Oxygen-rich Material Research Articles

Imaging the oxygen-rich disk toward the silicate carbon star EU Andromedae

Context. Silicate carbon stars are characterized by oxygen-rich circumstellar environments as revealed by prominent silicate emission, despite their carbon-rich photospheres. While the presence of a circumbinary disk or a disk around an unseen, low-luminosity companion has been suggested to explain the peculiar dust chemistry, the origin of silicate carbon stars is still a puzzle to date. Aims. We present multi-epoch, high-angular resolution observations of 22 GHz H2O masers toward the silicate carbon star EU And to probe the spatio-kinematic distribution of oxygen-rich material. Methods. EU And was observed at three epochs (maximum time interval of 14 months) with the Very Long Baseline Array (VLBA). Results. Our VLBA observations of the 22 GHz H2O masers have revealed that the maser spots are distributed along a straight line across ∼20 mas, with a slight hint of an S-shaped structure. The observed spectra show three prominent velocity components at VLSR= −42, −38, and −34 km s −1 , with the masers in SW redshifted and those in NE blueshifted. The maser spots located in the middle of the overall distribution correspond to the component at VLSR = −38 km s −1 , which approximately coincides with the systemic velocity. These observations can be interpreted as either an emerging helical jet or a disk viewed almost edge-on (a circumbinary or circum-companion disk). However, the outward motion measured in the VLBA images taken 14 months apart is much smaller than what is expected from the jet scenario. Furthermore, the mid-infrared spectrum obtained with the Spitzer Space Telescope indicates that the 10 µm silicate emission is optically thin and the silicate grains are of sub-micron size. This lends support to the presence of a circum-companion disk, because an optically thin circumbinary disk consisting of such small grains would be blown away by the intense radiation pressure of the primary (carbon-rich) star. If we assume Keplerian rotation for the circum-companion disk, the mass of the companion is estimated to be 0.5–0.8 M� . We also identify CO2 emission features at 13–16 µm in the Spitzer spectrum of EU And–the first unambiguous detection of CO2 in silicate carbon stars.

Modeling core collapse supernovae in 2 and 3 dimensions with spectral neutrino transport

The overwhelming evidence that the core collapse supernova mechanism is inherently multidimensional, the complexity of the physical processes involved, and the increasing evidence from simulations that the explosion is marginal presents great computational challenges for the realistic modeling of this event, particularly in 3 spatial dimensions. We have developed a code scalable to computations in 3 dimensions that couples PPM Lagrangian-withremap hydrodynamics, multigroup flux-limited diffusion neutrino transport (with many improvements), and a nuclear network. The neutrino transport is performed in a ‘‘ray-by-ray-plus’’ approximation, wherein all the lateral effects of neutrinos are included (e.g., pressure, velocity corrections, advection) except lateral transport. A moving radial grid option permits the evolution to be carried out from initial core collapse with only modest demands on the number of radial zones. The inner part of the core is evolved after collapse, along with the rest of the core and mantle, by subcycling the lateral evolution near the center as demanded by the small Courant times. We present results of 2-D simulations of a symmetric and an asymmetric collapse of both a 15 and an 11 M⊙ progenitor. In each of these simulations we have discovered that once the oxygen-rich material reaches the shock there is a synergistic interplay between the reduced ram pressure, the energy released by the burning of the shock-heated oxygen-rich material, and the neutrino energy deposition that leads to a revival of the shock and an explosion.

