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The Sloan Digital Sky Survey has confirmed the existence of populations of broad absorption line (BAL) quasars with various unusual properties. We present and discuss 23 such objects and consider the implications of their wide range of properties for models of BAL outflows and quasars in general. We have discovered one BAL quasar with a record number of absorption lines. Two other similarly complex objects with many narrow troughs show broad Mg II absorption extending longward of their systemic host galaxy redshifts. This can be explained as absorption of an extended continuum source by the rotation-dominated base of a disk wind. Five other objects have absorption that removes an unprecedented ∼90% of all flux shortward of Mg II. The absorption in one of them has varied across the ultraviolet with an amplitude and rate of change as great as ever seen. This same object may also show broad Hβ absorption. Numerous reddened BAL quasars have been found, including at least one reddened mini-BAL quasar with very strong Fe II emission. The five reddest objects have continuum reddenings of E(B-V) ≃ 0.5, and in two of them we find strong evidence that the reddening curve is even steeper than that of the SMC. We have found at least one object with absorption from Fe III but not Fe II. This may be due to a high column density of moderately high ionization gas, but the Fe III level populations must also be affected by some sort of resonance. Finally, we have found two luminous, probably reddened high-redshift objects that may be BAL quasars whose troughs partially cover different regions of the continuum source as a function of velocity.

We present images from VLBI Space Observatory Programme (VSOP) observations of 14 compact extragalactic southern hemisphere radio sources, including a description of the observations, the data reduction techniques, and the parameters of the resulting images and model fits. These images provide the highest resolution information to date for many of these objects. Comparisons are made between VSOP and previous ground-based VLBI results, including images from data extracted from the geodetic VLBI archive at the United States Naval Observatory. From the VSOP data, we find that the two radio galaxies observed have lower peak brightness temperatures than the 12 quasars. Also, these data show (1) no evidence for obvious differences between the brightness temperature distributions of gamma-ray-loud and gamma-ray-quiet radio-loud active galactic nuclei and (2) no evidence for obvious correlations between brightness temperature and spectral index, radio polarization, flux density, or month timescale modulation index. These results are consistent with previous work by Lister, Tingay, & Preston, who found that the only observable significantly correlated with VSOP-derived brightness temperature is intraday variability, which is strongly correlated with many relativistic beaming indicators. For one source, PKS 1127-145, we undertake a detailed investigation of the milliarcsecond-scale component positions as a function of time, taking data from the literature and the current work, to estimate proper motions. As a result, we suggest that two components previously reported as stationary, C1 and C2, have apparent transverse speeds of (9.1 ± 3.8) and (5.3 ± 2.3) h^-1c, respectively. We also make the first investigation of the apparent motion in the nearest GHz-peaked spectrum radio galaxy, PKS 1718-649, finding an upper limit on the apparent separation speed of 0.08c. Comparison of geodetic VLBI and VSOP data show no significant detection of component motion in PKS 0208-512, (2.4 ± 3.1) h^-1c, and only a tentative detection in PKS 0537-441, (2.8 ± 2.2) h^-1c. A significant detection of component motion is found in PKS 1610-771, solely from the geodetic VLBI data, (9.4 ± 3.5) h^-1c.

We have carried out two-dimensional axisymmetric numerical simulations of light, supersonic jets propagating into constant density atmospheres over a broad range of parameter space. We examine the evolution of the global properties of the sources as a function of source size, for a range of Mach numbers, density contrast, and jet power. We also compare our results with the expectations of current analytical self-similar models. The derived global parameters are not sensitive to small changes in input parameters. The material content of the relativistic jet does affect its propagation and the overall structure and energetics (see Paper II) of the source. The jet in case 1 (pressure dominated by relativistic electrons) propagates faster, the cocoon has a smaller aspect ratio and maintains higher pressure, and the bow shock expands at higher lateral velocity than case 2 jets (pressure dominated by relativistic electrons and protons). However, these differences generally become less important as the jet Lorentz factor increases. We have confirmed the suggestion of Wilson & Falle that the location of the first shock in the jet depends linearly on the jet radius and Mach number. We show that the result is largely independent of density contrast and that over a wide range in Mach number the relation can be used to make a crude estimate of the jet Mach number. We find that the pressure in the cocoon and the bow-shocked region varies both along and across the source axis. The degree to which the cocoon comes into pressure balance with the ambient medium depends on the jet Mach number, with intermediate-M jets having cocoons that are in pressure balance with the ambient medium over much of the length of the source, while high- or low-M jets have cocoons that are overpressured or underpressured, respectively. The bow shock lateral expansion decelerates quickly behind the jet head, but the velocity remains at least somewhat supersonic. On the other hand, the cocoon lateral expansion velocity quickly drops behind the jet head and becomes subsonic with respect to the post-bow shock gas. The strong time dependence of the cocoon and bow shock pressure and lateral expansion speed is expected to influence the properties of the emission-line nebula associated with the radio source. The slow expansion of the cocoon and bow shock over most of their length will limit the maximum velocity to which ambient clouds can be accelerated. The behavior of the time evolution of the source size (z_h ∝ t^m) is in general more complex than the predictions of the self-similar models. The time dependence of the source size exhibits up to three phases whose relative length depends on the jet Mach number. The radius of the jet head is a weak function of density ratio and a stronger function of Mach number, with higher Mach number jets tending to have smaller jet heads. The advance speed of the jet head depends on the head radius in agreement with the expectations of ram pressure balance. As a result of the dependence of the growth rate of the jet head with Mach number, the advance speed of the head decreases slowly for low Mach number and remains roughly constant for high Mach number. The volume of the region enclosed by the bow shock increases with time at a rate that is close, but not identical to, the predictions of the constant velocity self-similar models. The bow shock expansion rate seems to increase with time for small Mach number but is relatively stable at high Mach number. The cocoon volume generally increases more slowly than the volume of the region enclosed by the bow shock. In low Mach number jets, the dissipation of energy through internal shocks is able to disrupt the jets and turn off the supply of energy to the cocoon. At this stage, the bow shock propagates as a sound wave and the morphology of the inferred radio-emitting material becomes faint and diffuse. Thus, we suggest that low Mach number jets may be able to transition between FR II- and FR I-type radio morphologies.

