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At least 109 records · Page 6

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NASA NTRS1976

H2O(+) ions in comets: Comet Kohoutek (1973f) and comet Bradfield (1974b)

The image tube Cassegrain slit spectra of comet Kohoutek and Bradfield calibrated and reduced to relative intensities are discussed. Monochromatic changes in the surface brightness for various neutral and ionized molecules are determined. The intensities of C2 and CN decreased approximately four times faster than the intensity change for the H2O(+) features. It is shown that the excitation mechanism for the observed H2O(+) bands is by fluorescent scattering of the incident solar radiation. The effects of solar activity on the photoionization rate of H2O in a comet are discussed. Observations of another bright comet at the time of maximum solar activity are needed to determine changes in band intensities of comet tail ions due to solar activity.

Wehinger, P.↗

NASA NTRS1976

Optical identification of A0620-00

Identification of the optical counterpart to the transient X-ray source A0620-00 was made using image tube photography. Spectra taken subsequent to the identification showed no stellar absorption or emission features. Photometric data gave a V magnitude of 11.2 + or - .1. This is about 8 magnitudes brighter than the object appears on the Palomar Sky Survey.

Wolfson, R.↗

NASA NTRS1976

Spectrophotometry of the unusual optical candidate for 3U 1728-24 (=GX 2+5 = GX 1+4) a recurrent nova?

The spectrum of the object suggested as a possible optical counterpart of GX 2+5, was studied, using the image tube scanner attached to the 3-m telescope of Lick Observatory. An improved X-ray error box obtained with Copernicus strongly supports this proposed identification. The candidate displays all the characteristics of the symbiotic stars and the related recurrent novae. The spectrum reveals the presence of an M star together with a blue component and a large number of emission lines displaying a wide range of ionization. There is evidence of variability of both the continuum and the line intensities. This object provides strong support for the often proposed association of some X-ray sources with nova-like systems.

Davidsen, A. F.↗

NASA NTRS1975

High resolution spectrograph

The high resolution spectrograph (HRS) is designed to be used with the Large Space Telescope (LST) for the study of spectra of point and extended targets in the spectral range 110 to 410 nm. It has spectral resolutions of 1,000; 30,000; and 100,000 and has a field of view as large as 10 arc sec. The spectral range and resolution are selectable using interchangeable optical components and an echelle spectrograph is used to display a cross dispersed spectrum on the photocathode of either of 2 SEC orthicon image tubes. Provisions are included for wavelength calibration, target identification and acquisition and thermal control. The system considerations of the instrument are described.

Peacock, K.↗

NASA NTRS1976

Optical counterparts of AFCRL infrared sources

The paper presents results of a search for optical counterparts of confirmed AFCRL infrared sources using the Palomar Sky Survey and direct photography with the Carnegie image tube camera. Positions and identification charts for possible counterparts to 26 AFCRL sources are presented. A list of AFCRL sources for which no optical counterparts were found is given, and some arguments to explain why the results of this search were negative are presented.

Lebofsky, M. J.↗

NASA NTRS1976

Recent progress in photoelectron image detection with CCDs

Intensified CCDs (ICCDs) were built and operated. These ICCDs were electrostatically and magnetically-focussed image tubes which use CCDs as anodes. The ICCDs detected single photoelectrons, and have electron gain very near that which was predicted. The first single-pixel pulse-height distributions were presented, and the leakage current was shown to increase as a function of photoelectron irradiation. The advantages and disadvantages of front- and rear-illuminated designs were discussed in light of differing applications requirements.

Choisser, J. P.↗

NASA NTRS1977

Feige 7 - A hot, rotating magnetic white dwarf

Results are reported for image-tube-scanner and digicon observations of Feige 7, a faint blue star identified as a probable white dwarf. It is found that this star is a magnetic white dwarf showing a very rich spectrum with Zeeman subcomponents of both hydrogen and neutral helium as well as periodic spectrum and circular-polarization variations. A polarization period of 2.2 hr is computed, and a surface magnetic-field strength of about 18 MG is determined by matching features of the absorption spectrum to Zeeman components. It is suggested that the only reasonable explanation for the periodic variations in circular polarization is an oblique rotator with the spin axis approximately in the plane of the sky and tilted by about 24 deg to the magnetic axis. An effective temperature in the range from 20,000 to 25,000 K is estimated, an absolute magnitude of about 10.5 is derived, and the atmosphere is shown to be helium-dominated. The evolution of Feige 7 is discussed in terms of possible magnetic-field effects on atmospheric composition, rotation velocity (5.5 km/s for a radius of 7000 km), and the origin of white-dwarf magnetic fields.

