katariina (Heidi) Nykyri, Et Al.
Publications
Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence and magnetic reconnection. In particular collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These 'wavefronts' maintain their integrity for tens of ion cyclotron times but eventually …
Book Review: Cosmic Dawn: The Search For The First Stars And Galaxies, T. D. Oswalt
Book Review: Cosmic Dawn: The Search For The First Stars And Galaxies, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Cosmic Dawn : the Search for the First Stars and Galaxies by George Rhee, springer, 2013. 279p, 9781461478126 $39.99, 9781461478133 $29.99.
Constraints On Violations Of Lorentz Symmetry From Gravity Probe B, James M. Overduin, Ryan D. Everett, Quentin G. Bailey
Constraints On Violations Of Lorentz Symmetry From Gravity Probe B, James M. Overduin, Ryan D. Everett, Quentin G. Bailey
Publications
We use the final results from Gravity Probe B to set new upper limits on the gravitational sector of the Standard-Model Extension, including for the first time the coefficient associated with the time-time component of the new field responsible for inducing local Lorentz violation in the theory.
Local Lorentz-Symmetry Breaking And Gravity, Q. G. Bailey
Local Lorentz-Symmetry Breaking And Gravity, Q. G. Bailey
Publications
The lagrangian-based Standard-Model Extension framework offers a broad description of possible gravitational effects from local Lorentz violation. In this talk, I review the status of the theoretical and phenomenological work in this area. The extension of previous results in linearized gravity to the nonlinear regime is discussed.
Interaction Of Magnetic Reconnection And Kelvin-Helmholtz Modes For Large Magnetic Shear: 1. Kelvin-Helmholtz Trigger, Xuanye Ma, Antonius Otto, Peter A. Delamere
Interaction Of Magnetic Reconnection And Kelvin-Helmholtz Modes For Large Magnetic Shear: 1. Kelvin-Helmholtz Trigger, Xuanye Ma, Antonius Otto, Peter A. Delamere
Publications
At the Earth's magnetopause, both magnetic reconnection and the Kelvin‐Helmholtz (KH) instability can operate simultaneously for southward interplanetary magnetic field conditions. The dynamic evolution of such a system can be expected to depend on the importance of KH wave evolution versus reconnection and therefore on the respective initial perturbations. In this study, a series of local three‐dimensional MHD and Hall MHD simulations are carried out to investigate the situation where the Kelvin‐Helmholtz instability is initially the primary process. It is demonstrated that magnetic reconnection is driven and strongly modified by nonlinear KH waves. The highest reconnection rate is close to …
Interaction Of Magnetic Reconnection And Kelvin-Helmholtz Modes For Large Magnetic Shear: 2. Reconnection Trigger, Xuanye Ma, Antonius Otto, Peter A. Delamere
Interaction Of Magnetic Reconnection And Kelvin-Helmholtz Modes For Large Magnetic Shear: 2. Reconnection Trigger, Xuanye Ma, Antonius Otto, Peter A. Delamere
Publications
A typical property of magnetopause reconnection is a significant perpendicular shear flow due to the fast streaming magnetosheath plasma. Therefore, the magnetopause represents a large magnetic and flow shear boundary during periods of southward interplanetary magnetic field, which can be unstable to Kelvin‐Helmholtz (KH) modes and to magnetic reconnection. A series of local three‐dimensional MHD and Hall MHD simulations is carried out to investigate the interaction of reconnection and nonlinear KH waves considering magnetic reconnection as the primary process. It is demonstrated that the onset reconnection causes a thinning of the shear flow layer, thereby generating small wavelength KH modes. …
Book Review: Robotic Exploration Of The Solar System: Pt. 4: The Modern Era, 2004-2013, T. D. Oswalt
Book Review: Robotic Exploration Of The Solar System: Pt. 4: The Modern Era, 2004-2013, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Robotic Exploration of the Solar System : Pt. 4: the Modern Era, 2004-2013 by Paolo Ulivi with David Harland Springer, 2014 567p bibl index afp, 9781461448112 $44.99, 9781461448129 $29.99
Book Review: The Observer's Guide To Planetary Motion: Explaining The Cycles Of The Night Sky, T. D. Oswalt
Book Review: The Observer's Guide To Planetary Motion: Explaining The Cycles Of The Night Sky, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of The Observer's Guide to Planetary Motion : Explaining the Cycles of the Night Sky by Dominic Ford. Springer, 2014 240p index afp, 9781493906284 $34.99.