Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “emission lines”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Intrinsic Lyman Alpha Profiles of High-Velocity G, K, and M Dwarfs

Observations of H I Lyman alpha, the brightest UV emission line of late-type stars, are critical for understanding stellar chromospheres and transition regions, modeling photochemistry in exoplanet atmospheres, and measuring the abundances of neutral hydrogen and deuterium in the interstellar medium. Yet, Lyman alpha observations are notoriously challenging due to severe attenuation from interstellar gas, hindering our understanding of this important emission line's basic morphology. We present high-resolution far- and near-UV spectroscopy of five G, K, and M dwarfs with radial velocities large enough to Doppler shift the stellar Lyman alpha emission line away from much of the interstellar attenuation, allowing the line core to be directly observed. We detect self-reversal in the Lyman alpha emission line core for all targets, and we show that the self-reversal depth decreases with increasing surface gravity. Mg II self-reversed emission line profiles provide some useful information to constrain the Lyman alpha line core, but the differences are significant enough that Mg II cannot be used directly as an intrinsic Lyman alpha template during reconstructions. We show that reconstructions that neglect self-reversal could overestimate intrinsic Lyman alpha fluxes by 60-100% for G and K dwarfs and 40-170% for M dwarfs.

Allison Ann Youngblood↗
NASA NTRS1996

The 0.8 day orbit of the precataclysmic binary EUVE J1016-053

The optical counterpart of the new extreme ultraviolet source EUVE J1016-053 (=RE 1016-053) is known to show intermittent sharp Balmer and HE I emission and traces of an M dwarf associated with a white dwarf optical spectrum. We present extensive optical spectroscopy showing the emission lines vary in velocity and intensity on a period of 0d.78929 +/- 0d.00003. The phase of the emission-line strengths lags that of the velocities by 0.237 +/- 0.013 cycle, consistent with the quarter-cycle offset expected if emission arises from the side of the secondary facing the hot white dwarf. EUVE J1016-053 is another example of an extreme ultraviolet illumination-effect binary, which only recently emerged from a common-envelope phase of binary evolution. Based on spectroscopic measurements and new BVR photometry, we find that the M dwarf secondary's contribution to the combined light is smaller than previously reported, probably because of the difficulty of avoiding contamination from a third star 3".2 distant. The velocity of the weak H II absorption is in antiphase to the emission, suggesting that it originates in the white dwarf photosphere. The mass function implied by the emission-line motion is f(M) = 0.28 +/- 0.08 M solar. Assuming the He II absorption does follow the white dwarf, the mass ratio MWD/MdM is 1.8 +/- 0.5, and the gravitational redshift is 45 +/- 14 km s-1. The modulation of the emission lines suggests the inclination i > 40 degrees, but plausible masses demand this inclination be well above the value.

Non-NASA Center↗
NASA NTRS2003

Elemental Abundances in NGC 3516

We present Reflection Grating Spectrometer data from an XMM-Newton observation of the Seyfert 1 galaxy NGC 3516, taken while the continuum source was in an extremely low flux state. This observation offers a rare opportunity for a detailed study of emission from a Seyfert 1 galaxy as these are usually dominated by high nuclear continuum levels and heavy absorption. The spectrum shows numerous narrow emission lines (FWHM approximately less than 1300 kilometers per second) in the 0.3 - 2 keV range, including the H-like lines of C, N, and O and the He-like lines of N, O and Ne. The emission-line ratios and the narrow width of the radiative recombination continuum of CVI indicate that the gas is photoionized and of fairly low temperature (kT approximately less than 0.01 keV). The availability of emission lines from different elements for two iso-electronic sequences allows us to constrain the element abundances. These data show that the N lines are far stronger than would be expected from gas of solar abundances. Based on our photoionization models we find that nitrogen is overabundant in the central regions of the galaxy, compared to carbon, oxygen and neon by at least a factor of 2.5. We suggest that this is the result of secondary production of nitrogen in intermediate mass stars, and indicative of the history of star formation in NGC 3516.

