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At least 217 records · Page 12

A line identification study of the IUE SWP high dispersion spectrum of the UV-bright star Barnard 29 of Messier 13

A line identification study was performed of the coaddition of three SWP high dispersion IUE exposures of the UV-bright star Barnard 29 of Messier 13. One of these images took two IUE shifts. The previous study by de Boer and Savage (1983) was extended and stellar lines of C I, C II, C III, C IV, N I, N III, O I, O III, O IV,Al III, Si II, Si III, Si IV, P III, S II, and S III and interstellar lines of C I, C II, C IV, N I, N III, N IV, N V, O I, Al II, Al III, Si II, Si IV, S II, and Fe II were found. These lines are the strongest expected lines in a hot Population II star. Apparent intensity minima corresponding to interstellar features are noted, especially those matching a high velocity cloud found by de Boer and Savage.

Adelman, S. J.↗

On planetary nebula nuclei of the spectral type 'continuous'

A detailed reexamination of existing and new International Ultraviolet Explorer (IUE) low-and high-resolution spectra, plus a search of recent literature, shows that for most of the central stars of planetary nebulae the spectral classification previously called 'continuous-type' does not really exist. The stellar continua show primarily photospheric absorption features of N V, O V, C IV, H, He II, Fe VII, Fe VI, and Fe V, and/or P Cygni profiles.

Feibelman, Walter A.↗

Chemical Compositions and Abundance Anomalies in Stellar Coronae ADP 99

Progress has been made using both EUVE (Extreme Ultraviolet Explorer) and ASCA (Advanced Satellite for Cosmology and Astrophysics) data and a new postdoctoral scientist has now been hired. Stars studied to date include YY Gem (dMe binary), xi Boo A (intermediate activity G8 V), xi UMa (more active G quadruple system) HR1099 (K1 IV + G5 V) RS CVn-like, AU Mic (dMe). In addition to a paper that concentrated on abundancies in HR1099, a paper was recently submitted on the coronal abundances of AR(tilde)Lac that revealed an interesting pattern of overabundances of very low FIP elements (Al and Ca) compared to the low FIP elements Si, Mg and Fe. Two papers are nearing completion on methods of analysis and on the abundances in the corona of AU(tilde)Mic. Additionally, two invited conference proceedings papers are being published on this work. The main conclusion of the study to date is that our existing ideas of coronal abundance anomalies need complete revision. The solar-like FIP effect is replaced by a pattern than appears to enhance high FIP elements rather than low FIP elements in very active stars. The archival studies we are undertaking now are revealing some key details of these patterns, and are beginning to map out the anomalies as a function of spectral type, a key goal of this study.

Drake, Jeremy↗

Hubble Space Telescope Faint Object Spectrograph and ground-based observations of the broad absorption line quasar 0226-1024

Faint Object Spectrograph data from the Hubble Space Telescope of the broad absorption line quasar 0226-1024 have revealed the presence of 8-10 absorbing ions between 680 and 1000 A (restframe): C III, N III, N IV, O III, O IV, O VI, S V, S VI, possibly Ne VIII, and possibly O V* arising from a metastable excited state. We also present ground-based optical observations of the broad line troughs for the following ions: H I, C IV, N V, Si IV, and possibly Fe III, S IV, P V, and C III* (also arising from a metastable excited state). The results of this fit are used to estimate the absorbing ionic column densities. There is evidence that the broad absorption line clouds are optically thick and either do not completely cover the continuum source or narrow unresolved lines are present.

Korista, Kirk T.↗

A High Signal-To-Noise Ultraviolet Spectrum of NGC 7469: New Support for Reprocessing of Continuum Radiation

