Although solar activity is seen to exhibit a very inhomogeneous and convoluted set of structures, and we have good reason to expect that stellar activity is also very structured, it is naturally quite difficult to resolve such structures on other stars. One of the best opportunities for doing so is afforded by an active eclipsing system of short period, in which both the eclipses and stellar rotation serve to cover and uncover features on reasonable time scales. AR Lac is the nearest and most suitable such system, it is an RSCVn system comprised of an active G dwarf and active K subgiant with a two day period. We report here on simultaneous X-ray and UV coverage of an eclipse in this system obtained with the Einstein and IUE observations. More details are given in reports in IAU Coll. No. 71 and IAU Symp. No. 102.

We have discovered hard and soft X-ray emission from W Puppis, the last of the four classical AM Her stars to be detected in X-rays. The orbital light curves in both soft and hard X-rays are in excellent agreement with the mean optical light curve, indicating that essentially all of the accretion luminosity originates from a very small region at the white dwarf’s magnetic pole. An X-ray dip occurs once per binary period, when the magnetic pole lies closest to our line of sight, and is probably due to absorption. The X-ray data and optical spectroscopy constrain fairly well the geometry of the system, dictating an inclina-tion angle i < 70º and a mass for the white dwarf in excess of 1.1 Mʘ. X-ray and UV observations constrain the temperature of the soft X-ray component to lie in the range 20–45 eV, while the hard X-ray component has a temperature in excess of 6 keV. The observed flux of soft X-rays is much larger than that of hard X-rays. However, when the energy band-passes of the observations are taken into account, the ratio of the soft and hard X-ray luminosities Ls/Lh = 0.5-50. The ratio is unity for Tbb = 30 eV and Tbr = 50 keV; ifc is smaller if Tbb and/or Tbr are larger and is larger in the opposite case. These results, taken together with those for AM Her using the Einstein OGS, suggest that the famous “soft X-ray problem” in the AM Her stars may have gone away.

The progress in the understanding of the high velocity component of the interstellar medium is reviewed. Emphasis is on the velocities seen outside the plane of the Milky Way, of gas in the galactic halo.

The extensive measurements of interstellar absorption lines in the late 1930’s demonstrated that the “stationary” lines in stellar spectra were extremely narrow and in many cases showed fine structure at the 10 km/s level. The quantisation of these data had to wait until about 1950. Adams (1949) presented data on Ca II lines toward some 300 stars and his compilation, supplemented with Na I data, led Routly and Spitzer (1952) to investigate the systematics of the Ca and Na abundances. Contrary to the non-solar abundance ratio of the majority of the interstellar clouds, the “high velocity” absorptions, defined by Routly and Spitzer as differing in velocity by more than 20 km/s from the local standard of rest, showed a near solar Ca/Na abundance ratio.

Giant (20 – 260 pc) and supergiant (600 – 1400 pc) filamentary ionized shells are found in several galaxies. Some giant shells are collisionally ionized supernova remnants but many surround ≃ 5 – 50 OB stars and, if approximately spherical, could be formed by the combined effects of successive, 1050 erg, supernova explosions, pressure of the Lyman photons and stellar winds. Other mechanisms are required for their supergiant counterparts for perhaps they are toroidal rings rather than radially expanding spherical shells.

Four regions of the galaxy, the Cygnus Superbubble, the ƞ Carina complex, the Orion/Eridanus complex, and the Gum Nebula, are discussed as examples of collective effects in the interstellar medium. All four regions share certain features, indicating a common structure. We discuss the selection effects which determine the observable x-ray properties of the superbubbles and demonstrate that only a very few more in our galaxy can be detected in x-rays. X-ray observation of extragalactic superbubbles is shown to be possible but requires the capabilities of a large, high quality, AXAF class observatory.

Maps in three energy bands from the recently-completed Wisconsin survey of the soft X-ray sky are presented. The lowest energy data require emission, almost certainly from hot interstellar gas, from regions within 100 pc of the sun. The data do not require diffuse emission from beyond the neutral galactic gas but are compatible with such emission under certain assumptions.

Molecular gas with velocity dispersions exceeding 100 km s-1 toward dense, interstellar clouds was discovered by microwave observers about a decade ago. It has now been established that this high velocity gas is a result of violent mass outflows (winds) originating from T-Tau stars, compact infrared sources or ultra-compact HII regions at the cores of the clouds. The mass outflow phenomena occur in regions of star formation covering five orders of magnitude in luminosity, and are of long duration . The observations suggest that violent mass loss is a new, important phase in the pre-main sequence evolution of newly-formed stars more massive than a few solar masses. The impact of the flows on the energy balance and dynamical stability of molecular clouds may be substantial. This review is mainly a summary of the observational facts, and gives a description of the physical conditions in an outflow zone. The impact of the flows on molecular clouds is discussed. Recent reviews of the outflow phenomena can also be found in (1, 2, 3, ).

As a cometary nucleus, regarded as an admixture of ices and dust (Whipple, 1950), approaches the sun, the ices sublimate and the resulting gases freely expand dragging along some of the dust.

