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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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NASA NTRS1979

X-ray line emission from Capella

X-ray emission-line components from Mg, Si, S, and Fe are unambiguously detected from Capella with the solid-state spectrometer onboard the Einstein Observatory. The X-ray spectrum is inconsistent with an isothermal corona, and requires components between 6-million K and at least 24-million K for an adequate fit. An inhomogeneous corona in which the X-ray emitting plasma is confined to magnetically contained loops appears to be reconcilable with all of the experimental evidence.

Holt, S. S.↗
NASA NTRS1985

The theory of emission-line regions in active galactic nuclei

The inability of photoionization models to predict the observed amount of energy in the Fe II lines and the Balmer continuum has led to the hypothesis that an additional, nonphotoionized region is present to supplement the intensities of low ionization lines. The question of reddening is addressed in light of its influence on the interpretation of the lines and continuum. It was found that X-rays can raise the gas temperature enough for collisional excitation to affect the Balmer decrement, and that narrow line emission from AGN (ranging in ionization level from Seyfert galaxies to low-ionization nuclei) can be attributed to photoionization by a nonthermal continuum for appropriate ionization-parameter values.

Ferland, G. J.↗
NASA NTRS1986

The effects of electron scattering opacity in the broad emission-line regions of quasars

It is demonstrated that three observational puzzles in quasars, nearly symmetric Lyman-alpha profiles, weakly asymmetric C IV 1549 A, and offsets between the peaks of these high ionization lines and the systematic velocity, can all be explained by the standard model of the physical state of the broad-line region with the addition of the simplest possible kinematics. Electron scattering in the intercloud medium is the essential ingredient that had been previously neglected. It is shown that the profiles depend at least as sensitively on the run of physical conditions as on the velocity law. Approximate analytic representations of the line emissivities based on detailed photoionization models are used to describe that dependence.

Kallman, T. R.↗
NASA NTRS1989

Soft X-ray emission lines from low-mass X-ray binaries. I - Collision-dominated models

The soft X-ray line emission from five low-mass X-ray binaries observed by the Einstein Observatory (HEAO 2) Objective Grating Spectrometer is examined. Observed spectra are fitted to model spectra consisting of emission from an optically thin plasma. Fits are performed using a variety of different assumptions for elemental abundances, heating and ionization mechanisms, and the distribution of gas temperature and ionization parameter. The results are discussed in the context of current models for the accretion flow in low-mass X-ray binaries.

Kallman, T. R.↗
NASA NTRS1990

Forbidden-line emission and infrared excesses in T Tauri stars - Evidence for accretion-driven mass loss?

It is suggested that disk accretion provides the requisite external source to power the winds of T Tauri stars. As a test of this hypothesis, a potential accretion diagnostic for a representative sample of stars is compared to diagnostics of the wind strength. The luminosity of H-alpha, formed in the inner wind, and the luminosity of the forbidden emission lines, formed in the outer wind, are used as wind diagnostics, while the excess infrared luminosity is used as a potential accretion diagnostic. It is found that forbidden-line O I 6300 A and H-alpha line luminosities are correlated with each other over two orders of magnitude; this is interpreted as the indication of a wide range of mass-loss rates among the given sample of T Tauri stars. The luminosity of each of these lines is also found to be correlated with excess infrared luminosity. However, neither the forbidden nor the H-alpha luminosity is well correlated with the photospheric luminosity, leading to a conclusion that it is the disk, not the star, which primarily determines the strength of wind indicators in T Tauri stars.

Cabrit, Sylvie↗
NASA NTRS1993

Double-peaked broad line emission from the LINER nucleus of NGC 1097

We report the recent appearance of a very broad component in the H-alpha and H-beta emission lines of the weakly active nucleus of the Sersic-Pastoriza galaxy NGC 1097. The FWZI of the broad component is about 21,000 km/s, and its profile is double-peaked; the presence of a blue, featureless continuum in the nucleus is also suggested. The broad component was first observed in H-alpha in November 2, 1991, and confirmed 11 months later. The H-alpha profile and flux did not change in this time interval. Comparison with previously published spectral data indicates that the broad lines have only recently appeared. Together with the relatively high X-ray luminosity and the compact nuclear radio source, our results characterize the presence of a Seyfert 1 nucleus in a galaxy which had previously shown only LINER characteristics. Obscuring material along our line of sight to the nucleus appears to have recently cleared, permitting a direct view of the active nucleus. We discuss two possible structures for the broad line region, biconical outflow and an accretion disk, that could give rise to the observed profile.

