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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Compact radio cores in three Seyfert galaxies - High resolution studies of Mkn 3, Mkn 231, and Mkn 463

The small-scale morphologies of Mkn 231 and Mkn 463 have been investigated using the European VLBI Network (EVN) at 1.6 GHz and the VLA at 15 and 22 GHz. Mkn 3 has been studied using the EVN at 1.4 and 1.6 GHz. All of the galaxies have a substantial fraction of their core radio flux in linear or elongated structures, typically tens of parsecs in extent. Agreement between the parsec- and kiloparsec-scale position angles of continuum radio emission suggests collimated outflow from the galaxy centers that continues over several orders of magnitude in scale. Supernova rates of order one hundred per year on scales of tens of parsecs are required to explain the nuclear radio emission as the result of bursts of star formation. The luminosities, small extents, and linear morphologies of the radio sources all support the idea that the nuclear radio sources are energized by active galactic nuclei and therefore support the more general picture of Seyfert galaxy nuclei being low-luminosity quasars. All of the galaxies appear to have undergone violent interactions in the recent past.

Neff, S. G.↗
NASA NTRS1988

Specification for wide channel bandwidth one-inch video tape

Standards and controls are established for the procurement of wide channel bandwidth one inch video magnetic recording tapes for Very Long Base Interferometer (VLBI) system applications. The Magnetic Tape Certification Facility (MTCF) currently maintains three specifications for the Quality Products List (QPL) and acceptance testing of magnetic tapes. NASA-TM-79724 is used for the QPL and acceptance testing of new analog tapes; NASA-TM-80599 is used for QPL and acceptance testing of new digital tapes; and NASA-TM-100702 is used for the QPL and acceptance testing of new IBM/IBM compatible 3480 magnetic tape cartridges. This specification will be used for the QPL and acceptance testing of new wide channel bandwidth one inch video magnetic recording tapes. The one inch video tapes used by the Jet Propulsion Lab., the Deep Space Network and the Haystack Observatory will be covered by this specification. These NASA stations will use the video tapes for their VLBI system applications. The VLBI system is used for the tracking of quasars and the support of interplanetary exploration.

Perry, Jimmy L.↗
NASA NTRS1988

Ultraviolet observations of selected astronomical sources

The results of the 9th and 10th IUE episode programs listed are summarized. Observations and basic data reductions were completed for 4 extragalactic programs which were allocated a total of 9 US1 shifts, and 2 stellar investigations which used 10 US2 shifts. Use was made of the Goddard RDAF to obtain better signal to noise ratio spectra using the Gaussian extraction routines. Highlights include the first IUE observations of H1821+643, the second brightest quasar in the sky, and the discovery of accretion disk emission line profiles in the elliptical Seyfert galaxy Arp 102B. Both of these observations were accompanied by nearly simultaneous optical spectrophotometry. As a result of the stellar programs, large amplitude variability associated with the rotation period of the Ap stars 78 Vir and 53 Cam was found.

Halpern, Jules P.↗
NASA NTRS1988

Evolution of photon and particle spectra in compact, luminous objects

The physics of high energy photons and particles (especially electrons and positrons) in the compact, high-energy-density of galactic nuclei and quasars was investigated. A numerical code was developed which follows the nonlinear spectral evolution of a pair/photon plasma, due to two-body scattering and interaction process, in an unmagnetized system. The code was applied both to static plasmas and to relativistic expanding winds.

Eilek, Jean A.↗
NASA NTRS1988

Accretion disk modeling of AGN continuum using non-LTE stellar atmospheres

Active galactic nuclei (AGN) accretion disk spectra were calculated using non-LTE stellar atmosphere models for Kerr and Schwarzschild geometries. It is found that the Lyman limit absorption edge, probably the most conclusive observational evidence for the accretion disk, would be drastically distorted and displaced by the relativistic effects from the large gravitational field of the central black hole and strong Doppler motion of emitting material on the disk surface. These effects are especially pronounced in the Kerr geometry. The strength of the Lyman limit absorption is very sensitive to the surface gravity in the stellar atmosphere models used. For models at the same temperature but different surface gravities, the strength of the Lyman edge exhibits an almost exponential decrease as the surface gravity approach the Eddington limit, which should approximate the thin disk atmosphere. The relativistic effects as well as the vanishing of the Lyman edge at the Eddington gravity may be the reasons that not many Lyman edges in the rest frames of AGNs and quasars are found.

