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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Observations of Paschen alpha in the broad-line radio galaxy 3C 445

P alpha line flux measurements of the broad-line radio galaxy 3C 445 made at the NASA IR Telescope Facility in September 1981 are discussed. Broad-band measurements were obtained at H of 1.65 micron and K of 2.2 microns. A line flux of P alpha was found at 3.4 times 10 to the -13th ergs/sq cm sec. No discernable variation was detectable regarding measurements made in 1976. Substantial reddening was concluded to exist, although the H gamma lines observed were not due to reddening. The total H alpha luminosity was determined to be 4 x 10 to the 43rd ergs/sec. Steep Balmer line decrements are concluded to be due to interposed dust.

Rudy, R. J.↗
NASA NTRS1984

Two new extremely hot pulsating white dwarfs

High speed photometry of the extremely hot, nearly degenerate stars PG 1707 + 427 and PG 2131 + 066 reveals that they are low-amplitude pulsating variables. Power spectral analysis shows both to be multiperiodic, with dominant periods of 7.5 and 6.4-6.9 minutes, respectively. Together with the known pulsators PG 1159 - 035 and the central star of the planetary nebula Kohoutek 1-16, these objects define a new pulsational instability strip at the hot edge of the H-R diagram. The variations of these objects closely resemble those of the much cooler pulsating ZZ Ceti DA white dwarfs; both groups are probably nonradial g-mode pulsators. Evolutionary contraction of the PG 1159 - 035 variables may lead to period changes that would be detectable in as little as 1 year. The optical and IUE spectra of the PG 1159 - 035 variables are characterized by absorption lines of C IV and other CNO ions, indicating radiative levitation of species heavier than helium. He II is also present in the spectra, but the hydrogen Balmer lines are absent. Effective temperatures near 100,000 K are required, and the He II 4686 A profiles indicate log g greater than 6. These helium-rich pulsators form the hottest known subgroup of the DO white dwarfs.

Bond, H. E.↗
NASA NTRS1983

Spectrophotometric observations of symbiotic stars and related objects

Calibrated optical spectrophotometric observations of 16 symbiotic and symbiotic-like objects are presented. The objects observed include Z And, T CrB, CH Cyg, CI Cyg, V1016 Cyg, V1329 Cyg, AG Dra, YY Her, RS Oph, XX Oph, AG Peg, AX Per, CL Sco, HM Sge, AS 289, and M1-2. Integrated emission-line intensities are tabulated for comparison with ultraviolet and infrared data, as well as with previous optical studies. The reddening to each of the objects is derived by assuming that Balmer lines are emitted in their case B recombination ratios. However, the values so derived are often systematically higher than reddening estimates from the ultraviolet 2200 A feature. Comparisons with the available data from other wavelength ranges are noted.

Blair, W. P.↗
NASA NTRS1990

Emission-line ratios at high densities

Photoionization calculations are used here to study the density dependence of important emission lines for nucleon densities significantly greater than those considered standard. It is found that strong permitted emission lines suffer depression of their emissivity due to photon trapping and collisional destruction. Hydrogen continuum emission and some weak lines of heavy elements become more prominent at n(e) greater than 10 to the 10th/cu cm as they become increasingly important coolants. At high density and column mass, the Balmer decrement flattens because of the significant population in excited states of hydrogen. The results suggest that high-density, large column mass clouds could contribute an appreciable fraction of the observed Balmer line flux.

Zheng, Wei↗
NASA NTRS1996

X-Ray Spectrum of a Narrow Line Quasi-Stellar Object

This AO-3 observation of a new narrow-line QSO was motivated by our extensive study of the unclassified X-ray sources from the ROSAT/IRAS survey of Boller et al. IRAS 2018.1-2244 was observed to have Balmer lines and forbidden lines of roughly equal width. There are possibly weak broad wings on the H-alpha line. One of the questions to be addressed by hard X-ray spectroscopy is whether or not these wings are to be interpreted as scattered or weakly transmitted flux from a hidden broad-line region. The optical spectrum of this QSO also has very weak permitted Fe II lines, possibly indicative of a hidden broad line region. A new wrinkle on the concept of the narrow-line QSO is the gradual realization that luminous objects with very strong but narrow Fe II lines are showing up preferentially in soft X-ray surveys. The AO-1 objective was to detect the Geminga Pulsar and to interpret its 2-10 keV spectrum and pulse profile in terms of its X-ray emission spectra. Also, the AO-1 observed the Seyfert galaxy NGC 3516 to obtain a high signal-to-noise ratio spectrum. We expected NGC 3516 to be one of the best candidates for a successful demonstration of the details of the warm-absorber model.