For a typical medium bright comet (e.g., P/Halley) at 1 AU, the cometary atmosphere is collision dominated within a radius Rc, within which the collision mean free path is equal to the radial distance itself. Within this radius, the cometary atmosphere may be considered as a continuum, and described by hydrodynamic equations. Admittedly, this definition of the regime of hydrodynamic flow is rather crude, and what one has is a gradual transition from pure hydrodynamic flow when r << Rc to slip and transitional flow when r ≈ Rc, to free molecular flow when r > Rc. Depending on whether one considers neutral-neutral collisions or neutral-ion collisions Rc ~ 5 × 103 – 104 km for a medium bright comet at a heliocentric distance of 1 AU.

During the past few years the field of comet spectroscopy has greatly expanded with observations of comets having nuclear magnitudes in the range of 10-19th magnitude. Although the total integrated magnitudes of several of the comets were brighter than 10th magnitude, the surface brightness of the coma of a comet is low and, with few exceptions, the night sky line at 5577A is brighter than any cometary emission line. The observational programs on which I will concentrate had their start under the P/Tempel 2 and P/Encke observing programs set up by R. Newburn at JPL.

Fortunately, the groups listed in Table 1 are regularly scheduled on large telescopes to observe comets. The regularly scheduled telescope time has enabled these groups to study systematically the activity of the available comets brighter than 20th magnitude. Observations have been made with respect to heliocentric distance and distance from the nucleus. The goal of the systematic study of comets is to acquire a uniform data set on comets. The great variety of comet spectra in the past did not provide a useful data base for statistical studies. These older observations ranged from high resolution spectra of brighter comets, to sporadic medium and low resolution spectra and filter photometry of the 10th magnitude comets, to nonexistent spectra of fainter comets.

I select three topics of current interest (and some current confusion) to complement the previous paper of Asoka Mendis. The topics are relevant particularly to the studies developing models and predictions of the comet Halley environment for the forthcoming missions to that comet. The idea that electromagnetic forces are important for the dynamics of submicron dust grains and so should produce fans and structures in the coma indicates that correlations with solar wind conditions should be sought.

Here I shall interpret ‘small-scale’ to mean a few kpc or less. Such jets occur over a wide range of emitted energies (e.g. 1039erg s–1 in M87, 1046 in 3C273) and we do not know if they are manifestations of the same basic phenomenon or whether Nature is fooling us in some way despite the morpholigicaI similarities. For the moment, it seems sensible to assume an underlying unity and to use the observations to explore the jet phenomenon in different guises.

With the highest resolutions obtainable with VLBI, our goal is to elucidate the nature and properties of the central energy source. To this end, we can ask various questions which our observations are expected to bear upon both now and in the future. How do jets form and propagate from the energy source? Are the jets ccnfined/colIimated or ballistic? Why are some jets much stronger than others - is this intrinsic or an evolutionary or relativistic effect - or all three? Why are only some sources superlumina Is? Why are most jets ore-sided? Does the relativistic velocity implied by super I urninaI motion on the pc-scale continue into the kpc-scale jets?

The purpose of this review is to outline the systematic properties of radio jets on kpc scales, as derived from the basic observations of surface brightness and linear polarization and to emphasize the uncertainties in the determination of their physical parameters. These results come primarily from observations of about 100 jets with the VLA: a fuller account is given by Bridle (1982) and the proceedings of IAU Symposium 97 contain many illustrations and references, which must be omitted here.

I take a “jet” to be a feature in the radio brightness distribution which is at least four times as long as it is wide, which can be clearly separated (spatially or by brightness contrast) from the rest of the source and points away from a radio core. Wilson (1982) has considered jets in spiral galaxies and I shall discuss only the more luminous jets found in elliptical radio galaxies and quasars.

What have I learned about jets since the Albuquerque meeting (IAL) Symposium No.97) last summer?

There is where most of the gravitational energy is released, the funnels on the rotation axis of the accretion torus provide the right sort of geometry, and radiation is abundant. But the experts (Sikora & Wilson 1981 and references therein) never can make radiation-driven jets with Lorentz factor γ >> 1. Why? It is because, when an electron moves up through the funnel at a substantial fraction of the speed of light c, it sees as much radiation striking it trom the front as from behind; acceleration then stops. Large γ are attainable only if the source of radiation subtends an angle ≲ 1/γ behind the source.

The radio source 3C293 has a bright, steep spectrum (α ≃ 0.7; Sν ∝ ν-α ) radio core with kiloparsec-sized structure (Bridle, Fomalont & Cornwell 1981, (BFC)). The core is misaligned by ~35° with respect to the extended radio lobes and both the core and lobes have a Z-shaped morphology. To explain this misalignment and morpholoqy. BFC propose a model in which beams ‘refract’ (buoyantly deflect) in a static hot gaseous halo. Alternatively, Wilson & Ulvestad (1982) have proposed that the source structure may be caused by ram pressure deflection of beams propagating through a rotating gaseous disk. Our optical imaging and spectroscopic observations reported here support the latter model.