Storchi-Bergmann, Thaisa↗
NASA NTRS1994

Search for gamma-ray emission lines from SS 433: 2: 1980-1989

We have searched through the Solar Maximum Mission satellite gamma-ray spectrometer database for evidence of red and blue Doppler-shifted 1.37 MeV (24)Mg* nuclear lines. The data were obtained between 1980 and 1989 and span a total of 720 days when SS 433 was in the field of view. No evidence of Doppler-shifted line emission was found in any of our spectra. The range of 3 sigma upper limits for individual 9 day integration periods was (0.8-2.4) x 10(exp -3) photons/sq cm/s for the blue beam, encompassing the approximately 1.5 MeV feature reported by Lamb et al., and (0.2-2.1) x 10(exp -3) photons/sq cm/s for the red beam, encompassing the reported approximately 1.2 MeV feature. The average 3 sigma upper limit in each beam for shifted 1.37 MeV was 1.5 x 10(exp -3) photons/sq cm/s for single 9 day integration. The 3 sigma upper limits over 56 9 day integration intervals (504 days) for the red beam and 69 intervals (621 days) for the blue beam are 1.2 x 10(exp -4) photons/sq cm/s. The new limits can be reconciled with the HEAO 3 results only if SS 433 emits gamma rays at or above the SMM sensitivity limit on rare occasions due to variable physical conditions in the system.

Geldzahler, B. J.↗
NASA NTRS2000

Detection of X-Ray Line Emission from the Shell of SNR B0540-69.3 with XMM-Newton RGS

We present X-ray observations of PSR 0540-69.3 with the XMM-Newton observatory. The spectra obtained with the Reflection Grating Spectrometer reveal, for the first time, emission from ionized species of O, Ne and Fe originating from the SNR shell. Analysis of the emission line spectrum allows us to derive estimates of the temperature, ionization timescale, abundances, location, and velocity of the emitting gas.

vanderHeyden, K. J.↗
NASA NTRS2003

Thermal Iron K and Alpha: Line Emission from the X-Ray Binary GX 339-4

The accretion rate of the black hole candidate X-ray binary GX 339-4 in the 'off' state is low, and an advection dominated accretion flow (ADAF) is present. Hydrogen-like and helium-like iron Kbalpha; emission lines at 6.7 and 6.95 keV from hot plasma of ADAF can be produced by recombination-cascade processes with moderately high intensities, which are markedly distinguished from the fluorescent iron Kα line at approximately 6.4 keV. We show that the observational features of GX 339-4 can be explained by the ADAF model, if the iron abundance is more than 10 times the solar value, though the reason for such a high abundance is still unclear. We suggest that the increase of the accretion rate makes GX 339-4 change from off, low, intermediate, to high and very high states, and the line center of iron Kbalpha; will therefore shift from approximately 6.83 to approximately 6.4 keV, i.e. to the fluorescent disc-line, since the disappearance of the ADAF due to its high accretion rate.

Xu, Y. D.↗
NASA NTRS2010

3D Modeling of Forbidden Line Emission in the Binary Wind Interaction Region of Eta Carinae

We present recent work using three-dimensional (3D) Smoothed Particle Hydrodynamics (SPH) simulations to model the high ([Fe III], [Ar III], [Ne III] and [S III]) and low ([Fe II], [Ni II]) ionization forbidden emission lines observed in Eta Carinae using the HST/STIS. These structures are interpreted as the time-averaged, outer extensions of the primary wind and the wind-wind interaction region directly excited by the FUV of the hot companion star of this massive binary system. We discuss how analyzing the results of the 3D SPH simulations and synthetic slit spectra and comparing them to the spectra obtained with the HST/STIS helps us determine the absolute orientation of the binary orbit and helps remove the degeneracy inherent to models based solely on the observed RXTE X-ray light curve. A key point of this work is that spatially resolved observations like those with HST/STIS and comparison to 3D models are necessary to determine the alignment or misalignment of the orbital angular momentum axis with the Homunculus, or correspondingly, the alignment of the orbital plane with the Homunculus skirt.

