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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 127 records · Page 7
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NASA NTRS1983

An ab initio study of core-valence correlation

Especially in the cases of the first two columns of the periodic table, the inclusion of core-valence correlation in ab initio CI calculations yields a contraction of the atomic valence shell and improves both calculated atomic ionization potentials and atomic energy separations. For the alkali dimers Na2, K2, and Rb2, the presently calculated bond lengths are in excellent agreement with experiments when core-valence is included. In addition, the valence dissociation energies are accurate.

Partridge, H.↗
NASA NTRS1983

The photometric variability of solar-type stars. III - Results from 1981-82, including parallel observations of thirty-six Hyades stars

A photometric survey of main-sequence stars in the Pleiades, Hyades, and Malmquist Field, to investigate variability among solar-type stars, had been continued at Cloudcroft Observatory for a second season. Possibly six of 40 Pleiades stars, two (possibly six) of 49 Hyades stars and possibly four of 42 stars in the Malmquist Field are found to be variable. Parallel observations of Hyades stars were obtained also at Lowell Observatory. These measurements, which achieved better precision, reveal significiant variations in eleven (possibly 16) of 36 Hyades stars, all of spectral type F7 V-K2 V. Agreement between the two surveys is acceptable. The two seasons of the Cloudcroft survey show that changes in the mean annual brightness of the Hyades stars accompany changes in the amplitude of their short-term variability, in the sense that a star tends to become fainter as its variability increases and vice versa. Color effects are absent.

Radick, R. R.↗
NASA NTRS1983

First detection of winds in red giants by microwave continuum techniques

Eight red giants and supergiants have been observed at 4885 MHz (6 cm) with the Very Large Array in an attempt to detect continuum emission. The bright giant Alpha-1 Her (M5 II) was detected at an average flux density of 0.9 + or - 0.13 mJy. Since the likely source of this emission is an ionized, optically thick component of a stellar wind, this detection implies a mass loss rate of 2 x 10 to the -9th solar masses per yr for the ionized gas. The fraction of the outflow in Alpha-1 Her that is ionized (0.002-0.02) seems to be similar to that previously found for Alpha Ori and Alpha Sco A. Alpha Boo (K2 IIIp) and Beta Gem (K0 III) are probable and definite detections, respectively. The derived ionized mass loss rates for these two stars are about 1 x 10 to the -10th solar masses per yr, implying in the case of Alpha Boo that the wind is largely ionized.

Drake, S. A.↗
NASA NTRS1984

Kinetics of the reaction O + ClO yields Cl + O2

The bimolecular rate constant for the reaction O + ClO yields Cl + O2 has been measured over the temperature range 236-422 K in a discharge flow system using atomic oxygen resonance fluorescence at 130 nm to monitor the decay of O in an excess of ClO. The results are found to be independent of the method used to produce the ClO radical. At 296 K, the rate constant is given by (3.6 + or - 0.7) x 10 to the -11th cu cm/sec and the temperature dependence expressed in Arrhenius form by k2 = (5.0 + or - 1.0) x 10 to the -11th exp-(96 + or - 20)/T cu cm/sec. The results are compared with earlier values, and the implications for stratospheric chemistry are discussed briefly.

Leu, M.-T.↗
NASA NTRS1985

Observation of super high energy big family with large scale Fe emulsion chambers

In order to get higher efficiencies for detecting hadrons and to make technical improvements in the chamber structure, the Mt. Kambala Emulsion Chamber Collaboration constructed 57 sq. m. of Fe chamber, with thickness 29 c.u.(1c.u.=17.6 mm Fe), using 300 tons of Fe plates and made the first exposure from Sept., 1982 to May, 1984. The photosensitive layers consist of X-ray films of Sakura N type, Fuji No. 100 type and Tianjin III type, some of them contain also emulsion plates of Fuji ET7B type. They are inserted between the Fe plates at 2 c.u., beginning at 5 c.u. from the chamber top. In a number of blocks, 3 mm spacings are provided at every 2 c.u. of Fe plates to facilitate the replacement of photosensitive layers, without disassembling the chamber. On the bottom of the chamber Fe plates of thickness 9 mm are placed in order to shield the chamber from the radioactivities of the ground. An event, numbered K2 58 of visible energy sigma E sub gamma = 7345 TeV was found in this exposure. No obvious halo is seen in the event and all the showers are clearly separated and easy to measure. A brief report of the preliminary results is presented.

Source record↗
NASA NTRS1985

Electrical coupling effects on the temporal evolution of F layer plasma structure

A time dependent model of F region structure decay by 'classical' cross field diffusion and electrical coupling along magnetic field lines to the E region is examined. The temporal behavior of the ion concentration fluctuations is determined by the electric field in the coupled system as well as by the initial perturbation spectra and the E region recombination rate. The formation of image structure in the E region ion concentration affects the lifetime of F layer structure in a scale size dependent way. Once an image is formed, the image amplitude and the driving F region structure amplitude decay at the same rate. At large scale sizes of at least lambda(2pi/k), this rate is proportional to k2 and the ratio of the temperatures in each region. At small scale sizes it depends on the E region recombination rate and the temperatures of the two regions but is only very weakly dependent on k. The background E region concentration determines the wave number beyond which the structure amplitude decay rate is almost independent of its scale size.

