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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 433 records · Page 24
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NASA NTRS1987

The moderately interacting Algol-type eclipsing binary RY Geminorum

Ultraviolet spectra of the Algol-type semidetached system RY Geminorum, whose components can be described as A0 V and K0 IV, have been matched to the ultraviolet spectrum by Kurucz (1979) model atmospheres, and a best fit is found for T(eff) = 9150 K. Comparison with standard star spectra requires that this value be raised to 9400 K. The color excess of the system is determined to be no more than E(B-V) = 0.03 mag; the distance to the system is about 360 pc. The masses are approximately 2.36 and 0.38 solar masses, and the radii are 2.5 and 5.8 solar radii, respectively. The separation of the two centers is 26 solar radii. Evidence for a circumstellar line absorption is found in optical and ultraviolet spectrograms, and evidence is found in IUE spectra taken in partial eclipse for circumstellar emission lines of the type detected previously in the WS Serpentis stars and in several semidetected systems of the Algol type.

Plavec, Mirek J.↗
NASA NTRS1987

Was the eclipse comet of 1893 a disconnected coronal transient?

The comet-like feature obsereved in the solar corona by the Lick Observatory eclipse expedition to Chile in 1893 bears an interesting resemblance to the disconnection coronal transient reported by Illing and Hundhausen. Reports of possibly-related limb activity are reviewed to see whether a pre-discovery observation of a relatively rare type of coronal mass ejection was mis-interpreted. The goal of this study is to learn more about the morphology of mass ejections by examining observations that extend down to the low corona of a disconnection event.

Cliver, E. W.↗
NASA NTRS1988

Colliding stellar winds in the eclipsing Wolf-Rayet binary V444 Cygni

High resolution spectra of V444 Cygni have been obtained using the International Ultraviolet Explorer Satellite. These spectra span both eclipses and include one observation at third quadrature. Together with seven archival spectra, they provide reasonably complete phase coverage for the system. The variations in the P Cygni profiles of the He(II) and N(IV) lines, imply the existence of a low density region in the WR wind. This region occupies a relatively narrow range of orbital phase coinciding with the highest terminal velocities observed in C IV. These data are interpreted to be evidence of an interaction region separating the winds of the O-star and Wolf-Rayet star.

Brown, Douglas N.↗
NASA NTRS1987

Time-resolved IUE studies of cataclysmic variables. I - Eclipsing systems IP Peg, PG 1030+590, and V1315 Aql

IUE time-resolved spectra of the high-inclination cataclysmic variables IP Peg, PG 1030+590, and V1315 Aql are analyzed in order to determine the characteristics of the disk, hotspots, and white dwarfs. The UV continuum flux distributions are generally flatter than systems of low inclination and high mass-transfer rate, and the white dwarfs/inner disk appear to be relatively cool (15,000-19,000 K) for their orbital periods, possibly because the boundary layers are blocked from view. The continuum fluxes increase at spot phases, with the spot providing the dominant flux in IP Peg. The spot temperatures range from hot (20,000 K) in IP Peg, and perhaps in PG 1030+590, to cool (11,000 K) in V1315 Aql. The C IV emission lines show slightly larger decreases at spot phases than during eclipse, which implies an extended stream area.

Szkody, Paula↗
NASA NTRS1987

Eclipse measurements of Io's sodium atmosphere

The satellites of Jupiter eclipsed each other in 1985, and these events allowed an unusual measurement of the sodium in Io's extended atmosphere. Europa was used as a mirror to look back through the Io atmosphere at the sun. The measured column abundances suggest that the atmosphere is collisionally thin above 700 km and may be collisionally thin to the surface. The sodium radial profile above 700 km resembles a 1500 K exosphere with a surface density near 20,000 sodium atoms per cubic centimeter, but a complete explanation of the dynamics requires a more complex nonthermal model: the calculated loss rates suggest that the atmosphere is being replaced on a time scale of hours.

Schneider, Nicholas M.↗
NASA NTRS1988

The atmospheric eclipse of 31 Cygni in the ultraviolet

Theoretical spectra are compared with high-dispersion IUE observations for the 1982 atmospheric eclipse of 31 Cyg. It is found that temperature increases with height in the chromosphere, showing a range of 5,000-14,400 K for four lines of sight. Turbulence remains in the range 20-25 km/s throughout the chromosphere. The turbulence and temperature values may be lower in chromospheric gas just above the temperature minimum. The temperature-minimum region of the upper photosphere was found to have a temperature near 2,500 K. The velocity structure of wind lines of O I, Si II, Mg II, and Fe II indicates that most of the wind on the side of the K supergiant toward the B dwarf is photoionized to the next higher ionization stage. Abundances of heavy elements are shown to be close to solar with anomalies that may be the result of systematic errors in the oscillator strengths.