Halpern, Jules P.↗
NASA NTRS1994

The pre-cataclysmic binary EUVE 2013+400

New optical spectroscopy shows a 0.706 d orbital period for Extreme Ultraviolet Explorer (EUVE) 2013+400 and confirms its membership in a class of close binary systems emerging from common-envelope evolution. This binary, like the prototype Feige 24, consists of an extreme ultraviolet (EUV) emitting hot white dwarf and a late-type dwarf. Bergeron et al.'s (1994) optical spectroscopy and ultraviolet spectrophotometry indicate that the white dwarf is hot (T(sub eff) approximately equals 50 000 K) and therefore very young (t(sub age) less than or equal 5 x 10(exp 6) yr), and extreme ultraviolet photometry places EUVE 2013+400 along a neutral hydrogen column density in the interstellar medium of n(sub H) approximately equal to 10(exp 19)/sq cm. The white dwarf is a DAO type and we obtained two independent estimates of the helium abundance from EUV photometric measurements (log(y) approximately equal to -3.2) and from the He II lambda-4686 line profile (log(y) approximately equal to -2.8). The data possibly indicate a level of heterogeneity expected in the context of on-going chemical separation in the photospheric layers. The Balmer lines show narrow emission that varies with binary phase with the equivalent widths of the emission trailing the radial velocities by 1/4 cycle: this phasing shows that most of the emission arises on the EUV-illuminated face of the red dwarf. A spectrophotometric decomposition shows that the secondary's spectral type is near M3 and that it contributes about 15%-25% of the total light near 6500 A; the resulting H-alpha emission is twice as strong as in Feige 24, with an equivalent width of 37-61 A with respect to the red dwarf continuum. EUVE 2013+400 is an important addition to the class of close binary stars discovered in EUV all-sky surveys.

Thorstensen, John R.↗
NASA NTRS1982

The detection of ultraviolet photospheric absorption in the spectra of two Wolf-Rayet stars

Narrow, unshifted UV absorption lines, principally of Fe v, have been detected in the spectra of two Wolf-Rayet stars, HD 93162 (WN7) and HD 193793 (WC7). Both stars are known to show upper Balmer-line absorption but exhibit no periodic Doppler shifts that might indicate the presence of a companion. If intrinsic to the Wolf-Rayet stars, these lines presumably form near the base of the envelope in the photosphere. The potential significance of absorption-line studies of Wolf-Rayet stars is discussed.

Fitzpatrick, E. L.↗
NASA NTRS1982

Infrared, optical, and ultraviolet observations of hydrogen line emission from Seyfert galaxies

Nearly simultaneous observations are reported of P-alpha, H-alpha, and H-beta emission from 18 Seyfert galaxies and of Ly-alpha from eight of these galaxies. In many cases, P-alpha is stronger relative to the Balmer lines than is predicted by recombination calculations; reddening appears to be required. Dispersion in the P-alpha/H-alpha/H-beta ratios orthogonal to the reddening track indicates that high densities or optical depths also affect the line flux ratios. Several galaxies, notably NGC 1275, have very low P-alpha/H-alpha ratios. High densities, large optical depths, and reddening probably all contribute to the low observed Ly-alpha/H-beta ratios.

Lacy, J. H.↗
DOE OSTI2025

A New Framework for Interstellar Medium Emission Line Models: Connecting Multiscale Simulations across Cosmological Volumes

The James Webb Space Telescope (JWST) and Atacama Large Millimeter/submillimeter Array have detected emission lines from the ionized interstellar medium (ISM) in some of the first galaxies at z ≳ 6. These measurements present an opportunity to better understand galaxy assembly histories and may allow important tests of state-of-the-art galaxy formation simulations. It is challenging, however, to model these lines in their proper cosmological context. In order to meet this challenge, we introduce a novel subgrid line emission modeling framework. The framework uses the high-z zoom-in simulation suite from the Feedback in Realistic Environments (FIRE) collaboration. The line emission signals from H II regions within each simulated FIRE galaxy are modeled using the semianalytic HIIL INES code. A machine learning approach is then used to determine the conditional probability distribution for the line luminosity to stellar-mass ratio from the H II regions around each simulated stellar particle. This conditional probability distribution can then be applied to predict the line luminosities around stellar particles in lower-resolution, yet larger volume cosmological simulations. As an example, we apply this approach to the IllustrisTNG simulations at z = 6. The resulting predictions for the [O II ], [O III ], and Balmer line luminosities as a function of star formation rate agree well with current observations. Our predictions differ, however, from related works in the literature, which lack detailed subgrid ISM models. This highlights the importance of our multiscale simulation modeling framework. Finally, we provide forecasts for future line luminosity function measurements from the JWST and quantify the cosmic variance in such surveys.

