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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Parameterizations of Chromospheric Condensations in dG and dMe Model Flare Atmospheres

The origin of the near-ultraviolet and optical continuum radiation in flares is critical for understanding particle acceleration and impulsive heating in stellar atmospheres. Radiative-hydrodynamic (RHD) simulations in 1D have shown that high energy deposition rates from electron beams produce two flaring layers at T approximately 10 (exp 4) K that develop in the chromosphere: a cooling condensation (downflowing compression) and heated non-moving (stationary) flare layers just below the condensation. These atmospheres reproduce several observed phenomena in flare spectra, such as the red-wing asymmetry of the emission lines in solar flares and a small Balmer jump ratio in M dwarf flares. The high beam flux simulations are computationally expensive in 1D, and the (human) timescales for completing NLTE models with adaptive grids in 3D will likely be unwieldy for some time to come. We have developed a prescription for predicting the approximate evolved states, continuum optical depth, and emergent continuum flux spectra of RHD model flare atmospheres. These approximate prescriptions are based on an important atmospheric parameter: the column mass (m(sub ref)) at which hydrogen becomes nearly completely ionized at the depths that are approximately in steady state with the electron beam heating. Using this new modeling approach, we find that high energy flux density (>F11) electron beams are needed to reproduce the brightest observed continuum intensity in IRIS data of the 2014 March 29 X1 solar flare, and that variation in m(sub ref) from 0.001 to 0.02 g cm (exp -2) reproduces most of the observed range of the optical continuum flux ratios at the peak of M dwarf flares.

Kowalski, Adam F.↗
NASA NTRS1988

The electron temperature and optical emission structure of the central component of CTB 80

Optical spectra on the central component of the galactic supernova remnant CTB 80 are presented. Long slit CCD spectra reveal relative line-intensity variations among individual filaments, the presence of Balmer-dominated emission in the core's east and west optical lobes, and no radial velocities in excess of 300 km/s. Aperture spectrophotometry of the temperature-sensitive forbiddden O III lines suggests Te = 25,000 K, thus favoring a shock-heated interpretation for the remnant's optical core emission. These results indicate that fundamental differences exist betweem the optical emission of CTB 80's central core component and the Crab Nebula, despite similarities in these remnants' radio and X-ray properties. The optical emission from CTB 80's core is likely to be a direct result of the interaction of an active pulsar with its adjacent partially neutral interstellar medium. The size of CTB 80's outer structure and the absence of either high velocity or enhanced abundances in the region local to CTB 80's pulsar argue for a considerably larger age for CTB 80 than the Crab Nebula's 1000 yr. A qualitative picture for CTB 80 that can plausibly explain many of the core's properties is proposed.

Blair, William P.↗
NASA NTRS1971

Simultaneous measurements of the hydrogen airglow emissions of Lyman alpha, Lyman beta, and Balmer alpha.

Comparison of Lyman-alpha, 740- to 1050-A, and Balmer-alpha airglow measurements made at 134 deg solar-zenith angle on Oct. 13, 1969, with resonance-scattering models of solar radiation. Model comparison with Lyman-alpha data fixes the hydrogen column abundance over 215 km to 2 x 10 to the 13th per cu cm within a factor of 2. Differences between the Lyman-alpha model and data indicate a polar-equatorial departure from spherical symmetry in the hydrogen distribution. A Lyman-beta model based on the hydrogen distribution found to fit the Lyman-alpha data fits the spatial variation of the 740- to 1050-A data well from 100 to 130 km, but it does not fit the data well at higher altitudes; thus the presence of more rapidly absorbed shorter-wavelength radiation is indicated. This same resonance-scattering model yields Balmer-alpha intensities that result in good spatial agreement with the Balmer-alpha measurements, but a fivefold increase in the measured solar line center Lyman-beta flux is required (as required for the Lyman-beta measurement). The intensity ratio of Lyman-beta and Balmer-alpha at night is found to be a simple measure of the hydrogen optical depth if measurements with good accuracy can be made in the visible and ultraviolet spectrum.

Weller, C. S.↗
NASA NTRS1981

The formation of emission lines in quasars and Seyfert nuclei

The photoionization and heating throughout a quasar emission-line cloud optically thick at the Lyman edge are calculated. Photoionization and collisional ionization from excited states of hydrogen are included, which maintain a substantial electron fraction after the exhaustion of Lyman continuum photons halts ground-state photoionization. Observed values are explained for Ly-alpha/H-beta, H-alpha/H-beta, P-alpha/H-alpha, He I 5876/H-beta, O I 8446/H-alpha, and Mg II 2798/H-beta. The dependence of line strengths on physical conditions is discussed, and plotting Fe II/4570/H-beta versus Balmer continuum/H-beta is suggested. Other observations are also suggested, and the degree of asymmetry is given between the forward and backward emission of lines from a finite slab to make possible the use of comparative line profile studies to elucidate cloud kinematics.

