We have mapped the CO J = 2 → 1 and J = 1 → 0 emission of the circumstellar envelope of Mira. Emission in both transitions extends to a distance of ~ 4 x 1016cm from the star. In the inner 2 x 1016cm the lines show the presence of three velocity components. The main component has the intermediate velocity and extends over the whole envelope. From this component we have estimated a mass loss rate of 3 x 107M⊙yr-1 and a total molecular mass of 1.2 x 10-3M⊙. We have shown that, from our data, the only reliable explanation for the lowest and highest velocity components is that they are due to an outflow located within the envelope.

The molecular gas lying in the interior of the Orion superbubble consists of sheets, filaments and bubbles in which the dense active star forming cloud cores are embedded. Many regions have a wind-swept or cometary appearance suggesting strong interaction with the Orion OB association. External heating dominates the cloud energy budget, resulting in cold (˜10K) cloud cores surrounded by hot (>20K) envelopes. Non-ionizing UV radiation emitted by late B and A stars may be the source of the kinetic energy needed to form some of the large scale cavities and contributes to the supersonic line widths seen in many clouds.

The Orion Nebula is the bench mark galactic HII region in which major advances have been made in our understanding of the ionization structure, energy balance, plasma dynamics, star formation and interactions of ionized plasmas with dense molecular clouds. Most of these studies require accurate comparison with radio continuum images.

Observations of H2 lines in the IR have been mostly restricted to those with upper levels of low energy, which can be excited either collisionally in shocks or radiatively by UV starlight. In order to discriminate between the two excitation mechanisms we have measured in 11 μm range lines of the v=2-0 band arising from high rotational levels J≤;13. Their intensities, together with those of the IR lines, allow an estimate of the line of sight effective extinction and a determination of the rotational temperature measuring their joint degree of excitation. The latter parameter provides information about the energy state of the molecules at their formation and ejection from grain surfaces and thus constrains the hypothetical models for H2 molecule formation.

We have made aperture synthesis maps of Orion-KL in NH3(1,1),(2,2) and CS(J=l-0) emissions using the Nobeyama Millimeter Array. Both NH3 and CS maps show new detailed structures that have not been recognized before. Two NH3 filaments in the size of ~0.45 pc x0.04 pc are found extending to the northwest direction of Orion-KL. These filaments are associated with the HH objects and the finger-like H2 emissions; they are probably formed through the interaction with high velocity, highly channeled winds from the KL region. The CS maps show, on the other hand, shell structures around IRc2 as well as the well-known rotating disk. These shells coincide with the two lobes of the shock-excited H2 emission, being interpreted as the shock-compressed shells of ambient molecular gas interacting with the outflow from IRc2.

We review the characteristics and discuss the nature of a dense group of compact radio sources found projected toward the Trapezium cluster of the Orion nebula. There are twenty-six radio sources, with flux densities greater than 2 mJy, clustered within a region of 35” radius around θ1C Orionis, the most luminous star of the Trapezium. The density of radio objects, of 1.4×104 pc-3, is extraordinarily high, about a thousand times greater than the density of stars in typical galactic clusters.

We have examined the radial and turbulent velocities of the Orion Nebula at the seeing limit, observing the [OIII]λ5007 line and the [OII]λ3727 doublet with the coudé feed system of the Kitt Peak National Observatory, at very high spatial and spectral resolution.

High-resolution CO J → 1 → 2 observations of the Orion B molecular outflow show that the outflow is unipolar, and that there is evidence of acceleration of molecular gas at up to 0.5pc from the driving star. The highest-velocity material, as well as being furthest from the source, seems to lie close to the central axis of the flow, and is presumably being accelerated by entrainment in the flow or jet emanating from the star. We have also mapped the HCO+J = 3 → 2 emission at 19-arcsec resolution. We derive an excitation temperature of around 25 K in the cloud core, and a core mass of about 75 M⊙, this estimate is in accord with a model in which the core has a kinetic temperature of 30-50 K, with no molecular depletion on to grains. This is in contrast to the recent suggestion that the core contains cold isothermal protostars.