(ISM:) H II regions↗
NASA NTRS1997

Polarization of Line Emission from an Accretion Disk and Application to ARP 102B

We model the polarization properties of line emission from an accretion disk under a range of assumptions about the source function and electron-scattering optical depth tau(sub es). For small values of tau(sub es) and modest viewing angles, polarization can be in excess of the Chandrasekhar result for tau(sub es) = infinity. The polarization vector can be either parallel or perpendicular to the projected direction of the disk axis. The polarization properties of the double-peaked H-alpha emission line of the broad-line radio galaxy Arp 102B observed by Antonucci, Hurt, and Agol can be understood in terms of electron scattering and line broadening within the line-emitting region if tau(sub es) is of order unity, and if the position angle of polarization is parallel to the projected disk axis. The required small tau(sub es) is consistent with the hypothesis that the Balmer lines in Arp 102B are produced by photoionization of the disk atmosphere.

Chen, Kaiyou↗
DOE OSTI2023

Fantastic Fits with fantasy of Active Galactic Nuclei Spectra: Exploring the Fe II Emission near the Hα Line

In this study, a refined approach for multicomponent fitting of active galactic nuclei (AGNs) spectra is presented utilizing the newly developed Python code Fully Automated pythoN Tool for AGN Spectra analYsis (fantasy). AGN spectra are modeled by simultaneously considering the underlying broken power-law continuum, predefined emission line lists, and an Fe II model, which is here extended to cover the wavelength range 3700–11000 Å. The Fe II model, founded solely on atomic data, effectively describes the extensive emission of the complex iron ion in the vicinity of the Hγ and Hβ lines, as well as near the Hα line, which was previously rarely studied. The proposed spectral fitting approach is tested on a sample of high-quality AGN spectra from the Sloan Digital Sky Survey Data Release 17. The results indicate that when Fe II emission is present near Hβ, it is also detected redward from Hα, potentially contaminating the broad Hα line wings and thus affecting the measurements of its flux and width. The production of Fe II emission is found to be strongly correlated with Eddington luminosity and appears to be controlled by a similar mechanism as the hydrogen Balmer lines. The study highlights the benefits of fitting type 1 AGN spectra with the fantasy code, pointing that it may be used as a robust tool for analyzing a large number of AGN spectra in the coming spectral surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

X-ray heating and ionization of broad-line emission regions in QSOs and active galaxies

The absorption of X-rays deep within the broad-line emitting clouds in quasars and the nuclei of active galaxies produces extensive zones of warm (about 10,000 K), partially ionized gas. Because Lyman-alpha photons are trapped in these regions, the X-ray energy is efficiently channeled into Balmer lines collisionally excited from the n = 2 level. These H I regions and the H II regions created by UV photons illuminating the surfaces of the clouds gives rise to integrated Lyman-alpha/H-alpha lines emission ratios between 1 and 2. Enhanced Mg II line emission from the H I regions gives rise to integrated Mg II/H-alpha ratios near 0.5. The O I line at 8446 A is efficiently pumped by trapped H-alpha photons; and an intensity ratio of I(8446 A)/I(H-alpha) of approximately equal to and not greater than 0.1 is calculated for the X-ray heated zone.

Weisheit, J. C.↗
NASA NTRS1986

The density and thickness of quiescent prominences

The electron density was determined for a number of quiescent prominences at various positions from the Stark effect. It was found that the intensity ratio of Mg I emission lines to SrII lines is independent of the observed electron density in the range of ten to the 10.2 power to 10 to the 11.4 power cm-3. This contrasts with Landman's (1984) theoretical expectation that the ratio is proportional to the electron density. From the intensity of Balmer lines and the electron density, it is inferred that the true diameter of a thread in prominence of high electron density may be smaller than 0.2". The averaged total number density of hydrogen N sub H sub of was found to be 3-6 times 10 to the 11th power cm-3, leading to a total gas pressure P =0.6 dyn cm-2 and a total density of approx. 10 to the minus twelth power g cm-3. Landman's large value of N sub H approx. 6 times 10 to the 12th power and P sub g approx. 6 may have resulted either from the fact that he has treated very bright prominences and/or from the derivation of the high electron density for all prominences he studied.

Hirayama, Tadashi↗
NASA NTRS1987

The ultraviolet and optical emission-line spectrum of III Zw 77

The high-ionization Seyfert I galaxy III Zw 77 has been simultaneously observed over the satellite ultraviolet to near-IR spectral regions. As in other AGN, the continuous energy distribution shows a roughly power-law decline across much of the optical region and a flatter-than-unity spectral index in the near-UV. The equivalent widths of the Balmer lines and Ly-alpha are very similar to those found in other AGN. The UV-to-optical emission-line spectrum for narrow lines is fairly similar to those deduced for Seyfert 2 galaxies. A surprising result is the detection of the semiforbidden O III 1661, 1666 A doublet with an intensity indicating high temperatures more suggestive of shock heating than photoionization equilibrium. An interpretation in terms of a multicomponent photoionized structure is proposed in which dense regions produce the UV lines and the lower density regions produce the optical lines.

