ALBERT

Description: Emission of CO and HCN was detected in 22 out of a sample of 53 IRAS sources classified as unidentified carbon-rich objects. The sample was selected according to the presence of the silicon carbide feature as revealed by low-resolution spectra. The molecular line widths indicate that the CO and HCN emission arises from the circumstellar envelopes of very highly evolved stars undergoing mass loss. The visible stars tend to be deficient in CO as compared with unidentified sources. Most the detected CO and HCN IRAS stars are distinct and thick-shelled objects, but their infrared and CO luminosities are similar to those of IRC + 102156 AFGL and IRC-CO evolved stars. The 12 micron flux seems to be a good indicator of the distance, hence a guide for molecular searches.

Description: IRAS 12-100 micron data on the Cas A remnant are presented, and various physical mechanisms and astrophysical sites that may contribute to the observed infrared emission are analyzed. The contributions of various sources of infrared emission to the IRAS fluxes are found to be small. The residual infrared emission is attributed to thermal emission from dust which is swept up by the expanding supernova blast wave and collisionally heated by the postshock X-ray emitting gas. The calculations are consistent with a shock velocity of 1800 km/s and a preshock gas density of about 2/cu cm. The mass of the swept-up gas is about 0.6 solar mass. An excess of 12 micron thermal emission in the spectrum of Cas A suggests the presence of very small particles in the preshocked gas.

Description: The diffusive acceleration of highly relativistic particles at a shock is reconsidered. Using the same physical assumptions as Blandford and Ostriker (1978), but dropping the restriction to nonrelativistic shock velocities, the authors find approximate solutions of the particle kinetic equation by generalizing the diffusion approximation to higher order terms in the anisotropy of the particle distribution. The general solution of the transport equation on either side of the shock is constructed, which involves the solution of an eigenvalue problem. By matching the two solutions at the shock, the spectral index of the resulting power law is found by taking into account a sufficiently large number of eigenfunctions. Low-order truncation corresponds to the standard diffusion approximation and to a somewhat more general method described by Peacock (1981). In addition to the energy spectrum, the method yields the angular distribution of the particles and its spatial dependence.

Description: The application of the matrix isolation technique to interstellar problems is described. Following a brief discussion of the interstellar medium (ISM), three areas are reviewed in which matrix experiments are particularly well suited to contribute the information which is sorely needed to further understanding of the ISM. The first involves the measurement of the spectroscopic properties of reactive species. The second is the determination of reaction rates and the elucidation of reaction pathways involving atoms, radicals, and ions which are likely to interact on grain surfaces and in grain mantles. The third entails the determiantion of the spectroscopic, photochemical, and photophysical properties of interstellar and cometary ice analogs. Significant, but limited, progress has been made in these three areas, and a tremendous amount of work is required to fully address the variety of unique chemical and spectroscopic questions posed by the astronomical observations.

Description: An abundance analysis using photographic region spectrograms and fully line-blanketed model atmospheres has been performed for the metallic-lined (Am) star 32 Aquarii consistent with previous papers of this series. Its pattern of abundance anomalies is not identical with those of the hot Am stars although there are definite similarities. Changes of up to order 1 dex are foundly by comparison with the previous analysis by Smith. Slightly better agreement is found with the recent analyses of singly-ionized rare earth lines by Magazzu and Cowley. Results are also presented for a model selected on the basis of photometric indices according to the formula of Moon and Dworetsky.

Description: It is shown that a generalized (or 'power law') inflationary phase arises naturally and inevitably in a simple (Bianchi type-I) anisotropic cosmological model in the self-consistent Einstein-Cartan gravitation theory with the improved stress-energy-momentum tensor with the spin density of Ray and Smalley (1982, 1983). This is made explicit by an analytical solution of the field equations of motion of the fluid variables. The inflation is caused by the angular kinetic energy density due to spin. The model further elucidates the relationship between fluid vorticity, the angular velocity of the inertially dragged tetrads, and the precession of the principal axes of the shear ellipsoid. Shear is not effective in damping the inflation.

Description: A summary of advances made during 1983-1985 in the theory of collisionless heliospheric shocks is presented (with reference to the latest observations of slow shocks in the geomagnetic tail) together with a summary of recently developed simulations of shock structure and shock propagation. Consideration is also given to the theoretical basis for the production of energetic particles by shocks in the solar wind and the corona. Finally, satellite-based observations related to interplanetary and coronal shocks and to heliospheric boundary shock are discussed.

Description: The evolution of models for star formation in galaxies with disk and halo components is discussed. Two phases for the halo (gas and stars) and three for the disk (including clouds) are used in these calculations. The star-formation history is followed using nonlinear phase-coupling models which completely determine the populations of the phases as a function of time. It is shown that for a wide range of parameters, including the effects of both spontaneous and stimulated star formation and mass exchange between the spatial components of the system, the observed chemical history of the galaxy can easily be obtained. The most sensitive parameter in the detailed metallicity and star-formation history for the system is the rate of return of gas to the diffuse phase upon stellar death.

Description: This paper examines the Mg II 2795-2802 A doublet in the Seyfert galaxy NGC 4151 at a higher resolution than has previously been used, searching for velocity systems in absorption and emission. Evidence is presented for a new, narrow, outflowing absorption system in Mg II having a velocity of 825 km/s relative to the sun, and -165 km/s relative to the systemic velocity of NGC 4151. This feature is not present in Ly-alpha or C IV and possible explanations for this are considered. For the Mg II and C IV lines, a model decomposition of the line profile is presented.

Description: COS-B viewed the Cyg X-3 region seven times between November, 1975, and February, 1982; a search for steady gamma-ray emission pulsed at the characteristic 4.8-hour period did not reveal its source. Leiden-MIT balloon experiment observations of Cyg X-3 in May, 1979 show the 4.8-hour modulation with sinusoidal light curve and modulation depth of 0.30, for energies of up to about 140 keV. The strong variability of Cyg X-3 over more than one order of magnitude at energies below 20 keV does not emerge in the data collected at hard X-ray energies.

Description: Emission lines of (O III) at 52 microns and 88 microns and of (N III) at 57 microns in the nucleus of the galaxy M82 have been observed from the Kuiper Airborne Observatory with the facility's cooled grating spectrometer. The (N III) line has not been previously detected in any extragalactic source. The fluxes in the lines indicate approx. 4 x 10 to the 7th power M of ionized gas and a large population of massive stars (equivalent to 5 x 10 to the 5th power 08.5 stars), sufficient to power the infrared luminosity of the nucleus. We use the 52 to 88 micron line intensity ratio to find an average electron density of 210 + or - 75 in the nucleus; this is 10 to 100 times lower than values typically observed in individual compact H II regions in our Galaxy. The relative line strengths of the (O III) and (N III) lines imply an N(++)/O(++) ratio of 0.45 + or - 0.1, significantly lower than is measured by the same method in individual H II regions at similar galactocentric distances (equal to or less than 400 pc) in our Galaxy. This lower N(++)/O(++) ratio may be due to a lower N/O ratio, higher stellar temperatures, or both, in M82. At spectral resolutions of approx. 90 km/s, all three line profiles are similarly asymmetric. They can be well fitted by two Gaussian distributions with widths of approx. 150 km/s and central velocities of approx. 110 and approx. 295 km/s, bracketing the systemic velocity of the nucleus of approx. 210 km/s. Within uncertainties, both the N(++)/O(++) ratio and the electron density are the same for both Gaussian components; this indicates no major large-scale gradient in either quantity within the nucleus.

