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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

ROSAT x ray survey observations of active chromospheric binary systems and other selected sources

The connection between processes that produce optical chromospheric activity indicators and those that produce x-rays in RS CVn binary systems by taking advantage of the ROSAT All-Sky Survey (RASS) results and our unique ground-based data set was investigated. In RS CVn systems, excess emission in the Ca 2 resonance (K & H) and infrared triplet (IRT) lines and in the Balmer lines of hydrogen is generally cited as evidence for chromospheric activity, which is usually modeled as scaled up solar-type activity. X-ray emission in RS CVn systems is believed to arise from coronal loop structures. Results from spectra data obtained from RASS observations are discussed and presented.

Ramsey, Lawrence W.↗
NASA NTRS1994

Observations of accretion and angular momentum regulation in young circumstellar disks and the implications for planetary formation

Accretion disks around young stars produce excess infrared continuum associated with the disk and excess optical and ultraviolet continua associated with the boundary layer or 'hot spot' as material falls from the disk onto the stellar photosphere. When we subtract the excess continuum and photospheric contributions to the total spectrum, we can obtain high-quality emission line profiles of the Balmer lines as well as permitted lines from other elements. These emission lines often exhibit redshifted absorption, indicative of infalling material. Remarkably, objects with large accretion rates tend to rotate slower than their counterparts that lack accretion disks. Hence, there must be some process, probably involving magnetic fields, that allows the star to accrete large amounts of material from the disk without increasing its rotational velocity. Young stars typically do not have optically thick inner disks that do not accrete. Hence, either planets form within accretion disks, or the timescale for planetary formation is considerably shorter than approx. 3 x 10(exp 6) yr, the duration of the classical T Tauri star phase of young stellar evolution.

Hartigan, P.↗
NASA NTRS1993

Emission spectroscopy and laser-induced fluorescence measurements on the plume from a 1-kW arcjet operated on simulated ammonia

Spectroscopic and laser-induced fluorescence measurements were performed on the exhaust plume from a 1 kW NASA Lewis arcjet, operated on simulated ammonia. In particular, emissions were analyzed from the Balmer lines of atomic hydrogen and from one of the rotational bands of the NH radical. The laser-induced fluorescence measurements were performed on the Balmer-alpha line of atomic hydrogen. We find that exit plane temperatures are in the range 1500 to 3500 K and that the electron density upstream of the exit plane is on the order of 1.5 x 10(exp 14)/cu cm as determined by the Stark width of the Balmer-alpha line. Both emission spectroscopy and laser-induced fluorescence were used to measure the plume velocities of atomic hydrogen. Using either technique, velocities on the order of 4 km/sec were found at the exit plane and significant acceleration of the flow was observed in the first 2 mm beyond the exit plane. This result indicates that the design of the arcjet nozzle may not be optimum.

Ruyten, Wilhelmus M.↗
NASA NTRS1983

Two hot, low-field magnetic DA white dwarfs

Two hot stars discovered in the Palomar Green survey which were found to exhibit peculiarly broad and strong Balmer lines possibly indicative of low magnetic fields are discussed. The stars, PG 1658+441 and PG 0136+251, were found to have extended trough-shaped Balmer and Lyman-alpha line profiles when compared to nonmagnetic dwarfs of similar temperatures. Further observations of PG 1658+441 show it to correspond to a 30,000 K pure hydrogen atmosphere and confirm its nature as a magnetic object with a longitudinal field strength of about 0.7 megagauss and a mean surface field of about 2.3 megagauss. PG 0136+251 is found to be a hotter star (40,000-50,000 K) with weaker lines. Although no strong evidence for magnetic line splitting was obtained, it is argued that neither a high surface gravity nor very rapid rotation can account for the Balmer line shapes. Results thus extend the range of magnetic degenerates to include very hot white dwarfs, and demonstrate the usefulness of line-widths as indicators of possible low-field magnetic sources.

Liebert, J.↗
NASA NTRS1988

Nuclear emission-line intensities and profiles in NGC 3783

High-resolution optical spectrophotometry is presented for the nucleus of the Seyfert 1 galaxy NGC 3783. The data suggest that the broadest components of the forbidden lines have blueshifts relative to systemic velocity which are correlated primarily with ionization potential, and FWHMs which are correlated primarily with criticl density. Similar trends also exist in the line components responsible for the larger part of the line emission, but are not as strong as for the broadest line components. Comparison of the profiles of the Balmer lines indicates that the Balmer decrement measured from the H-beta/H-alpha ratio flattens in the line wings. However, the H-gamma and H-delta line profiles are more similar to the H-alpha line profile than to the H-beta line profile, suggesting that the H-beta profile may be anomalous.

