A5002198584- Astrophysics and Cosmic Phenomena
- Astrophysics and Star Formation Studies
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Solar and Space Plasma Dynamics
- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- Astro and Planetary Science
- Astronomy and Astrophysical Research
- Ionosphere and magnetosphere dynamics
- Astronomical Observations and Instrumentation
- Atmospheric Ozone and Climate
- Atomic and Molecular Physics
- Particle Accelerators and Free-Electron Lasers
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Atmospheric aerosols and clouds
- Spectroscopy and Laser Applications
- Crystallography and Radiation Phenomena
- Atomic and Subatomic Physics Research
- Geomagnetism and Paleomagnetism Studies
- X-ray Spectroscopy and Fluorescence Analysis
- Radio Astronomy Observations and Technology
- Laser-induced spectroscopy and plasma
- Coal Properties and Utilization
University of Georgia
2011-2023
Johns Hopkins University
1999-2013
Goddard Space Flight Center
1997-2008
University of Maryland, Baltimore County
2004
Bloomberg (United States)
2001
University of Wisconsin–Madison
1994-1999
Marshall Space Flight Center
1962
The launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed by an extensive period calibration and characterization as part preparation for normal satellite operations. Major tasks carried out during this include initial coalignment, focusing, four instrument channels a preliminary measurement resolution throughput performance instrument. We describe results from test program present estimates on-orbit FUSE based on combination these data prelaunch laboratory measurements.
We show that many observations of W44, a supernova remnant in the Galactic plane at distance about 2500 pc, are remarkably consistent with simplest realistic model. The model is evolving smooth ambient medium fairly high density, 6 cm-3 on average, substantial density gradient. At observed time it has an age 20,000 yr, associated pulsar, and radius 11-13 pc. Over most outer surface, radiative cooling become important postshock gas; denser end there been sufficient compression cooled gas to...
Highly ionized species, such as C iv, N v, and O vi, are commonly observed in diffuse gas various places the universe, our Galaxy's disk halo, high velocity clouds (HVCs), external galaxies, intergalactic medium. These ions often used to trace hot whose temperature is a few times 105 K. One possible mechanism for producing turbulent mixing of cool (such that or intermediate cloud) with hotter (a 106 K) locations where these gases slide past each other. By using hydrodynamic simulations...
Interstellar material (ISMa) is observed both inside and outside of the heliosphere. Relating these diverse sets ISMa data provides a richer understanding interstellar medium The galactic environment Sun dominated by warm, low-density, partially ionized consisting atoms dust grains. properties heliosphere are dependent on pressure, composition, radiation field, ionization, magnetic field ambient ISMa. very low-density interior Local Bubble, combined with an expanding superbubble shell...
We present measurements of the Galactic halo's X-ray emission for 110 XMM-Newton sight lines selected to minimize contamination from solar wind charge exchange emission. detect few million degree gas on ∼4/5 our lines. The temperature is fairly uniform (median = 2.22 × 106 K, interquartile range 0.63 K), while measure and intrinsic 0.5–2.0 keV surface brightness vary by over an order magnitude (∼(0.4–7) 10−3 cm−6 pc ∼(0.5–7) 10−12 erg cm−2 s−1 deg−2, respectively, with median detections 1.9...
In a previous paper, we presented the analytical background for new model W44; in this report hydrocode experiments verifying many of details. Our remnant is evolving moderately dense (~6 cm-3), ambient medium having substantial density gradient. At observed age (~20,000 yr), shock radiative over much surface, with expansion speeds only ~130-200 km s-1 and rare ends, respectively. With these speeds, has cool periphery does not produce limb-brightened X-ray image. It thermal conduction within...
Far Ultraviolet Spectroscopic Explorer spectra of the white dwarf stars G191-B2B, GD 394, WD 2211-495, and 2331-475 cover absorption features out ground electronic states N I, II, III, O Ar I in far-ultraviolet, providing new insights on origin partial ionization local interstellar medium (LISM) and, for case cloud that immediately surrounds solar system. Toward these targets abundances sometimes are significantly below their cosmic relative to H I. In diffuse medium, elements not likely be...