Description: In a recent report, Atherton et al. (1986) announced the detection of the central, exciting star of the planetary nebula NGC2440 on a narrow-band CCD image. Here, the detection of the same star in ultraviolet spectra taken with the IUE satellite is reported. The stellar parameters derived from these spectra are temperature of about 200,000 K, luminosity of 1500 solar, log g = 7, and mass 0.6 solar. These results are in accord with stellar evolutionary theory.

Description: High-resolution (300 Hz) OH 1612-MHz spectra of the supergiant OH-IR sources VY CMa, VX Sgr, IRC 10420, and NML Cyg are presented. Linewidths as small as 550 Hz (0.1 km/s) are found for narrow components in the spectra. The present results are consistent with current models for maser line-narrowing and for the physical properties in the OH maser regions. A significant degree of circular polarization is noted in many of the narrow components. The circular polarization suggests the presence of magnetic fields of about 1 mG in the circumstellar envelopes which would be strong enough to influence the outflow from the stars, and which may explain asymmetries found in the circumstellar envelopes.

Description: Radial velocities and v sin i values for the stars in the Taurus-Auriga region that were found to have strong Ca II H and K emission by Herbig, Vrba, and Rydgren 'HVR', (1986) are reported. Most of the velocities are determined to better than 2 km/s precision. The kinematic properties of the Ca II emission stars with strong Li are found to be indistinguishable from conventional T Tauris in Taurus-Auriga, contrary to HVR. These Li-rich stars also rotate like T Tauris. Most of the stars that lack Li are probable or possible members of the Hyades, in the foreground, and are among the brightest and most active stars in that cluster for their spectral types. It is suggested following Jones and Herbig (1979), that the apparent absence of low-mass stars older than 10 Myr in Taurus-Auriga is real, and is due to the finite lifetime of the cloud.

Description: A tidal explanation for the observation by Holmberg that the satellites of edge-on disk galaxies tend to avoid the sector within + or - 30 deg of the major axes of the disk galaxies is considered. It is shown that satellites with small orbit-to-disk inclinations are likely to become compact and consequently be left out in Holmberg's survey due to the resemblance to stars. The explanation is supported by the observation of an excess of compact galaxies near the major-axis direction of edge-on disk galaxies. The disk tidal explanation also predicts that the asymmetry should be weaker with larger satellites. It is found that the Karachentsev (1972, 1980) binary galaxy sample, where the typical companion is comparable to the primary galaxy, shows no Holmberg effect. The case of M32 as a compact satellite of the Andromeda galaxy is discussed as a nearby observationally supported example of the above processes.

Description: A model of convective turbulence which takes radiative dissipation, rotation, and convective motion anisotropy into account, on the basis of a closure for the nonlinear interactions that employs the growth rates of hydrodynamic instabilities, is used to obtain a theoretical framework for modeling the primordial solar nebula. It is assumed that convection is the sole source of turbulence causing the solar nebula to evolve. Vertical structure equations in the thin disk approximation are developed and a detailed comparison with the previous solar nebula convective models of such workers as Lin et al. (1981, 1982) is undertaken. The present values for the turbulent efficiency are much lower and more sensitive to opacity and surface density, resulting in low turbulent speeds, a more massive disk, a lower accretion rate 'best value', and a longer characteristic dispersal time for the disk. It is concluded that convection may not be the dominant source of turbulence needed to evolve young solar/stellar nebulae.

Description: Neutral hydrogen (at the wavelength of 21 cm) and carbon monoxide (at 2.6 mm) line observations of the interstellar medium in the neighborhood of the association Ara OB1 are reported. The observed H I distribution indicates the presence of an expanding structure. The total H I mass associated with such feature amounts to 4800 solar masses, and its momentum and kinetic energy are about 40,000 solar mass km/s and 3 x 10 to the 48th erg, respectively. The H I structure, 42 pc in diameter, expands at a speed of 10 km/s. A possible origin for the expanding H I structure, and a genetic link between such structure and Ara OB1 are proposed.

Description: Flash background rates are measured from August 18-September 5, 1985 using the Lowell 0.61-m telescope at CTIO and the 28-cm f/10 Schmidt-Cassegrain telescope at ESO. During 230.1 hours of observing 40 flash events were detected, and it was observed that the background events were dominated by meteors and satellites passing through the field-of-view. The measured flash rate is compared with that of Pedersen et al. (1984), and it is determined that the background flash rate that is applicable to the data of Pedersen et al. for February 8, 1984 is 0.023 events/hr. The morphology of that flash, which appears to be controlled by a gamma-ray burster, is examined.

Description: The thermal diffusion equation for the internal temperature of cometary nuclei is exactly solved by means of a one-dimensional numerical model in order to shed light on the complex behavior of these temperatures with varying orbital and thermal parameters and in order to consider possible cometary nucleus thermal evolution targets for comet rendezvous and/or sample-return missions. The concept of 'new' and 'old' comets, classified in terms of how many passages around the sun have been made, may take on new meaning in view of the present demonstration that differences in eccentricity between two comets having the same period and number of apparitions may yield significantly different internal temperature profiles.

Description: US 943 has been shown to exhibit large (greater than about 5 mag) amplitude variations on time scales of one to two years. New time-resolved CCD photometry presented herein shows it also to be variable on time scales of 20 to 40 minutes with amplitude variation of up to 1 mag. Its membership as a cataclysmic variable is suggested. This assignment would place US 943 at a galactic distance of about 700 pc.

Description: Infrared Astronomical Satellite (IRAS) observations of the region in Orion containing HH 1 and 2 reveal for the first time the large-scale distribution of newly formed stars. New infrared sources discovered in these observations are discussed, and attempts are made to untangle the complex infrared morphology of this field. A major finding of this study is that HH 1 is near the peak of an intense and broad plateau of 60 and 100 micron emission that spatially corresponds well with the boundaries of a previously detected molecular cloud. Other findings include the detection of an emitting circum-HH object dust complex around HH 2, 25 micron emission associated with the putative HH 1 and 2 exciting source discovered with the VLA, a new luminous far-infrared source, and numerous infrared source complexes, some in blank optical fields and others in fields containing optical emission-line stars.

Description: A new SIS receiver with extremely low noise temperature, used on the Columbia 1.2-m telescope has permitted mapping CO rapidly with full sampling. Results are presented of a survey for which the angular resolution of the telescope was reduced to 0.5 deg, allowing the observations for the complete region of 750 square degrees to be finished within four months, while retaining sufficient resolution to see significant substructure. Most positions with emission are in the Taurus-Auriga dark nebulae, a cloud associated with IC 348 and NGC 1333, and a cloud associated with the California nebula (NGC 1499) and NGC 1579, which overlaps the northern Taurus-Auriga nebulae but is separated from them in velocity. Also seen were several small clouds at Galactic latitude -25 deg to -35 deg southwest of the Taurus clouds, and the L1558 and L1551 clouds in the south.

