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At least 127 records · Page 7
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NASA NTRS1978

The spectrum of the halo surrounding the quasar PHL 1070

The quasar PHL 1070 and its surrounding halo of light have been observed with the Palomar multichannel spectrophotometer using circular and annular apertures. The central quasar has a magnitude of 16.6 and an emission-line redshift of 0.076 + or - 0.002. The halo light has a magnitude of 19.0 and a possible absorption-line system with an absorption redshift of 0.067 + or - 0.008. The magnitude, possible absorption lines, and probable spectral energy distribution of the halo are consistent with those of a normal galaxy at the redshift of the quasar.

Morton, D. C.↗
NASA NTRS1977

Halo orbit station keeping for International Sun-Earth Explorer-C /ISEE-C/

The ISEE-C spacecraft must be kept close to an unstable 'halo' orbit with a series of discrete orbital maneuvers set at intervals at least one month apart. A numerical algorithm has been developed to compute a velocity correction at any point on the trajectory which will minimize the distance between the satellite orbit and the nominal halo path. This algorithm is used to generate a number of station keeping histories with fixed time intervals between maneuvers to ascertain bounds on fuel cost, tightness of fit to nominal path and expected duration between thrust applications. The difference between a third order analytic representation of the halo orbit and a numerically improved nominal path as a reference orbit in the station keeping scheme is investigated as well as the distinction between a tight control and a loose control. A simulation of an operational approach to station keeping is also presented which shows that intermittant propulsive maneuvers can be used to control the spacecraft with very modest fuel expenditure.

Heuberger, H.↗
NASA NTRS1978

The metallicity of globular clusters in the halo of M87

The energy distributions of one 20th and two 21st magnitude globular clusters in the halo of the giant elliptical galaxy M87 (NGC 4486) of the Virgo cluster have been obtained between 0.32 and 1.1 microns with the multichannel spectrophotometer of the Hale 5-m telescope. Comparisons with globular clusters in M31 show line strength indices L ranging from 4 plus or minus 2 to 9.5 plus or minus 2.0, with a mean for the three clusters of 7.5 plus or minus 1.5. On average they thus have metal deficiencies relative to the sun by a factor of about 5. The distribution over abundance in the halo globular clusters of M87 is the same as that in M31, but different from that in the halo of the Galaxy.

Racine, R.↗
NASA NTRS1979

The dynamical halo and the variation of cosmic-ray path length with energy

It is shown that the dynamical halo model offers a natural explanation for the form of the variation of the cosmic-ray path length with energy. The variation above about 1 GeV per nucleon can be understood as due to the variation of the diffusion coefficient, and hence the resident time, with energy. The flattening of the curve below 1 GeV per nucleon is seen to mark a transition to a convection-dominated regime where the diffusion coefficient is no longer the determining parameter. A fit to the observations yields a halo outflow velocity of 8 km/s. An attempt is made to determine the overall scale of the halo and the diffusion coefficient using recent Be-10 flux measurements, but the data do not agree well enough to pin down these variables to within less than four or five orders of magnitude.

Jones, F. C.↗
NASA NTRS1979

Alphonsus-type dark-halo craters - Morphology, morphometry and eruption conditions

The Alphonsus dark-halo craters are sites of volcanic eruptions with a characteristic crater radius of approximately 1 km. They are characterized by dark haloes ranging from 3 to 4 km, by substantial amounts of nonjuvenile material within the deposits, and by a lack of any associated lava flows or prominent constructional features, such as cones or domes. In the present paper, possible eruption styles are analyzed, using these observational constraints. It is concluded that an eruption process analogous to terrestrial volcanian explosive activity provides the most reasonable explanation for the characteristics of the deposits. The dark-halo craters appear to have formed contemporaneously with the emplacement of lavas in the adjacent Mare Nubium.

Head, J. W., III↗
NASA NTRS1980

Faraday rotation in the M87 radio/X-ray halo

Comparison of polarization maps at various wavelengths demonstrates the existence of a large Faraday rotation uniform over the radio core of M87. Much of this rotation must be external to the core, lest it appear completely depolarized when the rotation is about 90 degrees. The Faraday rotation is shown to occur primarily in the surrounding radio/X-ray halo. Using the electron density inferred from X-ray observations, the magnetic field in the halo is found to be 2.5 microgauss. The deduced magnetic field strength permits an evaluation of the importance of Compton scattering of 3 K background photons by relativistic electrons in the radio halo. The emergent Compton-scattered spectrum is calculated, and its contribution to the observed X-ray flux is small, probably about a percent or so, while the rest is due to thermal bremsstrahlung.

Dennison, B.↗
NASA NTRS1981

A comparison of quasar absorption line systems with absorption by the galactic halo

Milky Way halo and quasar absorption spectra contain a number of remarkable similarities which include mixed ion absorption, a general absence of excited fine structure levels with the possible exception of excited C II, similar column densities, and similar multicomponent line profiles. The extreme sensitivity of UV lines to small amounts of gas is well illustrated in a comparison of 21-cm H I emission with UV absorption toward the Large Magellanic Cloud. This sensitivity shows that galaxies are likely to appear significantly larger in UV absorption than in 21-cm emission and that the size problem for galactic halos is probably not a serious one. It is concluded that many of the absorption line systems seen in the spectra of quasars are probably produced in the gaseous halos of intervening galaxies.

