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NASA NTRS1987

Discrete X-ray sources and the X-ray background

Since the discovery of a highly uniform X-ray background (XRB) in the 2 to 10 keV range, its nature is not yet fully explained. It appears clear from the results of Einstein medium and deep surveys that at least 50% of the XRB is due to individual extragalactic sources when their contribution is integrated to Z = 3. This includes contribution from Quasi Stellar Objects (QSOs), Active Galactic Nuclei (AGNs), galaxies, and clusters of galaxies. The average spectrum of each of the individual contributing sources is softer than that of the observed XRB. Therefore, the remaining contribution must have a rather hard spectrum of alpha nearly equal to 0.0 to 0.2. It is unlikely that this spectrum can be produced by diffuse processes. Therefore, the remainder of the XRB must be due to individual sources with the appropriate spectrum. This requires either that the spectrum of the already identified sources changes at early epochs or a new class of objects. Advanced X-ray Astrophysics Facility (AXAF) observations will extend survey sensitivity to limiting fluxes of order of 3 x 10 to the minus 16 erg/sq cm/s, some 50 times fainter than any previous survey. There will be sufficient sensitivity and angular resolution to permit identification and study of these objects.

Giacconi, Riccardo↗
NASA NTRS1987

Stream structures in the outer heliosphere

Nineteen magnetic clouds are identified in the years from 1978 through 1982 and studied by the superimposed epoch method. The magnetic fluctuations, density, and temperature are enhanced ahead of the clouds preceded by shocks. Strong magnetic field intensities and low proton temperatures are observed in the clouds. A relatively large (2.5%) decrease in cosmic ray intensity is caused by the turbulent sheath behind an interplanetary shock ahead of a magnetic cloud. Only a small (0.5%) decrease in intensity is associated with the magnetic cloud itself. Magnetic clouds can produce geomagnetic activity with a decrease in the Dst index of the order of 100 gammas. The magnitude of the change in Dst index for the case when southward fields arrive first is comparable to that for the case of northward fields first, and the phase is such that geomagnetic activity is associated with the southward fields.

Whang, Y. C.↗
NASA NTRS1986

Impact-induced atmospheres and oceans on earth and Venus

The effects of planetesimal-impact induced atmosphere formation on the earth and Venus are modeled to gain an indication why the two planets, at relatively equal distances from the sun, evolved so differently. Both planets gained approximately 10 to the 21 kg of water from the impacts. The water mass of the accreting planetesimals would have remained, initially, as a hot atmosphere. A two-stream approximation is defined for the temperature profile of a plane parallel atmosphere in radiative equilibrium. It is shown that the Venus atmosphere did not, as happened on earth, condense into a hot ocean after the impact epoch. Instead, the greenhouse effect caused the Venus equilibrium thermal structure to remain higher than the vapor pressure, keepinig the atmosphere in a vapor phase until the vapor dissociated and H2 atoms eventually escaped into space.

Matsui, T.↗
NASA NTRS1986

Dark matter and cosmological nucleosynthesis

Existing dark matter problems, i.e., dynamics, galaxy formation and inflation, are considered, along with a model which proposes dark baryons as the bulk of missing matter in a fractal universe. It is shown that no combination of dark, nonbaryonic matter can either provide a cosmological density parameter value near unity or, as in the case of high energy neutrinos, allow formation of condensed matter at epochs when quasars already existed. The possibility that correlations among galactic clusters are scale-free is discussed. Such a distribution of matter would yield a fractal of 1.2, close to a one-dimensional universe. Biasing, cosmic superstrings, and percolated explosions and hot dark matter are theoretical approaches that would satisfy the D = 1.2 fractal model of the large-scale structure of the universe and which would also allow sufficient dark matter in halos to close the universe.

Schramm, D. N.↗
NASA NTRS1986

Evolution of the luminosity function of extragalactic objects

A nonparametric procedure for determining the evolution of the luminosity function (LF) of extragalactic objects is described. The following steps are required: (1) selection of complete samples with known observational selection effects, (2) choice of a cosmological model, (3) statistical analysis of the sample and determination of the evolution of the luminosity function, and (4) the use of the luminosity function for the determination of the formation rate and the physical evolution of the objects. When the present technique is applied to a sample of optically selected quasars with redshifts less than two, it is shown that the LF evolves more strongly for higher luminosities, indicating a larger quasar activity at earlier epochs and a more rapid evolution of the objects during their higher luminosity phases.