Reactive polar precipitation via ether cross-linkage: A new mechanism for solid bitumen formation

Analysis of solid bitumens from the Tengiz Field, Kazakhstan by X-ray photoelectron spectroscopy provides evidence for a new reservoir alteration process – reactive polar precipitation via the formation of ether cross-linkages. Solid bitumens, which may occupy >30% of the pore space, were analyzed in situ and as isolated concentrates of the material in vein/fracture-fills or encapsulated within micropores. Their compositions were found to vary greatly, particularly in the amounts of aromatic carbon and in the organic oxygen mostly present in C–O single bond environments. While most solid bitumen in Tengiz reservoir rocks arose from asphaltene precipitates, surfaces are coated with a relatively aliphatic- and oxygen-rich material. Organic sulfur occurs exclusively in aromatic sulfur environments in most samples, while nitrogen is in pyrrolic and pyridinic environments. To account for the average organic composition of solid bitumen, we propose that the coatings are formed by condensation of low-molecular weight polar compounds that are normally soluble in most oils. A likely reaction mechanism involves free radicals, produced by thermally labile non-aromatic sulfur (–SH) forms, reacting with hydroxyls. This reaction results in a release of H 2S and the formation of compounds with at least one ether-linkage and multiple heteroatoms within the aromatic cores. Similar reactions are believed to convert the reactive polar precipitate and previously precipitated asphaltenes into toluene-insoluble bitumens. This hypothesis explains the chemical nature of the solid bitumens, accounts for previously reported anomalies in reflectance, and is fully consistent with current geohistory models. Whether this reservoir alteration process occurs outside of the North Caspian Basin is not known, but we suspect that the process occurs elsewhere. Thin coatings of polar precipitates, which may be undetectable by conventional optical microscopy, could have significant impact on reservoir properties, such as surface wetability or mineral diagenesis.

High angular resolutionN-band observation of the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument

We present the results of N-band spectro-interferometric observations of the silicate carbon star IRAS08002-3803 with the MID-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO). The observations were carried out using two unit telescopes (UT2 and UT3) with projected baseline lengths ranging from 39 to 47 m. Our observations of IRAS08002-3803 have spatially resolved the dusty environment of a silicate carbon star for the first time and revealed an unexpected wavelength dependence of the angular size in the N band: the uniform-disk diameter is found to be constant and ∼36 mas (72 R� ) between 8 and 10 µm, while it steeply increases longward of 10 µm to reach ∼53 mas (106 R� )a t 13µm. Model calculations with our Monte Carlo radiative transfer code show that neither spherical shell models nor axisymmetric disk models consisting of silicate grains alone can simultaneously explain the observed wavelength dependence of the visibility and the spectral energy distribution (SED). We propose that the circumstellar environment of IRAS08002-3803 may consist of two grain species coexisting in the disk: silicate and a second grain species, for which we consider amorphous carbon, large silicate grains, and metallic iron grains. Comparison of the observed visibilities and SED with our models shows that such disk models can fairly – though not entirely satisfactorily – reproduce the observed SED and N-band visibilities. Our MIDI observations and the radiative transfer calculations lend support to the picture where oxygen-rich material around IRAS08002-3803 is stored in a circumbinary disk surrounding the carbon-rich primary star and its putative low-luminosity companion.

Electric-dipole spin-resonance signals related to extended interstitial agglomerates in silicon

Three electric-dipole spin-resonance signals, labeled TU7, TU8, and TU9, were detected after subjecting oxygen-rich silicon samples to two-step annealing procedures at 450 and 650°C for prolonged times. The formation and structural evolution of large interstitial agglomerates, known as rodlike defects, occur in oxygen-rich silicon material during similar annealing procedures. Comparison of parameters and formation peculiarities of the defects, inferred from the investigation of the detected signals, with those previously reported for rodlike defects, allowed the assigning of the TU7, TU8, and TU9 spectra to the line-interstitial defects, the planar defects, and the dislocation dipoles, respectively. Correlations of the spin-resonance signals and peculiarities in the photoluminescence spectra for the samples are reported and analyzed.