Sun, Wei-Hsin↗
NASA NTRS1989

Statistical and physical evolution of QSO's

The relationship between the physical evolution of discrete extragalactic sources, the statistical evolution of the observed population of sources, and the cosmological model is discussed. Three simple forms of statistical evolution: pure luminosity evolution (PLE), pure density evolution (PDE), and generalized luminosity evolution (GLE), are considered in detail together with what these forms imply about the physical evolution of individual sources. Two methods are used to analyze the statistical evolution of the observed distribution of QSO's (quasars) from combined flux limited samples. It is shown that both PLE and PDE are inconsistent with the data over the redshift range 0 less than z less than 2.2, and that a more complicated form of evolution such as GLE is required, independent of the cosmological model. This result is important for physical models of AGN, and in particular, for the accretion disk model which recent results show may be inconsistent with PLE.

Caditz, David↗
NASA NTRS1988

Far Ultraviolot Space Telescope (FAUST)

The Far Ultraviolet Space Telescope is a compact, wide field-of-view, far ultraviolet instrument designed for observations of extended and point sources of astronomical interest. It was originally used in sounding rocket work by both French and American investigators. The instrument was modified for flight on the space shuttle and flew on the Spacelab 1 mission as a joint effort between the Laboratoire d'Astronomie Spatiale and the University of California, Berkeley. The prime experiment objective of this telescope on the Atmospheric Laboratory Applications and Science (ATLAS 1) NASA mission is to observe faint astronomical sources in the far ultraviolet with sensitivities far higher than previously available. The experiment will cover the 1300 to 1800 A band, which is inaccessible to observers on earth. The observing program during the mission consists of obtaining deep sky images during spacecraft nighttime. The targets will include hot stars and nebulae in our own galaxy, faint diffuse galactic features similar to the cirrus clouds seen by the Infrared Astronomical Satellite (IRAS), large nearby galaxies, nearby clusters of galaxies, and objects of cosmological interest such as quasars and the diffuse far ultraviolet background.

Bowyer, S.↗
NASA NTRS1987

Ultraviolet observations of starburst systems with Astro and the Hubble Space Telescope

The capabilities of the Astro observatory and the Hubble Space Telescope (HST) for UV astronomical observations are discussed. The advantages of using UV for studying extragalactic problems are reviewed, including sensitivity to hot sources, the rich UV line spectra, sensitivity to interstellar dust, and dark UV sky background. The HST and Astro instrumentation and plans for launching the systems are described. Possibile uses of HST and Astro include the study of massive stars in the Galaxy and nearby galaxies, interstellar medium, the UV excess component in old stellar populations, deep UV surveys (filter imaging and slitless spectroscopy), active galactic nuclei, quasars, and starburst systems.

O'Connell, Robert W.↗
NASA NTRS1988

Ultraviolet and optical spectra of broadline radio galaxies

Near-simultaneous ultraviolet and optical spectra of three broadline radio galaxies (3C 382, 3C 445, and PKS 2349-014) have been obtained, and the emission lines of Ly-alpha, H-beta, and H-alpha have been deconvolved into narrow and broad components; published fluxes for 3C 390.3 are also included in this study. Although the broad Ly-alpha/H-beta ratios in these objects cover a large range (1.2-22.3), there is no evidence that these ratios are intrinsically different from those of Seyfert 1 galaxies or quasars. Thus, in general, the higher H-alpha/H-beta ratios in these broadline radio galaxies cannot entirely be due to additional reddening of the broadline region. However, in the specific case of 3C 445, there is evidence that the nonstellar continuum and broadline region are highly reddened.

Crenshaw, D. Michael↗
NASA NTRS1988

The infrared universe revealed by IRAS

Some of the astrophysical phenomena revealed by IRAS are reviewed. The relation of IRAS data to understanding the origin of the interplanetary dust cloud, to the discovery of protoplanetary disks around other stars, to understanding the birth and death of stars, and to comprehending the energetics of the interstellar medium are addressed. Extragalactic results suggesting that IRAS may have found the birthplace of quasars are examined, and the surprising cosmological implications of the IRAS catalog are considered.

Beichman, C. A.↗
NASA NTRS1988

VLBI structure of the QSO 3C286

Observations of the quasar 3C286 with the EVN at 609 and 1420 MHz are reported. Results are presented on source size, the steepening of the spectral index, the IC X-ray flux, and surface brightness temperature. It is concluded that 3C286 appears to be not as energetic as the other 3C sources of the class.