Liebert, J.↗

NASA NTRS1977

The spectrum of HM Sagittae: A planetary nebula excited by a Wolf-Rayet star

A total of image tube spectrograms of HM Sagittae were obtained. More than 70 emission lines, including several broad emission features, were identified. An analysis of the spectra indicates that HM Sagittae is a planetary nebula excited by a Wolf-Rayet star. The most conspicuous Wolf-Rayet feature is that attributed to a blend of C III at 4650 A and He II at 4686 A.

Brown, L. W.↗

NASA NTRS1979

Reversal of the /O III/lambda 4363/H sub gamma lambda 4340 ratio in the planetary nebula IC 4997

Five image-tube spectrograms of the planetary nebula IC 4997 obtained during August 1977 show that the intensity forbidden ratio O III 4363 A/H-gamma 4340 A was equal to unity, but a sixth one obtained in April 1978 showed the ratio to be 0.91. These results represent a significant increase in the intensity ratio, which had been declining from 1895 to 1962 (when it was considerably less than unity), and is interpreted as resulting from a gradual increase in temperature of the nebula's central star accompanied by a transient event which led to a temporarily high value for the ratio in mid-1977.

Feibelman, W. A.↗

NASA NTRS1979

The diameter and reflectance of Triton

The surface reflectance, radius and geometric albedo of Triton are investigated. Image tube spectra of the reflectance of the satellite between 3200 and 7400 A are presented which indicate that the surface is composed mainly of rocky (non-icy) material, with violet absorption suggesting a composition similar to that of lunar fines, terrestrial igneous rocks and chondrites. Photometric/radiometric calculations based on measurements of the 20-micron thermal flux and the known visual magnitude of Triton reveal an upper limit of 5280 km to its diameter, and a lower limit of 0.19 to its geometric albedo. Computations of Rayleigh scattering in a potential inert atmospheric component are also presented which appear to preclude the presence of large quantities of nitrogen and noble gases on Triton.

Cruikshank, D. P.↗

NASA NTRS1980

Spectroscopy of faint asteroids, satellites, and comets

Nineteen asteroids with orbital elements comparable to those of short-period comets and the outer Jovian satellites J6 Himalia and J7 Elara have been observed with the 228-cm telescope and image-tube spectrograph of Steward Observatory. No activity indicating cometary outgassing was detected. If comets are being perturbed into asteroidal orbits, then this lack of activity can be explained by an apparently short transition time between active and extinct phase. In addition, spectra of the faint comets Sanguin 1977p, Chernykh 1977l, Arend-Rigaux 1950 VII, West 1978a, and van Biesbroeck 1954 IV were obtained, showing CN(0,0) and in some cases C2(1,0) and C3 emission. Comet Arend-Rigaux was active again in the fall of 1977 and Comet West showed on May 31, 1978 a weak tail at a distance from the sun of 6.0 AU.

Degewij, J.↗

NASA NTRS1981

Optical studies of the regions of the gamma-ray bursts of 19 November, 1978 and 5 March, 1979

Optical studies were made of two well-located gamma-ray burst regions in the Southern Hemisphere using the 1.5 m telescope at the Cerro Tololo Inter-American Observatory in Chile. Multi-filter image tube plates and UBV photometry surveys were made of both regions. The field of the 19 November, 1978 gamma-ray burst shows no early star or star with unusual colors out to several diameters of the nominal error box. The region of the 5 March, 1979 gamma-ray burst, which includes N49, contains several blue giants in the LMC, two of which deserve further study.

Fishman, G. J.↗

NASA NTRS1981

Studies of bipolar nebulae. VII - The exciting star of OH 0739-14 /equals OH 231.8 plus 4.2/

A spectral classification for the exciting star of the bipolar reflection nebula OH 0739-14, which has also been observed to be an OH/H2O maser source, is obtained from the spectrum of the nebulosity in the range 6000-9000 A. Spectrophotometry of the visible nebula was obtained with the Cassegrain image-tube scanner on the Lick Observatory 3-m telescope at a resolution of approximately 7 A. The red spectrum is found to be distinguished by TiO absorption at the bandheads at 8206, 8303, 8432, 8442 and 8452 A and VO in the 7400 and 7900 A regions. On the basis of the depths of these bandheads and the K I 7699 A and Ca II infrared triplet, OH 0739-14 is determined to be of spectral type M9 III. The underlying star thus represents the coolest known star to occur in a bipolar system.