Turner, T. J.↗
NASA NTRS1977

The nebulosity near the quasar 3C 249.1

Spectroscopic observations made 2 arcsec away from 3C 249.1 with a cooled SIT camera spectrograph and with a multichannel spectrometer yield convincing evidence for the presence of fairly narrow emission lines of forbidden O II, forbidden O III, forbidden Ne III, and perhaps H-beta. The redshift of these emission lines, z = 0.3125, is, within the accuracy of the observations, the same as that of the broad emission lines in the quasar itself; this appears to rule out a gravitational-redshift interpretation for the quasar redshift. The main difficulty in making models for the extended emission-line region is that of understanding the strong forbidden O II lines. For this purpose, shell, cloud, and disk models are discussed, as is time-dependent ultraviolet illumination of the nebula. Simple models, in which the nebular is exposed to the unaltered extrapolated quasar continuum flux, fail to produce the observed line ratios.

Richstone, D. O.↗
NASA NTRS1983

Digital analysis of narrow-band imagery of the Cygnus Loop

Calibrated surface brightness and spectral line ratio maps which involve emission from six different ionic species are derived from the digital analysis of narrow passband direct imagery of a field in the southeast part of the Cygnus Loop SNR, and the spatial structure is categorized on the basis of the presence or absence of features in images isolating different emission lines. While features present in all emission lines are found to have spectral behavior consistent with steady flow shock model calculations for a range of v(s), the features present only in such 'hot' lines as the O III forbidden line 5007 A are found to account for relative intensities of that line greater than can be matched by steady flow model calculations.

Parker, R. A. R.↗
NASA NTRS2002

What Is Happening at Spectral Type F5 in Hyades F Stars?

Aiming at a better understanding of the mechanisms heating the chromospheres, transition regions, and coronae of cool stars, we study ultraviolet, low-resolution Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra of Hyades main-sequence F stars. We study the B-V dependence(s) of the chromospheric and transition layer emission line fluxes and their dependences on rotational velocities. We find that the transition layer emission line fluxes and also those of strong chromospheric lines decrease steeply between B-V = 0.42 and 0.45, i.e., at spectral type F5, for which the rotational velocities also decrease steeply. The magnitude of the line-flux decrease increases for lines of ions with increasing degree of ionization. This shows that the line-flux decrease is not due to a change in the surface filling factor but rather due to a change of the relative importance of different heating mechanisms. For early F stars with B-V < 0.42 we find for the transition layer emission lines increasing fluxes for increasing v sin i, indicating magnetohydrodynamic heating. The v sin i dependence is strongest for the high-ionization lines. On the other hand, the low chromospheric lines show no dependence on v sin i, indicating acoustic shock heating for these layers. This also contributes to the heating of the transition layers. The Mg II and Ca II lines show decreasing fluxes for increasing v sin i, as long as v sin i is less than approx. 40 km/s. The coronal X-ray emission also decreases for increasing v sin i, except for v sin i larger than approx. 100 km/s. We have at present no explanation for this behavior. For late F stars the chromospheric lines show v sin i dependences similar to those observed for early F stars, again indicating acoustic heating for these layers. We were unable to determine the v sin i dependence of the transition layer lines because of too few single star targets. The decrease of emission line fluxes at the spectral type F5, with steeply decreasing v sin i, indicates, however, a decreasing contribution of magnetohydrodynamic heating for the late F stars. The X-ray emission for the late F stars increases for increasing v sin i, indicating magnetohydrodynamic heating for the coronae of the late F stars, different from the early F stars.

Boehm-Vitense, Erika↗
NASA NTRS1993

A model of an X-ray-illuminated accretion disk and corona

The X-ray-illuminated surface of the accretion disk in a low-mass X-ray Binary (LMXRB) and the X-ray-heated corona above the disk produce optical, UV, and soft X-ray emission lines. This paper presents 1D models of the emission line spectra and the vertical temperature and density structures at different radii. The models include a detailed treatment of the important atomic processes and an escape probability treatment of radiative transfer. Soker and Raymond (1993) use the density structure predicted by these models for a 2D Monte Carlo simulation of the photon scattering in the accretion disk corona (ADC) to examine the effects of the ADC on the angular distribution of X-rays and the flux of X-rays incident on the outer disk. This paper concentrates on the emission line fluxes for various elemental abundances and disk parameters. The UV lines of the classic LMXRBs are consistent with the model predictions. Some CNO processing is necessary to account for the nitrogen and helium abundances in Sco X-1 and other LMXRBs. Comparison of the models with observed spectra also points to a soft X-ray component with luminosity comparable to the hard X-rays. The models predict a substantial luminosity in the group of highly ionized iron lines near 100 A.