Separation and characterization of foulant material in coker gas oils from Athabasca bitumen

Gas oil streams from the upgrading of oilsands bitumen contain toluene insoluble, gummy, solid foulants that cause process problems by plugging hydrotreater feed filters and catalyst beds. From a process optimization standpoint, it is of considerable interest to determine the exact origin and nature of this material in order to design remedial measures. We selected coker heavy gas oil (KHGO) from bitumen upgrading as the primary test material for this work but also include samples from other parts of the process. Typically, solids content of gas oils are determined by a filtration method. For the KHGO sample used here, this approach yielded a value of 45 ppm. We also compared solids content using ultra- and low-speed centrifugation techniques. With toluene as the diluent, both of these centrifugation methods gave virtually the same toluene insolubles (TI) value, i.e. 24 and 23 ppm, respectively. For paraffinic diluents the measured TI contents ranged from about 50 to 200 ppm. Our results demonstrate that KHGO may contain significant amounts of TI not measured by conventional filtration. Characterization of gas oil TI from different sampling points in the bitumen upgrading circuit showed that it is a nitrogen and oxygen rich organic material, associated with minor amounts of inorganic elements representative of ash-forming iron minerals and alumino-silicate clay. The most likely source for this intractable toluene insoluble fraction appears to be a low molecular weight pyrrollic species present in heavy gas oil. Such compounds are easily oxidized to produce insoluble polymers that can interact with inorganic minerals and metals, producing gummy material capable of blinding filters.

Second-order generation of point defects in highly irradiated float zone silicon—annealing studies

Isothermal and isochronal annealing experiments have shown that the I defect (the main cause for the changes in silicon diodes characteristics after high levels of gamma-irradiation) is stable up to 325–350°C. Possible reactions, which can explain the behavior of different defects formed during the annealing experiments, are discussed. All the experimental results concerning the I center (second-order irradiation induced defect, formed most likely via VO center, suppressed in oxygen rich material, high thermal stability) make it the favorite for being associated with the V2O2 complex.

Radiation-induced defects in oxygen-enriched silicon detector materials

A brief review of the influence of oxygen-enrichment on the damage parameters of silicon detectors is given, highlighting important conclusions for detector operation in high-energy physics radiation environments. With this background, defect spectroscopy data is presented for oxygen-rich detector materials using deep-level transient spectroscopy, photoluminescence, and electron-paramagnetic resonance. Among other observations, a defect level at E C −0.067 eV is reported to be introduced at an enhanced rate in oxygen-rich material. The limitations of the spectroscopic techniques in identifying the microscopic origins for damage-induced doping changes are discussed.

The A center binding a single hydrogen atom in crystalline silicon observed by EPR

Electron paramagnetic resonance measurements on proton- and deuteron-implanted silicon crystals reveal a new signal from a vacancy-type defect with spin S=12, which is observable only in oxygen-rich material. The signal is strongly temperature-dependent, displaying monoclinic-I symmetry below 180K and orthorhombic-I symmetry above 240K in the proton-implanted samples. Resolved proton-hyperfine splittings show that a single hydrogen atom is located ∼2.5Å from the silicon atom carrying the dangling bond. The observed properties, including the change of symmetry, allow an unambiguous identification of the signal with VOH0, the neutral charge state of the monovacancy–oxygen complex (known as the A center) binding one hydrogen atom. The hydrogen atom is observed to jump readily between two equivalent sites in the (110) mirror plane of the defect.

Bond-centered hydrogen in silicon studied byin situdeep-level transient spectroscopy

