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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The discovery of an O VII emission line in the ASCA spectrum of the Seyfert galaxy NGC 3783

We report the first observation of an O VII 0.57 keV emission line in a Seyfert 1 galaxy. NGC 3783 was observed by ASCA twice over a period of 4 days in 1993 December. The source exhibited a approximately 30% change in intensity between the two observations, with most of the variability taking place as a result of steepening of the continuum less than or approximately equal to 1 keV. Spectra from both observations show intense absorption features in the 0.5-1.5 keV band, which can be well fitted by an ionized absorber model of solar composition, column density of 10(exp 22.2)/sq cm and ionization parameter of approximately 7-8; the strongest absorption features being due to O VII and O VIII. Two emission features are also seen in the spectra which we identify as O VII 0.57 keV (equivalent width approximately equals 36 eV) and O VIII 0.65 keV (equivalent width approximately equals 11 eV). We also show that the 3-6 keV continuum of the source is well fitted by a Gamma = 1.3-1.4 power-law continuum, a narrow neutral iron K-shell fluorescence line and a strong iron K-shell absorption edge, possibly corresponding to highly ionized iron.

George, I. M.↗
NASA NTRS1974

Sodium D-line emission from Io - Sputtering and resonant scattering hypothesis

A model is presented in explanation of the observation of sodium D-line emission from Io. The model involves: (1) charged-particle sputtering of sodium from Io's surface, (2) ejection of sodium into a cloud surrounding Io, and (3) resonant scattering of incident sunlight. Observational consequences and tests of the proposed model are also discussed.

Matson, D. L.↗
NASA NTRS1979

X-ray observations of high-excitation emission-line galaxies with the HEAO 1 scanning modulation collimator

Data from the scanning modulation collimator on HEAO 1 are presented which firmly establish high-excitation emission-line galaxies as a class of X-ray source. For NGC 5506 and M82, the X-ray emission (1-13 keV) is shown to originate in the nuclear region of the galaxy; NGC 2992 and NGC 526a are also identified as X-ray emitters, but are not resolved. The latter is a new identification for 2A 0120-353, previously associated with the NGC 526/527 group. In these four particular cases, the observed X-ray-emitting galaxies have a close companion, and the X-ray emission may have been triggered by a close encounter

Griffiths, R. E.↗
DOE OSTI2025

DESI Emission-line Galaxies: Clustering Dependence on Stellar Mass and [O II] Luminosity

We measure the projected two-point correlation functions of emission-line galaxies (ELGs) from the Dark Energy Spectroscopic Instrument One-Percent Survey and model their dependence on stellar mass and [O II] luminosity. We select ∼180,000 ELGs with redshifts of 0.8 < z < 1.6, and define 27 samples according to cuts in redshift and both galaxy properties. Following a framework that describes the conditional [O II] luminosity–stellar mass distribution as a function of halo mass, we simultaneously model the clustering measurements of all samples at fixed redshift. Based on the modeling result, most ELGs in our samples are classified as central galaxies, residing in halos of a narrow mass range with a typical median of ∼10 12.2−12.4 h −1 M ⊙ . We observe a weak dependence of clustering amplitude on stellar mass, which is reflected in the model constraints and is likely a consequence of the 0.5 dex measurement uncertainty in the stellar mass estimates. The model shows a trend between galaxy bias and [O II] luminosity at high redshift (1.2 < z < 1.6) that is otherwise absent at lower redshifts.

Cosmology↗
NASA NTRS1978

The soft X-ray spectrum of Capella - Discovery of intense line emission

A soft X-ray spectrum of Capella has been obtained with the HEAO 1 satellite. Only models which include intense line emission at 0.85 keV can adequately explain the data. The spectrum is consistent with emission from an isothermal solar-abundance plasma with a temperature of 10.5 million (+ or - 2.8 million) K. It is also consistent with a blend of temperatures between 4 and 20 million K. The intensity of the X-ray emission is constant over 2 days and similar to the intensity observed by ANS.

Cash, W.↗
NASA NTRS1979

The radiation pressure-driven Rayleigh-Taylor instability - Analysis and application to QSO emission line clouds

The growth of perturbations in a photoionized gas slab accelerated by radiation pressure under conditions like those in QSO emission-line regions is analyzed. A linear dispersion relation is derived, and numerical radiation-transfer calculations are performed to evaluate the coefficients and roots of that dispersion relation for L-alpha optical depths between 0.1 and 10,000. The nonlinear growth of the waves is estimated, and it is concluded that complete dispersal of the clouds is likely. On the basis of qualitative arguments it is suggested that clouds of greater optical depth are linearly stable.