The term AGN or Active Galactic Nucleus, although with rather ill-defined boundaries, signifies extragalactic systems with non-stellar nuclear activity. Non-stellar activity indicators are: high luminosity, presence of broad emission lines, variability, nuclear UV excess, x-ray emission, radio emission, variable polarization, jets, etc.

We present the first results of an extensive study of the stellar content and the ionized gas structure for a sample of BCGs. Deep broad (BVRI Johnson) and narrow (Hα) CCD images have been obtained for about 25 galaxies. For a subset of objects, selected on the basis of their apparent structure, long-slit spectroscopy has also been obtained in order to investigate the interaction between the underlying stellar population and the ionized gas.

Hα + [NII] and red continuum CCD images as well as high resolution aperture synthesis CO maps were obtained in order to study the optical jet of the barred spiral galaxy NGC 4258. The CO observations show two clouds near the center of the galaxy; these clouds outline a channel and the Hα jet follows this channel. The observations are consistent with the jet being in or making a small angle with the galaxy plane. It is concluded that the interstellar medium may play an important role in making jets detectable optically and in shaping their forms.

Close links appear to exist between the optical narrow line region (NLR) in Seyfert galaxies and the nuclear non-thermal radio emission. Both occur on similar scales (~ 102 —103 pc), and correlations have been found between the 21 cm radio power and both the [OIII] λ5007Å luminosity and linewidth (de Bruyn & Wilson 1978; Whittle 1985). Approximate balance appears to exist between the thermal pressure of the NLR gas and the relativistic and magnetic pressure of the radio components (de Bruyn & Wilson 1978; Unger et al. 1985; Pedlar, Dyson & Unger 1985). There are also several examples of a direct spatial association between the optical and radio components, for example Mkn 78 (Pedlar et al. 1988).

The basic equations for treating a multicomponent medium: stars, gas clouds and an ambient gas are discussed elsewhere (Yorke, et al., this meeting). Here we apply the 2-D multicomponent code to the problem of explosions in a clumpy medium (cool “clouds” embedded in a warm T ~ 104K or hot T ~ 106K gas). The evolution of supernova remnants and supershells in media of varying degrees of dumpiness are compared and contrasted to the results of earlier calculations.

Spatial inhomogeneities for a sample of Giant Extragalactic HII Regions (GEHR) have been analyzed. The results indicate that, whitin the observational errors, the O/H and He/H abundance ratios are constant for a given GEHR. The Ne/O ratio on the other hand shows a trend with the evolution of the ionizing stellar clusters.

Measurements of Hα-emission in fields known to emit 21cm radiation at intermediate and high velocities are presented. The observations are partial results of a survey being carried out at the Calar Alto Observatory with a dedicated Fabry-Perot spectrometer of 15cm aperture, providing velocity and angular resolutions of 11km s-1 and 0.5 deg2. The limited material available indicates that the Hα-emission, when detected at a radial velocity nearly the same as that measured in 21cm, appears more extended in the sky than the HI-radiation.

High-resolution (λ/δλ ⋍ 6 x 104) spectra of R136 (the central object of 30 Dor) and of 2 LMC supergiants obtained at ESO with the 1.4-m telescope have been analysed in order to study the high-velocity absorption components at VLSR ⋍ +60 km s-1 and ⋍ +130 km s-1 first seen in satellite ultraviolet spectra in the general direction of the LMC. Our data have been integrated with previous literature results of SN1987a and of other 4 LMC supergiants obtained from spectra of similar spectral resolution.