Description: New information obtained by the EXOSAT satellite on the nature of the X-ray variability in AGNs is discussed. From the EXOSAT data, it is seen that many more AGNs vary on short timescales; in some cases, the character of the time variability is quantitatively and qualitatively different than expected from the flare model of the variability. Data on the two active galaxies NGC5506 and NGC4051, which exemplify these findings, are discussed.

Description: The thermal evolution of a spherical cometary nucleus, composed initially of very cold amorphous ice and moving in comet Halley's orbit, is simulated numerically for 280 revolutions. It is found that the phase transition from amorphous to crystalline ice constitutes a major internal heat source. The transitions occur in five distinct rounds, with the phase transition front advancing into the nucleus to progressively greater depths. At the time of crystallization, the temperature of the transformed ice rises to 180 K. It is argued that gas tends to accumulate in pockets that eventually explode, forming 'volcanic calderas' and exposing gas-laden amorphous ice which may be a major source of gas and dust jets into the coma. The activity of new comets and, possibly, cometary outbursts and splits may also be explained in terms of explosive gas release following the transition from amorphous to crystalline ice.

Description: Ultraviolet and X-ray observations of the eclipsing SU UMa dwarf nova OY Car early in the decline from a superoutburst are presented. From the UV emission line spectrum and lack of X-ray eclipse, the presence of an extended coronal region is deduced.

Description: Implications of high-energy gamma-ray observations of the Andromeda galaxy with the next generation of satellites Gamma-1 and GRO are discussed in the context of the origin of cosmic rays and gamma-ray processes. The present estimate of the total gamma-ray flux of this galaxy at energies above 100 MeV is a factor of about three less than previous estimates.

Description: New three-filter light curves of AG Per are given. These yield times of minimum light in accord with the known rate of apsidal rotation but do not improve that rate. These light curves and all other published historical ones have been treated with the code EBOP and are shown to give largely consistent geometric and photometric parameters no matter which orientation of the orbit is displayed to the observer.

Description: Twenty-three transient interplanetary shocks observed near earth during 1978-1982, and mostly reported in the literature, have also been identified at the Pioneer Venus Orbiter spacecraft. There seems to be a fairly consistent trend for lower shock speeds, farther from the sun. Shock normals obtained using the Pioneer Venus data correspond well with published values from near earth. By referring to the portion of the Pioneer Venus plasma data used here from locations at longitudes within 37 deg of earth, it is found that shocks are weaker at earth, compared with those closer to the sun.

Description: The first laboratory and astronomical observations of the carbene ring molecule C3H2 briefly reported in a recent Letter are described in detail. In the laboratory, 22 millimeter-wave lines have been measured in a He and C2H2 discharge. From these the three rotational constants and the five fourth-order centrifugal distortion constants of C3H2 have been determined to high precision, allowing, in turn, calculation to 0.1 km/s of the most important lines in the radio and far-IR spectrum; 123 lines in the rotational spectrum with E/K less than 100 K are tabulated. Eleven astronomical transitions have been identified, and in Sgr B2 and Orion KL, rotational temperatures and column densities were derived and compared with those of other hydrocarbons with a similar number of C atoms.

Description: Ground-based 2-23 micron photometry and 10.3 micron imaging of comet Halley taken within hours of the Giotto spacecraft encounter are presented. The photometry shows a color temperature of 360 K and silicate emission features at 10 and 20 microns, and the image shows jet activity similar to that observed by Giotto, but on a scale of thousands of km. The expected 10 micron surface brightness, based on the particle mass distribution measured by Giotto and assuming solid, spherical grains, is a factor of six lower than the observed value. It is suggested that fluffy particles could remove this discrepancy.

Description: The NASA 64-m and CSIRO 64-m antennas at Tidbinbilla and Parkes, respectively, have been used to observe the star-forming region associated with HH46 and HH47 in the Bok globule known as ESO 210-6A or Sa III. The (1,1), (2,2), and (3,3) transitions of ammonia were observed at the position of the infrared point source, which is the star energizing this complex. Ammonia was not detected at other nearby locations in the globule. The ammonia emission is attributed to a circumstellar toroid or disk with a gas temperature of 17 + or - 2 K, a density of 7 + or - 20,000/cu cm, a size of 6000-7500 Au, and a mass of 0.09-0.14 solar masses, assuming an ammonia abundance of 10 to the -7th. Such a low disk mass may imply more than mere confinement as the mechanism for achieving high collimation observed in the outflow from this region.

Description: In association with an ammonia survey of the southern Galaxy (Peters et al., 1986), a search was made for improved analytical formulas to expedite the data analysis. Semi-empirical formulas are presented which relate the kinetic temperature of a molecular cloud to the kinetic temperature used in full statistical equilibrium calculations. The formulas can be used in a simple way to improve the estimate of the kinetic temperature obtained from ammonia observations.

Description: The deuterated cyclopropenylidene ring molecule, C3HD, has been detected toward several sources in four rotational lines, at 19, 79, 104, and 107 GHz. The relative integrated intensities of the 2-sub-12 - 1-sub-01 lines of C3HD and C3H2 are found in the ratio 1:5, indicating a high deuterium fractionation ratio for cyclopropenylidene. The detection of the C-13 isotope of C3H2 at the same position allows a determination of the optical thickness (about 3) of the line. The detection of such a large enhancement in the deuterated form of C3H2 very strongly suggests that a molecular ion is the chemical precursor of the molecules. Consideration of the amount of the enhancement relative to that in other molecules suggests that the precursor ion is C3H3+.

Description: The infrared source R CrA IRS 5 in the R CrA dark cloud has been mapped, and it is found that it is extended at H (1.6 micron) and at K (2.2 micron). The geometry of the data suggest that this object consists of a disk and polar reflection lobe surrounding a star, similar to GSS 30 in the Ophiuchus dark cloud and to SGS 1 in the NGC 1333 dark cloud. The illuminating star has an effective temperature below 8000 K, a luminosity less than 9 solar luminosities, and lies above the main sequence. The luminosity of this star is smaller than the luminosity of any other known star which illuminates an infrared reflection nebula.

Description: Stromgren and H-beta colors have been determined from spectrophotometric observations for two Be stars without published photometry in the association Per OB1: HD 12856 (B0 pe) and HD 13890 (B1 III:pe). Stellar parameters and improved spectral types are then derived from the color indices using the calibrations of Jakobsen (1986), and independently from the BCD classification method. The intrinsic properties of HD 12856 and HD 13890 are compared with those of normal B stars and are used to estimate their evolutionary status.

Description: The high galactic latitude planetary nebula 75+35 deg 1 was observed in the low-dispersion mode of the IUE satellite. The UV spectrum is characterized by a strong continuum that matches the energy distribution of a blackbody curve of 90,000 K + or - 5000 K. The color temperature of 94,000 K + or - 4000 K is derived from the UV color indices. The spectral type mimics that of an O7.5 V star; a very strong N V 1240-A feature with a P Cygni profile is present, in addition to a very weak C IV P Cygni line. A very slight depression in the 2200-A region suggests very little interstellar absorption with an upper limit of E(B-V) = 0.025 mag, as would be expected for a high galactic latitude object. The ultraviolet observations, in context with the optical data, indicate that this object is not a typical planetary.