Kwan, J.↗
DOE OSTI2025

Identification and control of the exhaust using gas perturbations in the DIII-D tokamak

This paper presents perturbative experiments that enable the validation and development of control-oriented models for exhaust control. We identify the response of the divertor plasma and scrape-off layer in the DIII-D tokamak to deuterium and nitrogen multi-sine perturbations, in favorable and unfavorable field directions for H-mode access. We obtained good signal-to-noise ratios in the 1–10 Hz frequency range by measuring Balmer-alpha, Lyman-alpha, and N 4+ line emission, radiated power, and neutral pressure. We find a similar phase response across gas species and magnetic field directions, while the gain response is nonlinear. With these experiments, we identify a control-oriented model to design a divertor radiated power controller to track specified reference waveforms in conjunction with resonant magnetic perturbations. Although the physics basis for compatibility between detachment and resonant magnetic perturbation edge-localized mode suppression remains to be demonstrated, the present results provide a robust controller that represents a promising step toward future joint control strategies.

detachment control↗
DOE OSTI2020

Follow-up Studies of Five Cataclysmic Variable Candidates Discovered by LAMOST

We report follow-up observations of five cataclysmic variable candidates from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) published by Hou et al. LAMOST J024048.51+195226.9 is the most unusual of the five; an early-M type secondary star contributes strongly to its spectrum, and its spectral and photometric behavior are strikingly reminiscent of the hitherto-unique propeller system AE Aqr. We confirm that a 7.34 hr period discovered in the Catalina survey data is orbital. Another object, LAMOST J204305.95+341340.6, appears to be a near twin of the novalike variable V795 Her, with an orbital period in the so-called 2–3 hr “gap.” LAMOST J035913.61+405035.0 is evidently an eclipsing, weakly outbursting dwarf nova with a 5.48 hr period. Our spectrum of LAMOST J090150.09+375444.3 is dominated by a late-type secondary and shows weak, narrow Balmer emission moving in phase with the absorption lines, but at lower amplitude; we do not see the He ii λ4686 emission evident in the published discovery spectrum. We again confirm that a period from the Catalina data, in this case 6.80 hr, is orbital. LAMOST J033940.98+414805.7 yields a radial-velocity period of 3.54 hr, and its spectrum appears to be typical of novalike variables in this period range. The spectroscopically selected sample from LAMOST evidently includes some interesting cataclysmic variables that have been unrecognized until now, apparently because of the relatively modest range of their photometric variations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1979

Optical studies of the Seyfert 2 X-ray galaxy NGC 2110

Spectrophotometry of the nucleus of the X-ray galaxy NGC2110 shows a typical Seyfert Type 2 spectrum with a strong galactic continuum. The widths of the forbidden lines are about 360 km/s (FWHM), H-beta being somewhat broader. The moderate Balmer decrement implies that the interstellar reddening is approximately 2.1 mag. The average electron density and temperature in the line-emitting region are approximately 300 per cu cm and 35,000 K, respectively. From measurements of the nebulium line, it is found that the extent of the nucleus measured along the major axis of the galaxy is about 10 arcsec (2100 pc) and the full range of gas velocities is about 700 km/s. A direct plate is discussed which shows faint spirallike features in NGC2110, a galaxy currently classified as elliptical. NGC2110 is a member of a new class (about 5 members) of very nearby (cz less than 2500 km/s) X-ray galaxies. Bradt et al. (1978) tentatively concluded that they are Seyfert Type 2 galaxies. This conclusion is supported, and it is shown that this is not inconsistent with the narrowness (less than 500 km/s FWHM) of their emission line.

Mcclintock, J. E.↗
NASA NTRS1982

The Crab Nebula. I - Spectrophotometry of the filaments

Relative line intensities in the 3700-7400 A region are obtained from new spectrophotometric measurements of ten positions in the Crab Nebula. O III forbidden line intensities imply electron temperatures of 11,000-18,300 K, while generally lower temperatures are indicated by the O II, N II and S II forbidden lines. The 6717 and 6731 A forbidden S II line ratio yields electron density estimates of 550-3500/cu cm, with a typical filament value of 1300 cu cm. While Balmer decrements are generally consistent with pure recombination, some filaments show steeper decrements. He line intensities are found to have significant variation. The presence of a moderately strong line at 7378 A, which may be due to the Ni II forbidden line is confirmed. Some filaments are found to exhibit a wide range of ionization states.