Krolik, J. H.↗
NASA NTRS1984

Optical Emission Line Studies and the Warm, Ionized Component of the Local Interstellar Medium

Observations of diffuse, galactic H alpha, N2 lambda 6583, and S2 6716 emission lines provide evidence for a warm (10,000K), primarily ionized component of the interstellar medium distribution throughout the galactic disk. This component of the interstellar gas has an electron density approximately equals 0.1-0.2/cu cm and occupies about 10 to 30% of the interstellar volume. Interstellar H alpha emission near the galactic poles, the dispersion measure of a nearby pulsar, and observations of interstellar gas flowing into the solar system indicate that this ionized component is an important constituent of the interstellar medium in the solar neighborhood. The intensity of the H alpha background at high galactic latitudes implies that this component is maintained by an average hydrogen ionization rate in the vicinity of the Sun of (2-4) x 100,000 s(-1) per square cm of galactic disk. The emission measure is 1.3 to 2.3 cm (-6) pc toward the galactic poles. The sources of this ionization were not identified but may include escaping Lyman continuum radiation from planetary nebulae, hot white dwarfs, and early type stars.

Reynolds, R. J.↗
NASA NTRS1989

Narrow ultraviolet emission lines from SN 1987A - Evidence for CNO processing in the progenitor

Results from UV observations of SN 1987A with the IUE satellite are presented, showing that emission lines of He II, C III, N III, N IV, N V, and O III increase in strength with time after May 24, 1987. It is found that increased emission originated in a photoionized low-density circumstellar gas, lost by the progenitor in its red supergiant phase. A nebular analysis reveals a large nitrogen overabundance, indicating that the gas has undergone substantial CNO processing. This suggests that the progenitor of SN 1987A lost much of its hydrogen envelope before the explosion. The findings are consistent with models in which a red supergiant evolves to the blue supergiant stage before exploding.

Fransson, C.↗
NASA NTRS1987

Different regions of line formation in the envelope of the early emission line star HD 190073

A description is presented of the spectral features that characterize the spectrum of HD 190073 both in the photographic region (360-660 nm), and in the IUE UV (115-320 nm). A number of different types of profiles can be distinguished, and this seems to imply that many different 'broad' regions of line formation coexist in the extended envelope of the star, including regions with densities differing in several orders of magnitude.

Ringuelet, A. E.↗
DOE OSTI2022

Abundance matching analysis of the emission-line galaxy sample in the extended Baryon Oscillation Spectroscopic Survey

We present the measurements of the small-scale clustering for the emission-line galaxy (ELG) sample from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) in the Sloan Digital Sky Survey IV (SDSS-IV). We use conditional abundance matching method to interpret the clustering measurements from 0.34 to 70 h -1 Mpc. In order to account for the correlation between properties of ELGs and their environment, we add a secondary connection between star formation rate of ELGs and halo accretion rate. Three parameters are introduced to model the ELG [O II ] luminosity and to mimic the target selection of eBOSS ELGs. The parameters in our models are optimized using Markov Chain Monte Carlo (MCMC) method. We find that by conditionally matching star formation rate of galaxies and the halo accretion rate, we are able to reproduce the eBOSS ELG small-scale clustering within 1σ error level. Our best-fitting model shows that the eBOSS ELG sample only consists of ~ 12 per cent of all star-forming galaxies, and the satellite fraction of eBOSS ELG sample is 19.3 per cent. We show that the effect of assembly bias is ~ 20 per cent on the two-point correlation function and ~ 5 per cent on the void probability function at scale of r ~ 20 h -1 Mpc.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

Emission-line diagnostics for the existence of thermal accretion disks in active galactic nuclei

The use of the relative strengths of optical and UV emission lines to infer information about the EUV continuum shape is demonstrated. The FeII/H-beta line ratio is strongly dependent on spectral shape, making it a good indicator of the UV spectrum. It is shown how the gravitational influence of a massive black hole may be seen in the nature of gas streaming motions and the orbits of gas clouds in the region where the black hole potential is comparable to the stellar galactic potential.

Krolik, J. H.↗
NASA NTRS1994

Mg IX emission lines in an active region spectrum obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

Theoretical electron-temperature-sensitive Mg IX emission line ratios are presented for R(sub 1) = I(443.96 A)/I(368.06 A), R(sub 2) = I(439.17 A)/I(368.06 A), R(sub 3) = I(443.37 A)/I(368.06 A), R(sub 4) = I(441.22 A)/I(368.06 A), and R(sub 5) = I(448.28 A)/I(368.06 A). A comparison of these with observational data for a solar active region, obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals excellent agreement between theory and observation for R(sub 1) through R(sub 4), with discrepancies that average only 9%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on board Skylab. However in the case of R(sub 5), the theoretical and observed ratios differ by almost a factor of 2. This may be due to the measured intensity of the 448.28 A line being seriously affected by instrumental effects, as it lies very close to the long wavelength edge of the SERTS spectral coverage (235.46-448.76 A).