From 1996 June 10 to 1996 July 29, the International AGN Watch monitored the Seyfert 1 galaxy NGC 7469 using the International Ultraviolet Explorer, the Rossi X-Ray Timing Explorer, and a network of ground-based observatories. On 1996 June 18, in the midst of this intensive monitoring period, we obtained a high signal-to-noise snapshot of the UV spectrum from 1150 to 3300 A, using the Faint Object Spectrograph (FOS) on the Hubble Space Telescope. This spectrum allows us to disentangle the UV continuum more accurately from the broad wings of the emission lines, to identify clean continuum windows free of contaminating emission and absorption, and to deblend line complexes such as Ly(alpha) + N V, C IV + He II + O III], Si III] + C III], and Mg II + Fe II. Using the FOS spectrum as a template, we have fitted and extracted line and continuum fluxes from the IUE monitoring data. The cleaner continuum extractions c o n h the discovery of time delays between the different UV continuum bands by Wanders et al. Our new measurements show delays increasing with wavelength for continuum bands centered at 1485, 1740, and 1825 A, relative to 1315 A with delays of 0.09, 0.28, and 0.36 days, respectively. Like many other Seyfert I galaxies, the UV spectrum of NGC 7469 shows intrinsic, blue-shifted absorption in Ly(alpha), N V, and C IV. Soft X-ray absorption is also visible in archival ASCA X-ray spectra. The strength of the UV absorption, however, is not compatible with a single-zone model in which the same material absorbs both the UV and X-ray light. Similar to other Seyfert galaxies, such as NGC 3516, the UV-absorbing gas in NGC 7469 has a lower ionization parameter and column density than the X-ray-absorbing material. While the UV and X-ray absorption does not arise in the same material, the frequent occurrence of both associated UV absorption and X-ray warm absorbers in the same galaxies suggests that the gas supply for each has a common origin.

Kriss, Gerard A.↗

Hunting for Planetary Nebulae toward the Galactic Center

We present near-infrared (IR) spectra of two planetary nebula (PN) candidates in close lines of sight toward the Galactic center (GC) using the Gemini Near-Infrared Spectrograph at Gemini North. High-resolution images from radio continuum and narrowband IR observations reveal ringlike or barrel-shaped morphologies of these objects, and their mid-IR spectra from the Spitzer Space Telescope exhibit rich emission lines from highly-excited species such as [S iv], [Ne iii], [Ne v], and [O iv]. We also derive elemental abundances using the Cloudy synthetic models, and find an excess amount of the s-process element krypton in both targets, which supports their nature as PNe. We estimate foreground extinction toward each object using near-IR hydrogen recombination lines, and find significant visual extinctions (A {sub V} > 20). The distances inferred from the size versus surface brightness relation of other PNe are 9.0 ± 1.6 kpc and 7.6 ± 1.6 kpc for SSTGC 580183 and SSTGC 588220, respectively. These observed properties along with the abundance patterns and close proximity to Sgr A* (projected distances ≲20 pc) make it highly probable that these objects are the first confirmed PN objects in the nuclear stellar disk. The apparent scarcity of such objects resembles the extremely low rate of PN formation in old stellar systems, but is in line with the current rate of sustained star formation activity in the Central Molecular Zone.

47 OTHER INSTRUMENTATION↗

Structural and photoelectrochemical properties in the thin film system Cu–Fe–V–O and its ternary subsystems Fe–V–O and Cu–V–O

Thin-film material libraries in the ternary and quaternary metal oxide systems Fe–V–O, Cu–V–O, and Cu–Fe–V–O were synthesized using combinatorial reactive co-sputtering with subsequent annealing in air. Their compositional, structural, and functional properties were assessed using high-throughput characterization methods. Prior to the investigation of the quaternary system Cu–Fe–V–O, the compositions (Fe 61 V 39 )O x and (Cu 52 V 48 )O x with promising photoactivity were identified from their ternary subsystems Fe–V–O and Cu–V–O, respectively. Two Cu–Fe–V–O material libraries with (Cu 29-72 Fe 4-27 V 22-57 )O x and (Cu 11-55 Fe 27-73 V 12-34 )O x composition spread were investigated. Seven mixed ternary and quaternary phase regions were identified: I (α-Cu 3 FeV 6 O 26 /FeVO 4 ), II (Cu 5 V 2 O 10 /FeVO 4 /α-Cu 3 Fe 4 V 6 O 26 ), III (Cu 5 V 2 O 10 ), IV (Cu 5 V 2 O 10 /FeVO 4 , V (FeVO 4 /γ-Cu 2 V 2 O 7 /α-Cu 3 Fe 4 V 6 O 26 ), VI (β-Cu 2 V 2 O 7 /α-Cu 3 Fe 4 V 6 O 26 /FeVO 4 ), and VII (β-Cu 3 Fe 4 V 6 O 26 /FeVO 4 ). Furthermore, in the investigated composition range, two photoactive regions, (Cu 53 Fe 7 V 40 )O x and (Cu 45 Fe 21 V 34 )O x , were identified, exhibiting 103 μ A/cm 2 and 108 μ A/cm 2 photocurrent density for the oxygen evolution reaction at 1.63 V vs reversible hydrogen electrode, respectively. The highest photoactive region (Cu 45 Fe 21 V 34 )O x comprises the dominant α-Cu 3 Fe 4 V 6 O 24 phase and minor FeVO 4 phase. This photoactive region corresponds to having an indirect bandgap of 1.87 eV and a direct bandgap of 2.58 eV with an incident photon-to-current efficiency of 30% at a wavelength of 310 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