Description: Theoretical prejudice and inflationary models of the very early universe strongly favor the flat, Einstein-de Sitter model of the universe. At present the observational data conflict with this prejudice. This conflict can be resolved by considering flat models of the universe which posses a smooth component of energy density. The kinematics of such models, where the smooth component is relativistic particles, a cosmological term, a network of light strings, or fast-moving, light strings is studied in detail. The observational tests which can be used to discriminate between these models are also discussed. These tests include the magnitude-redshift, lookback time-redshift, angular size-redshift, and comoving volume-redshift diagrams and the growth of density fluctuations.

Description: 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.

Description: Relativistic beaming of radiation is generally invoked to explain the extreme properties of blazars. The simplest synchrotron-self-Compton (SSC) model is applied to all blazars that have been observed in the X-ray region and have known VLBI sizes, and the minimum kinematic Doppler factor for each source is derived. All high polarization quasars (HPQs), but only half of the 30 BL Lac objects in the sample require relativistic enhancement of radiation due to beaming effects. The different Doppler factor distributions for the two classes of sources argue against the hypothesis that BL Lacs could be low-luminosity HPQs whose strong emission lines are swamped out by the boosted nonthermal continuum. Thus HPQs and BL Lacs could be intrinsically different in their physical structure.

Description: A model for the appearance of the all-sky low-energy X-ray background on a fine angular scale is presented which is based on primeval hot gas clouds associated with the formation of clusters of galaxies according to the Sunyaev-Zel'dovich (1972) model. It is noted that the background could have both granular and diffuse components if it is due to such gas clouds. The observed appearance of the granular component is predicted along with the observable characteristics of collapsing protoclusters. The effects of distant X-ray-emitting QSOs, radio galaxies, and normal galaxies on the observations are considered, and these sources are shown not to interfere with the possibility of observing the protoclusters. It is concluded that if sufficient heating occurred in an intracluster medium within some clusters of galaxies at the protocluster epoch, the ensemble properties of protoclusters could be observed with an X-ray telescope, and the time at which protoclusters formed could perhaps be estimated.

Description: Three incoherent synchrotron models are used to account for the very flat radio spectrum of the BL Lac object PKS 0735+178. The first interpretation is that the spectrum results from optically-thin synchrotron emission from relativistic electrons with a particular energy distribution. The second posits a single nonuniform, self-absorbed source generated by a wind flowing from a central object. The third suggests that sources with flat spectra are caused by the presence of multiple (three or more) discrete uniform components, and that the magnetic field and relativistic electron distribution for each source is correlated with the size of the individual components. It is proposed that the last model is the most tenable explanation of the phenomenon, and multi-frequency VLBI observations are suggested for the evaluation of the detailed structure of compact radio sources.

Description: A search for interstellar scintillation (ISS) of low-frequency variable radio sources is reported. Observations of 28 confirmed or suspected low-frequency variables, 21 nonvariable sources, and two pulsars were made at 408 MHz. As expected, the pulsars showed ISS, but scintillation was not detected in any other source. A typical upper limit to the rms modulation due to ISS is 150 mJy, giving lower limits to the apparent angular diameter of about 10 to the -6th arcsec. The possibilities that a true point source is broadened to an apparent angular diameter greater than or roughly equal to 10 to the -6th arcsec by scattering local to the source or in a general intergalactic medium are discussed.

Description: Observations at 90 GHz of a sample of 38 sources chosen to have flat or rising spectra between 0.318 and 5 GHz are reported. Roughly 25% of the sources were found to have flat or rising spectra between 5 and 90 GHz. The optical magnitude of each of the sources from the E print of the Palomar Sky Survey has also been estimated. Evidence is found for a correlation between the 90-GHz flux density and the optical magnitude, suggesting a relationship between the emission processes at these frequencies. Little evidence is found for a correlation between the low- and high-frequency spectral indices of the sources. This suggests that the sources tend to be opaque at centimeter wavelengths and optically thin at millimeter wavelengths. The properties of two of the more interesting sources are also discussed. Evidence is presented that strong millimeter activity may be generally associated with the BL Lac phenomenon.

Description: The X-ray emitting system GX 339-4 contains one of the prime candidates for a stellar mass-sized black hole. Determining the observational similarities and differences between the members of this group is of value in specifying which characteristics can be used to identify systems containing a black hole, especially those for which no mass determination can be made. The first observations of the E greater than 20 keV spectrum of GX 339-4 during a transition between luminosity states are reported here. The hard spectral state is the lower luminosity state of the system. GX 339-4 has a power-low spectrum above 20 keV which pivots during transitions between distinct luminosity states. The only other X-ray sources known to exhibit this behavior, Cyg XR-1 and (probably) A0620-00, are leading candidates for systems containing a black hole component based on their measured spectrocopic mass function.

Description: In this paper, the zodiacal component is subtracted from the 60 and 100 micron Galactic plane emission by applying an empirical model derived from IRAS data in regions of the sky not dominated by the Galaxy. The corrected observations are used to derive the large-scale physical conditions such as temperature, optical depth, and total FIR brightness of the dust residing in the Galactic disk. (C-12)O, H I, and 5 GHz radio continuum observations are also used to compare the large-scale properties of the gas and dust distributions in the Galaxy. Possible scenarios to explain the findings are suggested.

Description: The small-scale structure of the interstellar magnetic field in the vicinity of the Herbig-Haro objects HH 7-11/HH 12 and HH 33/40 is derived from CCD imaging polarimetry of stars nearby to these young stellar object driven outflows. The outflow associated with SVS 13/HH 7-11 lies approximately parallel to the local field direction. The outflow mapped by HH 33/HH 40 is also well aligned with the local magnetic field. However, the orientation of the outflow associated with HH 12 located 2 arcmin to the north of HH 7-11 is offset from the inferred magnetic field direction by 60 deg. These results taken together with those of previous studies suggest: (1) magnetic fields are directly or indirectly responsible for the observed orientation of outflows associated with newborn stars in the majority of cases; and (2) in some cases, the flow properties may depend upon other characteristics of the parent cloud core.

Description: B and R broadband CCD photometry of the jet of 3C 273 is presented. Several knots are found within the jet. The knots at either end have a difference in color indices, with the knot at the outermost end being redder by about 1/2 magnitude in (B-R). Also, a variation in color may have been observed along the jet. This latter result would place constraints upon the jet-forming mechanism involved; the variation in color may be due to a nonthermal emission decay process.

Description: Radial-velocity curves for both components of the short-period, white dwarf M dwarf binary systems Case 1 and HZ 9 have been determined from 1-A-resolution spectra obtained at the MMT. The radial-velocity curves for the M dwarf components agree well with previous determinations. The new data have been used to estimate masses for the white dwarfs, yielding 0.38 solar mass for the Case 1 DA and 0.51 solar mass for the HZ 9 DA, with 1sigma uncertainties of about 0.1 solar mass.