Keenan, F. P.↗
NASA NTRS1993

X-rays from emission-line stars in the Herbig-Haro 1 region

We have observed the region in Orion containing Herbig-Haro 1 as well as a number of young, active stars. This observation shows a similar X-ray morphology to that in the first X-ray imaging observation about 10 years ago. The ROSAT High Resolution Instrument with its approximately arcsecond spatial resolution allows us in most cases to make definite optical identifications of the 0.1-2.4 keV X-ray sources. New identifications with emission-line stars are made, and prior identifications using lower resolution observations are confirmed or corrected. The X-ray emission previously detected from the vicinity of HH-1 is not associated with HH-1 but with a known T Tauri star. The observed relationships among X-ray, optical line, and infrared excess emission do not simply fall into the suggested classifications for T Tauri or T Tauri-like stars. This could be an indication of another X-ray emission region such as accretion disks that add to the emission from the stellar atmospheres.

Pravdo, Steven H.↗
DOE OSTI2020

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: measurement of the BAO and growth rate of structure of the emission line galaxy sample from the anisotropic power spectrum between redshift 0.6 and 1.1

We analyse the large-scale clustering in Fourier space of emission line galaxies (ELG) from the Data Release 16 of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey. The ELG sample contains 173,736 galaxies covering 1,170 square degrees in the redshift range 0.6 < z < 1.1. We perform a BAO measurement from the post-reconstruction power spectrum monopole, and study redshift space distortions (RSD) in the first three even multipoles. Furthermore, photometric variations yield fluctuations of both the angular and radial survey selection functions. Those are directly inferred from data, imposing integral constraints which we model consistently. The full data set has only a weak preference for a BAO feature (1.4σ). At the effective redshift zeff = 0.845 we measure $D_{\rm V}(z_{\rm eff})/r_{\rm drag} = 18.33_{-0.62}^{+0.57}$, with DV the volume-averaged distance and rdrag the comoving sound horizon at the drag epoch. In combination with the RSD measurement, at zeff = 0.85 we find $f\sigma _8(z_{\rm eff}) = 0.289_{-0.096}^{+0.085}$, with f the growth rate of structure and σ8 the normalisation of the linear power spectrum, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 20.0_{-2.2}^{+2.4}$ and DM(zeff)/rdrag = 19.17 ± 0.99 with DH and DM the Hubble and comoving angular distances, respectively. These results are in agreement with those obtained in configuration space, thus allowing a consensus measurement of fσ8(zeff) = 0.315 ± 0.095, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 19.6_{-2.1}^{+2.2}$ and DM(zeff)/rdrag = 19.5 ± 1.0. This measurement is consistent with a flat ΛCDM model with Planck parameters.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2016

Flash Spectroscopy: Emission Lines From the Ionized Circumstellar Material Around 10-Day-Old Type II Supernovae

Supernovae (SNe) embedded in dense circumstellar material (CSM) may show prominent emission lines in their early-time spectra (< or =10 days after the explosion), owing to recombination of the CSM ionized by the shock-breakout flash. From such spectra ("flash spectroscopy"), we can measure various physical properties of the CSM, as well as the mass-loss rate of the progenitor during the year prior to its explosion. Searching through the Palomar Transient Factory (PTF and iPTF) SN spectroscopy databases from 2009 through 2014, we found 12 SNe II showing flash-ionized (FI) signatures in their first spectra. All are younger than 10 days. These events constitute 14% of all 84 SNe in our sample having a spectrum within 10 days from explosion, and 18% of SNe II observed at ages <5 days, thereby setting lower limits on the fraction of FI events. We classified as "blue/featureless" (BF) those events having a first spectrum that is similar to that of a blackbody, without any emission or absorption signatures. It is possible that some BF events had FI signatures at an earlier phase than observed, or that they lack dense CSM around the progenitor. Within 2 days after explosion, 8 out of 11 SNe in our sample are either BF events or show FI signatures. Interestingly, we found that 19 out of 21 SNe brighter than an absolute magnitude M(sub R) = −18.2 belong to the FI or BF groups, and that all FI events peaked above M(sub R) = −17.6 mag, significantly brighter than average SNe II.

supernovae: general↗
NASA NTRS1976

Absence of iron line emission in Cyg X-3

An observation of Cygnus X-3 was made with soft X-ray detectors launched on an Aerobee rocket. The iron line emission observed one month later and in May 1975 was not found. A 3 sigma upper limit for this feature is 0.006 ph/2 cm/s.

Shulman, S.↗
NASA NTRS1981

Interplanetary particle observations associated with solar flare gamma-ray line emission

Observations of particle emissions during three solar flares which were observed to emit 2.22 MeV gamma rays as recorded by the Solar Maximum Mission are discussed. The 2.22 MeV line is produced by neutron capture by hydrogen, and additional attention is given to a 4.4 MeV emission line of June 7, 1980, with estimates made of the particle density 1 AU from the sun assuming a good magnetic connection between the earth and the sun. The measurements were made from the ISEE-3 and HELIOS-1 spacecraft. The connectedness of the earth and the sun in a magnetic field leads to conclusions that few particles actually escaped into interplanetary space.

Von Rosenvinge, T. T.↗