Fesen, R. A.↗
NASA NTRS1979

The bizarre spectrum of SS 433

Results are reported for extensive spectrophotometric observations, over the wavelength range from 3800 to 7800 A, of the peculiar 14th-mag emission-line object Stephenson-Sanduleak (SS) 433, which has been identified with a variable nonthermal radio source and is positionally coincident with the X-ray source A1909+04. It is found that the spectrum is dominated by intense variable Balmer and He I emission, that three of the He I lines have very prominent P Cygni profiles, and that virtually all the emission features undergo changes in equivalent width on a time scale of days. Anomalous emission features are described which consist of three previously unreported, very strong, broad emission lines at unfamiliar wavelengths in the green, red, and IR, and which vary nightly in intensity, profile, and wavelength. SS 433 is inferred to be a luminous object with an absolute visual magnitude of -3.1 or brighter.

Margon, B.↗
NASA NTRS1975

Stellar model chromospheres. IV - The formation of the H-epsilon feature in the sun /G2 V/ and Arcturus /K2 III/

The formation of the Balmer-series member H-epsilon in the near-red wing of the Ca II H line is discussed for two cases: the sun (H-epsilon absorption profile) and Arcturus (H-epsilon emission profile). It is shown that although the H-epsilon source functions in both stars are dominated by the Balmer-continuum radiation field through photoionizations, the line-formation problems in the two stars are quantitatively different, owing to a substantial difference in the relative importance of the stellar chromosphere temperature inversion as compared with the stellar photosphere.

Ayres, T. R.↗
NASA NTRS2001

The Strontium Filament within the Homunculus of Eta Carinae

During a series of HST/STIS observations of Eta Carinae and associated ejecta, we noticed a peculiar emission filament located a few arcseconds north of the central source. While bright in nebular standards, it is submerged in a sea of scattered starlight until moderately high dispersion, long-slit spectroscopy with the STIS (R- 8000) brings the emission lines out. The initial spectrum, centered on 6768A with the STIS G750M grating, led to identification of twenty lines from singly-Ionized species including [Sr II], [Fe II], [Ti II], [Ni II], [Mn II], and [Co II] (Zethson, etal., 2001, AJ 122,322). No Balmer emission is detected from this filament and the Fe II 2507,9 lines, known to be pumped by Lyman alpha radiation in other regions near the central source, are not detected. Followup observations have led to detection of hundreds more emission lines from iron group elements in neutral and singly-ionized states. Thus far all are excited by less than 10 eV. This peculiar nebular emission is thought to be due to very intense stellar radiation, stripped of uv flux shortward of Lyman alpha, bathing a neutral structure. We are systematically identifying the many lines (over 90% identified) and measuring line intensities that will then be modeled to determine excitation mechanisms, temperature and density. Two [Sr II] and two Sr II lines have now been measured. Bautista, etal. (in preparation) have modeled the strontium flux ratios and find that large radiation fluxes and/or high strontium abundances may account for the detected emission. These observations were supported by STIS GTO funding and GO funding through the STScI

Gull, Theodore R.↗
NASA NTRS1981

A spectrophotometric search for the halo of Markarian 10

Observations of a faint halo around the Mk 10 galaxy nucleus with the Palomar multichannel spectrophotometer reveal blue continuum emission forbidden lines of O II and O III, the hydrogen Balmer series, and stellar absorption series. The flux is detected at the surface brightness of 27.2 + or - 0.2 mag arc/sq sec at wavelengths of 5000 A at the radial distance of 27 kpc from the nucleus. The surface photometry of the inner parts of Mk 10 are depicted, and the radial brightness profile is decomposed into disk and bulge components. No evidence of a halo component was observed; the extended bulge is sufficient for the stabilization of the disk against bar-like instabilities.

Williams, T. B.↗
NASA NTRS1987

Observations of SN 1986J in NGC 891

Supernova SN 1986J was discovered at radio wavelengths with the VLA. The object is currently strongest at 6 cm wavelength and probably turned on at 6 cm wavelength in early 1984 and at 20 cm wavelength one or two years later. H I absorption-line observations show that the SN is about 7.7 kpc from the center and within 170 pc of the plane of NGC 891. SN 1986J is, in the radio, both the brightest and most luminous supernova yet found.The supernova has been identified optically with a 20th-magnitude (September, 1986) point source in NGC 891, and was approximately 1 mag brighter in January, 1984. The spectrum is dominated by emission lines; H I, He I, forbidden O I, and probably Fe I and Fe II are seen. The Balmer decrement is very large, with an H-alpha/H-beta flux ratio of about 60. The He I line spectrum and the current optical brightness both suggest that only a small amount of this decrement can be attributed to extinction. The spectrum is similar to those seen in the late phases of type II supernovae; however, the small linewidth (FWHM of about 1000 km/s) suggests that SN 1986J is actually type V.