Eaton, Joel A.↗
NASA NTRS1988

Physical implications of the eclipsing binary pulsar

The observed characteristics of the msec pulsar P1957+20, discovered in an eclipsing binary by Fruchter et al. (1988), are considered theoretically. Model equations for the stellar wind and optical emission are derived and used to estimate the effective temperature and optical luminosity associated with wind excitation; then the energy levels required to generate such winds are investigated. The color temperature of the pulsar-heated stellar surface calculated under the assumption of adiabatic expansion is 1000-10,000 K, in good agreement with the observational estimate of 5500 K.

Wasserman, Ira↗
NASA NTRS1988

Colliding stellar winds in the eclipsing Wolf-Rayet binary V444 Cygni

High resolution spectra of V444 Cygni have been obtained using the International Ultraviolet Explorer Satellite. These spectra span both eclipses and include one observation at third quadrature. Together with seven archival spectra, they provide reasonably complete phase coverage for the system. The variations in the P Cygni profiles of the He(II) and N(IV) lines, imply the existence of a low density region in the WR wind. This region occupies a relatively narrow range of orbital phase coinciding with the highest terminal velocities observed in C IV. These data are interpreted to be evidence of an interaction region separating the winds of the O-star and Wolf-Rayet star.

Shore, Steven N.↗
NASA NTRS1989

Further observations of the eclipsing X-ray burst source MXB 1659-29

An analysis is presented of data for MXB 1659-29 obtained during October 2-10, 1976 and June 6-11, 1977 using the SAS 3 X-ray Observatory (Lewin et al., 1976) and during September 8-13, 1978 using the A-1 experiment aboard HEAO 1 (Wood et al., 1984). The data confirm the 7.1 hr orbital period and provide evidence for the 15-min X-ray eclipse reported by Cominsky and Wood (1984). A total of 32 X-ray bursts are detected during the SAS 3 observations. By combining the data with previously published results, the orbital period is found to be about 0.29650474 days.

Cominsky, L. R.↗
NASA NTRS1991

Eclipse earthshine

Earthshine is the sunlight reflected off the earth's surface that illuminates the dark side of the moon. In this paper, it is predicted that the earthshine is sufficiently bright during a total solar eclipse that lunar maria and craters can be distinguished visually and photographically. The predicted contrast ratio for prominent lunar features is typically 0.06. Proper shielding from glare and reasonable magnification are prerequisites for success.

Schaefer, Bradley E.↗
NASA NTRS1991

Submillimeter solar limb profiles determined from observations of the total solar eclipse of 1988 March 18

Observations were made of the extreme solar limb in six far-infrared wavelength bands ranging from 30 to 670 micron using the Kuiper Airborne Observatory during the total eclipse of the sun on 1988 March 18. By observations of the occultation of the solar limb by the moon, it was possible to obtain a spatial resolution of 0.5 arcsec normal to the limb. The solar limb was found to be extended with respect to the visible limb at all of these wavelengths, with the extension increasing with wavelength. Limb brightening was observed to increase slightly with increasing wavelength, and no sign of a sharp emission spike at the extreme limb was found at any of these wavelengths. The observations can be well fitted by a chromospheric model incorporating cool dense spicules in the lower chromosphere.

Roellig, T. L.↗
NASA NTRS1992

Coronal density and temperature structure from coordinated observations associated with the total solar eclipse of 1988 March 18

This paper explores and compares diagnostics for temperature and density within large-scale structures of the inner corona based on cospatial and cotemporal spectrophotometric observations made at the time of the total solar eclipse of 1988 March 17/18. In the analysis a determination of plasma temperature T can be derived unambiguously from the intensity ratios Fe XIV/XUV or Fe XIV/Fe X since all the emission lines come from the ionized state of Fe and the ratios are only weakly dependent on density. These temperatures and the densities found in well-defined large-scale coronal structures are discussed. The emission-line temperature is found to be high (local maxima) in the coronal structures with enhanced white-light emission and associated with new cycle high-latitude magnetic fields separated from the old cycle polar field of opposite polarity. Also the average of the ratio of scale-height temperature/temperature over the entire range of position angle is roughly unity although the ratio is higher than unity (1.3-1.6) in the three most prominent streamers.

