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Jupiter was imaged in the near-infrared K band on July 22–24, 1994, i.e., shortly after the impact of Comet Shoemaker–Levy 9 (S-L9). Using the IRAC-2b near-infrared camera with Fabry–Perot-interferometer at the MPG/ ESO 2.2-m Telescope of the European Southern Observatory on La Silla in Chile, we obtained full disk images of Jupiter's H + 3 and H 2 emission at 2.093 and 2.121 μm, respectively. In two nights almost one full jovian rotation was covered. Our observations represent the first ground-based narrow-band images of Jupiter's H + 3 and H 2 emission in the K band. No impact-related line emission is detected. In the north polar cap the aurora is clearly visible at 2.093 μm. Some emission at 2.121 μm appears close to the limb. It has different morphology and a different λ III dependence and is fainter than the H + 3 emission. Despite H 2 being a major auroral emitter in the far-UV spectral range it is not clear how its infrared emission relates to auroral phenomena. Shortly after the S-L9 impacts the intensity at 2.093 μm is slightly larger and at 2.121 μm the intensity is three times larger as compared to values provided by Drossart et al. (1989, Nature 340 , 539–541). No emissions are detected in the south polar cap. This agrees with observations in the L band (Miller et al. 1997, Planet. Space Sci. 45 , 1237–1250). The north polar aurora was close to normal and its vibrational temperature close to 1100 K. The Io footprint is not visible.

Multislit spectra of comet P/Halley were ob- tained on April 10, 1986, using a focal reducer with a eld of 0:5 angular diameter. The number and ar- rangement of the slits allowed a reconstruction of the spa- tial distribution of principal neutral and ionic coma con- stituents within a frame of about 4 10 5 41 0 5 km 2 at the comet. Radial proles and two-dimensional maps for the dust continuum, CN, C3 ,C H, CO + , and especially CO + , are presented in absolute intensity and column den- sity units, respectively. Scale lengths and production rates for the radicals were determined within the Haser model. The molecular ions are not only restricted to the plasma tail but are also present in the sunward coma. Instead of forming a peak at the nucleus like the neutral radicals the ion column densities decrease rapidly in the solar direc- tion and form a plateau extending from the nucleus into the antisolar direction. The distribution of CO + shows a stronger decrease in the tailward direction than that of CO + .

An investigation of brightness and color of Comet SL9 was carried out, when the comet had a phase angle less than 1°. The color of the subnuclei was the same within error limits and was close to solar color. The g–r color of the dust increases along the tails of the subnuclei until they merge in the common dust envelope. Similarly in the common dust envelope there seems to be a trend of increased reddening with increased distance from the chain of subnuclei. The brightness peaks at minimum phase angle. Comparison with other observers indicates a phase curve similar to the phase dependence observed in C-type asteroids. The comet did not change its appearance when it passed minimum phase angle. This means that there is no evidence for fresh dust leaving the subnuclei in the form of syndyne tails or ongoing fragmentation producing micrometer-sized particles in the common dust envelope. We conclude that most of the dust present in the image was emitted either at breakup of the parent nucleus or a little later. As in this case the grains must be large as compared to the visual wavelength we can interpret the color as color of a macroscopic body. The fact that it is close to the solar color is consistent with the color of C-type asteroids. The color trend, if real, could then be due to separation of brighter and redder grains from the dark carbonaceous component by radiation pressure.

For observations of solar system objects an imaging polarimeter has been constructed as an auxiliary instrument for a f/15 focal reducer. With this instrument simultaneous measurement of theQ andU Stokes parameters is possible. It contains no moving parts such as a moving λ/2 retarder. The polarizer consists of two Wollaston prisms which are combined to form a single optical element. Their polarization angles differ by 45°. This compound polarizer is placed in the exit pupil of the afocal telescope-collimator system of the focal reducer and splits the exit pupil into halves. In this way four polarized beams with E-vector orientations 0°, 90°, 45°, and 135° emerge from the exit pupil. These are intercepted by the camera lens of the focal reducer system and imaged simultaneously on the CCD detector. With a properly designed field mask at the Cassegrain focus, the four beams are imaged without overlap.

Narrow-band images of Comet Austin 1990 V in the light of the red (0-8-O) H 2 O + emission (6199 A) are presented. The observations were carried out in the period April 30-May 7, 1990, with a focal reducer, Fabry-Perot interferometer, and a CCD camera attached to the 1-m telescope of Hoher List Observatory. The high spectral resolution of the images allowed a precise subtraction of the dust continuum even at the nucleus and a reliable absolute calibration. Thus, for the first time, the spatial distribution of water ions and its temporal behavior is observed in the cometary coma including the area close to the nucleus. Peak column densities between 10 11 and 2 × 10 11 cm -2 were obtained in the observational period. Close to the nucleus the column density distribution is strongly asymmetric. Toward the Sun the column density gradient is steep. In this direction the column density decreases by a factor of ≈4 over a distance of 10 4 km. In the tailward direction the distribution is flat. Frequently the column density maximum is shifted tailward. The contour passing through the nucleus usually extends more than 10 4 km tailward. This is caused by the mass loading of new ions into the tailward cometary plasma flow. We have integrated the column densities perpendicular to the tail direction and calculated the number of water ions per unit tail length. The derived profiles always have their maximum significantly shifted tailward. They are compared with a simple model of H 2 O + production by photoionization of water. Good qualitative agreement is obtained but the mean ion velocities deduced from the model are too high by about a factor of 10. Probably a significant part of the ions in the flanks of the tail is not detected in our observations. The time interval of 22-23 min between successive images allows to study turns of the plasma tail and the formation of ray structures near the cometary nucleus. Even strong changes in morphology have only a minor influence on the ion content per unit tail length. This indicates that tail rays are usually not caused by a modulation of the ion production but that the tail ray phenomenon represents a redirection (rechanneling) of the ion flux out of the coma from old rays (main tail) into new rays. We compare our observations with MHD model calculations of magnetic field tangential discontinuities passing through the cometary coma.