Petrosian, V.↗
NASA NTRS1986

Solar wind control of Jupiter's decametric radio emission

Observations of the solar wind close to Jupiter are compared with the decametric radio emission (DAM), using data recorded by Voyager 1 and Voyager 2 during 1979. The Non-Io DAM, recorded by both spacecraft and combined using the superposed epoch technique, is found to correlate with the solar wind density and velocity, as well as with the interplanetary magnetic field (IMF) magnitude. In agreement with earlier work using ground-based observations, there are indications that the Non-Io DAM is somehow associated with magnetic sector structure although the precise details of the relationship are still not known and it is not clear if this is a fundamental effect or some secondary effect of intercorrelation.

Barrow, C. H.↗
NASA NTRS1986

Disruption of a coronal streamer by an eruptive prominence and coronal mass ejection

The coronal mass ejection of August 18, 1980 is analyzed using images from the coronagraph on the Solar Maximum Mission (SMM) satellite. The event occurred at the site of a large coronal helmet streamer and evolved into the three-part structure of a bright frontal shell, followed by a relatively dark space surrounding a bright filamentary core as seen in many mass ejections of the SMM epoch. The bright core can be identified as material from a prominence whose eruption was observed from the ground. The mass of the frontal shell is equal to that of the coronal helmet streamer, indicating that the shell is the coronal material previously in the helmet streamer, displaced and set into motion by the erupting prominence and surrounding cavity. The mass ejected in the bright core (or prominences) is estimated to be 50 percent larger than the 'coronal' material in the front loop.

Illing, R. M. E.↗
NASA NTRS1986

Multiple quasars for multiple images

Consideration is given to the possibility that the two quasar images of 1146 + 111, 1635 + 267, and 2345 + 007 respectively are pairs of physically distinct quasars in galaxy associations. It is shown that, at the same redshifts as the quasars, only galaxy associations of exceptional richness would be identifiable in the existing data. Calculations are performed to assess the probability of pairs of quasars appearing in galaxy associations and it is found that physical pairs could appear with the observed frequency provided that quasars are more common relative to galaxy associations at earlier epochs.

Bahcall, John N.↗
NASA NTRS1986

Precise VLA positions and flux-density measurements of the Jupiter system

VLA C array configuration observations at 2 and 6 cm are presented for Europa, Ganymede, and Callisto at eastern and western elongations with respect to Jupiter, which allowed measurements in right ascension and declination of the satellites with an rms precision of about + or - 0.03 arcsec. The transfer of the mean offsets of Ganymede to Jupiter yields offsets of -0.185 + or - 0.03 arcsec and -0.06 + or - 0.03 arcsec, with respect to JPL-DE-200, at the mean epoch of April 28, 1983; the large offset in right ascension is a combination of the Jupiter ephemeris error and the error in the frame tie of the Jovian planets with the VLBI system of precise positions which was used as the absolute reference frame for the observations. A significant error is noted in the orbital position of Callisto with respect to Ganymede.

Muhleman, Duane O.↗
NASA NTRS1986

The ABC of Population III

The author discusses the circumstances in which Population III stars are expected to form and examines their cosmological consequences. Consideration of their production of light, metals, and remnants places a strong constraint on their formation epoch and mass spectrum. However, these constraints would still allow Population III stars to provide the dark matter in galactic halos, a helium abundance of around 25 percent, a detectable background of gravitational waves, a possible infrared background, and the generation of large-scale cosmological structure through explosions. All of these features could be achieved by VMOs in the range 100 to 100,000 solar masses. On the other hand, the Population III scenario would be most compatible with the standard Big Bang picture if the stars were SMOs with mass around a million solar masses. Such stars could still provide the dark matter and detectable gravitational waves.

Carr, B. J.↗
NASA NTRS1986

Variability of Markarian 1018 - Seyfert 1.9 to Seyfert 1

Simultaneous IUE and optical spectrophotometry of the Seyfert 1.9 galaxy Markarian 1018 is presented. The strength of H-beta(broad) has increased by a factor of 6.6 in 4 yr, and the galaxy now shows strong broad UV and optical line emission similar to that seen in normal Seyfert 1 galaxies, but with markedly asymmetric line profiles. As in other variable Seyfert galaxies, H-alpha emission has also increased but by a lesser amount than H-beta. Furthermore, Ly-alpha (not observed during the first epoch) is now quite strong relative to H-beta and H-alpha. Inspection of the line profiles reveals nearly identical blue asymmetric line profiles in all permitted lines; these show evidence of significant profile evolution over a 1 yr time scale. The present line ratios and the nature of their variability suggest that the enhancement in the broad-line emission is not caused by the removal of obscuring dust but by the 'lighting up' of the broad-line region.

Cohen, Ross D.↗
NASA NTRS1986

Heliospheric current sheet and its solar cycle variations

The three-dimensional structure of the heliospheric current sheet is constructed for Carrington rotations 1647, 1654, 1661, 1667, 1693, 1699, and 1719. These rotations are chosen from different epochs during the sunspot cycle 21, so that geometrical changes of the current sheet during a sunspot cycle can be inferred. Only for relatively simple neutral lines on the source surface, do the structures of the current sheet approximate those envisaged by Svalgaard and Wilcox (1976) and Thomas and Smith (1981).