SN 1987 A: A Unique Laboratory for Shock Physics

Supernova 1987 A has given us an unprecedented view of the evolution of the explosion debris and its interaction with circumstellar matter. The outer supernova debris, now expanding with velocities approx.8000 km/s, encountered the relatively dense circumstellar ring formed by presupernova mass loss in the early 1990s. The shock interaction is manifested by UV-optical "hotspots", an expanding X-ray ring, an expanding ring of knotty non-thermal radio emission, and a ring of thermal IR emission from silicate dust Recent ultraviolet observations of the emissions from the reverse shock and the ring with the HST/COS reveal new details about the shock interaction. Lyman alpha emission from the reverse shock is much stronger than H alpha and they have different emission morphologies, pointing to different emission mechanisms. The reverse shock was detected for the first time in C IV 1550. The N V to C IV brightness ratio indicates the N/C abundance ratio in the expanding debris is about 100X solar, about 3X N/C in the inner ring.

Sonneborn, George↗

Ultraviolet spectra of HZ Herculis/Hercules X-1 from HST: Hot gas during total eclipse of the neutron star

The Faint Object Spectrograph (FOS) aboard Hubble Space Telescope (HST) has been used in the UV to observe the prototypical X-ray pulsar Her X-1 and its companion HZ Her. Optical spectra were also obtained contemporaneously at the Kitt Peak National Observatory (KPNO) 2.1 m. The FOS spectra encompass the 1150-3300 A range near binary orbital phases 0.5 (X-ray maximum) and at 0.0 (mid-X-ray eclipse). The maximum light spectra show strong, narrow C III, N V, O V, Si IV + O IV), N IV), C IV, He II, and N IV emission lines, extending previous IUE results; the O III lambda 3133 Bowen resonance line is also prominent, confirming that the Bowen mechanism is the source of the strong lambda lambda 4640, 4650 emission complex, also seen at maximum light. Most remarkable, however, are the minimum light spectra, where the object is too faint for reasonable observations from IUE. Despite the total eclipse of the X-ray-emitting neutron star, our spectra show strong emission at N V lambda 1240, S IV + O IV) whose emission dominates the UV light at phase 0.0 might be associated with the 'accretion disk corona,' it is more likely the source is somewhat less hot (but extended) gas above and around the disk, or perhaps circumstellar material such as a stellar wind.

Anderson, Scott F.↗

Plutonium Oxidation State Distribution under WIPP Relevant Conditions (Rev. 2)

The oxidation state of plutonium in the Waste Isolation Pilot Plant (WIPP) environment has been a topic of interest since the initial compliance certification application. Plutonium (Pu) was initially expected to be present primarily as Pu(IV), but since the presence of Pu(III) could not be ruled out, it was also included in performance assessment (PA) calculations. The redox of the other variant actinides, uranium (U) and neptunium (Np), are also coupled to the plutonium redox. This led to a position in performance assessment calculations that is commonly referred to as “50/50”. In which half of the PA realizations assume solubility is dominated by the low oxidation state [U(IV), Np(IV), Pu(III)] and the other half assume solubility is dominated by the higher oxidation state [U(VI), Np(V), Pu(IV)]. Recently, a joint group of WIPP project participants from Los Alamos National Laboratory (LANL), Sandia National Laboratories (SNL), and the Department of Energy’s Carlsbad Field Office (DOE-CBFO) agreed on a new path forward for the oxidation state model in PA which will decouple the redox active actinides and will instead consider their redox as a function of E h . This will take the current binary approach and turn it into a system with four possible redox states.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