Cohen, M.↗

NASA NTRS1981

The optical and ultraviolet spectra of the high excitation planetary nebula, CD -23 deg 12238 = Me 2-1

Planetary nebula are now recognized as a penultimate stage in the evolution of many stars. Me 2-1 offers advantages meriting a detailed analysis. A description is presented of measurements regarding this object which have been conducted with a photoelectric scanner and a 3 m telescope Cassegrain image tube scanner. The chemical composition of Me 2-1 appears to fit well that of other planetaries. The values for N, O, and Ne fall slightly above those for an 'average' planetary, but Me 2-1 would not qualify as a nitrogen-rich object. When a comparison is made with the sun, there appears to be an enhancement of carbon, possibly slight enhancements of nitrogen and neon, but a slight reduction in oxygen.

Aller, L. H.↗

NASA NTRS1981

IUE observations of pre-main-sequence stars. I - Mg II and Ca II resonance line fluxes for T Tauri stars

IUE satellite and Lick 3 m reflector image tube scanner measurements of the Mg II and Ca II resonance lines in a sample of T Tauri stars are the basis of a discussion of the Mg II h and k line emission and the Ca II H and K line emission, within the context of stellar chromospheres. Corroborative evidence is presented for the chromospheric origin of these resonance lines, and chromospheric radiative loss rates in the Mg II and Ca II resonance lines are derived. It is found that the degree of nonradiative heating present in the outer atmospheres of T Tauri stars generally exceeds that of the RS CVn systems, as well as the dMe stars and other active chromospheric dwarfs, and it is inferred that the surfaces of such pre-main sequence stars are covered by regions similar to solar plages. The mean chromospheric electron density of T Tauri stars is determined as 10 to the 11th/cu cm.

Giampapa n, M. S.↗

NASA NTRS1982

IUE and optical observations of MV Lyrae at intermediate and low states

Ultraviolet observations of MV Lyrae were obtained with the aid of the International Ultraviolet Explorer (IUE) spacecraft on 1979 December 2 when MV Lyr was at a normal low state and on 1980 December 8. The optical observations were obtained at Kitt Peak, Lick Observatory, and the University of Washington Observatory with various image-tube scanners and photometers. The photometric colors were found to be very blue at the very low state and at the normal low state. Robinson et al. (1981) have identified three components in their very low-state optical spectra. The significance of the observations is discussed.

Szkody, P.↗

NASA NTRS1982

10830 A He I observations of 455 stars

A comparison with K line, X-ray and other data, of 10830 A equivalent widths (EW) measurements in 890 image tube spectra of 455 stars shows that for the case of G stars, the EW correlates well with K line intensity. Good correlation is also found between 10830 A EW and soft X-ray fluxes, confirming the excitation of the line by coronal soft X-rays, which can serve as a measure of coronal emission. It is also found that, in contradiction to published models, 10830 A is weak or absent in O, B and A stars, and is absent in F and M supergiants. Moderate to high 10830 A EW is frequent in F and M dwarfs, G and K supergiants, and class K3 III. The 58 stars whose 10830 A EW was found to be of 300 A or more should be relatively intense X-ray emitters. Almost all RS CVn stars show strong 10830 A absorption, and T Tauri stars show both absorption and emission.

Zirin, H.↗

NASA NTRS1983

Chemical compositions of planetary nebulae

The chemical compositions of 41 planetary nebulae are established on the basis of an analysis of image tube scanner measurements, supplemented by IUE data. An attempt is made to calculate a theoretical model that gives satisfactory values of the observed intensities, as well as a number of excitation-sensitive ratios, in order to obtain ionization correction factors applicable to the ionic concentrations that will lead to total abundance values. The quality of individual nebular analyses varies, depending on the completeness and accuracy of the observational data and the complexity of the nebular structure. Quality estimates are assigned for each element in each nebula, and an overall reliability index is given to each object. It is concluded that the confidence with which one can speak of the chemical composition of a nebula varies significantly.

Aller, L. H.↗