Evans, I. N.↗
NASA NTRS1979

The emission-line spectrum of 3C 48

The spectrum and absolute energy distribution of the quasar 3C 48 are analyzed, yielding the following results. The forbidden lines are blueshifted with respect to the permitted lines by 600 km/s. The Balmer lines can be decomposed into a narrow and a broad component, with the narrow component having the redshift of the forbidden lines. The Mg II profile fits well the broad components of H-beta and H-gamma along with the Fe II profiles, and the forbidden O II profile fits well the profiles of forbidden O III and higher-ionization forbidden lines. The spatial coverage in the broad-line region is large, ranging from 0.1 to 0.4, and the optical depth at the Lyman limit is much greater than unity; the electron density is greater than 10 million per cu cm. The forbidden-line region has a lower density (less than 1 million per cu cm) and is subdivided into a low-excitation (forbidden O II) and high-excitation (forbidden O III) zone. The helium abundance appears to be normal.

Thuan, T. X.↗
NASA NTRS1983

Physical conditions in the cool parts of prominences

A spectral analysis of the cool parts of seven prominences reported by Shin-Huei (1961) and Yakovkin and Zel'dina (1964) is presented. The analysis requires only measurements of the Na and Sr(+) resonance lines and the middle H Balmer lines, all of which are optically thin, and uses the Na and Sr(+) statistical equilibrium solutions of Landman (1983). It is shown that the Na/H integrated intensity ratios alone are sufficient to determine the degree of H ionization. The major result of this investigation is that the degree of H ionization in the cool prominence parts is very low and the total gas pressure very high.

Landman, D. A.↗
NASA NTRS1993

PG 0308 + 096 and PG 1026 + 002 - Two new short period binary stars resulting from common-envelope evolution

Ultraviolet spectroscopy, optical spectroscopy, and spectrophotometry have been used to study the excess UV stars PG 0308 + 096 and PG 1026 + 002. Both objects are short-period binary systems, each containing a DA white dwarf star and a dM star. Orbital periods of approximately 0.284 day for PG 0308 + 096, and aproximately 0.597 day for PG 1026, have been found by spectroscopic analysis of the H-alpha emission line. Ly-alpha and Balmer line profile fitting were used to estimate the mass of white dwarf stars; mass estimates for the dM stars are based on their spectral types. The orbital inclinations are derived from these masses, the periods, and amplitudes of the H-alpha radial velocity curves. The equivalent width of the H-alpha emission line, in each binary system, varies with the orbital phase in such a manner as to imply that it arises, in large part at least, from the hemisphere of the M star that faces the white dwarf star.

Saffer, Rex A.↗
NASA NTRS2020

Imagery and UV Spectroscopy of the LMC Supernova Remnant N103B Using HST

We present Hubble Space Telescope(HST)/Wide Field Camera 3 multiband imagery of N103B, which is the remnant of a SN Ia in the Large Magellanic Cloud, as well as HST/Cosmic Origins Spectrograph(COS)ultraviolet spectroscopy of the brightest radiatively shocked region. The images show a wide range of morphology and relative emission-line intensities, from smooth Balmer-line dominated collisionless shocks that are due to the primary blast wave to clumpy radiative shock filaments that are due to secondary shocks in density enhancements. The COS data show strong FUV line emissions, despite a moderately high extinction along this line of sight. We use the COS data with previous optical spectra to constrain the shock conditions, we refine the abundance analysis, and we find abundances that are typical of the local interstellar medium within the uncertainties. Under an assumption that the material being shocked was shed from the pre-supernova system, this finding places constraints on any significant enrichment in that material, and thus on the non-degenerate star in what was presumably a single-degenerate SN Ia.

William P. Blair↗
NASA NTRS1993

Lick slit spectra of thirty-eight objective prism quasar candidates and low metallicity halo stars

Lick Observatory slit spectra of 38 objects which were claimed to have pronounced UV excess and emission lines are presented. Eleven QSOs, four galaxies at z of about 0.1, 22 stars, and one unidentified object with a low S/N spectrum were found. Of 11 objects which Zhan and Chen (1987, 1989) suggested were QSO with z(prism) not greater than 2.8; eight are QSOs. Six of the QSOs show absorption systems, including Q0000+027A with a relatively strong associated C IV absorption system, and Q0008+008 with a damped Ly-alpha system with an H I column density of 10 exp 21/sq cm. The equivalent widths of the Ca II K line, the G band, and the Balmer lines in 10 stars with the best spectra are measured, and metallicities are derived. Seven of them are in the range -2.5 to -1.7, while the others are less metal-poor.

Tytler, David↗
DOE OSTI2020

Emission-line Data Cubes of the HH 32 Stellar Jet

We analyze data cubes of over 60 emission lines in the HH 32 stellar jet acquired with the Keck Cosmic Web Imager (KCWI). The data cover the less explored blue portion of the spectrum between 3586 and 6351 Å and have both high spectral (R ∼ 10,000) and spatial (≲1″) resolution. The study includes all three major ionization states of oxygen, three Balmer lines, multiple lines of Fe ii and Fe iii, and the first data cubes ever acquired for important unblended diagnostic lines such as He ii λ4686, Ca i λ3933, and Mg i] λ4571. The data cubes generally sort according to excitation and have a relatively continuous progression from the highest-excitation ions (He ii, O iii) through the intermediate-excitation ions (O i and H i) to the lowest-excitation ions (Ca ii and Mg i). Merging the KCWI cubes with Hubble Space Telescope images leads to several new insights about the flow, including evidence for bow shocks, partial bow shocks, spur shocks, Mach disks, jet deflection shocks, a wiggling jet, and potential shock precursors. The most surprising result is that one of the velocity components of Fe ii in the Mach disk suddenly increases in flux relative to other lines by a factor of two, implying that the Mach disk vaporizes dust in the jet. Hence, jets must accelerate or entrain dust to speeds of over 300 km s{sup −1} without destroying the grains.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Quadratic Zeeman effect in hydrogen at 2–3 MG magnetic fields