Heelis, R. A.↗
NASA NTRS1985

Ultraviolet spectra and chromospheres of R stars

Long-wavelength IUE spectra of 13 normal R stars and two hydrogen-deficient R0 supergiants were obtained. Early R stars are noted to have line spectra and levels of flux in the ultraviolet characteristic of G5-K2 III stars, whereas late R stars were observed to have colors and line spectra similar to late K and M stars, but with greatly enhanced strength of low-lying multiplets of neutral metals. Hydrogen-deficient carbon stars show readily apparent differences from the normal early R stars, reflecting their luminosity and somewhat higher temperatures. The lines of neutral metals in these stars are weakened, while those of ionized metals are strengthened.

Eaton, J. A.↗
NASA NTRS1986

A survey of chromospherically active stars

Photometric and/or spectroscopic observations have been obtained of 52 late-type stars which are suspected or known to be chromospherically active. Although not all types of observations were obtained for each star, these observations include all-sky BVRI Johnson photometry, ultraviolet spectrograms, low-dispersion blue-wavelength spectrograms, and high-dispersion red-wavelength spectrograms. From the spectroscopic observations v sin i's, radial velocities, and the appearance of the Ca II H and K emission lines have been determined as well as the H-alpha line. The photometric observations indicate that chromospherically active stars have V - R and V - I color excesses. Such excesses will affect the surface fluxes determined with the surface brightness-color relationship. On the other hand all-sky BVRI photometry appears to be an excellent way to identify chromospherically active stars. A small group of moderately rapidly rotating, possibly single G8-K2 giants has been found. These stars have very modest chromospheric activity and so are not FK comae stars. A number of other unusual chromospherically active stars are identified.

Fekel, F. C.↗
NASA NTRS1986

Kinetic studies of the reaction of the SO radical with NO2 and ClO from 210 to 363 K

The rates of the reactions of the SO radical with NO2 and ClO (significant in the upper atmosphere of earth and Venus) were determined in a discharge flow system near 1 torr pressure with detection of radical and molecular species using collision-free sampling mass spectrometry. The rate constants were obtained from the decay of SO radicals in the presence of an excess of NO2 and ClO. The NO2 reaction was examined between 210 and 363 K and found to be temperature invariant: SO + NO2 yields SO2 + NO; k1 = (1.37 + or - 0.10) x 10 to the -11th cu cm/s. In addition, the ClO reaction was observed to be independent of temperature between 248 and 363 K: SO + ClO yields SO2 + Cl; k2 = (3.22 + or - 0.48) x 10 to the -11th cu cm/s. A comparison was made with previous investigations of these reactions at room temperature and with other radical-radical reactions involving SO or ClO.

Brunning, J.↗
NASA NTRS1986

Rotational modulation in IUE spectra of cool dwarf chromospheres: Data analysis and period search techniques

The IUE spectra of bright F-K dwarfs were used to investigate rotational modulation in chromospheric and transition region emission lines, with Stellingwerf's phase dispersion minimization (PDM) technique as the basis of time series analysis. Sampling-related aliases are found to dominate the PDM spectra in these sparsely sampled, irregularly spaced time series. The star chosen to illustrate the techniques is epsilon Eridani, a young, chromospherically active K2 dwarf. Strong indications of a rotation period close to 2.8 days in epsilon Eridani from 2 seasons of observations, with evidence for the persistence in longitude of the active area(s) over several hundred rotation cycles are found.

Altner, B.↗
NASA NTRS1986

High dispersion IUE observations of hybrid-chromosphere stars

High dispersion, wavelength calibrated IUE spectra of the hybrid-chromosphere stars alpha TrA (K2 IIb-IIa) and upsilon Aql (K3 II) are presented. These observations allow accurate measurement of the wind terminal velocities as seen in the Mg II emission line profiles. The terminal velocities deduced for upsilon Aql and alpha TrA are 110 and 120 km/sec respectively. The terminal velocity for alpha TrA is significantly reduced from the 180 km/sec seen in spectra obtained 2 yr earlier. The intersystem emission lines of C I (1993 A), C II (2325 A), C III (1908 A), O I (1641 A; fluoresced) and Si III (1892 A) are at essentially their rest wavelengths. The upsilon Aql C II intersystem multiplet line fluxes indicate an electron density near 1 billion/cc in their line formation region. Results suggest that the transition region intersystem lines are unlikely to be formed in the high velocity wind seen in the Mg II lines but are certainly formed in a region with significant turbulence.