Raymond, John C.↗
NASA NTRS1978

Spectroscopy of the extreme-ultraviolet source Feige 24 - The binary orbit and the mass of the white dwarf

Results are reported for coude spectroscopy of the extreme-ultraviolet white dwarf Feige 24. Radial velocities of the H-alpha, He I 5876-A, and He I 6678-A emission lines, and the underlying M-dwarf absorption features, were determined from spectrograms obtained with the Lick 3-m telescope. The velocities show a binary period of 4.239(+ or - 0.0015) days. The emission-line and absorption-line velocities agree in phase, which indicates that the emission lines originate in the atmosphere of the M-dwarf secondary as a result of reprocessing of the EUV radiation. This effect is modeled, and the observed amplitude of the emission-line variability is used to place a lower limit on the orbital inclination. From these and other data it is shown that the mass of the white dwarf lies between 0.46 and 1.24 solar masses. Some possible implications for the evolution of binary stars are briefly discussed.

Thorstensen, J. R.↗
DOE OSTI2022

Kinematics of the H α and H β broad-line region in an SDSS sample of type-1 AGNs

Here, we investigate the kinematics of the part of the broad-line region (BLR) in active galactic nuclei (AGNs) emitting H β and H α emission lines. We explore the widths and asymmetries of the broad H β and H α emission lines in a sample of high-quality (i.e. high signal-to-noise ratio) spectra of type-1 AGN taken from the Data Release 16 of the Sloan Digital Sky Survey in order to explore possible deviation from the gravitationally bound motion. To find only the broad component of H β and H α, we use the FANTASY (Fully Automated pythoN Tool for AGN Spectra analYsis) code for the multicomponent modelling of the AGN spectra and for careful extraction of the broad emission-line parameters. Here, we show that based on the broad-line profiles widths and asymmetries, the BLR gas emitting H β and H α lines follows similar kinematics, and seems to be virialized in our sample of type-1 AGN.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

Ultraviolet observations of the structure and dynamics of an active region at the limb

The structure and dynamics of active region NOAA 7260 at the limb have been studied using ultraviolet spectra and spectroheliograms obtained during the eighth rocket flight of the Naval Research Laboratory's High Resolution Telescope an Spectrograph (HRTS). The instrument configuration included a narrow-bandpass spectroheliograph to observe the Sun in the lines of C IV lambda 550 and a tandem-Wadsworth mount spectrograph to record the profiles of chromospheric transition region and coronal lines in the 1850-2670 A region. The combination of high spatial resolution and high spectral purity C IV slit jaw images with ultraviolet emission-line spectra corresponding allows examination of a variety of active region phenomena. A time series of spectroheliograms shows large-scale loop systems composed of fine-scale threads with some extending up to 100 Mm above the limb. The proper motion of several supersonic features, including a surge were measured. The accelerated plasmas appear in several different geometries and environments. Spectrograph exposures were taken with the slit positioned at a range of altitudes above the limb and provide a direct comparison between coronal, transition region and chromospheric emission line profiles. The spectral profiles of chromospheric and transition region emission lines show line-of-sight velocities up to 70 km/s. These lower temperature, emission-line spectra show small-scale spatial and velocity variations which are correlated with the threadlike structures seen in C IV. Coronal lines of Fe XII show much lower velocities and no fine structure.

Korendyke, C. M.↗
NASA NTRS1980

IUE observations of circumstellar emission from the late type variable R Aquarii /M7 + pec/

IUE observations of R Aquarii (M7 + pec) have been obtained in low dispersion in order to study its circumstellar emission. Strong permitted, semiforbidden, and forbidden emission lines are identified that are superposed on a bright ultraviolet continuum. From the analysis it is deduced that the strong emission-line spectrum that involves semiforbidden C III, C IV, semiforbidden Si III, forbidden O II, and forbidden O III probably arises from a dense compact nebula the size of which is comparable to the binary system of which R Aqr is the primary star. Low-excitation emission lines of Fe II, Mg II, O I, and Si II suggest the presence of a warm chromosphere (T less than about 10,000 K) in the primary M7 late type giant. The secondary is identified as a white dwarf, comparable to or somewhat brighter than the sun, since such a star can produce enough ionizing photons to excite the continuum and emission-line spectrum and yet be sufficiently faint to escape detection by direct observation. The UV continuum observed is attributed to Balmer recombination and not to blackbody emission from the hot companion. The general spectral properties of R Aqr between 1200 A and 3200 A are discussed in the context of the model for the circumstellar nebula, the companion, and the mass-loss rate of the primary star.