In situ deep level transient spectroscopy (DLTS) has been applied to investigate n-type silicon implanted with protons at low temperatures. Two DLTS signals, labeled ${E3}^{\ensuremath{'}}$ and ${E3}^{\ensuremath{''}},$ originate from hydrogen-related donor centers. The electron emission rates of the donors are similar and the two signals are discernible only because they form and anneal differently. In n-type silicon, the ${E3}^{\ensuremath{'}}$ and ${E3}^{\ensuremath{''}}$ centers transform into negatively charged centers at \ensuremath{\sim}100 K and at \ensuremath{\lesssim}65 K, respectively. Both signals can be regenerated at 65 K: ${E3}^{\ensuremath{'}}$ by forward-bias injection of holes and ${E3}^{\ensuremath{''}}$ by illumination with band-gap light under reverse-bias conditions. During the ${E3}^{\ensuremath{'}}$ regeneration long-range migration of hydrogen occurs, whereas ${E3}^{\ensuremath{''}}$ regenerates without migration. In the space-charge layer of reverse biased diodes, ${E3}^{\ensuremath{'}}$ converts into ${E3}^{\ensuremath{''}}$ with an activation enthalpy of 0.44 eV in oxygen-rich material, whereas ${E3}^{\ensuremath{''}}$ converts into ${E3}^{\ensuremath{'}}$ with an activation enthalpy of 0.72 eV in oxygen-poor material. It is found that the density of hydrogen sites associated with ${E3}^{\ensuremath{''}}$ approximately equals the oxygen concentration, whereas the density of ${E3}^{\ensuremath{'}}$ sites is about ${10}^{23}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$ These results provide further evidence for our previous assignment of ${E3}^{\ensuremath{'}}$ to isolated hydrogen at a bond center site and leads to the assignment of ${E3}^{\ensuremath{''}}$ to bond centered hydrogen perturbed by a nearby oxygen atom. We argue that dilated Si-Si bonds in the strain fields around impurities and defects are trapping sites for hydrogen.

Evolution of defect structures in silicon after low temperature implantation of hydrogen

Proton implantation into n-type silicon at initiates the formation of two deep donor centers containing hydrogen. These centers, denoted E3′ and E3′′, can be observed when deep-level transient spectroscopy is applied in-situ to as-implanted diodes . The emission rates of E3′ and E3′′ are very similar, and the centers are discernible only because they form and anneal differently. In their neutral charge states (i.e. zero-bias annealing) E3′ anneals in ≈10 min at 100 K and E3′′ anneals in ≈50 ms at 75 K. The zero-bias anneals lead to a negatively charged center from which both E3′ and E3′′ can be recovered at low temperature: E3′ by forward-bias injection of holes, and E3′′ by reverse-bias illumination with band-gap light. The E3′ recovery is associated with fast migration of hydrogen, while E3′′ recovers instantly without migration. The analogous anneals in the positive charge states (i.e. reverse-bias annealing) differ for oxygen-rich and oxygen-poor material. In Cz silicon E3′ converts at ≈220 K to E3′′ which then subsequently anneals at ≈260 K. In Fz silicon the order of anneals is reversed. Here E3′′ converts to E3′ at ≈230 K. Both centers disappear in the temperature range 240–260 K. We analyze the annealing scenario within a quantitative diffusion model that complies with the present theoretical understanding of isolated hydrogen in silicon. We conclude that the density of hydrogen sites associated with E3′′ approximately equals the oxygen concentration while the density of E3′ sites corresponds to the atomic density of silicon. We identify the E3′ center as isolated bond-center hydrogen and E3′′ as bond-center hydrogen which is perturbed (and stabilized in the positive charge state) by nearby interstitial oxygen. We argue that dilated Si–Si bonds, present in the strain field around impurities and defects, rather generally may act as trapping sites for otherwise isolated hydrogen resulting in the formation of a family of bond-center type centers that are very much alike.

A Circumbinary Reservoir around BM Geminorum?

We report the detection of both (J = 1-0) and (J = 2-1) CO emission from the oxygen-rich circumstellar envelope around a carbon star with an oxygen-rich circumstellar envelope, BM Gem. The line has two distinct components. Unique among mass-losing carbon stars, there is a feature that is much narrower (FWHM ~ 1 km s-1) than the normal CO emission detected from winds. This narrow feature sits on top of a broader (FWHM = 15 km s-1) line, which is probably the emission from the normal wind. The most plausible interpretation of the narrow feature is that we are observing emission from a circumbinary reservoir of material, probably in the form of a distorted or puffed-up disk. We propose that this circumbinary reservoir is composed of oxygen-rich material left over from a previous phase of mass loss that was trapped in the system by the action of an as yet undetected companion.