Description: Elemental abundance analyses based on the coaddition of at least 10 2.4 A/mm Ila-O Dominion Astrophysical Observatory spectrograms have been performed for three mercury-manganese stars, 53 Tauri, Mu Leporis, and Kappa Cancri. These fine analyses show a greater degree of internal consistency than previous studies based on lower signal-to-noise data. Lines as weak as of order 3 mA are employed in these studies, and lines of atomic species not previously identified have been discovered. The status of 53 Tau as an anomalous member of this class is confirmed in that it lacks a Hg II 3984 A line even at the 2 mA level. Further, its surface gravity indicates it is less evolved than Mu Lep and Chi Cnc. Violations of the odd-even effect in the photospheric abundances of all three stars suggest that nonnuclear processes have operated in their atmospheres. Some of the values are substantially changed from their presumably initial solar values.

Description: The results of a high-resolution spectroscopic study of 10 T Tauri stars (TTS) and two Herbig emission stars are presented based on red echelle spectra including the lines of forbidden O I 6300 A, forbidden N II 6584 A, forbidden S II 6716, 6731 A, as well as H-alpha. The forbidden lines display a continuous progression of profile types. The velocity structure in the forbidden lines is critically examined and compared to computed line profiles for a number of different wind models. Constant velocity spherical or conical winds fail to reproduce the observed line profiles, which are better explained by a wind with a latitude-dependent velocity field. A prediction of the wind model correlating the velocity of the reversal at H-alpha and the forbidden line velocity structure as a function of the view angle to the star is explored. Estimates of the average densities and sizes for the TTS forbidden emission regions are presented, and mass-loss rates are computed. IRAS far-IR fluxes are used to estimate the disk sizes.

Description: An analytical procedure is developed to solve the MHD equations for a stellar wind in the strong-magnetic-field, optically thick limit for hot stars. The slow-mode, Alfven, and fast-mode critical points are modified by the radiation terms in the force equation but in a manner that can be easily treated. Once the velocities and distances are known at the critical points, the streamline constants are determined in a straight-forward manner. This shows the structure of the wind with a relatively simple numerical scheme. The magnetic field and a radiation parameter specify the terminal wind velocity. High rotation rates and a modified slow-mode critical point close to the stellar surface determine the high mass-loss rates. Wolf-Rayet stars are modeled with 1000-G fields but require stellar rotational velocities approaching breakup values. The physical conditions that correspond to Wolf-Rayet models are so rare that another mechanism must be operating in these winds.

Description: Radio continuum observations of the R Aqr symbiotic star system, using the compact D configuration of the VLA at 6-cm wavelength, reveal a large-scale about 2-arcmin structure engulfing the binary, which has long been known to have a similar optical nebula. This optical/radio nebula possesses about 4 x 10 to the 42nd ergs of kinetic energy which is typical of a recurrent nova outburst. Moreover, a cluster of a dozen additional 6-cm radio sources were observed in proximity to R Aqr, most of these discrete sources lie about 3 arcmin south and/or west of R Aqr and, coupled with previous 20-cm data, spectral indices limits suggest a thermal nature for some of these sources. If the thermal members of the cluster are associated with R Aqr, it may indicate a prehistoric eruption of the system's suspected recurrent nova. The nonthermal cluster members may be extragalactic background radio sources.

Description: Given the current understanding of polycyclic aromatic hydrocarbons (PAHs), the spectroscopic data suggest that are at least two components which contribute to the interstellar emission spectrum: (1) free molecule-sized PAHs producing the narrow features and (2) amorphous carbon particles (which are primarily composed of an irregular 'lattice' of PAHs) contributing to the broad underlying components. An exact treatment of the IR fluorescence from highly vibrationally excited large molecules demonstrates that species containing between 20 and 30 carbon atoms are responsible for the narrow features, although the spectra match more closely with the spectra of amorphous carbon particles. It is concluded that, since little is known about the spectroscopic properties of free PAHs and PAH clusters, much laboratory work is required along with an observational program focusing on the spatial characteristics of the spectra.

Description: It is argued that radio observations of the supernova 1987A can be interpreted in terms of its interaction with circumstellar matter. The early turn-on of the radio emission implies a relatively low density circumstellar medium. The optical properties of the supernova imply that the progenitor star had a smaller radius than that of a typical type II supernova progenitor. The mass loss properties are consistent with this hypothesis. The thermal X-ray luminosity of the supernova is predicted and noted to be below the current upper limit. A bright infrared dust echo is not expected, although a weak echo from an earlier mass loss phase is possible. Weak ultraviolet emission lines from cicumstellar gas may be visible. Although the circumstellar density is low, it is possible that the progenitor star did lose a substantial fraction of its mass prior to the supernova explosion.

Description: An investigation is conducted concerning the possibility that observed Mg-26 anomalies in meteorites may be related to a nucleosynthetic event which preceded the formation of the solar system by at most a few million years. The Al-26, which decayed to form the observed excess Mg-26, could have been produced in either explosive carbon burning or in a high temperature carbon burning shell source immediately preceding the explosion. The results of supernova grain condensation calculations are presented and related to the hypothesis that a 'last event' supernova was indeed related to the formation of the solar system and thus might have created the observed isotopic anomalies in magnesium, oxygen, neon, and xenon.

Description: Questions concerning the origin of comets are considered. It is pointed out that the molecular composition of a dense interstellar cloud appears to have exactly the composition needed to produce the observed features of the visible cometary spectrum, which consists mainly of emission bands of unstable free radicals. A working model of cometary structure is discussed together with the classical observations which have led to it. The discussed model was originally described by Whipple (1951). It is emphasized that the model can serve only as a rough guide in efforts to interpret the evolution of cometary behavior. A survey is provided of new techniques which have only recently been applied to cometary observations, taking into account the spectrum of a comet, radio observations, and ultraviolet observations.

Description: Pulsational eigenfrequencies and stability coefficients of the lowest modes of nonradial quadrupole (l = 2) oscillation have been obtained for chemically homogeneous stellar models constructed with Carson's (1976) radiative opacities. Instability is found to develop as a result of the same operation of the kappa-mechanism in the CNO ionization zone and at nearly the same stellar masses as was the case for the radial (l = 0) modes studied previously. A survey of the l = 5 modes indicates that the instability gradually declines with increasing degree of the spherical harmonics.

Description: Data on X-ray bursts recorded by the OSO-8 and SAS-3 satellites and criteria (rise time, duration, recurrence) for X-ray bursts are examined in a study of possible correlation between the galactic longitude distribution of X-ray burst sources and globular clusters. Correlations are weak, with only two X-ray bursts sources (NGC6624 and the rapid burster) coinciding with globular clusters, another seven possibly coinciding, most not correlated. Ad hoc explanations (globular clusters obscured by dust clouds, bursts associated with remnants of disrupted globular clusters evolved into supermassive black holes) are considered briefly.

Description: Non-LTE calculations for the ultraviolet C I and Si I continuous opacity show that LTE results overestimate the importance of these sources of opacity and underestimate the emergent flux in Alpha Lyr. The largest errors occur between 1100 and 1160 A, where the predicted flux in non-LTE is as much as 50 times larger than in LTE, in reasonable accord with Copernicus observations. The discrepancy between LTE models and observations has been interpreted to result from the existence of a chromosphere. Until a self-consistent non-LTE model atmosphere becomes available, such an interpretation is premature.