At least 6 (possibly 9) interstellar components are found in the range +40 km s-1 ≤ VISR ≤ + 150 km s-1, suggesting that the IUE features at ⋍ +60 km s-1 and ⋍ +130 km s-1 are in fact splitted in several components when observed at higher resolution. Two components originally discovered toward SN1987a (VLSR ⋍ +42 km s-1 and +107 km s-1), are detected for the first time in the Call interstellar spectrum of R136. A component at VLSR ⋍ +49 km s-1 shows significant variations both in Call and in Nal along the different lines of sight. A relatively broad component at VLSR ⋍ +58 km s-1 is present in Call toward R136, but is generally undetected in Nal in the other lines of sight. Also the components in the range +100 km s-1 ≤ VLSR ≤ +150 km s-1 are detected in Call, but not in Nal. Two weak absorptions, detected at +125 km s-1 and +141 km s-1 toward R136, may be associated with the ⋍ +130 km s-1 component characteristic of the ultraviolet spectra.

The almost perfect velocity coincidence of the +107 km s-1, +42 km s-1, +49 km s-1 and +57 km s-1 components along different lines of sight suggests a common origin of the absorbing gas and a location close to our Galaxy. In spite of the low detection limit in our spectra (Wλ ⋍ 5 mÅ), the lack of detection of Nal is compatible with the presence of foreground gas clouds with hydrogen column density N(HI) ≤ 2 x 1019 cm-2, or even greater. The fact that we can detect more easily Call absorptions than the corresponding Nal absorptions indicates a very low value of Call depletion.

This contribution reports results of recent absorption-line studies on La Palma and reviews earlier work done elsewhere. CaII has been found in absorption in five HVCs, mostly against extragalactic background sources. The CaII/HI ratios differ strongly, from 0.002 to 0.1 times solar, suggesting different origins of HVCs. Nondetections of CaII absorption in stellar spectra may provide lower limits to HVC distances, or be caused by small-scale structure or a low CaII/HI ratio in the HVC. Proper interpretation requires comparison of CaII/HI ratios in stellar and extragalactic probes, and use of high-resolution HI maps. No solid direct distance determinations of HVCs are available yet. The distance of Complex C is controversial.

I highlight the evidence for inflow of neutral gas toward the disk of the Galaxy. The Milky Way is accreting 0.2-0.5 M⊙/yr of extragalactic atomic hydrogen at very high velocities. The interaction of infalling clouds with galactic material produces large-scale disturbances in the interstellar medium. Although the injection of energy into the galactic disk by infalling neutral gas is only 1% of the energy from supernovae, the impinging of high velocity neutral gas may be a relatively important source of energy in localized regions of the outer Galaxy.

In the solar neighborhood the downfall rate of HI at intermediate velocities is 2.72 x 10-8 z-1(kpc) M⊙ pc-2 yr-1, which if representative of the whole galactic disk, is at least 10 times more massive than the estimated accretion rate of extragalactic HI at very high velocities. This implies that most of the neutral gas that is infalling in the solar vicinity has originated in the galactic disk. It is concluded that in the Milky Way galaxy there is a moderate inflow of extragalactic neutral gas on top of a more intensive disk-halo circulation.

Since the earliest optical absorption line studies of Munch and Zirin (1961) identified clouds of gas located at large distances from the galactic plane, considerable effort has gone into trying to understand the origin and nature of Milky Way halo gas. Subsequent high resolution optical absorption studies (Albert 1981; Blades et al 1989) have expanded on the early results, demonstrating clearly that (1) halo clouds are more likely to have velocities outside the range allowed by galactic rotation and (2) halo clouds show smaller depletion of refractory elements compared to their disk counterparts (i.e. the Spitzer-Routley effect).

For almost three decades neutral hydrogen moving at velocities unexplicable by galactic rotation has been observed. These so-called high-velocity clouds (HVCs) have been invoked as evidence for infall of neutral gas to the galaxy, as manifestations of a galactic fountain, as energy source for the formation of supershells, etc. No general consensus about their origin has presently been reached. However, it is becoming clear that no single model will suffice to explain all HVCs. A number of clouds may consist of material streaming toward the galactic center, as Mirabel (this conference) has advocated for several years, though their origin still remains unclear. A better understanding is mainly hampered by the fact that the distance remains unknown. An overview of the current status of the distance problem is given by van Woerden elsewhere in this volume.