The transition regions of Capella

We have used the Goddard High Resolution Spectrometer (GHRS) to observe the spectoscopic binary system Capella (G8 III + G1 III). Exposures with the G140L, G140M, G160M, G200M, and echelle gratings provide emission line profiles with unprecedented signal-to-noise and spectral resolving power (lambda/Delta-lambda) up to 92,000. Multi-Gaussin fits to the line profiles show that the hotter star contributes 60%-70% of the total flux in the chromospheric O I and Mg II resonance lines, but about 90% of the flux in the Si III, Si IV, and C IV lines formed in the transition region at T less than or = 10(exp 5) K. We find clear evidence that the emission lines from the hotter star are systemtically redshifted relative to the photosphere with Doppler shifts of 5 +/- 1 km/s for the +9 +/- 3 km/s in the chromospheric Mg II and O I lines, respectively, increasing to +24 +/- 5 km/s for the transition region Si IV 1393.8A line. The multi-Gaussian fits to permitted transition region lines of SI III, Si IV, C IV, and N V indicate the presence of three components: moderately broad lines formed in the transition region of the hotter star (component H), narrow lines formed in the transition region of the cooler star (component C), and very broad lines that we think are formed in microflares on the hotter star (component B). The He II 1640.4 A feature has an broad profile, which indicates that it is formed by collisional excitation primarily from the hotter star, and a weak narrow component that we interpret as due to radiative recombination on the cooler star. We observed spin-forbidden emission lines of C III), O III), Si III), O IV), O V), and S IV) that are sensitive to electron density. Fainter members of the O IV) multiplet and all of the S IV) lines have never before been seen in any star than the Sun. We determine electron densities in the transition regions of the Capella stars using lines ratios of O IV) lines and emission measure analysis. The emission measures are self-consistent only when the fluxes from each emitting component are considered separately. In particular, the transition region abundance distributions appear to be different on the two stars, and the spin-forbidden lines were not detected in the B component. The emission measures for component H (the G1 star) are consistent with a constant electron pressure (or hydrostatic equilibrium) transition region with P(sub e) = 10(exp 15 + 0.1)/cu cm K and possibly solar 'coronal' abundances.

Linsky, Jeffrey L.↗

The high-resolution spectrum of the pulsating, pre-white dwarf star PG 1159-035 (GW VIR)

High-resolution and low-resolution UV spectra and a high-resolution optical spectrum were obtained for PG 1159-035, revealing apparent photospheric absorption features with defined cores from N V 1240 A, N IV 1270 A, O V 1371 A, and C IV 1550 A. The photospheric velocity derived using all of these lines except for C IV is about +35 km/s. Equivalent-width measurements determined for all of the features may provide a tighter constraint on the photospheric temperature in a detailed model atmosphere analysis treating the CNO ions.

Liebert, James↗

First Detection of the Hatchett-McCray Effect in the High-Mass X-ray Binary

The orbital modulation of stellar wind UV resonance line profiles as a result of ionization of the wind by the X-ray source has been observed in the high-mass X-ray binary 4U1700-37/HD 153919 for the first time. Far-UV observations (905-1180 Angstrom, resolution 0.05 Angstroms) were made at the four quadrature points of the binary orbit with the Far Ultraviolet Spectroscopic Explorer (FUSE) in 2003 April and August. The O6.5 laf primary eclipses the X-ray source (neutron star or black hole) with a 3.41-day period. Orbital modulation of the UV resonance lines, resulting from X-ray photoionization of the dense stellar wind, the so-called Hatchett-McCray (HM) effect, was predicted for 4U1700-37/HD153919 (Hatchett 8 McCray 1977, ApJ, 211, 522) but was not seen in N V 1240, Si IV 1400, or C IV 1550 in IUE and HST spectra. The FUSE spectra show that the P V 1118-1128 and S IV 1063-1073 P-Cygni lines appear to vary as expected for the HM effect, weakest at phase 0.5 (X-ray source conjunction) and strongest at phase 0.0 (X-ray source eclipse). The phase modulation of the O VI 1032-1037 lines, however, is opposite to P V and S IV, implying that O VI may be a byproduct of the wind's ionization by the X-ray source. Such variations were not observed in N V, Si IV, and C IV because of their high optical depth. Due to their lower cosmic abundance, the P V and S IV wind lines are unsaturated, making them excellent tracers of the ionization conditions in the O star's wind.

Sonneborn, G.↗

Satellite emission features in two Seyfert galaxies: New evidence that radio-quiet AGN possess subrelativistic winds

Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) spectra are presented for three bright Seyfert galaxies including one (PG 1351+64) which possesses blue-displaced absorption features in C IV, Si IV, N V, and Ly-alpha (but not in Mg II) similar to those seen at high redshift in the broad-absorption-line (BAL) quasi-stellar objects (QSOs). Several features of the absorptions in PG 1351+64, including variability seen in archival International Ultraviolet Explorer (IUE) data, confirm their similarity to the BAL clouds rather than to the 'associated absorber' phenomenon which they superficially resemble. In PG 1351+64 'satellite' emission lines (called herein E1 and E2) have been detected nearly symmetrically placed at +/- 4000 km/s around the Mg II emission line; this velocity is just larger than the most blue-displaced of the BALs, suggesting that these two phenomena are related. The satellite line luminosity, L(E1) approximately = (3 x 10(exp 41) erg/s)/sq. h(sub 75), requires a cloud emission measure n(sub e)(exp 2)V(sub c) approximately = (1 x 10(exp 64)/cc)/sq. h(sub 75) at T approximately = 30,000 K. We believe the Mg II lines are produced by 50-90 km/s shocks driven into dense (approximately 10(exp 6)/cc, pre-shock) clouds by the ram pressure of a 0.1 solar mass/yr wind leaving the nucleus at velocity 4000 km/s. The detection of satellite lines in Mg II, the detection of the blue-shifted cloud in H-alpha and H-beta and the nondetection of this cloud in C IV restricts the cloud shocks to velocities v(sub c) less than or = 90 km/s and requires a cloud/wind density contrast greater than or = 10(exp 3). In this model, the emitting clouds are located at distances of R(sub eff) approximately = 10(exp 18-19) cm from the nucleus and are entrained and shock-accelerated to approximately 4000 km/s. The possible detection of similar 'satellite' emission features in the non-BAL Seyfert, Ton 951, suggests that the subrelativistic wind that accelerates BAL clouds is a physical feature of many radio-quiet active galactic nuclei (AGN).

Stocke, John T.↗

Ultraviolet interstellar absorption toward HD 156359, a halo star at 11 kiloparsecs in the direction l = 329 deg and b = -15 deg

Results based on high-quality multiple IUE high-dispersion spectra are presented for the HD 156359 sight line in the direction l = 328.7 deg and b = -14.5 deg. The UV stellar spectrum of HD 156359 is consistent with an MK classification of O9.7 Ib-II. The high-ionization UV interstellar absorption line in the star's UV spectrum are very broad with negative velocity extensions. Comparison of apparent column density profiles Na(v) for lines within each doublet indicates that there is no significant unresolved saturated structure in the Si IV or N V profiles. Direct integration of the Na(v) profiles for Si IV, C IV, and N V over velocities from -150 km/s to +40 km/s yields total column densities of log N = 14.10, 14.77, and 14.09, respectively. The definite detection of N V absorption lines with profile shapes similar to the Si IV and C IV profiles favors a common origin for all three species.

Sembach, Kenneth R.↗

Structure and evolution of solar radio bursts at 26.4 MHz

Results are reported for multiple-baseline interferometric measurements of type II, III, IV, and V solar radio bursts at 26.4 MHz. Thirty-two burst events in a two-month period are analyzed by fitting a double-Gaussian two-dimensional source-brightness distribution model to the observed interferometer visibility function. The multibaseline time-sharing interferometer system employed is described in detail, the model-fitting technique is outlined, and values of the model-fit parameters are given for all 32 cases, which include two type II bursts, three type IV bursts, 17 type III bursts, seven type V bursts, and three bursts of type III, V pairs. The temporal evolution of source structure, size, and motion is examined for the different burst types. The core-halo source structure for the type III bursts is interpreted in comparison to two models, one of which assumes scattering and refraction of a point source while the other postulates primarily refraction from an ensemble of sources distributed over a wide sector in solar longitude.

Chen, H. S.-L.↗

The critical role of synthesis conditions on small polaron carrier concentrations in hematite—A first-principles study

Achieving highly efficient energy conversion with transition metal oxides necessitates overcoming conductivity limitations due to the formation of small polarons. Detailed understanding of the interplay among intrinsic defects, dopants, and electron polarons can help devise strategies for achieving higher carrier concentrations, therefore improving carrier conductivity. This work employs first-principles calculations to reliably predict electron polaron concentrations in a prominent polaronic oxide, hematite (Fe 2 O 3 ), by resolving interactions between charged defects and electron polarons and keeping charge neutrality condition among all charged species. This work addresses that both V O and Fe i can be primary donors in undoped hematite depending on the synthesis conditions, such as synthesis temperature and oxygen partial pressure, despite the fact that V O owns an extremely high ionization energy compared to k B T. Furthermore, from calculations of a plethora of n-type dopants (group IV and V elements), we find that Ti, Ge, Sb, and Nb are able to raise electron polaron concentrations in hematite significantly without considering dopant clustering. However, the magnitude of electron polaron concentration increase would be smaller if the dopant has a high tendency of clustering, such as Ti. Here we reveal the critical role of synthesis conditions on tuning electron polaron concentrations of both undoped and doped hematite. Our theoretical analysis provides important insights and general design principles for engineering more conductive polaronic oxides.

36 MATERIALS SCIENCE↗