We present two-dimensional numerical hydrodynamical simulations of light, supersonic jets propagating in atmospheres that decline in density with increasing distance in several ways: isothermal King law atmospheres with the power-law exponent β = 1 and β = 0.75 and in an isobaric King law atmosphere with power-law exponent β = 1. We explore the same very broad range of parameter space in Mach number M and density contrast η as in Paper I in this series. We compare our results with those for the constant density and pressure atmosphere simulations and with the predictions of the self-similar models (Paper I). We also discuss the global energetics of the sources in these different environments. Our comparison of the constant and declining density results shows the following. The overall morphology of the jet, cocoon, and bow shock is similar. However, there are some differences that start to appear when the jet has propagated about twice the core radius. In a declining density atmosphere, (1) there is less structure in the cocoon as a result of turbulence and (2) at a given source size, the cocoon seems to be underexpanded relative to a constant density atmosphere for a broad range of Mach numbers ∼5-30 (outside this range the cocoon may actually be wider). In an isobaric atmosphere with density gradient the general appearance of the source is similar to that of an isothermal atmosphere although the source size increases much faster. The overall distribution of pressure in the shocked ambient gas (SAG) region and cocoon and its decline with distance from the jet head are similar in both types of atmospheres. However, in jets in declining density atmospheres, for case 1 (pressure dominated by relativistic electrons), the cocoon and SAG region remain much more overpressured with respect to the ambient medium than in jets in constant density atmospheres. The lateral expansion speeds of the bow shock and cocoon are similar in the constant and declining density atmospheres. In a constant density atmosphere the jet head velocity decelerates slowly with time, while in the declining density atmosphere the jet head accelerates with time with a rate given by exponent z_h ∝ t^m with 1 < m < 1.5. However, at high Mach number and/or high jet density, the acceleration decreases with time and the head velocity approaches a nearly constant velocity, consistent with the predictions of the self-similar models. In an isothermal atmosphere with a density gradient, the volume of the region enclosed by the bow shock tends to increase with source size in agreement with the predictions of the type III models, i.e., V ∝ t³. The estimated volume of the cocoon tends to vary with time possibly as a result of the influence of Kelvin-Helmholtz instabilities on the contact discontinuity, but in general V ∝ t² - t³. We find that for all environments the behavior of the source volume as a function of time is closer to the self-similar predictions than the behavior of the source size as a function of time. This suggests that the shape of the bow shock adjusts to keep the time dependence of the source volume roughly self-similar. We examine the dependence of the pressure on the source volume as a function of the source age for the sources in different environments. In the constant density atmosphere, the pressure evolution of cylindrical slices of the SAG region departs from that expected for adiabatic expansion both near the head and near the jet inlet. Near the jet head the departure is due to energy input to the SAG region from the jet head (i.e., there is an effective "source term"), and near the jet inlet the departure is due to the source coming into pressure balance with the ambient medium. The average global pressures in the SAG region and cocoon vary more slowly with volume than predicted by the self-similar models. These results for the evolution of the pressure are similar for the constant density or isothermal King atmosphere, although for the King atmosphere there tends to be better agreement with the predictions of the self-similar models. In general, the energetics of the source are similar whether the source is propagating in an isobaric or isothermal atmosphere, with some caveats. For both the SAG region and the cocoon, the pressure declines more slowly with source size in the isobaric atmosphere than in the isothermal atmosphere with a density gradient. In addition, the sources in an isobaric atmosphere show somewhat larger departure from the predictions of the self-similar models than do the sources in either a uniform atmosphere or an isothermal atmosphere with declining density gradient. The behavior of the source and the energetics are similar in the β = 1 and β = 0.75 King model atmospheres. However, we do note that some of the global parameters are more in agreement with the self-similar models for β = 1. The self-similar models assume that the source is highly overpressured with respect to the ambient medium and thus do not explicitly consider a functional form for the ambient pressure. However, we have found that the agreement of the simulations with the predictions of the self-similar model does depend on the degree to which the source is overpressured and thus on the assumed ambient pressure profile for the source. The agreement between the self-similar models and the simulations tends to improve as the atmosphere declines more steeply, i.e., from an atmosphere with β = 0 to β = 0.75 and β = 1.

