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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 343 records · Page 19
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NASA NTRS1981

Voyager 1 encounter with the Saturnian system

The Voyager 1 Saturn flyby mission of March 1979 is reviewed, with brief discussions of its flight, trajectory, science plan formulation and telemetered data. Analytical results of such data with respect to Saturn's atmosphere, rings, icy satellites, Titan satellite atmosphere and the Saturn magnetosphere, are summarized. The Voyager science investigations comprise imaging science (ISS), infrared radiation (IRIS), photopolarimetry (PPS), ultraviolet spectroscopy (UVS), radio science (RSS), magnetic fields (MAG), plasma particles (PLS), plasma waves (PWS), planetary radio astronomy (PRA), low energy charged particles (LECP), and cosmic-ray particles (CRS).

Stone, E. C.↗
NASA NTRS1981

HR 4511 - A probable Cepheid with a supergiant-like hot companion

IUE observations have shown HR 4511 to have an early B-type companion with a strong stellar wind. Fitting the energy distribution of the system from far-UV to middle-IR yields a difference of about 3.2 mag at the V passband. Since HR 4511 is in the small cluster Stock 14 and has M(V) = -7.8, M(V) for the secondary is about -4.6, which is only slightly more luminous than the known BO.5 III and B1 stars at the turnoff point. This implies an inconsistency between the deduced luminosity of the secondary and the nature of its UV spectrum, which mimics stars of considerably greater luminosity. It is suggested that the secondary may have been observed in a brief stage between core and shell H burning.

Parsons, S. B.↗
NASA NTRS1981

UBV photometry of Triton

UBV measurements of Triton relative to Neptune were obtained with an area-scanning photometer on 11 nights during the 1977 apparition. Observed orbital brightness variation shows that Triton is locked in synchronous rotation around Neptune. Its leading side, seen at greatest western elongation, is found to be 0.06 mag brighter than its trailing hemisphere.

Franz, O. G.↗
NASA NTRS1981

Measurement of stratospheric aerosol on Saturn using an eclipse of Titan

Measurements of the aerosol content in the Saturn atmosphere made during an eclipse of Titan by Saturn are presented. Observations of the ingress of Titan into the shadow of Saturn on December 20.08, 1979 were made by the 74-in telescope at Kottamia Station in Egypt at an effective wavelength of 6728 A with FWHM of 1000 A. The deviation of the observed light curve after a satellite darkening of 3 mag from that predicted for a clear Saturn atmosphere is interpreted in terms of an aerosol layer decreasing in extinction coefficient from a base altitude 5 km below the planetary tropopause to an altitude of up to 75 km above the tropopause. For an aerosal layer extending to 75 km above the tropopause calculations reveal possible optical depths ranging from 0.020 to 0.050. The range of the optical depth is comparable to that of the Jupiter atmosphere, and suggests that similar processes may be responsible for the stratospheric haze on both planets.

Smith, D. W.↗
NASA NTRS1981

A spectroscopic, photometric, and magnetic study of the starspot on II Pegasi

A description is presented of extensive observations of II Peg during 1977 and 1978, taking into account multicolor broad-band photometry, high-dispersion spectroscopy, low-dispersion spectrophotometry, and Zeeman analysis. During this time the star showed periodic light variations in excess of a 0.4 mag range attributable to the presence of a large starspot or an equivalent nonuniform surface brightness distribution. The high-precision multicolor photometry, which differed greatly from previous photometric results, illustrates that the starspots on II Peg are continually evolving on time scales of approximately 1 year or less. A low-dispersion spectrum of the large spot showed pronounced VO and TiO molecular adsorption features. A high-resolution, high signal-to-noise Reticon spectrum at lambda 6707 does not show any compelling evidence of previously reported lithium in this star.

Vogt, S. S.↗
NASA NTRS1981

Discovery of three X-ray luminous pre-main-sequence stars

Three X-ray sources found serendipitously in Einstein images of the Taurus-Auriga cloud complex were observed at the McGraw-Hill Observatory and are found to be associated with stars of approximately 12 mag with weak H-alpha emission. The stars lie on the edges of dark clouds and are spectroscopically similar to the least active emission-line pre-main-sequence stars. Although they lie well above the ZAMS in the H-R diagram, they do not exhibit ultraviolet excess, strong optical variability, or evidence for mass outflow/inflow characteristics of the more active T Tauri stars. Their only unusual property is high X-ray luminosity (approximately 10 to the 30th ergs/s). It is suggested that the X-ray emission from pre-main-sequence stars is not closely linked to the conditions giving rise to their unusual spectroscopic properties. The emission may instead represent an enhanced form of the coronal activity producing X-rays observed in late-type main-sequence stars.

Feigelson, E. D.↗
NASA NTRS1981

Monitoring solar-type stars

Old UBV and recent uvby photometry of solar-type dwarfs and other standard stars yield an upper limit of variability (determined by observational errors) of about 0.004 mag rms. A factor two improvement in this upper limit is achievable.