Madura, Thomas↗
NASA NTRSDate not supplied

Spectrally Resolving High Redshift Dual AGNs with the Line Emission Mapper

The Line Emission Mapper (LEM) is an X-ray Probe-class Mission concept which combines 1-2 eV spectral resolution in the soft X-ray band (0.2-2 keV) with an effective area of ~2600 cm^2 at 1 keV, and 10’’ HPD over a large 30'x30' field of view. The mission will directly address the Astro2020 Decadal Report’s Priority Area of Unveiling the Drivers of Galaxy Growth through the study of merging galaxies, which offer one of the most dramatic channels for galaxy growth and evolution and can potentially trigger both star formation and supermassive black hole (SMBH) growth. Dual and binary AGNs in late-stage mergers are predicted to be a critical stage of merger-induced SMBH growth and coincide with the most transformative period for the host galaxies. Thus, dual and binary AGNs represent ideal laboratories for studying examples of SMBH-galaxy co-evolution. Recent discoveries of dual AGNs at redshifts of z~>2 have been made via optical observations, but such dual AGNs are inaccessible to current X-ray observatories due to a lack of instrumental capabilities, including sensitivity, spectral and spatial resolution. LEM will be uniquely suited to study AGNs at z > 3, where the intrinsic X-ray power law continuum and Iron K alpha emission line - a nearly ubiquitous signpost for AGN accretion – are redshifted into the LEM bandpass. In this poster, we present a simulation-based study on LEM’s ability to discern dual, binary, and/or clustered AGNs at high redshift. We demonstrate the unique capabilities of LEM to spectrally resolve Iron K-alpha lines emitted by distinct AGNs with sufficient line-of-sight velocity differences, even in cases of convolved point sources. Using a suite of simulations probing a range of velocity differences, line strengths, and column densities, we demonstrate LEM’s ability to constrain the spectral properties of dual AGNs at z>3 for a variety of physically realistic pairings. LEM will uniquely provide crucial constraints on dual AGN environments and activity as a function of redshift and will complement optical and infrared observations from upcoming Extremely Large Telescopes.

Ryan W Pfeifle↗
NASA NTRS2000

Evidence for Supermassive Black Holes in Active Galactic Nuclei from Emission-Line Reverberation

Emission-line variability data for Seyfert 1 galaxies provide strong evidence for the existence of supermassive black holes in the nuclei of these galaxies and that the line-emitting gas is moving in the gravitational potential of that black hole. The time-delayed response of the emission lines to continuum variations is used to infer the size of the line-emitting region, which is then combined with measurements of the Doppler widths of the variable line components to estimate a virial mass. la the case of the best-studied galaxy, NGC 5548, various emission lines spanning an order of magnitude in distance from the central source show the expected V proportional to r(sup -l/2) correlation between distance and line width and are thus consistent with a single value for the mass. Two other Seyfert galaxies, NGC 7469 and 3C 390.3, show a similar relationship. We compute the ratio of luminosity to mass for these three objects and the narrow-line Seyfert I galaxy NGC 4051 and find that the gravitational force on the line-emitting gas is much stronger than radiation pressure. These results strongly support the paradigm of gravitationally bound broad emission line region clouds.

Peterson, Bradley M.↗
NASA NTRS1991

Compton backscattered 511 keV annihilation line emission and the 170 keV line from the Galactic center direction

It is shown that Compton scattering of 511 keV electron-positron annihilation radiation produces a linelike reflection feature at 170 keV from backscattered photons. Assuming simple models of clouds and accretion disks around a compact source, the paper explores the spectrum of Compton-scattered annihilation line emission for a range of geometries, opacities, and observing angles, and finds that the linelike feature is produced under a wide variety of conditions. It is further shown that such Compton backscattering of slightly redshifted annihilation line emission from the inner edge of an accretion disk could account for the 170 keV line emission and higher energy continuum observed together with the 511 keV annihilation radiation from the direction of the Galactic center. Identification of the observed 170 keV line as a slightly redshifted annihilation line reflection feature provides strong new evidence that the source of this emission is a compact object surrounded by a disk of presumably accreting matter.

Lingenfelter, Richard E.↗
NASA NTRS1993

Infrared coronal emission lines and the possibility of their maser emission in Seyfert nuclei