An oxygen-rich dust disk surrounding an evolved star in the Red Rectangle

The Red Rectangle1 is the prototype of a class of carbon-rich reflection nebulae surrounding low-mass stars in the final stages of evolution. The central star of this nebula has ejected most of its layers (during the red-giant phase), which now form the surrounding cloud, and is rapidly evolving to a white dwarf. This star is also a member of a wide binary system2, which is surrounded by a thick, dusty disk of material3,4. Here we report infrared observations of the Red Rectangle that reveal the presence of oxygen-rich material: prominent emission bands from crystalline silicates, and absorption lines arising from carbon dioxide. The oxygen-rich material is located in the circumbinary disk, in contrast to the previously known carbon-rich dust, which is found mainly in the extended nebula5,6. The properties of the oxygen-rich dust are similar to those of dusty disks surrounding young stars7, which are believed to be the sites of planet formation. Grain processing, and perhaps even planet formation, may therefore also be occurring in the circumbinary disk of this evolved star.

Dust around main sequence and evolved stars

Data for several main sequence and evolved stars, from the photopolarimeter on ISO (ISOPHOT), are presented. Dust shells are resolved for Y CVn and RS Lib at 60μm. Low resolution spectra from ISOPHOT are shown for several evolved stars, and compared to the spectrum of Vega (a stellar photosphere) and HD 169142 (showing emission features from Polycyclic Aromatic Hydrocarbons). W Lyr shows the signature of oxygen-rich circumstellar material around 3μm, V Aql and Y CVn the signature of carbon-rich material.

Hubble Space TelescopeSpectrum of SN 1987A at an Age of 8 Years: Radioactive Luminescence of Cool Gas

The Hubble Space Telescope 2000-8000 A spectrum of SN 1987A observed on 1995 January 7 (7.87 yr after the explosion) is dominated by Hα and UV lines, including Mg II-Mg I λ2825 (equal to Hα in luminosity), Fe II UV 2 (two-thirds the intensity of Hα), Fe II UV 3 (one-half the intensity of Hα), and a 3730 A emission feature identified with a blend of [O II] λ3727 and Fe I emission lines. [O I] λ6300 and lines of [Ca II] and Na I, as well as some Fe II optical forbidden and permitted lines are present at visual wavelengths. Also present are a number of weak emission features, which are presumably metal lines produced by photon degradation as a result of reprocessing of UV radiation into metal lines. Modeling the Mg II-Mg I lines provides the velocity of the outer visible radius of the envelope, 9000 ± 500 km s-1 in the Mg II λ2800 line, which is consistent with the earlier direct HST imaging at near-UV wavelengths. The UV/optical emission lines originate from the radioactive luminescence of the cool gas (T ≈ 130-160 K). The metal lines reflect the instantaneous reprocessing of the energy deposited from 44Ti radioactive decays through collisions with fast electrons, while the Hα emission primarily comes from the recombination of previously ionized hydrogen. The overall luminosity of the Fe II emission lines, ~1035 ergs s-1, can be explained if the bulk of the positrons from a mass (1-2) × 10-4 M☉ of 44Ti release their energy in the iron-rich material, which suggests the presence of a magnetic field B > 5 × 10-13 G prohibiting the escape of positrons into oxygen and hydrogen gas. The ionized fraction in the iron-rich material is small (0.2-0.3), and the total UV/optical emission from Fe I should be comparable to that from Fe II. Most of the 1036 ergs s-1 deposited by the 44Ti positrons should be emitted in the Fe II 26 μm line. The observed Hα luminosity decrease, by 5 orders of magnitude between the ages of 1 to 8 yr, is reproduced in a time-dependent model of ionization and cooling with the standard amount of radioactive nuclides. However, an additional source of energy at the present epoch with a deposition rate 30 ergs s-1 g-1 (≈ 1036 ergs s-1 in the whole envelope) is not ruled out. The present average temperature in the hydrogen envelope predicted by the time-dependent model is 130 K, which is lower than the value T ≈ 350 K obtained from the observed Balmer continuum shape. However, the shape is affected by a possible contribution of metal lines to the Balmer continuum. The luminosity of the [O I] λ6300 doublet is consistent with that expected for the deposited energy of γ-rays from (1-2) × 10-4 M☉ of 44Ti for an assumed 1.5-2 M☉ of oxygen. If the oxygen mass does not exceed 2 M☉, 1 × 10-4 M☉ is a lower limit for the amount of 44Ti in SN 1987A. The maximum fraction of the 44Ti positron energy deposited into oxygen-rich material does not exceed 5%, which is consistent with positron trapping in Fe-rich material. The [O I] λ6300 line intensity rules out the presence of a central source of γ-radiation (hν > 100 keV) with a luminosity Lγ > 4 × 1036 ergs s-1.