Brown, A.↗
NASA NTRS1986

Chromospherically active stars. II - HD 82558, a young single BY Draconis variable

It is presently noted that the HD 82558 chromospherically active star is a young and rapidly rotating K2 V single BY Draconis variable with very strong far-UV emission features and an H-alpha line filled to the continuum level by emission. HD 82558 has constant velocity and is not a member of the Hyades Supercluster. Its light curve behavior, which appears to have been stable for several hundred rotation cycles, is reminiscent of that of the young, rapidly rotating, single K V variable H II 1883 in the Pleiades; this stability may be characteristic of young, single, chromospherically active stars.

Fekel, Francis C.↗
NASA NTRS1987

Flux distribution in the Algol binary system RW Persei

IUE low-dispersion spectra and optical TIS scans of the Algol-type binary system RW Persei show that the primary has a spectrral type of B9.6 and that it is a Be star. The cooler component has a spectral type that is less accurately determined to as K2 III-IV, and it is probably a star of very low mass. The system is heavily reddened, with an E(B-V) color excess of 0.40 + or - 0.05 mag. The present results suggest that the hotter component is actually an opticaly thick accretion disk. The expected W Serpentis-type emission lines are not found in the UV spectrum near mideclipse, although two very broad emissions and several weaker ones seem to be present.

Dobias, Jan J.↗
NASA NTRS1987

A spectrophotometric study of the Algol binary system RX Geminorum

IUE low-dispersion spectra and optical ITS scans of the semidetached Algol-type binary system RX Gem have been obtained. The spectral type of the primary component was determined to be A0, with good accuracy. Since the primary eclipse is only partial, the spectral type of the cooler component has been determined with less accuracy as K2 (+ or - 2). The system is only slightly reddened: its color excess is E(B-V) = 0.04 + or - 0.01 mag. Two models of the system are considered, depending on the luminosity class of the hotter star. Optically, the system is a Be star, since it displays Balmer line emission, visible most clearly during the primary eclipse. The ultraviolet spectrum observed near mideclipse does not display the expected 'W Serpentis-type' emission lines. Probably the main reason is that the primary eclipse is only partial.

Dobias, Jan J.↗
NASA NTRS1988

The band systems of alkali vapors

A number of band edges of the molecules, Na2, K2, NaK, NaCs, LiK, LiRb, LiCs, and NaRb are arranged in edge schemes. The vibrational quanta of the base terms and the upper terms can be approximately determined. Viewpoints are produced for interpreting electron terms. The terms Na2 are interpreted as terms of a photo-electron.

Weizel, W.↗
NASA NTRS1989

Chromospherically active stars. VI - HD 136901 = UV CrB: A massive ellipsoidal K giant single-lined spectroscopic binary

The variable star HD 136901 = UV CrB is a chromospherically active K2 III single-lined spectroscopic binary with an orbital period of 18.665 days. It has modest-strength Ca H and K emission and UV features, while H-alpha is a strong absorption feature containing little or no emission. The inclination of the system is 53 + or - 12 deg. The v sin i of the primary is 42 + or - 2 km/s, resulting in a minimum radius of 15.5 + or - 0.8 solar. When compared with the Roche lobe radius, this results in a mass ratio of 2.90 or larger. Additional constraints indicate that the secondary has a mass between 0.85 and 1.25 solar. Thus, the mass of the primary is at least 2.5 solar and probably is in the range 2.5-4 solar.

Fekel, Francis C.↗
NASA NTRS1988

TH28 (Krautter's star) and its string of Herbig-Haro objects

A high-quality spectrogram of the unusual T Tauri-like star Th28 and its string of Herbig-Haro (HH) objects has been obtained. New velocities and line intensities for the star and the gaseous knots are reported, and data are given for a third HH object located 87 arcsec to the SE along the same collimation axis as defined by the other features. Th28 has a heliocentric velocity of +5 km/s which is close to the velocity of the CO in the area. The star's spectral type is probably in the G8-K2 range.

Graham, J. A.↗
NASA NTRS1990

Detection of the secondary star in HT Cassiopeiae

Low-resolution spectra of the eclipsing dwarf nova HT Cas, taken over the range 5000-9800 A show TiO bands and Na I absorption lines from the secondary star. From the TiO band ratio at mid-eclipse it is estimated that the secondary star contributes about 37 percent of the light at 7500 A during the eclipse, and that it has a Boeshaar spectral type M5.4 + or - 0.3. The mass, radius, and luminosity of the secondary star are all consistent with main-sequence values. The TiO band strength diminishes greatly near phase 0.5, but an eclipse by the disk is not sufficient to explain this. The radial velocity is measured from the Na line near 8200 A for most of the spectra and (after a correction for the asymmetric distribution of absorption over the secondary star) its radial velocity semiamplitude K2 = 430 + or - 25 km/sec.

Marsh, T. R.↗