We present X-ray light curves (1.5-12 keV) for 15 gamma-ray bursts (GRBs) detected by the All-Sky Monitor (ASM) on the Rossi X-Ray Timing Explorer. We compare these soft X-ray light curves with count rate histories obtained by the high-energy (>12 keV) experiments BATSE, Konus-Wind, the BeppoSAX Gamma-Ray Burst Monitor, and the burst monitor on Ulysses. We discuss these light curves within the context of a simple relativistic fireball and synchrotron shock paradigm, and we address the possibility of having observed the transition between a GRB and its afterglow. The light curves show diverse morphologies, with striking differences between energy bands. In several bursts, intervals of significant emission are evident in the ASM energy range with little or no corresponding emission apparent in the high-energy light curves. For example, the final peak of GRB 970815 as recorded by the ASM is detected only in the softest BATSE energy bands. We also study the duration of bursts as a function of energy. Simple, singly peaked bursts seem consistent with the E^-0.5 power law expected from an origin in synchrotron radiation, but durations of bursts that exhibit complex temporal structure are not consistent with this prediction. Bursts such as GRB 970828 that show many short spikes of emission at high energies last significantly longer at low energies than the synchrotron cooling law would predict.

We present optical long-slit spectroscopic observations of 21 low-luminosity, extreme late-type spiral galaxies. Our sample is comprised of Sc-Sm Local Supercluster spirals with moderate-to-low optical surface brightnesses and with luminosities at the low end for spiral disk galaxies (M_V ≥ -18.8). For each galaxy we have measured high spatial resolution position-velocity (P-V) curves using the Hα emission line, and for 15 of the galaxies we also derive major-axis rotation curves. In ∼50% of our sample, the P-V curves show significant asymmetries in shape, extent, and/or amplitude on the approaching and receding sides of the disk. A number of the P-V curves are still rising to the last measured point or reach a clear turnover on only one side. In most instances we find good agreement between the kinematic centers of extreme late-type spirals as defined by the global H I emission profile and by their optical continuum, although in a few cases we see evidence of possible real offsets. In spite of their shallow central gravitational potentials, at least six of the galaxies in our sample possess semi-stellar nuclei that appear to be compact nuclear star clusters; in five of these cases we see kinematic signatures in the P-V curves at the location of the nucleus. Finally, we find that like giant spirals, our sample galaxies have higher specific angular momenta than predicted by current cold dark matter models.

An atlas of the 900-1200 Å region in the spectra of 47 OB stars in the Large and Small Magellanic Clouds, observed at high resolution by the Far Ultraviolet Spectroscopic Explorer (FUSE), is presented and discussed. The systematic trends in the numerous stellar-wind features in this region, some from species (and ionizations) not represented at longer wavelengths, are charted as a function of the optical spectral types. The FUSE sample is by far the most powerful to date for that purpose. A special effort has been made to verify the spectral types of all stars included in the atlas, in a number of cases with new optical observations that are also illustrated, to avoid uncertainties from that source in the stellar-wind trends. A new O2 star has been found in the process. Most of these stars have been previously observed at longer ultraviolet wavelengths by the Hubble Space Telescope and in the optical from the ground with high-resolution, digital instruments; thus very comprehensive physical modeling of these OB atmospheres and winds now becomes possible. This atlas will serve as a guide to the FUSE Magellanic Cloud OB database for that purpose. The Magellanic Cloud sample provides a very important complement to the FUSE database of Galactic OB counterparts (Pellerin et al. 2002), both because the lower extinction and interstellar H₂ absorption toward the Cloud stars allow a much clearer view of the stellar spectra below 1100 Å, and because of the metallicity differences among the three galaxies. In particular, most wind features in the SMC spectra are seen to be significantly weaker than those in the LMC at the same spectral types.