Detection of Water after the Collision of Fragments G and K of Comet Shoemaker–Levy 9 with Jupiter

We observed Jupiter on 17–19 July 1994 using NASA's Kuiper Airborne Observatory (KAO) deployed out of Melbourne, Australia. The KAO Echelle Grating Spectrograph (KEGS) uses an array detector with 128 spectral elements and 20 spatial elements. The spectral resolution was 0.19 cm−1, equivalent to a resolving power of 6800. We detected three H2O emission lines near 7.7 μm as well as numerous emission features of CH4. At the peak of the fallback phase for the ejecta from the G and K fragments, we infer temperatures between 1000 and 1200 K at the 3-μbar pressure level on Jupiter. The H2O lines at 7.7 μm were visible for only about 10 to 20 min. We obtained line-of-sight abundances of H2O for both G and K of 1.0 to 1.5 × 1018cm−2. The inferred mass of H2O in each fragment ranges from 1.4 to 2.8 × 1012g, equivalent to spheres of ice 140 to 180 m in diameter at unit density. This should be considered a lower limit to H2O as the 7.7-μm data are sensitive only to the hottest component of water. The G and K impact sites exhibited remarkably similar spectra at the time of peak infrared emission about 14 min after impact. The inferred abundance of H2O at this time was comparable to that of CH4. We interpret the observed CH4emission as due to heating of pre-existing jovian CH4in the upper stratosphere. Water in the impact sites can be explained by shock chemistry provided that the C/O ratio is less than 1. Our observations are consistent with a scenario in which oxygen-rich cometary material combines with jovian H2to produce H2O during the fallback phase. Combining our observations with spectra acquired from the Near Infrared Mapping Spectrometer on the Galileo spacecraft, we do not believe that the fragments reached the 6-bar level in order to excavate jovian water.

Chemical evolution of irregular and blue compact galaxies

We discuss the chemical evolution of metal poor galaxies and conclude that their oxygen deficiency is not due to: the production of black holes by massive stars or a varying slope of the Initial Mass Function, IMF, at the high-mass end. A varying IMF at the low-mass end alone or in combination with: (a) an outflow of oxygen-rich material, (b) an outflow of well-mixed material, and (c) the presence of dark matter that does not participate in the chemical evolution process, is needed to explain their oxygen deficiency. Outflow of material rich in oxygen helps to account for the large helium to oxygen mass ratio values derived from these objects, but it works against explaining the carbon to oxygen mass ratio and the heavy elements minus carbon and oxygen to oxygen mass ratio values.