We report the results of a survey O VI λ1032 absorption along lines sight to 25 white dwarfs in local interstellar medium (LISM) obtained with FUSE. find that all is generally weak, and number cases, completely absent. No was detected significance greater than 2 σ for 12 stars, where 1 uncertainty ~4 mÅ, equivalent an column density ~3 × 1012 cm-2. Of remaining most have densities N(O ) < 1013 cm-2, no exceed 1.7 For hot (Teff > 40,000 K) dwarfs, there some evidence may be at least partially...
The model of a Local Hot Bubble has been widely accepted as providing framework that can explain the ubiquitous presence soft X-ray background diffuse emission. We summarize current knowledge on this local interstellar region, paying particular reference to observations sample emission from presumed million degree K hot plasma. However, we have listed numerous are seemingly in conflict with concept Bubble. In particular, discovery solar wind charge exchange generate an appreciable signal...
We present hydrodynamic simulations of high-velocity clouds (HVCs) traveling through the hot, tenuous medium in Galactic halo. A suite models was created using FLASH hydrodynamics code, sampling various cloud sizes, densities, and velocities. In all cases, cloud-halo interaction ablates material from clouds. The ablated falls behind clouds, where it mixes with ambient to produce intermediate-temperature gas, some which radiatively cools less than 10,000 K. Using a non-equilibrium ionization...
This paper reports on detailed, nonequilibrium hydrodynamic simulations of supernova remnants (SNRs) evolving in a warm, low-density, nonthermal pressure-dominated ambient medium (T = 104 K, n 0.01 cm-3, Pnt 1.8 × 103 K cm-3), with the goals characterizing their structure and C+3, N+4, O+5 content, emission, line profiles investigating effects lower Galactic halo. If undisturbed by external objects, these have great longevity, surviving for ~1.7 107 yr. During adiabatic phase, they contain...
We compare the predictions of three physical models for origin hot halo gas with observed X-ray emission, derived from 26 high-latitude XMM-Newton observations soft background between l = 120° and 240°. These were chosen a much larger set as they are expected to be least contaminated by solar wind charge exchange emission. characterize emission in band single-temperature plasma model. find that temperature is fairly constant across sky (∼(1.8–2.4) × 106 K), whereas measure varies an order...
view Abstract Citations (65) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hot Gas in the Interstellar Medium: A Reanalysis of O VI Absorption Data Shelton, R. L. ; Cox, D. P. The Copernicus O(+5) column densities toward 72 stars provide a rare and valuable tracer 105.5 K gas interstellar medium. original analysis data by Jenkins provided important clues about distribution ions, but our understanding local medium has since grown...
We present the result of a Chandra ACIS observation pulsar PSR B1853+01 and its associated wind nebula (PWN), embedded within supernova remnant W44. A hard band map cleanly distinguishes PWN from thermal emission The is extended in north-south direction, with an extent about half that radio emission. Morphological differences between X-ray images are apparent. Spectral fitting reveals clear difference spectral index (Gamma ~ 1.4) 2.2). more accurate values for flux used refine estimates...
We present an analysis of a pair Suzaku spectra the soft X-ray background (SXRB), obtained from pointings on and off nearby shadowing filament in southern Galactic hemisphere. Because different column densities two pointing directions, observed emission halo has shape spectra. make use this difference when modeling to separate absorbed unabsorbed foreground Local Bubble (LB). The temperatures measures we obtain are significantly those determined earlier XMM-Newton same directions. attribute...
Abstract The fundamental collisional process of charge exchange (CX) has been established as a primary source X-ray emission from the heliosphere, planetary exospheres, and supernova remnants. In this process, results capture an electron by highly charged ion neutral atom or molecule, to form excited, high-charge state ion. As captured cascades down lowest energy level, photons are emitted, including X-rays. To provide reliable CX-induced spectral models realistically simulate these...