Guhathakurta, M.↗
NASA NTRS1992

Limb observations of the 12.32 micron solar emission line during the 1991 July total eclipse

The limb profile of the Mg I 12.32-micron emission line is determined by occultation in the July 11, 1991 total solar eclipse over Mauna Kea. It is shown that the emission peaks are very close to the 12-micron continuum limb, as predicted by recent theory for this line as a non-LTE photospheric emission. The increase in optical depth for this extreme limb-viewing situation indicates that most of the observed emission arises from above the chromospheric temperature minimum, and it is found that this emission is extended to heights well in excess of the model predictions. The line emission can be observed as high as 2000 km above the 12-micron continuum limb, whereas theory predicts it to remain observable no higher than about 500 km above the continuum limb. The substantial limb extension observed in this line is quantitatively consistent with limb extensions seen in the far-IR continuum, and it is concluded that it is indicative of departures from gravitational hydrostatic equilibrium, or spatial inhomogeneities, in the upper solar atmosphere.

Deming, Drake↗
NASA NTRS1992

EC 19314 - 5915 - A bright, eclipsing cataclysmic variable from the Edinburgh-Cape Blue Object Survey

A deeply eclipsing cataclysmic variable, with an orbital period of 4.75 hr, has been discovered in the southern Edinburgh-Cape Blue Object Survey. The star, EC 19314 - 5915, lies close to the positional constraints of a previously unidentified HEAO-1 hard X-ray source, 1H1930 - 5989. Its optical spectrum is unusual in that it shows, apart from the emission lines characteristic of a novalike, or dwarf nova cataclysmic variable (Balmer, He I and He II), metallic absorption lines typical of a late-G star. The individual time-resolved spectra, with the tertiary absorption lines removed, show absorption reversals in the Balmer emission lines, increasing in strength for the higher series. The Balmer emission radial velocities are therefore severely distorted in comparison to the He II 4686-A emission and He I 4471-A absorption radial velocity curves. An independent distance estimate of about 600 pc is derived for EC19314 - 5915, from the spectroscopic parallax of the third star.

Buckley, D. A. H.↗
NASA NTRS1992

The hot subdwarf in the eclipsing binary HD 185510

High-resolution spectroscopic measurements of radial velocity are employed to characterize the eclipsing binary HD 185510 in terms of masses and evolutionary status. The IUE is used to obtain the radial velocities which indicate a large mass ratio Mp/Ms of 7.45 +/- 0.15, and Teff is given at 25,000 +/- 1000 K based on Ly alpha and UV spectrophotometry. Photometric observations are used to give an orbital inclination of between 90 and 70 deg inclusive, leading to masses of 0.31-0.37 and 2.3-2.8 solar mass for the hot star and the K star, respectively. The surface gravity of HD 185510B is shown to be higher than those values for sdB stars suggesting that the object is a low-mass white dwarf that has not reached its fully degenerate configuration. The object is theorized to be a low-mass helium main-sequence star or a nascent helium degenerate in a post-Algol system.

Jeffery, C. S.↗
NASA NTRS1992

X-rays from the eclipsing pulsar 1957+20

The detection of soft X-rays of about 1 keV energy from the eclipsing pulsar PSR1957+20 is reported. This high-energy radiation should be a valuable diagnostic of the wind in this recycled pulsar system. Possible sources of the X-ray emission are the interstellar nebula driven by the pulsar wind, the interaction between the pulsar and its evaporating companion, and the pulsar itself. The small apparent size of the X-ray object argues against the first of these possibilities and suggests that the X-rays are produced within the binary.

Fruchter, A. S.↗
NASA NTRS1992

Measurement of the solar limb brightness profile at 3 millimeters during the total eclipse of 1991 July 11

Observations of the solar limb at the point of first contact during the eclipse of 1991 July 11, with a spatial resolution of about 1.6 arcsec, are reported. The visibility amplitude and phase were modeled to yield the height of the 3-mm limb above the visible photosphere, and the data were differentiated to yield the brightness profile of the limb in strips about 1.6 arcsec wide. The 3-mm limb was found to extend 7.5 +/- 0.8 arcsec above the visible photosphere, with no evidence of a limb spike. The 3-mm limb, at a temperature of about 6500 K, extends to altitudes far beyond the expected location of the transition region in the model of Vernazza et al. (1981). A comparison of the 3-mm profile and an off-band H-alpha photograph of the limb reveals a close correspondence between the 3-mm limb and the height of H-alpha spicules.

Belkora, L.↗