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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 1,261 records · Page 70
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NASA NTRS1982

Gamma radiation and photospheric white-light flare continuum

It is noted that recent gamma-ray observations of solar flares have provided a better means for estimating the heating of the solar atmosphere by energetic protons. This type of heating has been suggested as the explanation of the continuum emission of the white-light flare. The effects on the photosphere of high-energy particles capable of producing the intense gamma-ray emission observed in the flare of July 11, 1978, are analyzed. A simple energy-balance argument is used, and hydrogen ionization is taken into account. It is found that energy deposition increases with height for the inferred proton spectra and is not strongly dependent upon the assumed angle of incidence. At the top of the photosphere, the computed energy inputs fall in the range 10-100 ergs/cu cm-s.

Hudson, H. S.↗
NASA NTRS1982

Detection of the 1400 A absorption in the ultraviolet spectrum of the DA white dwarf LB 3303

Low-resolution ultraviolet International Ultraviolet Explorer spectra of the southern white dwarf LB 3303 show the presence of the wavelength 1400 absorption feature reported by Greenstein in the spectrum of 40 Eri B. The equivalent width is 5.7 A, and the measured wavelength is 1394 A. A comparison of the ultraviolet fluxes with model atmospheres confirms that LB 3303 has an effective temperature near 16,000 K, as found earlier from visual wavelength data. There are still problems with the identification of this line. The star is not hot enough to explain the presence of Si IV, and the agreement with the spectrum of the H2 molecule is not convincing.

Wegner, G.↗
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 NTRS1983

X-ray evidence for white dwarf binaries in globular clusters

Data from an X ray survey of globular clusters by means of instrumentation on the Einstein Observatory indicate the existence of a distinct class of low-luminosity (L) sources. L was measured in the 10 to the 32nd to 10 to the 34th ergs/sec range when viewing point-like objects. The L-value is three orders of magnitude less than that of neutron star binaries, and is consistent with projections for binaries with 0.5 solar mass white dwarfs. They were located outside the cluster cores, which was taken as an indication of low mass. More than three sources at the lowest luminosity bound were observed in two clusters, suggesting a steep rise in the luminosity function, which agreed with observational data on galactic plane cataclysmic variables.

Hertz, P.↗
NASA NTRS1983

Gamma-ray observational constraints on the origin of the optical continuum emission from the white-light flare of 1980 July 1

Results are presented for the flare of July 1, 1980, which started at approximately 1627 UT and in which simultaneous measurements were made of X-ray, gamma-ray, and optical continuum emission for the entire duration of the flare. The X-ray and gamma-ray observations were made by the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite. The optical measurements were taken at the Sacramento Peak Observatory and the Big Bear Solar Observatory (Zirin and Neidig, 1981). It is found that the major white-light emission that occurs in the late phase of the flare could not have been due to heating by electron or ion precipitation. This conclusion derives from the fact that the X-ray and gamma-ray flux peaks approximately 1 minute before the maximum of the optical continuum mission emission. It is also found that approximately 73 percent of the optical continuum emission, representing a spatially and temporally distinct bright point, follows this maximum with little or no X-ray or gamma-ray emission in the same period.

Ryan, J. M.↗
NASA NTRS1984

Spatial interferometry for white light processing: The coherence interferometer

An optical systems design approach for a parallel optical processor that has an information throughput capacity in excess of one petabit per second is discussed. This system enables predetection processing of white light, passively illuminated scenes. Integrated with a programmable Van der Lugt filter, this system is an effective data compression method. A program to implement this parallel optical processing by interferometry system is discussed.

Breckinridge, J. B.↗
NASA NTRS1984

White Cliffs: Operating Experience

The fourteen dish white cliffs solar power station area is remote and subject to extreme environmental conditions, solution of the associated problems required careful and thoughtful attention and the application of resources. Notwithstanding the wide range and harshness of conditions, the difficulties caused by remoteness and the lack of a technological base and the need for relatively rapid demonstration of success, the project has had a very positive outcome. Qualitative and quantitative information and lessons are now available to enable considerable simplifications to be made for a new system, reducing both hardware and operation and maintenance costs. Experience and lessons are presented, particularly in relation to: system performance in various environmental conditions; design philosophies for collectors, the array, control systems, engine and plant; operation and maintenance strategies and cost reducing possibilities. Experience so far gives encouragement for the future of such paraboloidal dish systems in appropriate areas.

Kaneff, S.↗
NASA NTRS1983

The cool DC white dwarf Stein 2051B

Visual scans from the Kitt-Peak 2.1-m telescope and UV spectra from the IUE satellite are combined in a spectroscopic study of the bright DC white dwarf, Stein 2051B. With a cooling age near 2 billion years, and a resulting atmospheric mass of hydrogen of the order of 6 x 10 to the 17th g, the accretion rate over the star's lifetime is less than 2 x 10 to the -25th solar masses/year. This is far below the predictions of standard accretion theories, and requires unreasonably strong suppression of hydrogen accretion in this star if the accretion-diffusion theory is to account for the carbon abundance found. It is suggested that the carbon may have been brought to the surface by convective mixing.

Wegner, G.↗
NASA NTRS1984

GD 323 - A white dwarf with a stratified H/He atmosphere?