Akasofu, Syun-Ichi↗
NASA NTRS1986

Primeval QSOs

The physical processes causing the formation of an increased number of QSOs at redshifts higher than 2 are discussed, along with the implications for the turn-on of active galactic nuclei (AGN) at the same time as QSOs. It is argued that optical and X-ray background data indicate that all but the brightest objects will decline in number at redshifts exceeding 2. Consideration is given to the possibility that accreting black holes are at the center of AGNs and formed within a few billion years of the turn-on of QSOs. A scenario is also explored wherein QSOs are remnant echoes of the epoch of galaxy formation and are thereby a suitable object with which to probe the parent population.

Cavaliere, A.↗
NASA NTRS1986

On the origin of some QSO absorption lines

Some QSO absorption-line systems (QSOALSs) may arise when a QSO sight line intersects a Magellanic-type irregular galaxy (i.e., a gas-rich dwarf). Much of the complexity in the line profiles of metals can be naturally explained in this manner. The frequency of occurrence of QSOALSs then requires that much of the mass of modern galaxies once resided in a halo of gas-rich dwarfs (at the epoch of QSOALS formation).

York, Donald G.↗
NASA NTRS1987

Realm of the comets

Studies of Jovian perturbations of the orbits of long-period comets led to the concept of the Oort cloud of 180 billion comets at 50,000-150,000 AU from the sun. Several comets are induced to move toward the sun every million years by the passage of a star at a distance of a few light years. The location of the cloud has since been revised to 20,000-100,000 AU, and comets are now accepted as remnant material fron the proto-solar system epoch. The galactic disk and random, close-passing stars may also cause rare, large perturbations in the orbits of the cloud comets, sending large numbers of comets through the inner solar system. The resulting cometary storm is a candidate cause for the wholesale extinction of dinosaurs in the Cretaceous-Terniary transition due to large number of planetesimals, or one large comet, striking the earth, in a short period of time. The IRAS instruments have detected similar clouds of material around other stars.

Weissman, Paul R.↗
NASA NTRS1987

Simultaneous multifrequency observations of the BL Lacertae object Markarian 421

Simultaneous multifrequency observations of the BL Lac object Mrk 421 covering radio through X-ray wavelengths were performed on two occasions separated by 5 weeks in January and March 1984, and each observation was coordinated for about 1 week. Composite multifrequency spectra of the central nonthermal component were obtained at the two epochs after subtracting the optical and infrared light of the underlying galaxy. The spectra show the gradual steepening toward high frequency; the power law indices are about 0.1, about 0.6, and about 1.0 for radio, infrared-optical, and UV bands, respectively. The UV and optical-infrared fluxes decreased by about 20 percent in 5 weeks, while the radio flux remained stable. The X-ray flux decreased by a factor of about 2, and the change was more pronounced at hard X-rays, which suggest that X-ray emission possibly consists of two components. The degree of polarization at the optical band varied on the time scale of a few days, while the position angle remained unchanged. Physical parameters of Mrk 421 are discussed in terms of the synchrotron self-Compton model.

Makino, F.↗
NASA NTRS1987

Two binary cycles of GX 301-2

The slow X-ray pulsar, GX 301-2, has been observed throughout two full binary cycles of 41.5 days in the energy range 13-170 keV by the UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment aboard HEAO 1. Increased intensity and variability was observed for about four days near periastron during the two binary cycles, which were separated by six months in 1978. The spectral shape was not observed to vary with binary phase, with the possible exception of a steepening of the continuum above 20 keV near superior conjunction in one of the two observing epochs. Evidence for a spectral line was found in the data at the 1-percent confidence level, but not confirmed in the remaining data. The temporal variability of GX 301-2 was not consistent with simple models of X-ray production by interaction of the stellar wind with the neutron star, implying that future modeling must include effects on wind density and speed caused by shocks in the wind, the X-ray flux from the neutron star, the gravitational influence of the neutron star, and possible mass accumulation near the neutron star.

Rothschild, Richard E.↗
NASA NTRS1987

A Palomar Observatory Sky Survey atlas of selected molecular clouds

Forty-three cold, dense molecular clouds are digitized from the Palomar Observatory Sky Survey glass plates and presented with epoch 1950.0 equatorial coordinates. Regardless of the cloud's extent, the digitized area is limited to a 23 arcmin square on the sky with pixel size of about 1.3 arcsec. The optical maps presented herein are useful for comparing complementary molecular cloud maps from radio or infrared instruments and can be obtained in FITS format for use on astronomical image-processing systems.

Klinglesmith, D. A.↗