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At least 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

A comparison of theoretical and solar-flare intensity ratios for the Fe XIX X-ray lines

Atomic data including energy levels, gf-values, and wavelengths are given for the Fe XIX transitions that give rise to lines in solar-flare and active-region X-ray spectra. Collision strengths and theoretical intensity ratios are presented for lines which occur in the 13.2-14.3-A range. Observed spectra are found to be consistent with those derived from the present Fe XIX atomic data. For the case of spectra in which the Fe XIX lines are very strong, such as those at the maxima of hot flares, two observed line features due to Fe XIX are shown to have larger intensities than calculated. The calculated Fe XIX and Ne IX line spectra are used to determine electron densities from Ne IX line ratios.

Bhatia, A. K.↗
NASA NTRS1989

Using X-ray absorption lines to determine the distances to clusters of galaxies

The stronger resonant X-ray lines from the intracluster gas should be observable as absorption lines in the spectrum of an X-ray emitting background quasar. The equivalent widths of the strongest absorption lines in a set of model clusters with typical parameters are calculated, and the strongest lines are found to have equivalent widths of several eV. By comparing the equivalent width of such a line and the flux from the same line seen in emission, the distance to the cluster can be directly determined, independent of the standard extragalactic distance scale. A method of analyzing the X-ray absorption and emission measurements is presented, and the effects of resonant scattering on the distances are discussed.

Sarazin, Craig L.↗
NASA NTRS1989

A modified equivalent-width technique for diode-laser line strength measurements

A modified equivalent-width method is introduced that improves the accuracy of spectral line strength measurements using diode lasers. This method differs from the standard method in that no attempt is made to calculate the true equivalent width in order to determine the line strength. Instead, the line strength is derived directly from a measurement of the area under the line close to the line center and ignore the normal correction terms. Tests with actual spectra and simulations indicate that this method is accurate to better than 1 percent with lines broadened by up to 50 percent by the laser instrument function.

Strow, L. Larrabee↗
NASA NTRS1990

The infrared coronal lines of recent novae

IR coronal line emissions are reported in the novae V1819 Cyg and V827 Her; high-resolution near-IR spectra of coronal line emission in the nova QU Vul have also been obtained, increasing the number of known IR coronal line novae from two to four. Each of the four is found to be characterized by approximately the same Si VI/Si VII line-intensity ratio, which indicates a common coronal-zone electron temperature of 300,000 K. The coronal-line novae are noted to possess a remarkably similar near-IR spectrum, suggesting that their coronal line emission will only occasionally be observed at optical wavelengths.

Greenhouse, Matthew A.↗
NASA NTRS1990

Theoretical line shapes for rotational spectra of HCl in Ar

An interaction potential for HCl-Ar recently derived from spectra of van der Waals complexes (Hutson,1988) has been used to obtain converged close-coupling scattering S matrices from which pressure broadening (linewidth, line shift, and line coupling) cross sections have been computed within the Fano-Ben-Reuven formalism. Linewidths agree well with experimental data with the exception of the 0-1 line at low temperatures (an error of about 15 percent at 125 K). Line shifts, especially the largest, for the 0-1 line, are also in reasonable accord with experimental data. Line coupling is predicted to be quite small. The coupled-states molecular scattering approximation is found to be accurate except at very low collision energies. The infinite-order sudden approximations, on the other hand, is not reliable for this system. Inelastic scattering out of the spectroscopic levels accounts for only a fraction of the linewidth at thermal energies, especially in the lower rotational levels.

Green, Sheldon↗
NASA NTRS1989

C II forbidden line emission from spiral galaxies

Measurements of 158-micron forbidden emission taken from a sample of 13 gas-rich galaxies are analyzed. The new data are combined with the previous sample of six infrared-bright galaxies. The 158-micron line emission line is bright in all of the galaxies detected, amounting to between 0.1 and 0.2 percent of the total nuclear far-infrared luminosity, and is therefore one of the primary gas coolants in these regions. A close association between 158-micron line emission and CO line emission is noted, with the integrated 158-micron/CO line intensity ratio being substantially less in galaxies than in Galactic star-formation regions. However, for the starburst galaxies the integrated line intensity ratio is the same as that for star-formation regions in the Galaxy.

Stacey, G. J.↗
NASA NTRS1989

A high resolution delay line readout for microchannel plates

Investigations are reported of delay line configurations used to encode photon event locations in microchannel plate (MCP) detectors. Several delay line schemes of planar and multilayer structure are discussed. The importance of the delay line substrate material is examined, and it is shown that the raw signals from delay lines are narrow (about 3-4 ns FWHM). The factors determining the delay line resolution are evaluated, and it is demonstrated that these are in agreement with measurements. Resolutions of about 18-micron FWHM have been achieved. Measurements of the linearity of the delay line readout show that event centroid locations deviate from perfect linearity by less than 50 microns, even with the very simple anode fabrication methods employed. The image stability has also been evaluated and it is shown that image shifts are less than one resolution element over a period of two months.