The Galaxy's population of High Velocity Clouds (HVCs) may include a subpopulation that is confined by dark matter minihalos and falling toward the Galactic disk. We present first magnetohydrodynamic simulational study matter-dominated HVCs colliding with weakly magnetized galactic Our have baryonic masses $5 \times 10^6\,$M$_{\odot}$ minihalo 0, $3 10^8$, or $1 10^9\,$M$_{\odot}$. They are modeled on Smith Cloud, which said to collided disk 70 Myr ago. find that, in all cases, cloud's...
We report on the Chandra observations of archetypical mixed-morphology (or thermal composite) supernova remnant W44. As with other remnants, W44's projected center is bright in X-rays. It has an obvious radio shell but no discernible X-ray shell. In addition, X-ray-bright knots dot image. The spectral analysis data shows that remnant's hot metal-rich and are regions comparatively elevated elemental abundances. Neon among affected elements, suggesting ejecta contributes to abundance trends....
We present measurements of the soft X-ray background (SXRB) O VII and VIII intensity between $l = 120\degr$ 240\degr$, first results a survey SXRB using archival XMM-Newton observations. do not restrict ourselves to blank-sky observations, but instead use as many observations possible, removing bright or extended sources by hand if necessary. The oxygen intensities are typically ~0.5-10 photons/cm^2/s/sr (line units, L.U.) for ~0-5 L.U. VIII. Our dataset includes 69 directions with multiple...
We present an all-sky catalog of diffuse O vii and viii line intensities, extracted from archival XMM-Newton observations. This supersedes our previous catalog, which covered the sky between l = 120° 240°. attempted to reduce contamination near-Earth solar wind charge exchange (SWCX) emission by excluding times high proton flux data. Without this filtering, we were able extract measurements 1868 With nearly half observations became unusable, only 1003 yielded measurements. The intensities...
In the Galactic halo, metal-bearing halo material mixes into high velocity clouds (HVCs) as they hydrodynamically interact. This interaction begins long before completely dissipate and slow to of material. order make quantitative estimates mixing efficiency resulting metal enrichment HVCs, we made detailed 2 3 dimensional simulations cloud-ISM interactions. Our track hydrodynamics time dependent ionization levels. They assume that cloud originally has a warm temperature extremely low...
We report the first Far-Ultraviolet Spectroscopic Explorer measurements of diffuse O VI (λλ1032, 1038) emission from general interstellar medium outside supernova remnants or superbubbles. observed a 30'' × region sky centered at l = 3150 and b -413. From intensities (2930 ± 290 [random] 410 [systematic] 1790 260 250 photons cm-2 s-1 sr-1 in λλ1032 1038, respectively), derived equations, assumptions about source location, we calculate intrinsic intensity, electron density, thermal pressure,...
This paper reports the first study of O VI resonance line emission (λλ1032, 1038) originating in Local Bubble (or Hot Bubble) surrounding solar neighborhood. In spite fact that absorption within has been observed, no was detected during our 230 ks Far Ultraviolet Spectroscopic Explorer observation a "shadowing" filament southern Galactic hemisphere. As result, tight 2 σ upper limits are set on intensities 1032 and 1038 Å lines: 500 530 photons cm-2 s-1 sr-1, respectively. These values place...
We present an analysis of the X-ray spectrum Local Bubble, obtained by simultaneously analyzing spectra from two XMM-Newton pointings on and off absorbing filament in Southern galactic hemisphere (b ~ -45 deg). use difference Galactic column density these directions to deduce contributions unabsorbed foreground emission due absorbed halo extragalactic background. find Bubble is consistent with a plasma collisional ionization equilibrium temperature $\log T_{LB} = 6.06^{+0.02}_{-0.04}$...
We used FUSE to observe ultraviolet emission from diffuse O VI in the hot gas Galactic halo. By comparing our result with another, nearby observation blocked by an opaque cloud at a distance of 230 pc, we could subtract off contribution Local Bubble, leading apparent halo intensity I_{OVI} = 4680^{+570}_{-660} photons/cm^2/s/sr. A correction for foreground extinction leads intrinsic that be as much twice this value. Assuming T ~ 3 x 10^5 K, conclude electron density, n_e, is 0.01-0.02 /cm^3,...