Michalitsianos, A. G.↗
NASA NTRS1990

Ultraviolet and optical spectroscopy of NGC 5548 and the nature of the broad-line region

The structure of the broad-line region in NGC 5548 is investigated by analysis of the integrated flux and profile variations observed in optical and ultraviolet emission lines. It is shown that the observations do not appear to be consistent with models which identify the variable part of the emission lines with a simple rotating disk structure. The variable continuum, and integrated emission-line fluxes are highly correlated and suggest a small broad-line region (18 light days = 5 x 10 to the 16th cm), although the size of the line-emitting region is not well-determined. At least some of the broad emission arises in a component which at times appears very prominently and distinctly in difference spectra. This emission component appears to arise in a region which is physically distinct from the rest of the broad-line region. Although the integrated fluxes in the various optical and ultraviolet emission lines seem to vary together, there clearly are differences between the profiles of various lines, which suggests that there is at least some ionization stratification within the broad-line region.

Peterson, Bradley M.↗
NASA NTRS1994

The Seyfert II nature of the IRAS source FSC 10214+4724

We have observed the rest-frame optical and UV spectra of the luminous, high redshift Infrared Astronomy Satellite (IRAS) source FSC 10214+4724. We find the optical emission lines to be characterized by ratios similar to those found in Seyfert II galaxies. We support the conclusion of previous work that the UV emission lines are similar to those attributed to Active Galactic Nuclei (AGN) rather than to star formation. The ratio H alpha/H beta greater than or equal to 20 (2 sigma lower limit) implies substantial reddening of the narrow line region with A(sub V) greater than 5.5, sufficient to hide a broad line region in our H alpha observations. Given this large inferred reddening and the strength of the UV continuum and emission lines, we conclude (as have others) that simple screen models of reddening are not appropriate for this object. These properties are very similar to those of the infrared luminous galaxies at lower redshift, suggesting that FSC 10244+4724 is the luminous extreme of the same population. We also present H band (1.6 micrometer) imaging polarimetry observations and find that the rest-frame optical emission is unpolarized (P = 3.2% +/- 22.0%). This deep image of the field shows FSC 10214+4724 to possess an unresolved core, with several companions located within 10 sec of the point source. We find it unlikely that this group of objects is physically associated with FSC 10214+4724 at z = 2.3, and we argue that their magnitudes and colors are more consistant with those expected with those expected for galaxies in a foreground group. While galaxy number counts would suggest that such a projection has a low probability of being observed randomly, a foreground group might gravitational lens the z = 2.3 source, making such random statistics inappropriate, and contribute to the large observed luminosity of FSC 10214+4724. Comparison of H band images taken on two occasions one year apart show that FSC 10214+4724 had varied by 0.16 +/- 0.03 mag relative to a nearby star during that time. The UV-optical emission line spectra, the bright dereddened continuum magnitude (K less than 12) of the unresolved core, its extremely large bolometric luminosity, strong UV polarization, and possible variability all suggest that FSC 10214+4724 harbors an obscured AGN. Given that we observe no spectral features attributable to star formation, it appears either that star formation in FSC 10214+4724 is more highly obscured at optical and UV wavelengths than the narrow line region of the AGN, or that the AGN (rather than star formation) dominates the large luminosity of this object.

Elston, Richard↗
NASA NTRS1988

Spectra of galaxies in the Case Low-Dispersion Sky Survey in the direction of the Bootes void

A sample of 34 galaxies selected from the Case Low-Dispersion Northern Sky Survey in the direction of the Bootes void. Emission-line redshifts were obtained for 33 objects; the spectrum of the thirty-fourth galaxy contains no obvious features. Three of the emission-line galaxies are lcoated within the boundaries of the Bootes void, including one not previously reported. To date, all the galaxies discovered in the void have emission-line spectra. Although more than half the galaxies in the sample are fainter than M(B) = -21.0 mag, all five of the galaxies that were detected by IRAS are brighter than M(B) = 21.5 mag. The relative strengths of the emission lines in most of the galaxies, including those in the void, indicate the lines are excited by photoionization due to young, hot O and B stars. Possible causes for the star formation occurring in these galaxies include interaction with nearby galaxies, star formation induced by nuclear activity, and/or recent development of physical conditions required for star formation.