Siegmund, O. S. W.↗
NASA NTRS1990

The 158 micrometer (CII) line: A measure of global star formation activity in galaxies

Some 158 micron (CII) fine structure line observations from a sample of fourteen gas rich galaxies are reported. These measurements confirm and generalize previous basic results that the (CII) line is bright amounting to approximately 0.1 to 1 percent of the Far Infra Red (FIR) luminosity of the nuclear regions of galaxies; the (CII) line is formed in the warm (temperature of the gas is greater than 200 K), dense (n sub H greater than 1000/cu cm) photodissociated gas at the interfaces between giant molecular clouds and ionized gas regions and is therefore associated with the molecular gas component in spiral galaxies; the (CII) line tracks the FIR continuum in a manner consistent with the PDR models; the integrated (CII) to isotope (12)CO (transition 1 to 0) line ratio is large (greater than or equal to 1000) in all galaxies studied, and is similarly large for galactic molecular clouds; the (CII) line is therefore energetically very important for the study of giant molecular clouds. Conclusions obtained from these results are given.

Stacey, G. J.↗
NASA NTRS1991

Far-infrared lines from G45.13 + 0.14 A and K3-50 A - Density fluctuations in compact H II regions

Properties of two compact H II regions, K3-50 A and G45.13 + 0.14 A, were investigated by measuring FIR fluxes from forbidden O III 51.8 and 88.4 micron lines, forbidden N III 57.3 micron line, forbidden S III 33.5 micron line, and forbidden Ne III 36.0 micron line of these regions, using a cooled grating spectrometer on NASA's Kuiper Airborne Observatory. For both H II regions, the ratio of the two FIR O(2+) lines indicates an electron density of about 1000/cu cm, which for K3-50 A is a factor of 10 to 100 lower than the density determined from optical line observations of the lower excitation species S(+) and N(+) and than the peak rms density deduced from radio continuum measurements by Turner and Matthews (1984). Detailed spherically symmetric models of the two sources were constructed using all available measurements.

Colgan, Sean W. J.↗
NASA NTRS1990

Transmission line design for the lunar environment

How the mass, operating temperature, and efficiency of a transmission line operating on the moon are affected by its operating parameters, the lunar environment, and the choice of materials is examined. The key transmission line parameters which have an effect on mass, operating temperature, and efficiency are voltage, power loss, and waveform. The choice of waveform for transmission will be influenced by the waveform of the source and load, and therefore an analysis of both DC and AC transmission is necessary for a complete understanding of lunar power transmission. The data presented are for the DC case only; however, the discussion of the environmental effects and of material selection is pertinent to both AC and DC transmission. The operating voltage is shown to be a key parameter in transmission line design. The role efficiency plays in transmission line design is also examined. The analyses include above- and below-the-surface operation for both a vacuum-insulated, two-wire, transmission line, and a solid-dielectric-insulated, coaxial, transmission line.

Gaustad, Krista L.↗
NASA NTRS1991

The 158 micron forbidden C II line - A measure of global star formation activity in galaxies

Some 158 micron forbidden C II fine structure line observations from a sample of fourteen gas rich galaxies are reported. These measurements confirm and generalize previous basic results that the C II line is bright amounting to approximately 0.1 to 1 percent of the FIR luminosity of the nuclear regions of galaxies; the C II line is formed in the warm (temperature of the gas is greater than 200 K), dense (n sub H greater than 1000/cu cm) photodissociated gas at the interfaces between giant molecular clouds and ionized gas regions and is therefore associated with the molecular gas component in spiral galaxies; the C II line tracks the FIR continuum in a manner consistent with the PDR models; the integrated C II to isotope (C-12)D (transition 1 to 0) line ratio is large (greater than or equal to 1000) in all galaxies studied, and is similarly large for galactic molecular clouds; the C II line is therefore energetically very important for the study of giant molecular clouds. Conclusions obtained from these results are given.

Stacey, G. J.↗
NASA NTRS1991

Ultraviolet high-excitation Fe II fluorescence lines excited by O VI, C IV, and H I resonance emission as seen in IUE spectra

Archival high-dispersion spectra from the IUE are used in a search for Bowen emission lines of Fe II excited by the stronger transition of the O VI resonance doublet. The possibility of using these Fe II emission lines as a diagnostic of the strength of the far-ultraviolet emission of O VI at 1032 A is explored. It is found that the Fe II emission lines are quite common and strong in symbiotic stars, particularly those of the type known as 'symbiotic novae', as well as in normal novae. The lines are observed in central stars of some planetary nebulae of the O VI sequence besides a few central stars of type WR. High density, high excitation, and high temperature are suggested to be requirements for the excitation of the Fe II fluorescence lines. It is pointed out that while these lines were observed in PG 1159-035 and K1-16, they were not observed in AGNs.