Young oxygen-rich supernova remnants. 1: Observations of three southern remnants

view Abstract Citations (30) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Young Oxygen-rich Supernova Remnants. I. Observations of Three Southern Remnants Sutherland, Ralph S. ; Dopita, Michael A. Abstract Narrowband imaging and two-dimensional spectrophotometery are combined in a series of observations of N132D, a young, oxygen-rich supernova remnant in the Large Magellanic Cloud. Comparison spectra of two galactic remnants, Pup A and SNR G292.0+ 1.8 are also examined. The observations permit the determination of some important physical parameters of the N132D remnant in particular. An expansion age of 2350 +/- 520 yr is obtained, significantly greater than the ~1300 yr obtained by Lasker (1980). Estimates of the densities and temperatures in the observed oxygen-rich material are made on the basis of simple homogeneous slab models. The models indicate that such simple models are unlikely to be appropriate; nevertheless they do highlight the difficulties of interpretation when the diagnostic plot trends lie in similar directions to that expected from reddening effects. Line fluxes are given in raw form, and estimates of the reddening that may be applicable are given. This forms the first paper in a short series, in the second paper an excitation mechanism for the oxygen-rich material, based on an R-type ionization front model, is presented. Publication: The Astrophysical Journal Pub Date: January 1995 DOI: 10.1086/175180 Bibcode: 1995ApJ...439..365S Keywords: Chronology; Density Distribution; Magellanic Clouds; Oxygen; Supernova Remnants; Temperature Profiles; Flux Density; Image Analysis; Spectrum Analysis; Stellar Spectrophotometry; Velocity Distribution; Astronomy; GALAXIES: MAGELLANIC CLOUDS; ISM: SUPERNOVA REMNANTS full text sources ADS | data products SIMBAD (3) NED (1) Related Materials (1) Part 2: 1995ApJ...439..381S

Young oxygen-rich supernova remnants. 2: an oxygen-rich emission mechanism

view Abstract Citations (57) References (62) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Young Oxygen-rich Supernova Remnants. II. an Oxygen-rich Emission Mechanism Sutherland, Ralph S. ; Dopita, Michael A. Abstract An emission mechanism is presented for the observed oxygen-rich plasma emission in young, oxygen-rich supernova remnants (OSNRs). The mechanism involves the interaction of a fast moving "blob" of oxygen-rich material with the SNR medium, forming a bow-shock/cloud-shock structure. The shock emission is then determined to drive a weak R-type ionization front through the oxygen-rich material. The combined shock and ionization front emission reproduces the major features of the observed optical and UV spectrum. Dynamical constraints based on the observed motions, lifetimes, and estimated densities of the oxygen-rich knots are used to determine model parameters. The plasma composition, predominantly [Ne/O] ~ -0.34, used is consistent with massive stellar evolution and explosive synthesis models. Significantly, the unusually high [O III] temperature-sensitive ratio is reproduced simultaneously with the low ionization, optical, [O I], and [O II] lines. The UV emission is predicted, and a good comparison is made with the UV spectrum of SNR E102.2 - 7219 from observations of Blair et al. (1989). Specific abundance variations were not used to make detailed fits to the observations, detailed abundance determination will require further observations. This forms the second paper in a short series; in the first paper observations for three southern OSNRs were presented. Those observations are used here along with other observations from the literature. Publication: The Astrophysical Journal Pub Date: January 1995 DOI: 10.1086/175181 Bibcode: 1995ApJ...439..381S Keywords: Oxygen; Shock Waves; Spectral Emission; Stellar Models; Supernova Remnants; Ultraviolet Spectra; Abundance; Cooling Flows (Astrophysics); Thermal Stability; Velocity Distribution; Astronomy; RADIATION MECHANISMS: NONTHERMAL; SHOCK WAVES; ISM: SUPERNOVA REMNANTS full text sources ADS | data products SIMBAD (6) NED (1) Related Materials (1) Part 1: 1995ApJ...439..365S

Wide-range oxygen doping of Bi2Sr2CaCu2O8+ delta.

The high-temperature superconductor ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ has been doped with oxygen at pressures ranging from a few \ensuremath{\mu}bar to 4 kbar. The doping is reversible by heat treatment in air at ambient pressure. Electrical-resistivity and infrared-optical-transmission measurements indicate that the carrier density increases monotonically with the oxygen annealing pressure. The superconductor transition goes through a maximum near 90 K and can be reduced by at least 30 K on both sides of the doping curve. In the oxygen-rich material the resistivity in the a-b plane exhibits a superlinear ${\mathit{T}}^{1+\mathit{x}}$ behavior while the c-axis resistivity shows a positive slope in the temperature dependence.