Savage, B. D.↗
NASA NTRS1982

The gaseous galactic halo as inferred from the line spectra of the galaxies Markarian 509 and Fairall 9

Narrow interstellar absorption lines of S II 1259.52, Si II 1260.42, and Fe II 1608.46 due to gas in the disk and the halo of the Galaxy have been detected in the spectrum of the Seyfert galaxy Mrk 509 with the International Ultraviolet Explorer. This gas is also seen at higher resolution in the Ca II and Na I absorption lines in two components at LSR velocities of +6 and +62 km/s. In addition, narrow Ly-alpha and C IV absorption near the Seyfert redshift seem to be present in the spectrum. Si II 1260.42 absorption from the galactic disk and from the Magellanic Stream or the halo of the SMC have been detected with the IUE in the spectrum of Fairall 9. The observations of these two objects when combined with existing results are shown to be consistent with a corotating galactic halo having a height of less than 10 kpc at the sun.

York, D. G.↗
NASA NTRS1982

Coma-type radio halos and cluster X-ray morphology

It is pointed out that there seems to be a characteristic X-ray morphology for clusters with Coma-type radio halos. This correlation may be the first evidence that the conditions conducive to formation of a radio halo influence or are influenced by the thermal gas distribution. It is suggested that heating of the intracluster gas by the cosmic rays that power the radio halo may be the source of the correlation. The anomalous gas temperature of Coma may be the result of this process. Future observations of cluster temperatures and velocity dispersions should provide a test of the cosmic-ray heating hypothesis

Vestrand, W. T.↗
NASA NTRS1983

Absorption by halo gas in the direction of M13

A high velocity cloud in the direction 1 = 59 degrees, b = 41 degrees is detected in absorption at approximately -80 km/s in high dispersion IUE spectra of the blue star Barnard 29 in the globular cluster M13. The cloud is also seen in the H I 21 cm emission data of Kerr and Knapp (1972). Its radial velocity agrees with Giovanelli's data (1980, 1981) for high velocity clouds seen in this general direction of the sky. The cloud's motion is incompatible with the suggestions that neutral halo gas corotates with disk gas. The motion could be explained if neutral halo gas rotates more slowly than disk gas with increasing distance from the galactic plane. Because of our very limited understanding of the actual motions of halo gas, the scale height of this gas is best derived from plots of N sin b versus z for galactic and extragalactic stars.

De Boer, K. S.↗
NASA NTRS1983

Neutral interstellar gas in the lower galactic halo

The optical interstellar absorption lines of Ti II, Ca II, Na I, and the 21 cm emission line of H I were observed at high resolution and high detection sensitivity toward none pairs of nearly aligned distant halo stars and foreground disk stars with well determined distances. Analysis of the column densities, velocities, and the directly determined variation of the titanium abundances with z-distance leads to a general picture of the neutral interstellar material in the lower galactic halo. Two types of gas with distinct distribution, kinematics, and abundances are found, a thick, low velocity disk (type I) extending from the plane to well beyond the thin disk of OB stars, and a high velocity, much less strongly depleted gas (type II) observed only at high z-distances, which constitutes at least 24 percent of the mass of the halo gas. The implications of this model for the observed neutral gas are discussed both in terms of the possible origins of the observed gas and in its comparison with quasi stellar object absorption lines. Previously announced in STAR as N82-29246

Albert, C. E.↗
NASA NTRS1984

Fabrication of glass gas cells for the HALOE and MAPS satellite experiments

The Halogen Occultation Experiment (HALOE) and the Measurement of Air Pollution from Satellites (MAPS) experiment are satellite-borne experiments which measure trace constituents in the Earth's atmosphere. The instruments which obtain the data for these experiments are based on the gas filter correlation radiometer measurement technique. In this technique, small samples of the gases of interest are encapsulated in glass cylinders, called gas cells, which act as very selective optical filters. This report describes the techniques employed in the fabrication of the gas cells for the HALOE and MAPS instruments. Details of the method used to fuse the sapphire windows (required for IR transmission) to the glass cell bodies are presented along with detailed descriptions of the jigs and fixtures used during the assembly process. The techniques and equipment used for window inspection and for pairing the HALOE windows are discussed. Cell body materials and the steps involved in preparing the cell bodies for the glass-to-sapphire fusion process are given.

Sullivan, E. M.↗
NASA NTRS1984

Role of 'core' and 'halo' solar electrons in ionization of the interstellar medium

In the present consideration of the probability of interstellar wind H and He atoms' survival of ionization by solar wind electrons, a dual temperature electron distribution is for the first time used to model the effects of 'core' (10 eV) and 'halo' (60 eV) solar electrons on survival probabilities. The interstellar wind has a higher probability of surviving halo rather than core electron ionization only at heliocentric distances smaller than 0.5 AU. For larger distances, halo and core survival probabilities are similar, and similarly insensitive to changes in (1) interstellar wind velocity at infinity, (2) the solar ratio of radiation to gravitational force, and (3) solar electron temperatures. At distances smaller than 0.5 AU, however, sensitivity significantly increases.