Description: Cygnus X-1 was observed on two occasions separated by a year by the same Goddard X-ray rocket payload. High-resolution temporal and spectral data reveal that Cyg X-1 was essentially unchanged in these two observations a year apart; the bursts of millisecond duration observed in the earlier flight were observed in the second as well. Analysis of these bursts has failed to reveal any internal temporal structure, either luminous or spectral. The shot-noise character of temporal fluctuations on time scales of at least 1 s can be explained by the presence of exponential pulses with a time constant of a fraction of a second and a rate near 8 per sec. The possible connection of these pulses with the bursts is examined.

Description: Envelope models for central stars of planetary nebulae have been constructed with Carson's (1976) radiative opacities. A stability analysis of these envelopes indicates that for a sufficiently high luminosity, the fundamental mode of radial pulsation is excited by the kappa mechanism operating in the CNO ionization zone. At somewhat higher luminosities the lowest overtones also become unstable. This may possibly explain the rapid variability that is observed in some central stars, if the time scale of the variations is minutes to hours.

Description: An analysis of the accretion process in an X-ray pulsar, whereby angular momentum is transferred to the star and its rotation period is changed, is presented, and an expression for the fractional rate of change of the pulse period in terms of X-ray luminosity and other star parameters is derived. It is shown that observed characteristic spin-up time scales for seven X-ray pulsars strongly support the view that in every source (1) the pulse period reflects the rotation period of a compact object, (2) the accretion is mediated by a disk surrounding the compact object and rotating in the same sense, and (3) the compact object is a neutron star rather than a white dwarf.

Description: Spectrophotometric observations from 2.1 to 4.1 microns of a variety of objects exhibiting the 3.3-micron emission feature (first detected in NGC 7027) are reported. The characteristics of the feature, the various environments in which it is found, and possible emission mechanisms are discussed in light of all the available observations of the feature to date. A resonance feature in solids is the most probable emission mechanism; however, no satisfactory identification has yet been made on the basis of infrared spectroscopy of terrestrial materials.

Description: The infrared spectrum of the Kleinmann-Low nebula in M42 has been measured from 80 to 350 kaysers (approximately 29 to 125 microns) with a Michelson interferometer aboard the NASA Kuiper Airborne Observatory. The frequency spectrum peaks at about 185 kaysers. A simple model of the emission implies that the temperature is in the range 70-95 K and that the optical depth is at least 0.2 at the peak frequency. A possible absorption is seen at about 176 kaysers. Thermal emission by dust at a temperature of 71 K, with the absorption cross section proportional to frequency, provides a good fit to the data. Other thermal-emission models can also fit the spectrum. The data are compared with previous broad-band measurements. Upper limits are placed on expected line emission from the surrounding H II region at the position of the nebula.

Description: It is suggested that the explosion of a Type II supernova triggered the collapse of a nearby interstellar cloud and led to the formation of the solar system. Estimates of the abundances resulting from nuclear processing of the supernova ejecta are presented. It appears promising that nucleosynthesis in this single supernova event can account for most isotopic anomalies and traces of extinct radioactivities in solar-system material.

Description: Recent progress in the study of the pulse profiles of the nine known binary X-ray pulsars is discussed. The sources considered include SMC X-1, Her X-1, Cen X-3, A0535+26, GX1+4, 3U 0900-40, A1118-61, GX301-2, and 3U 0352+30. Sample X-ray profiles for these sources are provided, and general features exhibited by the profiles are identified. It is noted that the apparent existence of a gap in the period distribution of X-ray pulsars, in the range from about 5 to 100 sec, seems to be genuine within obvious statistical limitations and is probably not an observational effect. Two explanations for the production of X-ray pulsations are examined: one requiring a temporal modulation of mass accretion onto the surface of a neutron star and another requiring the funnelling of matter along magnetic field lines to the neutron star's surface.

Description: The spectrum of comet West (1975 n) was recorded on March 7 and 11, 1976, in the wavelength interval from 5700 to 8200 A at an intermediate resolution. One hundred twenty-two emission lines are reported, with 78 lines having identifications with spectral features of NH2, H2O(+), C2, O I forbidden emission, and Na I.

Description: A detailed study of the hydrostatic equilibrium of the gas-field system perpendicular to the galactic plane in the neighborhood of the sun, assuming that the magnetic field is parallel to the plane, has been carried out. It is found that the distribution of pressure due to cosmic rays and the magnetic field is different from that due to the gas. The observed radio spectrum in the direction of the galactic pole can be understood if one includes in the hydrostatic equilibrium the distribution of gas in the halo. The results of this analysis show that in the galactic plane, the cosmic-ray density is approximately 2 to 3 eV/cu cm with a magnetic-field strength of about 5 to 6 microgauss. It is inferred that cosmic rays are confined to a more extended volume in the Galaxy (with an equivalent thickness of at least 2 kpc in the solar neighborhood) than the gas disk, and the magnetic-field strength slowly decreases to a value of 1 microgauss only beyond about 5 kpc from the plane. Further, there is no evidence for a quasi-spherical radio halo, although the radio emission extends beyond the gas disk with scale height of at least 1 kpc. A lower limit of about 6 million years for the confinement of cosmic rays in the Galaxy has been set.

Description: The paper develops certain aspects of a model wherein a QSO is a massive black hole located in a dense galactic nucleus, with its growth and luminosity fueled by tidal disruption of passing stars. Cross sections for tidal disruptions are calculated, taking into account the thermal energy of stars, relativistic effects, and partial disruption removing only the outer layers of a star. Accretion rates are computed for a realistic distribution of stellar masses and evolutionary phases, the effect of the black hole on the cluster distribution is examined, and the red-giant disruption rate is evaluated for hole mass of at least 300 million solar masses, the cutoff of disruption of main-sequence stars. The results show that this black-tide model can explain QSO luminosities of at least 1 trillion suns if the black hole remains almost maximally Kerr as it grows above 100 million solar masses and if 'loss-cone' depletion of the number of stars in disruptive orbits is unimportant.

Description: The fractional abundances of the isotopic species of carbon monoxide in interstellar clouds are calculated on a basis of gas-phase ion-molecule reactions. The (C-13)O/(C-12)O ratio varies significantly with extinction of the ultraviolet radiation field, and in the outer regions of dark dense clouds (C-13)O may be enhanced by a factor of 10. The observational interpretation of the CO to H2 or interstellar-reddening relation and the isotopic abundances of carbon are complicated by these effects.

Description: Measurements of the 104 sec pulse profile of A0535+26 at energies near 50 keV are reported. The data were obtained with a balloon-borne detector system which was launched on May 22, 1975 with the objective to observe transient or periodic emissions from X-ray or gamma-ray sources. The presence of the source was detected by a superposed epoch analysis. The pulse profile of A0535+26 in two energy channels is presented in a graph.

Description: The All-Sky X-ray Monitor on board Ariel-5 has observed the 3-6 keV decline of the bright transient X-ray source A0620-00 on a virtually continuous basis during the period 1975 September-1976 March. The source behavior on time scales greater than about 100 minutes is characterized by smooth, exponential decays interrupted by substantial increases in October and February. The latter increase was an order-of-magnitude rise above the extrapolated exponential falloff, and was followed by a final rapid decline below a level of about 0.05 per sq cm per sec by late March. Upper limits of 2.5% and 10% were found for any periodicities in the range 0.2-10 days during the early and later decay phases, respectively. A probable correlation between the optical and 3-6 keV emission from A0620-00 has been noted, effectively ruling out models involving traditional optical novae in favor of Roche-lobe overflow in a binary system. The existing data on the transient X-ray sources are consistent with two distinct luminosity-lifetime classes of these objects.