New optical and ultraviolet (IUE) spectrophotometry of the hot white dwarf GD 323 are presented. The optical spectra exhibit broad, shallow Balmer lines, together with weaker He I lambda-4471, lambda-4921 lines. However, the effective temperature and helium abundance derived from the optical spectrum appear incompatible with parameters derived from the optical colors and the overall energy distribution - thus suggesting that GD 323 does not have a homogeneous, mixed composition atmosphere. The alternative interpretations of substantial reddening, a rapidly rotating subdwarf, an accreting short-period binary, and a detached DA + DB binary system are ruled out. It is suggested instead that GD 323 may have a stratified atmosphere, with an optically thin hydrogen layer overlying a helium envelope at T(e) about 30,000 K; however, this conclusion must be properly tested.

Liebert, J.↗
NASA NTRS1984

The absorption near 1400 A in the spectra of additional DA white dwarfs

Ultraviolet spectroscopic observations of five white dwarfs having published spectral types of DA made with the International Ultraviolet Explorer (IUE) satellite are reported. The three coolest objects: GD279 (0148 + 46), W485A (1327 - 08), and G231 - 40 (2117 + 53) have easily detected absorptions near lambda 1400. Of the two remaining stars, PG0039 + 045 may not be a true DA and GD140 (1134 + 30) is apparently too hot to show any feature near lambda 1400. It is argued that the lambda 1400 feature is produced by the lambda 1420 photoionization edge of Ca II.

Wegner, G.↗
NASA NTRS1984

On the magnetic field in the white dwarf Grw + 70.8247 deg

Greenstein (1984) has estimated a 3.5 x 10 to the 8th gauss magnetic field strength for the case of a sharp absorption feature near 1345 A, from the white dwarf Grw + 70.8247 deg that is interpreted as a component of hydrogen Lyman-alpha in a strong magnetic field. A highly accurate multiparameter variational method is the basis of the present deduction of a maximum Lyman-alpha obtainable wavelength of 1342.6 A, with a magnetic field of 5.6 x 10 to the 8th gauss. Alternative explanations of the 1345 A line as H-alpha or H-beta components, or a combination of the two, are given.

Henry, R. J. W.↗
NASA NTRS1984

Rotation of the sun measured from Mount Wilson white-light images

The instrumentation, data and data reduction procedures used in white light observations of sunspot rotation rates are described. The study covered 62 yr of rotation observations. The data were all gathered using the same Mt. Wilson telescope, which has had three different main lenses in the interval 1981-82. Details of the exposure calibration and lens operation procedures are provided. The data were treated in terms of eight evenly space determinations of the solar limb and account was taken of all sunspots within 60 deg of the central meridian. Spot movements were traced in terms of groups of contiguous individual spots. Large spots rotated slower than small spots, a condition attributed to greater viscous drag in the larger flux tubes in the photosphere. The data tend to confirm theories that the photospheric gas revolves at a different rate than the sunspots.

Howard, R.↗
NASA NTRS1985

White Light Coronograph (WLC) and Ultra-Violet Coronal Spectrometer (UVCS)

The white light coronagraph (WLC) and ultraviolet coronal spectrometer (UVCS) together reveal the corona and the roots of the solar wind from 1.5 to 6 solar radii from Sun center. The WLC measures the plasma density and spatial structure of the corona and coronal mass ejections at a resolution of about 20 arcseconds. The UVCS, in combination with the WLC, measures the temperature and radial outflow speed of the coronal plasma. These instruments will detect mass ejections from active regions and high speed solar wind streams from coronal holes a few days before the source regions rotate onto the face of the Sun, thus giving a week or more of advanced warning for disturbed geomagnetic conditions at Earth.

Moore, R. L.↗
NASA NTRS1984

The discontinuity near 1600 A in the spectra of DA white dwarfs

Ultraviolet spectroscopic observations of two relatively cool DA white dwarfs, L481 - 60 (= WD 1544 - 37) and BPM 1266 ( = WD 2105 - 82), with the International Ultraviolet Explorer (IUE) satellite show a strong drop in their spectral energy distributions below 1600 A. Published model atmospheres and thier visual spectra suggest that these two stars have effective temperatures in the vicinity of 9,000-10,000 K, and it is proposed that the 1600 A feature could be due to the 342(1S) 3s2(1S) photoionization edge of Mg I.

Wegner, G.↗
NASA NTRS1985

Characteristics of the white-light source in the 1981 April 24 solar flare

Observations of the white-light solar flare event of April 24, 1981 are presented. The observations were carried out in the optical, hard X-ray, and radio wavelengths from land-based observatories and from the International Sun-Earth Explorer (ISEE-3) satellite. Time-intensity profiles were derived for three lines of continuum emissions. The derived profiles are interpreted in terms of the energetics of the flare, and the role of energetic electrons in the production of optical continuum emission is examined in detail.

Kane, S. R.↗
NASA NTRS1985

On the ultraviolet iron spectrum of pre-white dwarfs

Numerous lines of Fe V, Fe VI, and Fe VII have been detected in high-resolution IUE spectra of two central stars and a number of very hot subdwarfs. The strengths of these lines vary widely from star to star, suggesting that the abundance of iron in the atmospheres of the immediate progenitors of white dwarfs is strongly variable. A possible explanation is elemental separation by gravity and radiation pressure.

Schoenberner, D.↗
NASA NTRS1985

Hydrogen spectrum in magnetic white dwarfs - H-alpha, H-beta and H-gamma transitions

Using the results of an accurate variational calculation, a graphical display of the wavelengths of the H-alpha H-beta, and H-gamma lines of hydrogen for magnetic field values ranging from 0 to 560 megagauss, which is believed to cover the range of fields found in magnetic white dwarfs. This is the first complete detailed compilation of such results.

Henry, R. J. W.↗