Lockwood, G. W.↗
NASA NTRS1982

Evidence for a distant ( 8700 R sub J) Jovian magnetotail: Voyager 2 observations

A correlative survey of magnetometer (MAG) and Planetary Radio Astronomy (PRA) 1.2 kHz continuum radiation measurements from Voyager 2 provide evidence for at least eight distant Jovian magnetotail sightings occurring about once a month over the first 2/3 of 1981 at distances of approximately 5,000 to 9,000 R sub J. The occurrences of these events are in good agreement with prior Plasma Wave Science and Plasma Science identifications. Observations of these distant magnetotail, or tail filament, encounters appear most prevalent in both MAC and PRA data sets when the spacecraft was closest to the Jupiter-Sun axis at approximately 6,500 R sub J from the planet; the PRA events are also most intense during those times. A specific tail encounter occurring in mid-February 1981 is analyzed and shown to possess a remarkably symmetric magnetic field signature and to have a bipolar field structure in the central region. The bipolarity is characteristic of most of the eight events.

Lepping, R. P.↗
NASA NTRS1982

IUE spectroscopy, visible-band polarimetry, and radiometry of V641 Mon

This hot, double line, ellipsoidal variable member of NGC 2264 has been shown previously to be either a semi-detached or contact close binary. Low-resolution IUE spectra are best fitted to a Kurucz model atmosphere for very small (approximately 0.08 mag) E(B-V). The familiar interstellar absorption dip near lambda 2200 is apparently absent. A suitable model atmosphere can be fitted to the IUE fluxes, but flux excesses (compared to the model) appear for all the published U through L magnitudes. The spectrum of the B through L excess appears to follow a .0001 lambda dependence. It is shown that this cannot be interpreted as arising from another star fortuitously observed in the visible band or IR. Ground based polarization measures indicate V641 Mon to be a polarization variable. Previous and new V light curves show the amplitude of light variability itself to be variable by about a factor of 2. It is suggested that all these observed characteristics are best explained by postulating "third light" and identifying part of it with Rayleigh scattered starlight very near to the stars. From this same region there arise circumstellar absorptions which give rise to nontheoretical strengths for Si II and Si III lines.

Koch, R. H.↗
NASA NTRS1981

A fireball in Jupiter's atmosphere

One fireball was photographed during two encounters with Jupiter. Its total luminosity was 120,000 0 mag s (at standard range 100 km). If the luminous efficiency proposed by Cook et al. (1981) for slip flow of a meteoroid in its own vapors is employed, an estimated mass of 11 kg is obtained. A rough absolute magnitude is -12.5. If it is noted that the search was conducted for a total of 223 s during two exposures, a number density near Jupiter of 10 to the -28th/cu cm is estimated for masses of meteoroids of 3 kg and greater. This value is about a factor of six smaller than a rough upper limit reached from an extrapolation from terrestrial observations of meteors and comets.

Cook, A. F.↗
NASA NTRS1981

Minor planets and related objects. XXIX - Asteroid 29 Amphitrite

UBV photometry and lightcurves of asteroid 29 Amphitrite from all observed apparitions (March 1956-May 1977) are combined to obtain a phase function having a linear phase coefficient of 0.030 + or - 0.002 mag/deg and a mean absolute magnitude of 6.19 + or - 0.04. Amphitrite displays a reddening of its B - V color index with increasing solar phase angle: 0.816 + or - 0.004 at a phase angle of 2 deg and 0.848 + or - 0.004 at 23 deg. Since Amphitrite's orbital inclination is low (6 deg) and its lightcurve amplitudes range between 0.06 and 0.11 mag, and are well distributed in longitude, it is concluded that the obliquity of its pole is significantly different from zero. During some apparitions Amphitrite's light curves display only one maximum and minimum per 5.3904 + or - 0.007-hr rotation period while in others as many as five of each are present. This is interpreted to mean that Amphitrite has a quasi-spherical shape with a highly irregular and/or variegated surface.

Tedesco, E. F.↗
NASA NTRS1981

Identification of 4U 1849-31 with V1223 Sagittarii and discovery of optical pulsations

The X-ray source 4U 1849-31 is identified with the 13 mag star V1223 Sgr, on the basis of a precise HEAO 1 modulation collimator X-ray position uniquely selected by the Ariel-5 sky survey location. It is shown by optical spectroscopy and photometry that V1223 Sgr is a cataclysmic variable, displaying a photometric period of 13.2 min that is interpreted as being due to the rotation of a degenerate dwarf. The similarity of this system to H2252-035 is noted.

Steiner, J. E.↗
NASA NTRS1981

Z Camelopardalis at standstill

Coude spectra of the H alpha region in Z Cam are used to study line structure and velocity variations during the current extended standstill. Orbital elements and fine structure in the line profiles are consistent with results of Robinson (1973), which indicates that the standstill does not alter the velocity structure of the inner parts of the accretion disk and that of a possible circumstellar shell. Mass loss rates of about 6 x 10 to the -10th solar mass/yr are derived for both quiescence and standstill, while the disk light from Z Cam at 4200 A is found to be brighter by about 2.8 mag at standstill compared to quiescence. It is concluded that if the standstill is related to increased mass accretion relative to quiescence, the line emission areas are apparently unaffected.