We have obtained linear polarization measurements of stars along the western side of the IRAS Vela Shell toward HD 62542. From 16 CCD fields distributed along the ionization front (I-front) we have built a catalog of 856 objects with polarization signal-to-noise ratio larger than 10. We detect very significant levels of polarization and hence an appreciable magnetic field throughout the region. Composite polarization maps around the I-front are shown. In some regions the polarization vectors are parallel to the I-front, but a perpendicular trend is also evident along parts of the front. In addition, the polarization pattern seems to be affected by gas streaming inside the cloud.

We consider a white dwarf model with differential rotation and magnetic field, assuming that (1) the symmetry axis of the toroidal magnetic field, the magnetic axis of the poloidal magnetic field, and the principal axis I₃ coincide permanently with each other (this common axis is called "magnetic symmetry axis") and (2) the model declines slightly from axisymmetry, i.e., its magnetic symmetry axis is inclined at a small angle χ relative to its spin axis (this angle is called "obliquity angle" or "turnover angle"). The latter assumption turns on the "magnetic dipole radiation mechanism," which is fed by the rotational kinetic energy and causes emission of weak electromagnetic power since χ is assumed small; thus, the model suffers from secular angular momentum loss. This fact leads to a gradual decrease of the moment of inertia I₃₃ along the principal axis I₃ and, in turn, to a gradual increase of the moment of inertia I₁₁ along the principal axis I₁, since the toroidal field (tending to derive prolate configurations and thus to increase I₁₁) becomes gradually more competitive against the combined action of both rotation and poloidal field (tending to derive oblate configurations and thus to increase I₃₃). So, a "dynamical asymmetry" is established in the sense that, after a particular time, I₁₁ becomes greater than I₃₃. However, a dynamically asymmetric model tends to turn over spontaneously and thus to become "oblique rotator" with its angular momentum remaining invariant. As a consequence, the turnover angle increases spontaneously up to 90° on a "turnover timescale," t_TOV, since the rotational kinetic energy of the model decreases from a higher level when χ ≃ 0° to a lower level when χ ≃ 90°; at this level the model becomes "perpendicular rotator" and reaches the state of least energy consistent with its prescribed angular momentum and magnetic field. The excess rotational kinetic energy due to differential rotation is totally dissipated due to the action of turbulent viscosity in the convective regions of the model. Thus, in the "turnover scenario" the casting of the roles has mainly to do with rotation, poloidal field, toroidal field, and turbulent viscosity. In the present paper, we study in detail this scenario.

We report radial velocities for 844 FGKM-type main-sequence and subgiant stars and 45 K giants, most of which had either low-precision velocity measurements or none at all. These velocities differ from the standard stars of Udry et al. by 0.035 km s^-1 (rms) for the 26 FGK standard stars in common. The zero point of our velocities differs from that of Udry et al.: 〈V_Present - V_Udry〉 = +0.053 km s^-1. Thus, these new velocities agree with the best known standard stars both in precision and zero point, to well within 0.1 km s^-1.

     Nonetheless, both these velocities and the standards suffer from three sources of systematic error, namely, convective blueshift, gravitational redshift, and spectral type mismatch of the reference spectrum. These systematic errors are here forced to be zero for G2 V stars by using the Sun as reference, with Vesta and day sky as proxies. But for spectral types departing from solar, the systematic errors reach 0.3 km s^-1 in the F and K stars and 0.4 km s^-1 in M dwarfs.

     Multiple spectra were obtained for all 889 stars during 4 years, and 782 of them exhibit velocity scatter less than 0.1 km s^-1. These stars may serve as radial velocity standards if they remain constant in velocity. We found 11 new spectroscopic binaries and report orbital parameters for them.

Total cross sections for the production of gamma-ray lines from nuclear deexcitation as a function of the projectile energy are evaluated and presented. Included are proton and α reactions with He, C, N, O, Ne, Mg, Al, Si, S, Ca, and Fe. Such functions are essential for interpretation of gamma-ray line observations of astrophysical sites which contain large fluxes of energetic particles such as solar flares, the Earth's atmosphere, planetary atmospheres and surfaces, the interstellar medium, and galactic nebulae.

Wavelengths and transition rates are given for E1 transitions between singlet ¹S, ¹P, ¹D, and ¹F states, between triplet ³S, ³P, and ³D states, and between triplet ³P₁ and singlet ¹S₀ states in ions of astrophysical interest: helium-like carbon, nitrogen, oxygen, neon, silicon, and argon. All possible E1 transitions between states with J ≤ 3 and n ≤ 6 are considered. Energy levels and wave functions used in calculations of the transition rates are obtained from relativistic configuration-interaction calculations that include both Coulomb and Breit interactions.