Ferland, Gary J.↗
NASA NTRS1995

An X-ray and optical study of the interaction of the Cygnus Loop supernova remnant with an interstellar cloud

We have used the ROSAT high-resolution imager and optical emission line data to study the structure of a bright optical knot on the southeastern rim of the Cygnus Loop supernova remnant. This knot has been identified as an encounter between the blast wave and a small isolated cloud. The knot appears in projection just behind the blast wave, which is traced by Balmer line filaments which bound the X-ray emission. The knot is a prominent X-ray feature, consisting of a numerb of filaments which are correlated with the optical line emission. These data permit a detailed view of the blast wave interaction. By combining the optical and X-ray data it is possible to trace the blast wave as a continuous surface from its southern edge around the western side of the cloud that then continues on to the north. The southeastern knot is an indentation on the surface of the blast wave. Thus the southeastern knot is not a small cloud that has been overrun by the blast wave, but the tip of a larger cloud. Bright X-ray emission is associated with bright radiative filaments. The location of this emission, upstream of the radiative shocks, implies that the enhanced X-rays come from a reverse shock. The presence of a reverse shock is further evidence that the southeastern knot represents an early stage of a blast wave encountering a large cloud. A consistent picture of the Cygnus Loop as an explosion within a preexisting cavity is emerging. These observations agree with that picture.

Graham, James, R.↗
DOE OSTI2022

Evaluation of a collisional radiative model for electron temperature determination in hydrogen plasma

A collisional-radiative (CR) model that extracts the electron temperature, T e , of hydrogen plasmas from Balmer-line-ratio measurements is examined for the plasma electron density, n e , and T e ranges of 10 10 –10 15 cm –3 and 5–500 eV, respectively. The CR code, developed and implemented in Python, has a forward component that computes the densities of excited states up to n = 15 as functions of T e , n e , and the molecular-to-atomic neutral ratio r(H 2 /H). The backward component provides ne and r(H 2 /H) as functions of the Balmer ratios to predict the T e . The model assumes Maxwellian electrons. Furthermore, the density profiles of the electrons and of the molecular and atomic hydrogen neutrals are shown to be of great importance, as is the accuracy of the line-ratio measurement method.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1995

Far-ultravoilet and optical spectrscopy of the detached white dwarf-M binary RE J1629+780

We present optical and far-ultraviolet observations, including IUE high- and low-dispersion spectroscopy, of the (DA2+dM4-5) close binary, RE J1629+780, a very bright ROSAT EUV source. The optical data reveal emission reversals in the cores of the Balmer lines, which vary in strength but reveal no evidence of wavelength shifts reflecting orbital motion, suggesting that the red dwarf and the white dwarf are widely separated. Thus it is unlikely that irradiation plays a dominant role in the activity of the red dwarf. One dramatic increase in the intensity of the H-beta emission strength in the course of one hour indicates that the observed intensity variations are most likely related to flare activity on the red dwarf. Our analysis of Balmer and Lyman alpha features yield T(sub eff) = 42,500 +/- 1300 K and log g = 7.6 +/- 0.3 for the DA2 white dwarf, which is consistent with the overall 900 to 3200 A energy distribution derived from Voyager and IUE low-dispersion spectra. Our analysis of three IUE echelle spectra reveal numerous lines of interstellar origin. Using a total of 13 interstellar matter (ISM) features we find a mean radial velocity of -13.57 +/- 1.66 km/s for the interstellar features. However, we found no evidence of trace metal absorbers levitated or accreted in the white-dwarf photosphere nor any evidence of circumstellar or wind features. We estimate a lower limit hydrogen layer mass of 2.1 x 10(exp -15) solar mass for a stratified atmosphere based upon the nondetection of He II (1640). Tighter constraints on the helium abundance and the hydrogen layer mass, from EUV and X-ray data, are presented for both homogeneous and stratified atmospheric configurations.

Sion, Edward M.↗
DOE OSTI2026

Enigmatic Line Broadening during Solar Flares: Magnetic Field Broadening?

The origin of the extreme broadening observed in chromospheric metal lines during solar and stellar flares—particularly Mg II h and k and Ca II H and K—remains poorly understood. These lines often display Lorentzian-like wings whose widths exceed standard Stark broadening predictions by factors of ∼30, with no known collisional mechanism capable of producing such enhancements. We posit that magnetic fields are responsible for this additional broadening, due to the increase of magnetic activity during flares. A magnetic field distribution of the form P(B) ∝ B −3 reproduces the observed Mg II profile wings while leaving H I Balmer lines and optically thin transitions largely unaffected. To explain the broadening using magnetic fields, the high-B tail can extend up to 10 6 G with extremely low probabilities where the filling factors are ≲10 −6 . We propose that observations of flares using spectropolarimetry can verify whether the anomalous broadening is from magnetic structures in flare ribbons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