Szkody, P.↗
NASA NTRS1981

BE Ursae Majoris /PG 1155 + 492/ - A unique cataclysmic-variable-like object

The variable spectrum of BE Ursae Majoris, which is similar to that of the cataclysmic variables (CVs), shows (1) an emission-line spectrum with the high-excitation CN 4650 A blend as the strongest optical feature, weaker H and He lines, and a strong Balmer jump, and (2) an absorption spectrum dominated by He. Although the object shows no evidence of photometric variability on either short or long time-scales, it has been shown by Kurochkin (1964, 1971) to have a 2.29-day, sinusoidal, 1.5-mag variation. The luminosity is dominated by a UV power-law component, though the 4000-10000 A continuum is flat. The hypothesis that this object is an active mass transfer binary is not supported by its photometric behavior, energy distribution and long period, despite the spectroscopic variability. Nevertheless, three components whose nature is not understood remain: (1) an ultraviolet source whose energy distribution is explainable neither by a uniform temperature primary star nor by an accretion disk; (2) a reprocessed component powered by the UV star; and (3) a component similar to a CV disk, producing the optically thick Balmer lines.

Ferguson, D. H.↗
NASA NTRS1981

Velocity dispersions of low luminosity ellipticals - L approximately equal to sigma-cubed

A complete sample of elliptical galaxies in the core of the Virgo cluster is used to derive a relation between stellar velocity dispersion and luminosity. L is found to approximately equal sigma to the nth power, where n = 3.2 + or - 0.2 over two decades of luminosity, with a scatter of 0.38 mag. The possibility of curvature in the relation or rotational support of the galaxies is examined, and a derivation of a law of slope 3 is presented and compared with the derivation for a slope of 4. It is concluded that the lack of increased scatter as the points deviate from a slope of 4 implies that rotation is not important.

Tonry, J. L.↗
NASA NTRS1981

Image tube spectroscopic studies of rapid variables. IV - Spectroscopic and photometric observations of AE Aquarii

Photoelectric and time-resolved spectroscopic observations of the short-period eruptive binary AE Aqr are presented. The system has a period of 0.4116537 days, and emission and absorption-line components equal to 135 km/sec and 159 km/sec, respectively. The spectral type of the absorption-line component is found to be K5V, from which M1 = 0.82 solar mass, M2 = 0.69 solar mass, and i = 64 deg. A predominantly Ca II emission region occurs on the hemisphere of the K5V star facing the broad emission-line component, whose center of light is located 0.64 of the way from the inner Lagrangian point to the center of mass of the K star. This emission appears to be associated with the transfer of mass from the K5V star to the accretion disk surrounding the primary. In the absence of flare activity, the light of the system is variable in the orbital period with a range in V of about 0.16 mag; maxima occurs near the times of maximum recession velocity and during the approach of each of the two components of the system (0.25 P and 0.80 P).

Chincarini, G.↗
NASA NTRS1981

X-ray and optical observations of HD 155638 - A remarkably active cool star

X-ray and optical observations of the 8.5-mag star HD 155638 are reported which reveal a remarkably active chromosphere and corona for the star. The object was first observed in soft X-rays with the HEAO 1 A2 low-energy detectors, and later reobserved with the HEAO 2 IPC. X-ray fluxes of about 2 x 10 to the -11th and 3 x 10 to the -12th ergs/sq cm per sec were obtained on the two occasions, indicative of source variability over the 2.5-year period between observations. SIT spectrographs taken in July-August 1980 show evidence of Ca II H and K core emission reversals and filled-in H alpha, while spectra taken in March and July 1981 show evidence of asymmetry and variability in the Ca II reversals. The spectral data are consistent with a G8 IV-V classification, from which is inferred a distance of 35-120 pc, and an X-ray luminosity from 4 x 10 to the 29th to 4 x 10 to the 31st ergs/sec. An absence of emission lines characteristic of mass transfer in binary systems indicates the X-rays to be coronal in origin. The properties of the star are noted to be similar to those of the RS CVn binaries.

Stern, R. A.↗
NASA NTRS1982

R associations. VI - The reddening law in dust clouds and the nature of early-type emission stars in nebulosity from a study of five associations

Positions, identification charts, UBVRIKLMN photometry and spectral types are given for stars, illuminating reflection nebulae that are visible on the POSS prints, which have been identified in five associations. With a ratio of total to selective extinction of 4.2, the reddening law applicable to the dust clouds in which the stars are embedded is steeper than normal. The five associations exhibit 18 early-type stars with circumstellar shells, of which those with spectral types earlier than B5 characteristically have weak IR excesses, in contrast to the strong excesses indicative of circumstellar dust, of later-type stars. Color-magnitude charts show a distribution lying above the ZAMS by up to about 2 mag for both the circumstellar shell stars and those classified as rapid rotators. It is suggested that (1) rapid rotation accounts for the scatter in the color-magnitude diagram, and (2) many of the nebulous early-type emission-line stars are rapid rotators rather than pre-main sequence objects.

Herbst, W.↗