The Zeeman effect is used for measurement of magnetic fields in astrophysical and laboratory plasmas. Magnetic fields in atmospheres of magnetic white dwarf stars are in the range 40 kG–1 GG. The quadratic Zeeman effect results in the additional split and shift of lines for magnetic fields >2 MG. Hydrogen Balmer lines were studied in magnetic fields delivered by a 1 MA pulse power generator. The magnetic field was generated by rod loads 0.8–1 mm in diameter. A droplet of CH oil on the load center was the source of hydrogen. A low ionized oil layer was backlit by blackbody emission from the rod with a temperature of 0.5–0.6 eV. Zeeman splitting of H-alpha and H-beta absorption lines were with a grating spectrometer. A spectral shift of the central component of the triplet indicated the quadratic Zeeman effect in hydrogen lines.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1974

Ultraviolet photometry from the orbiting astronomical observatory. XVI - The stellar Lyman-alpha absorption line

The stellar Lyman-alpha line at 1216 A was observed in 29 lightly reddened stars of spectral type B2.5 to B9 by a far-UV spectrophotometer on OAO-2. The equivalent widths obtained range from 15 A at type B2.5 to 65 A at type B8; in the late-B stars, the L-alpha line removes 2 to 3% of the total stellar flux. In this sampling, the strength of the L-alpha line correlates well with measures of the Balmer discontinuity and Balmer line strengths; luminosity classification does not seem to affect the line strength. The observed line widths also agree with the predictions of Mihala's grid of non-LTE model atmospheres. In some cases, the L-alpha line influences the interstellar column densities reported in the interstellar OAO-2 L-alpha survey. Hence, these data toward lightly reddened B2 and B1.5 stars should be regarded as upper limits only.

Savage, B. D.↗
NASA NTRS1982

Discovery of a narrow line quasar

A stellar object is reported which, while having X-ray and optical luminosities typical of quasars, has narrow permitted and forbidden emission lines over the observed spectral range. The narrow-line spectrum is high-excitation, the Balmer lines seem to be recombinational, and a redder optical spectrum than that of most quasars is exhibited, despite detection as a weak radio source. The object does not conform to the relationships between H-beta parameters and X-ray flux previously claimed for a large sample of the active galactic nuclei. Because reddish quasars with narrow lines, such as the object identified, may not be found by the standard techniques for the discovery of quasars, the object may be a prototype of a new class of quasars analogous to high-luminosity Seyfert type 2 galaxies. It is suggested that these objects cannot comprise more than 10% of all quasars.

Stocke, J.↗
NASA NTRS1990

Non-LTE model calculations for SN 1987A and the extragalactic distance scale

This paper presents model atmospheres for the first week of SN 1987A, based on the luminosity and density/velocity structure from hydrodynamic models of Woosley (1988). The models account for line blanketing, expansion, sphericity, and departures from LTE in hydrogen and helium and differ from previously published efforts because they represent ab initio calculations, i.e., they contain essentially no free parameters. The formation of the UV spectrum is dominated by the effects of line blanketing. In the absorption troughs, the Balmer line profiles were fit well by these models, but the observed emissions are significantly stronger than predicted, perhaps due to clumping. The generally good agreement between the present synthetic spectra and observations provides independent support for the overall accuracy of the hydrodynamic models of Woosley. The question of the accuracy of the Baade-Wesselink method is addressed in a detailed discussion of its approximations. While the application of the standard method produces a distance within an uncertainty of 20 percent in the case of SN 1987A, systematic errors up to a factor of 2 are possible, particularly if the precursor was a red supergiant.

Schmutz, W.↗
NASA NTRS1992

The 3 micron spectrum of the classical Be star Beta Monocerotis A

A 3.1-3.7-micron spectrum of the classical Be star Beta Mon A is presented at a resolution of lambda/Delta-lambda of 700-800. The spectrum shows strong hydrogen recombination lines, including Pf-delta and a series of Humphreys lines from Hu 19 to Hu 28. The relative recombination line strengths suggest that Pf-delta has a large optical depth. The Humphreys lines have relative strengths consistent with case B and may be optically thin. The line widths observed are broader than the Balmer lines and similar in width to Fe II lines, consistent with a disk model in which optically thinner lines arise primarily from a faster rotating inner disk, while optically thicker lines come mainly from a slower rotating outer disk. The apparent lack of Stark broadening of the Humphreys lines is used to place an upper limit on the circumstellar electron density of about 10 exp 12/cu cm.

Sellgren, K.↗