Weistrop, Donna↗
NASA NTRS1999

Keplerian Motion of Broad-Line Region Gas as Evidence for Supermassive Black Holes in Active Galactic Nuclei

Emission-line variability data on NGC 5548 argue strongly for the existence of a mass of order 7 x l0(exp 7) solar mass, within the inner few light-days of the nucleus in the Seyfert 1 galaxy NGC 5548. The time-delayed response of the emission lines to continuum variations is used to infer the size of the line-emitting region, and these determinations are combined with measurements of the Doppler widths of the variable line components to estimate a virial mass. The data for several different emission lines spanning an order of magnitude in distance from the central source show the expected V proportional to r(sup -1/2) correlation and are consistent with a single value for the mass.

Peterson, Bradley M.↗
NASA NTRS1995

Ionization Nebulae Surrounding CAL 83 and Other Supersoft X-ray Sources

We present the results of an optical search for ionized gaseous nebulae surrounding luminous, "supersoft" X-ray sources in the Large and Small Magellanic Clouds. This relatively new and mysterious X-ray class has characteristic luminosities approximately 10(exp 37) - 10(exp 38) ergs/s with effective temperatures in the range of 2 - 6 x 10(exp 5) K. The presence of a large flux of UV and soft X-ray photons from these objects has led to predictions of bright optical emission lines from the local interstellar medium. One such object, CAL 83 in the LMC, was known to have an associated nebula, and we quantify here the asymmetry and luminosity of this remarkable nebula. Deep images were made using narrowband filters to isolate the emission lines of H.alpha and [O III] (lamda5007). In these emission lines, the nebula is detected out to distances as far as 25 pc from the central object, and the integrated luminosity in each line is of order approximately 100 solar luminosity. Model calculations of such nebulae for chemical abundances characteristic of the LMC indicate that approximately 1% of the X-ray luminosity of the central source is reprocessed into the nebular H.alpha and [O III] lamda5007 emission lines, from which we conclude that the time-averaged X-ray luminosity of the central source, CAL 83, is greater than 3 x 10(exp 37) ergs/s. The bright inner nebula contains approximately 150 solar mass within 7.5 pc of CAL 83, which clearly indicates that the nebular material has its origin in the interstellar medium. In sharp contrast, there were null detections for nebulae associated with nine other luminous, supersoft X-ray sources in the LMC and SMC, with upper limits for the [O III] luminosity that are a factor of approximately 10 below that for CAL 83. For eight of these latter sources, we conclude that either their time-averaged luminosity is substantially below that of CAL 83, or that the local interstellar medium is much less dense. The latter effect may be enhanced by expansion of the ionized nebula during the last several million years.

Remillard, R. A.↗
NASA NTRS1995

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.↗
NASA NTRS1981

Optically pumped laser lines of Na2 pumped by Kr/+/ /6471 A/ and HeNe /6328 A/ lasers - Identification of old lines and prediction of possible new lines

The laser emission lines of a sodium dimer laser pumped by Kr(+) and HeNe lasers at wavelengths of 6471 and 6328 A, respectively, are identified. The Na2 fluorescence was excited in a crossed heat pipe oven at a sodium pressure of about 1 torr, and recorded spectra were compared with transition probability calculations. For the 6471-A pump, three series excited by absorption through the transitions v-prime = 13, J-prime = 35 - v-double prime = 4, J-double prime = 34; v-prime = 13, J-prime = 83 - v-double-prime = 2, J-double prime = 84 and v-prime = 20, J-prime = 98 - v-double prime = 6, J-double prime = 99 are observed in the region 6100-8350 A. At 6328 A, series excited through the transitions v-prime = 14, J-prime = 45 - v-double prime = 2, J-double prime = 46; v-prime = 16, J-prime = 17 - v-double prime = 4, J-double prime = 18; v-prime = 22, J-prime = 86 - v-double prime = 6, J-double prime = 85 and v-prime = 25, J-prime = 87 - v-double prime = 8, J-double prime = 86. Most of the previously observed optically pumped lines are found to correspond to the three level laser system. Additional wavelengths expected to undergo lasing under slightly improved conditions are also identified.

Verma, K. K.↗