Kus, A. J.↗
NASA NTRS1988

Spectroscopic evidence supporting the gravitational lens hypothesis for 1635+267 A,B

The gravitational lens hypothesis is tested for 1613+267 A,B by comparing the detailed line widths and shapes of the 2799-A Mg II and semiforbidden 1909-A C-III lines in each component. Following subtraction of an interpolating polynomial fit to the continua and the determination of a single optimum scaling factor (an amplification ratio of 2.83), reasonable agreement between the profiles of both lines in the two composites is obtained. Comparison of these lines to those in an unrelated quasar with a similar redshift and apparent magnitude does not produce a good match. It is suggested that the observed match in the 1635+267 A,B spectra arises from gravitational lensing.

Turner, Edwin L.↗
NASA NTRS1988

VLBI observations of the gravitational lens system 0957+561 - Structure and relative magnification of the A and B images

Gravitationally lensed images of the quasar 0957+561 have been observed at 13 cm wavelength using a six-antenna VLBI array with nearly milliarcsecond resolution. Models of the observed surface brightness distribution of each of the A and B images provide support of the gravitational lens hypothesis. A value of the magnitude of the relative image magnification A/B of 0.64 + or - 0.03 is obtained.

Gorenstein, M. V.↗
NASA NTRS1988

The gasdynamics of compact relativistic jets

The gasdynamics of compact relativistic jets is explored by analyzing a specific idealized flow problem using the method of characteristics. The basic flow pattern of the gas and pressure waves within a jet experiencing a drop in external pressure is calculated, with analytic expressions given for many of the important parameters. Scaling laws which relate the intrinsic properties of the jet to the pressure of the surrounding medium are obtained and discussed. The physical properties of the jet depend critically on the value and abruptness of the decrease in external pressure, as well as on the initial Lorentz factor of the flow. A variety of the flow patterns can result, including jets of oscillating cross section, jets with standing shocks, and broad, nearly hollow beams which can break up into multiple jets. These results are discussed in relation to the observed characteristics of superluminal radio sources in general and the superluminal quasar 4C 39.25 in particular.

Daly, Ruth A.↗
NASA NTRS1988

Measuring H0 and q0 with X-ray lines from galaxy clusters

A new method of measuring angular diameter distances, and hence H0 and q0, by means of X-ray observations of galaxy clusters is proposed. It resembles the method which combines maps of X-ray continuum emission with maps of the Suniaev-Zel'dovich effect, but substitutes measurements of X-ray absorption lines in the spectra of background quasars for the Suniaev-Zel'dovich effect. When the high resolution permitted by the AXAF microcalorimeter becomes available, this method should yield results with significantly smaller uncertainty.

Krolik, Julian H.↗
NASA NTRS1988

Spectral types for objects in the Kiso survey. IV - Data for 81 stars

Spectroscopy and spectral types for 81 ultraviolet-excess objects found in the Kiso Schmidt-camera survey are reported. The data were secured with the McGraw-Hill 1.3 m telescope at 8-A resolution covering the wavelength interval 4000 -7200 A using the Mark II spectrograph. Descriptions of the spectra of some of the more peculiar objects found in this sample are given and include 14 sub-dwarfs, 23 definite DA white dwarfs, including a magnetic one, and one DQ whie dwarf, eight quasars and emission-line objects, and a new composite DA + dM system. More spectroscopy of the new cataclysmic variable KUV 01584-0939 and a possibly related object is also described.

Wegner, Gary↗
NASA NTRS1988

VLBI tracking of the TDRS

The use of radio interferometry is being investigated by NASA/Goddard Space Flight Center as a means to track the TDRS geostationary satellites. This technique offers the advantages of very high accuracy using a ground network confined to the continental U.S. and minimal (or no) impact on spacecraft systems as the downlink transmissions can be used passively. A demonstration experiment was performed using very long baseline interferometry (VLBI). The TDRS-E was observed at S-band over a 28-hour definitive period together with dual X/S-band calibration observations of quasars. An orbit was determined for TDRS-E which agrees within estimated error bars with the orbit solution from NASA's operational tracking system but with about half the uncertainty. It was found that, for S-band tracking, the ionosphere is the largest source of orbit error. Use of Ku-band tracking instead would permit geostationary orbits accurate at the 10-m level.

Ray, J.↗
NASA NTRS1989

A method to estimate the motion of unresolved VLBI components in extragalactic radio sources - The case of NRAO 140

A method is proposed for estimating the relative motion of two blended VLBI compact components from measurements of the motion of their brightness centroid. The method requires a priori information about the source components, such as flux densities and separate knowledge of the motion of one of the blended components. Observations of the superluminal quasar NRAO 140 are analyzed to test the technique. Superluminal motion is found for the blended component A2 at 6-cm wavelength with an apparent velocity of about 5c (H0 = 100 km/s/Mpc, q0 = 0.5, z = 1.258).

Charlot, P.↗