Energetic emitting regions have traditionally been studied via x-ray, UV and optical emission lines of highly ionized intermediate mass elements. Such lines are often referred to as 'coronal lines' since the ions, when produced by collisional ionization, reach maximum abundance at electron temperatures of approx. 10(exp 5) - 10(exp 6) K typical of the sun's upper atmosphere. However, optical and UV coronal lines are also observed in a wide variety of Galactic and extragalactic sources including the Galactic interstellar medium, nova shells, supernova remnants, galaxies and QSOs. Infrared coronal lines are providing a new window for observation of energetic emitting regions in heavily dust obscured sources such as infrared bright merging galaxies and Seyfert nuclei and new opportunities for model constraints on physical conditions in these sources. Unlike their UV and optical counterparts, infrared coronal lines can be primary coolants of collisionally ionized plasmas with 10(exp 4) less than T(sub e)(K) less than 10(exp 6) which produce little or no optical or shorter wavelength coronal line emission. In addition, they provide a means to probe heavily dust obscured emitting regions which are often inaccessible to optical or UV line studies. In this poster, we provide results from new model calculations to support upcoming Infrared Space Observatory (ISO) and current ground-based observing programs involving infrared coronal emission lines in AGN. We present a complete list of infrared (lambda greater than 1 micron) lines due to transitions within the ground configurations 2s(2)2p(k) and 3s(2)3p(k) (k = 1 to 5) or the first excited configurations 2s2p and 3s3p of highly ionized (x greater than or equal to 100 eV) astrophysically abundant (n(X)/n(H) greater than or equal to 10(exp -6)) elements. Included are approximately 74 lines in ions of O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, and Ni spanning a wavelength range of approximately 1 - 280 microns. We present new results from detailed balance calculations, new critical densities for collisional de-excitation, intrinsic photon rates, branching ratios, and excitation temperatures for the majority of the compiled transitions. The temperature and density parameter space for dominant cooling via infrared coronal lines is presented, and the relationship of infrared to optical coronal lines is discussed.

Greenhouse, Matthew A.↗
NASA NTRS2022

Line Emission Mapper Probing Physics of Cosmic Ecosystems

The Line Emission Mapper (LEM) is an X-ray Probe for the 2030s that will answer the outstanding questions of the Universe’s structure formation. It will also provide transformative new observing capabilities for every area of astrophysics, and to heliophysics and planetary physics as well. LEM’s main goal is a comprehensive look at the physics of galaxy formation, including stellar and black-hole feedback and flows of baryonic matter into and out of galaxies. These processes are best studied in X-rays; as emphasized by the 2020 Decadal Survey, emission-line mapping is the pressing need in this area. LEM will use a large microcalorimeter array/IFU (that builds on Athena XIFU technology developments), covering a 30 × 300 field with 1000 angular resolution, to map the soft Xray line emission from objects that constitute galactic ecosystems. These include supernova remnants, star-forming regions, superbubbles, galactic outflows (such as the Fermi/eROSITA bubbles in the Milky Way and their analogs in other galaxies), the Circumgalactic Medium in the Milky Way and other galaxies, and the Intergalactic Medium at the outskirts and beyond the confines of galaxies and clusters. LEM’s 1–2 eV spectral resolution in the 0.2–2 keV band will make it possible to disentangle the faintest emission lines in those objects from the bright Milky Way foreground, providing groundbreaking measurements of the physics of these plasmas, from temperatures, densities, chemical composition to gas dynamics. While the mission is optimized to provide critical observations that will push our understanding of galaxy formation, LEM will provide transformative capability for all classes of astrophysical objects, from the Earth’s magnetosphere, planets and comets to the interstellar medium and X-ray binaries in nearby galaxies, AGN, and cooling gas in galaxy clusters. In addition to pointed observations, LEM will perform a shallow all-sky survey that will dramatically expand the discovery space.

Ralph Kraft↗
NASA NTRS1988

Line variability and the broad emission line region of quasi-stellar objects. II - Changes in Balmer decrements

Evidence is presented for significant variations of broad emission lines in five QSOs supporting an earlier report by Zheng et al. (1987). The Balmer decrements before and after variations are compared in an effort to extract information on the broad-line regions. The broad hydrogen lines are found to vary in step with the underlying continuum, indicating that the continuum is the probable energy source for emission lines. The ratios of H-beta/H-alpha for both the varying and steady parts of the the broad lines are about 0.2, suggesting that the regions in which these line fluxes originate are exposed to similar ionizing flux and are therefore at about the same distance to the central source. The average ratio of H-gamma/H-beta is 0.8 for the variable components, considerably higher than that of the constant components. Thus, the region producing the varying line fluxes may have higher density and lower optical depth.

Zheng, Wei↗
NASA NTRS1994

The HST quasar absorption line key project. 9: An emission-line study of PG 2251+113

We present Hubble Space Telescope (HST) and quasi-simultaneous ground-based observations of the z = 0.3252 QSO PG 2251+113. We find a correlation between line widths and the critical density for de-excitation of the forbidden emission lines observed in this object. We can show that this correlation also applies to the semiforbidden and possibly also the permitted lines which arise in the broad emission-line region. While this result was predicted from statistical studies, it has never previously been shown to hold in detail in any individual object. This relationship between the narrow and broad emission-line regions may help constrain dynamical models of both regions. We examine the implications of this result for a simple radial infall model of the emitting gas developed to explain the origin of narrow-line profiles.

Espey, Brian R.↗