Feibelman, Walter A.↗
NASA NTRS1991

Spectroscopy of an unusual emission line M star

Moderate-resolution spectroscopy of an unusual late-type faint emission-line star, PC 0025 + 0047, is reported. A very strong (greater than 250 A equivalent width) an H-alpha emission line was detected by the present automated line search algorithm. The spectrum was found to have two unresolved emission lines (H-alpha and H-beta) near zero velocity, superposed on the absorption spectrum of a very red M dwarf which has strong K I, and relatively weak bands of TiO. From the weakness of the subordinate lines of Na I (8192 A) and other spectral features, it is inferred that it is definitely a cooler, and probably fainter, analog of LHS 2924. The strength of the emission lines indicates that PC 0025 + 0447 is very young and may be a fading predecessor brown drawf at an estimated M(bol) approaching 14m at a distance of about 60 pc.

Schneider, Donald P.↗
NASA NTRS1991

Fe II emission lines. I - Chromospheric spectra of red giants

A 'difference filtering' algorithm developed by Ayers (1979) is used to construct high-quality high-dispersion long-wavelength IUE spectra of three giant stars. Measurements of all the emission lines seen between 2230 and 3100 A are tabulated. The emission spectrum of Fe II is discussed in comparison with other lines whose formation mechanisms are well understood. Systematic changes in the Fe II spectrum are related to the different physical conditions in the three stars, and examples are given of line profiles and ratios which can be used to determine conditions in the outer atomspheres of giants. It is concluded that most of the Fe II emission results from collisional excitation and/or absorption of photospheric photons at optical wavelengths, but some lines are formed by fluorescence, being photoexcited by other strong chromospheric lines. Between 10 and 20 percent of the radiative losses of Fe II arise from 10 eV levels radiatively excited by the strong chromospheric H Ly-alpha line.

Judge, P. G.↗
NASA NTRS1992

Compton backscattered annihilation line emission: A new diagnostic of accreting compact sources

It is shown that Compton scattering of 511 keV electron-positron annihilation radiation produces a line like feature at approx. 170 keV from backscattered photons. Assuming a simple model of an accretion disk around a compact source, the spectrum is explored of the spectrum of Compton scattered annihilation line emission for a range of conditions. It is further shown that such Compton baskscattering of annihilation line emission from the inner edge of an accretion disk could account for the previously unidentified 170 keV line emission and high energy continuum observed from a variable, compact source, or sources, of annihilation radiation near the Galactic Center. Identification of the observed 170 keV line as an annihilation line reflection feature provides strong new evidence that the source of the emission is an accreting compact object. Further study of these features in existing spectra and in forthcoming GRO observation of these and other sources can provide unique new diagnostics of the innermost regions of accretion disks around compact objects.

Lingenfelter, Richard E.↗
NASA NTRS1992

Systematic QSO emission-line velocity shifts and new unbiased redshifts

A novel method for determining mean line velocities which is an order of magnitude more accurate than past work is presented. Using a large sample of 518 lines from 160 QSOs, it is found that each UV emission line has a well-determined mean velocity, with a surprisingly small QSO-to-QSO dispersion of under 200 km/s. All correlations between emission-line velocities and QSO properties are found to be explained by just three basic correlations. Both N V and Mg II tend to be at less negative velocities in radio-quiet vs radio-loud QSOs, and C IV lines with small equivalent widths are at more negative velocities, probably because of the line asymmetry. The finding of Sargent et al. (1989) that the UV spectral index increases with UV luminosity is confirmed, but their claim that radio-loud and radio-quiet QSOs have different indices is not confirmed.

Tytler, David↗
NASA NTRS1992

CCD observations of additional interstellar lines in stars associated with the Vela Remnant and Eta Carinae nebulosity

Nine stars from the Vela Remnant and seven stars in the Eta Carinae complex are examined with CCD spectrograms with high signal-to-noise ratios for data regarding the optical interstellar lines. These data are supplemented by observations of objects with known high-velocity components and substantial interstellar Ti II lines. The CCD spectrograms have signal-to-noise ratios of 100-300, a 2-pixel resolving power of 20,000, and cover features of Na I, Ti II, Ca I, CH(+), and CH in the 3200-4400-A range. The Ca I line confirms the high H density in Vela, and the Ti II lines show evidence of shock-induced grain evaporation. Weak shocks are thought to contribute to the CH(+) component, and a high H I density in some clouds is inferred from the CH line. The high H I density is supported by IUE data on Ca I and on the fine-structure carbon lines. The data point to a significant difference in spectroscopic morphology between the two groups of stars, and the need for theoretical support is underscored.

Wallerstein, George↗
NASA NTRS1993

Hydrogen broadening and collision-induced line shifts of methane at 4200/cm

Many of the lines of the nu1 + nu4 and nu3 + nu4 bands of methane in the vicinity of 4200/cm have been assigned and are reported in the HITRAN data-base which is commonly used for atmospheric transmission calculations in the IR. The collision-induced broadening coefficients of hydrogen for more than 200 of these lines are reported. Also, by using the water-vapor lines which occur in the spectra as calibration marks, the frequencies of the broadened lines are determined. This permitted the collision-induced line shifts to be measured for lines sufficiently isolated from interfering blends: all of the shifts which could be reliably determined in this way were negative.

Margolis, Jack S.↗