Rupen, M. P.↗
NASA NTRS1987

The ionization structure of planetary nebulae. 8: NGC 6826

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 1700 A were made in seven positions in the planetary nebulae NCG 6826. The O(++) electron temperature varies little from 8900 K throughout the nebula; the Balmer continuum electron temperature averages 1500 K higher. The wavelength 4267 C II line intensities imply C(++) abundances that are systematically higher than those determined from the wavelength 1906, 1909 C III lines, but because of uncertainties in the intensities of the ultraviolet lines relative to the optical ones, this discrepancy is less conclusively demonstrated in NGC 6826 than in other planetaries in this series. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give results that are consistent and also in approximate agreement with abundances calculated using ultraviolet lines in the few cases where the relevant ultraviolet lines are measurable. The results of the logarithmic abundances differ somewhat from the recent study by Aller and Czyzak, in part because their measured electron temperatures are somewhat higher. The Ar, Ne, and, to some extent, O and S abundances appear to be somewhat low, suggesting that the progenitor to NGC 6826 like that to NGC 7662, may have formed out of somewhat metal-poor material.

Barker, Timothy↗
NASA NTRS1988

The ionization structure of planetary nebulae. VIII - NGC 6826

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 1700 A were made in seven positions in the planetary nebulae NGC 6826. The O(++) electron temperature varies little from 8900 K throughout the nebula; the Balmer continuum electron temperature averages 1500 K higher. The wavelength 4267 C II line intensities imply C(++) abundances that are systematically higher than those determined from the wavelength 1906, 1909 C III lines, but because of uncertainties in the intensities of the ultraviolet lines relative to the optical ones, this discrepancy is less conclusively demonstrated in NGC 6826 than in other planetaries in this series. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give results that are consistent and also in approximate agreement with abundances calculated using ultraviolet lines in the few cases where the relevant ultraviolet lines are measurable. The results of the logarithmic abundances differ somewhat from the recent study by Aller and Czyzak, in part because their measured electron temperatures are somewhat higher. The Ar, Ne, and, to some extent, O and S abundances appear to be somewhat low, suggesting that the progenitor to NGC 6826 like that to NGC 7662, may have formed out of somewhat metal-poor material.

Barker, Timothy↗
NASA NTRS1992

Hydrogen recombination at high optical depth and the spectrum of SN 1987A

A general theory is presented for hydrogen recombination line formation in an expanding medium in which some of the lines are optically thick. This theory is used to calculate the time evolution of the hydrogen lines of SN 1987A at t equal to or greater than 150 days, assuming that the supernova envelope is a homologously expanding uniform sphere. The theoretical luminosities and ratios of the recombination lines agree remarkably well with the observations. For the first 2 yr, the supernova envelope is optically thick to Balmer continuum. For t equal to or less than 400 days, hydrogen is ionized primarily from the n = 2 level by Balmer continuum photons, which are provided partly by the two-photon decay of the 2s state and partly by emission lines of heavy elements.

Xu, Yueming↗
NASA NTRS1982

Observations of B-type supergiants

Methods are presented for determining the effective temperatures, radii and bolometric corrections for B-type supergiants. Absorption lines from hydrogen and from other elements, the H alpha, Balmer progression, and evidence for outflow from the invisible spectrum of these supergiants are considered. Luminosity effects, outflow velocities, and variability in the UV spectrum at high resolution are examined as well as the infrared and radio spectra. Spectroscopic characteristics of the peculiar supergiant P Cyg and superluminous supergiants; X-ray binaries; the properties of the photosphere and mantle; and mass loss are elaborated. A general model for the mantle of B stars is included and the properties of B type stars in the main sequence are compared with those of the B-type supergiants.

Source record↗
NASA NTRS1988

Spectroscopic observations of H-alpha emission stars from the Stephenson and Stephenson-Sanduleak lists

Spectroscopic observations were obtained for 111 objects from the lists of H-alpha emission stars of Stephenson (1986) and Stephenson and Sanduleak (1977). A total of 26 T Tauri stars, six symbiotic stars, three cataclysmic variables, 17 Be stars, five Me stars, two forbidden BQ stars, two emission-line galaxies, one planetary nebula, and one carbon star with Balmer emission was discovered. Descriptions are given for the spectra of the more unsual objects. A total of 47 objects failed to show emission.

Downes, Ronald A.↗