Description: In order to understand the seemingly erratic V/R variations and radial velocity curves of emission edges and central absorption of some Be stars, we have advanced, for the changes of structure of the gaseous ring around these stars, a theory that is based on the interaction between the existing ring and the newly ejected matter from the star. It shows that the structural change of the ring is completely controlled by the angular-momentum input factor and the dissipation factor. In light of this understanding, we have gone on to interpret the observed results of Beta-1 Mon and Pi Aqr.

Description: Ariel V All-Sky Monitor observations of Aql X-1 are reported and compared with previous observations that indicate the existence of 'low' and 'high' intensity states. All the data considered are shown to be consistent with flaring episodes having a mean flare interval of 435 days with an rms scatter of about 10%. It is suggested that the observations are most easily interpreted in terms of an 'X-ray dwarf nova' binary of the type proposed for the transient X-ray source A0620-00. Constraints on more detailed features of the source model are discussed.

Description: A survey of 73 sources has been made in the emission lines of N2H(+) and HCO(+), including detailed maps of four sources (Ori A, OMC-2, DR 21 OH, and NGC 6334). These data are combined with equally extensive data for HCN and CN to make a detailed study of the spatial relationship of these four species. Actual abundance ratios are shown to vary, often sharply, over small scale lengths (of the order of 1 arcmin) within the mapped sources. Excitation temperatures also vary. All four species appear to be subthermally excited. The abundance ratios and their spatial variations are interpreted in terms of ion-molecular formation and destruction processes. It is concluded that the relative abundances of CO may be considerably lower in some regions than previously believed. No evidence is found for variations in the C/O ratio over small scale lengths in Ori A. The degree of ionization of the Ori A molecular cloud may be significantly different from that of other molecular clouds.

Description: In connection with information considered by Illarianov and Sunyaev (1975) and van den Heuvel (1975), a simple physical model for an X-ray burst source in the galactic disk is proposed. The model includes an unevolved OB star with a relatively weak stellar wind and a compact object in a close binary system. For some reason, the stellar wind from the OB star is unable to accrete steadily on to the compact object. When the stellar wind is sufficiently weak, the compact object accretes irregularly, leading to X-ray bursts.

Description: The structure and nature of 'discontinuities' in the interplanetary magnetic field at 1 AU in the period from March 18 to April 9, 1971, is determined by using high-resolution magnetic-field measurements from Explorer 43. The discontinuities that were selected for this analysis occurred under a variety of interplanetary conditions at an average rate of 0.5/hour. Both tangential and rotational discontinuities were identified. Tangential discontinuities were observed every day, even among Alfvenic fluctuations. In particular, on one day during which Alfvenic fluctuations were intense and persistent in a high-speed stream, tangential discontinuities (TD's) were seen throughout the day at an average rate of 0.5/hour; rotational discontinuities (RD's) were also observed during this day at a higher than usual rate, the ratio of TD's to RD's being approximately one. The structure of most of the current sheets was simple and ordered; i.e., the magnetic field usually changed smoothly and monotonically from one side of the current sheet to the other. The thickness distributions of the TD's and RD's with very smooth current sheets were similar. The average thickness of the RD's was 1200 km (13 proton Larmor radii), and the average thickness of the TD's was 1300 km (12 proton Larmor radii).

Description: We have found that the rate of mass loss M increases with an increase in the period of pulsation for Mira-type variables. This result suggests that the rate of mass loss is accelerated with time until a maximum value is reached before the ejection of the outer envelope. The matter from the continuous mass loss during the evolution of the star produces supersonic shock waves that sweep up the interstellar gas upon encountering the interstellar medium, so that a shell is formed. This phenomenon may account for the observations of extended regions of emission that surround planetary nebulae.

Description: The spectral region about the Mg II doublet lines near 2800 A of Be and shell stars has been observed. The star Gamma Cas shows narrow components to each resonance doublet line shifted 215 km/s toward shorter wavelengths. The resonance and subordinate lines of Zeta Tau are shifted toward shorter wavelengths by 75 km/s, and the subordinate lines are greatly strengthened. The star Kappa Dra, which is much later in spectral type, shows a comparatively normal doublet spectrum.

Description: Generalized Einstein equations invariant under scale transformations are presented, and several astrophysical tests studied. It is assumed that the dynamics of atoms or clocks used as measuring apparatus is given a priori. Connection with gauge fields and broken symmetries is made through the cosmological constant.

Description: The meaning of the term 'cometary nucleus' is discussed, taking into account observations of comets with different characteristics. It is pointed out that for some comets, there may be no nucleus to be seen at any time, while in others as the comet brightens or undergoes changes, a nucleus may develop to be seen for a time or even intermittently, while occasionally more than one nucleus may be seen to be present. On the basis of a study of observational reports it emerges that no more than about 30 per cent of comets exhibit anything resembling a starlike nucleus.

Description: Swan-band emission from the C2 molecule provides important information for a study of the physical processes occurring in comets. It is, therefore, a disturbing factor that many quantitative Swan-band observations are in clear contradiction of predictions of resonance fluorescence excitation of the Swan bands. A description is presented of an investigation involving an application of resonance fluorescence theory to C2. The investigation takes into account all important electronic transitions which determine the population distribution of the lowest energy states. It is found that the previous discrepancy for the brighter band sequences disappears.

Description: The evolution of helium stars in the mass range from 4 to 15 solar masses has been followed from the initial helium main sequence to the end of carbon burning in the core, with the use of Carson's (1976) radiative opacities. As compared with earlier work based on smaller opacities, the main-sequence band in the H-R diagram is now both wider and cooler than before. If neutrino losses are neglected in the stellar models, the phase of carbon burning in the core occurs in the red-supergiant region; otherwise, it occurs, as it does in the earlier models with or without neutrino emission, close to the helium main sequence. Observational data for Wolf-Rayet stars and R Coronae Borealis variables are found to lend some support to the present models.

Description: The rate of hydrogen production of Comet West is studied through rocket observation of solar Lyman-alpha radiation resonantly scattered by the escaping hydrogen atoms. Two sets of Lyman-alpha exposure sequences are used to obtain computer-smoothed brightness contour (isophote) maps covering a density range of 100:1. A simple radial outflow model is applied to the contour maps to determine the rate of hydrogen production (3.2 by 10 to the 30th power atoms/sec.) Discrepancies between the observed shape of the outer isophotes and predicted models may be explained by optical depth effects, or by the presence of small pieces of the comet's nucleus distributed along the orbit. Hydrogen, carbon, and oxygen production for Comet West and Comet Kohoutek are compared; differences may be accounted for by variations in the composition or evolution of the two comets.

Description: Data obtained from the Copernicus Orbiting Astronomical Observatory, launched in 1972 and still obtaining information, are used in a discussion of the interstellar medium. The Copernicus instruments have facilitated direct estimates for the density and temperature of individual interstellar clouds, and improved the ability to determine where along the line of sight a cloud lies with respect to background stars. The physical characteristics of hydrogen molecules are considered, with attention to the formation and destruction of interstellar hydrogen. The differences between 'thin' clouds, in which molecular hydrogen is optically thin, and 'thick' clouds are examined. Several features of the interstellar medium are described.