Askew, S. D.↗
NASA NTRS1985

Dark Halo Craters and the Thickness of Grooved Terrain on Ganymede

Dark halo craters on grooved terrain on Ganymede represent potential probes of the subsurface geology. These craters are surrounded by a broad, diffuse low albedo annulus, or halo and have apparently lost the bright rim and ray deposits associated with very young craters. The recognition of dark halo craters, almost all greater than 12 km in diameter, indicates that material darker and redder than grooved terrain material forms a stratigraphy horizon at about 1 km depth the present surface of grooved terrain in Uruk Sulcus. This material is most likely downdropped cratered terrain material, which only larger craters have excavated into. This is most consistent with extensional tectonic models for grooved terrain formation whereby the lithosphere is stretched and blocks of ancient cratered terrain are downdropped along bounding faults, and subsequently resurfaced by a shallow layer of relatively clean icy material. Evidence for the preservation of cratered terrain material at shallow depth beneath grooved terrain material poses great difficulties for alternative grooved and smoothed terrain formation mechanisms.

Schenk, P. M.↗
NASA NTRS1985

A halo event created at 200 m above the Chacaltaya emulsion chamber

The results of analysis on a cosmic-ray induced nuclear event with the total visible energy approx. = 1300 TeV which is characterized by the central (halo) part of a strong energy concentration and the outer part of a large lateral spread are presented. The event (named as P06) was detected in the 18th two-storied emulsion chamber exposed at Chacaltaya by Brasil-Japan Collaboration. As the nuclear emulsion plates were inserted at every layer of the concerned blocks in the upper and the lower chambers together with RR- and N-type X-ray films, it is possible to study the details of the event. Some results on P06 have already been reported 1 based on the general measurement of opacity on N-type X-ray films: (1) the total energy of halo is approx. = 1000 TeV; (2) the shower transition reaches its maximum at approx. 16 cu; and (3) the radius of halo is 6.5 mm (at the level of 10 to the 6th power electrons/sq.cm.). The results in more details will be described.

Amato, N. M.↗
NASA NTRS1985

Dark halo craters and the thickness of grooved terrain on Ganymede

On the basis of a morphological analysis of recent Voyager images of the dark halo craters and grooved terrain in the Uruk Sulcus region on Ganymede, it is proposed that dark halos result from the incorporation of cratered terrain material into crater ejecta. In Uruk Sulcus, only craters greater than about 12 km in diameter have halos, indicating that the cratered material there forms a stratigraphic horizon buried in the grooved terrain. A depth of excavation of cratered terrains of 1.0 to 1.6 km is calculated. It is shown that the estimated depth is consistent with current theoretical models of grooved terrain, where relatively clean ice is emplaced over downdropped blocks of cratered terrain. Several Voyager 2 images of the Uruk Sulcus region on Ganymede are provided.

Schenk, P. M.↗
NASA NTRS1985

The nondetection of continuum radiation from Comet IRAS-Araki-Alcock (1983d) at 2- to 6-cm wavelengths and its implication on the icy-grain halo theory

The Comet IRAS-Araki-Alcock was observed with the VLA at 6 and 2 cm, when the comet was at geocentric distances of 0.08 and 0.035 AU, respectively, and the results are discussed. The three sigma upper limits to the flux density are 90 and 750 micro-Jy at the two wavelengths, respectively, values fully two orders of magnitude below the flux densities predicted by the icy-grain halo theory as initially developed. The corrected theory also indicates that the icy grain halo theory does not give an adequate description of the cometary environment. It is shown that the halo is either very optically thin, with a filling factor of the order of 10 to the -5th, or that the maximum size of the grain that can be lifted off the nuclear surface is only of the order of 10-100 microns.

De Pater, I.↗
NASA NTRS1985

Faint photometry of edge-on spiral galaxies - A search for massive halos

Upper limits have been set to the luminosity from the massive halos of three late-type edge-on spiral galaxies: NGC 2683 (Sb), NGC 4244 (Scd), and NGC 5907 (Sc). The limits resulted from simultaneous photometry in the visual (V) and 2.2-micron (K) photometric bands which is sensitive to both luminosity and color changes along the minor axes of the three galaxies. The mass-to-light ratios for the halo of NGC 5907 are the largest ever recorded: M/L(V) greater than 2000 and M/L(K) greater than 64 in solar units. The results virtually eliminate the possibility that hydrogen-burning stars comprise more than a fraction of the halo masses. Variations of the V-K color along and perpendicular to the disks show no sign of population changes toward redder objects at large galactocentric radii. The nucleus of NGC 5907 contains an unresolved source less than 330 pc in size with a 2.2-micron luminosity of order 5 x 10 to the 9th solar luminosity and may be an example of a starburst galactic nucleus overlooked by visual observations.

Skrutskie, M. F.↗