Description: The atmospheric properties of seven planetary nuclei which have O or Of-type spectra were determined by use of the Zanstra method and by analysis of the visual line spectra. One finding is that the O-type spectral sequence may extend to effective temperatures of 90,000 kelvins or more, if the results of the Zanstra method are to be believed. However, there are some indications of internal inconsistency in the Zanstra method and some outstanding discrepancies between the effective temperatures indicated by the Zanstra method and those indicated from analysis of the visual line spectra. Two ways to resolve these discrepancies are to postulate an excess of extreme-UV stellar flux or to postulate a hot binary companion for some central stars. In either case the validity of the Harmon-Seaton evolutionary sequence for central stars becomes questionable.

Description: The concept that cosmic-ray density is related to the matter to which cosmic rays are dynamically coupled through magnetic fields on the scale of galactic arm segments is considered with specific reference to gamma-ray astronomy. A model of the galactic-matter and cosmic-ray distributions is developed on the basis of 21-cm radio surveys and recent observations of the 2.6-mm CO emission line by assuming that cosmic rays are galactic in origin, their column density is proportional to the total interstellar-gas column density, their scale height is considerably larger than that of the matter, and the Galaxy is a spiral with an arm/interarm density ratio of about 3 to 1. It is found that there is a good correlation between the observed gamma-ray intensity and that predicted on the basis of essentially complete coupling of cosmic rays to the best estimate of atomic and molecular hydrogen in the Galaxy. Individual maxima observed in gamma-radiation from the central region of the Galaxy are shown to be well correlated with those predicted to result from certain spiral-arm tangents if all the matter is assumed to be modulated in a particular spiral-arm segment pattern.

Description: The X-ray spectrum of Her X-1 was observed in the energy range from 2 to 24 keV from August 29 to September 3, 1975. Emission features are observed near the K-alpha iron-line energy which exhibit both broadening and a double line structure. The total luminosity in these features is about 4 by 10 to the 35th power ergs/s. Iron line fluorescence from an opaque cool (not exceeding 1 million K) shell of material at the Alfven surface provides the necessary luminosity in this feature. The double line structure and the line energy width can be due to Doppler shifts if the shell is forced to corotate with the pulsar at a radius of at least 800 million cm. Implications of this model regarding physical conditions near Her X-1 are discussed.

Description: Mass loss from an accretion disk around a supermassive (of the order of 100 million solar masses) black hole is proposed as the origin of the broad permitted lines of Seyfert galaxies and QSOs. The material is expelled by ionizing radiation emitted near the center of the disk and striking it at a radius of approximately 10 to the 16.5 power cm. The escaping gas initially has a density of about 1 trillion per cu cm, high enough for radiation pressure to accelerate the gas to high radial velocities. The model leads to line emission from tiny dense filaments moving at about 10,000 km/s in a region roughly 10 to the 17th power cm across. This agrees with the observed broad line widths, variability time scales, and the absence of broad forbidden-line emission.

Description: The paper reports the observation of pulsed fractions in the primary and secondary peaks, as well as in the interpulse region, of the high-energy X-ray light curve of NP 0532. A statistical analysis of light-curve data is performed, and a similar analysis is carried out using simulated data. It is concluded that a previously reported third peak in the light curve was transient in nature.

Description: The large numbers hypothesis (LNH) linking the magnitude of large dimensionless ratios in physics (on the order of 10 to the 40th power) to cosmic time is examined. The LNH is checked against evidence on 3K background radiation of the universe and the (log N, log S)-relation for radio galaxies. Earlier criticisms of LNH by Gamow and Teller are examined, and alternative hypotheses put forth by Dicke and Carter (1974) are discussed. The discussion covers: continuous (additive or multiplicative) creation of matter, the Einstein metric and the atomic metric, and general cosmological and local astronomical implications of LNH. LNH is also viewed in relation to solar evolution and pulsar physics.

Description: The observed transitions at energies above 20 keV show that the spectrum of Cyg XR-1 exhibits the pivoting effect during intensity transitions expected from two-temperature accretion disk models of the X-ray emitting region. Cyg XR-1 was observed with the high-energy X-ray spectrometer on board the OSO-8 satellite from November 11-19, 1975 and from October 27 to November 15, 1976 (excluding the period from November 1 to November 7, 1976).

Description: The accretion-disk model for the optical continuum of QSOs has been investigated using the standard viscous-stress ('alpha-P') formalism. It is found that with a maximum allowable mass of 10 billion solar masses, the standard model with sub-Eddington flow falls a factor of 10 short of the luminosity of the brightest QSOs. Models with the higher mass-flow rates required to reach the maximum luminosities produce most of their energy in an optically thin region which has not yet been self-consistently treated. The disk model with sub-Eddington flow has difficulty in producing a power law of the correct slope over the optical band. It is suggested that nonthermal processes may be needed to explain the optical properties of QSOs.

Description: Radiative acceleration as a mechanism for ejection of matter from quasistellar objects is considered, and calculations are presented showing that a strongly beamed outflow will result if the source of the driving radiation is a disk. The net forces exerted by an infinitesimally thin, optically thick disk emitting thermal radiation with given intensity on clouds or particles is calculated, and conditions for beaming are obtained. Apparently it is possible to establish strong beaming within a distance of the order of the disk radius.

Description: The paper studies the detailed spectral characteristics of the planetary nebulae N97 and N153 in the Large Magellanic Cloud (LMC), the planetary nebula N67 in the Small Magellanic Cloud (SMC), and the small H II regions N9, N61, and N81 in the SMC. Electron temperatures and densities for each nebula are derived from emission-line strengths determined by photographic spectrophotometry, and relative abundances are estimated for H, He, N, O, Ne, Ar, and S. The results show that: (1) N67 has a 60% overabundance in He/H while N97 and N153 have approximately normal He/H values; (2) all three planetaries have N/H values comparable to those of galactic planetaries but substantially higher than found in the H II regions of their respective Cloud; (3) the O/H values in the planetaries are similar to or lower than those in the H II regions of the respective Cloud; (4) the O/Ne, O/S, and O/Ar ratios in the two LMC planetaries are comparable to those in galactic planetaries; (5) the compositions of the small H II regions in the SMC are nearly identical to those of previously studied large H II regions in the same Cloud; and (6) the He/H ratio of the interstellar gas in the SMC is about 25% less than that in the Galaxy. It is concluded that most of the N abundance in both Clouds arose from nucleosynthesis sources other than planetary nebulae.

Description: The baryon symmetric big-bang cosmologies offer an explanation of the present photon-baryon ratio in the universe, the best present explanation of the diffuse gamma-ray background spectrum in the 1 to 200 MeV range, and a mechanism for galaxy formation. In the context of an open universe model, the value of omega which best fits the present gamma-ray data is omega equals approx. 0.1 which does not conflict with upper limits on Comptonization distortion of the 3K background radiation. In regard to He production, evidence is discussed that nucleosynthesis of He may have taken place after the galaxies were formed.