Comet Levy 1990c was observed from 16 to 25 August 1990 at the Observatory Hoher List, Daun, Germany, using a focal reducer and a CCD camera, giving a field of view of ∼25 arcmin. The heliocentric distance of the comet was 1.46 AU; its geocentric distance was 0.47 AU. A Fabry-Perot etalon with a fixed gap of 0.9 mm was used in imaging mode to measure the Doppler shift of the emission lines of the cometary H 2 O + ions at 6159 A, allowing the determination of the line-of-sight velocity of ions in the plasma tail. Two-dimensional fields of the ion Doppler speed in the plasma tail out to 10 6 km from the nucleus have been derived for 4 nights. To compare the velocity fields with the optical appearance of the cometary plasma tail, images taken through a narrow-band interference filter at 6159 A were also obtained, alternating with velocity measurements. The change of the appearance from one image to another has been computed using measured velocities and compared with the observed appearance. Structures were transported to the position where they were actually observed in the following image, showing that they move by real particle motions and are not caused by wave compressions. A mean H 2 O + production rate of 1.5 × 10 27 sec -1 has been derived. The comparison of the derived production rate to the value expected from photoionization rates shows that only a small portion of the ions is concentrated in the inner plasma tail and visible in our groundbased observations, in agreement with results obtained by the ICE spacecraft.

Comet Wilson (1986l) was observed with the MPAE/Hoher List focal reducer-based CCD camera and grism spectrometer having spectral resolution of 4.9 A per pixel, coupled to the ESO 1-m reflector. The data base consists of six long slit spectra, one of them is taken on the nucleus and the others at 1.5 × 105 km in the tail, and images with filters centered at 6600 and 4250 A. A “ray” structured tail longer than 400,000 km is detected in the emissions of CO+. The H2O+/CO+ ratio in the tail is found 1.7±0.2 at 51,000 km and 1.6 ± 0.2 at 150,000 km from the nucleus. The H2O+ flux at a distance of 150,000 km in the tail changed by a factor of 0.4 within 3 hr of our observations. The continuum profile extracted from the spectrum centered on the nucleus shows a distinct sunward asymmetry. From the imaging data we see that most of the dust ejection occurs in a “beam” on the sunward side, producing a “fan” like structure. The particles in the dust fan are redder than the solar color. Most of the particles are redder by ∼8–9% per 1000 A, the highest being ∼10% per 1000 A. The maximum reddened area is situated at a distance of ∼7 × 104 km from the nucleus in the northeast direction. The fan is about 7° wide and originates at about 12° east of the subsolar point. The dust column density derived from the spectrum centered on the nucleus is found to be asymmetric in the sun-antisun direction and deviates from π−1 dependence at ∼12,000 km on the sunward side and at ∼4000 km in the tailward direction. The water production rate derived from the [OI] flux is 2.7 ± 1.8 × 1029 molecules/ sec. The C2 and NH2 production rates are 0.5 ± 0.1 × 1027 and 0.8 ± 0.2 × 1026 molecules/sec.

Two-color polarimetric observations of C-type asteroid 2100 Ra-Shalom were conducted when its phase angle was 59.7°. No other C-type asteroid has so far been observed at such a large phase angle. We relate the new data point to the available data on C-type asteroids and on Phobos and Deimos and compare the phase curve of these objects with the phase curve of dusty comets. The observed polarization of Ra-Shalom is slightly lower than expected from a common curve of the other C-type asteroids and the martian moons. We conclude that this may be caused by the immature regolith on the surface of this small asteroid.

Since many years cometary ions have been observed by the authors and their coworkers in order to study the comet-solar wind interaction. Comets with water production rates ranging from 1028 (46P/Wirtanen) to 6 1030 molecules s-1 (C/1995 01 Hale-Bopp) have been observed. In this paper we briefly introduce the physics of the comet-solar wind interaction. New observations of comet C/1996 Q1 (Tabur) are presented, where for the first time H2O+ and CO+ ions have been recorded exactly simultaneously with a two-channel system. They are compared with previous observations of comets C/1989 X1 (Austin), 46P (Wirtanen) and 109P (Swift-Tuttle). We use a new method of Wegmann et al. (1998), based on the MHD scaling law, to determine the water production of comet Tabur from its H2O+ column density map and obtain a value of 3.3 1028 water molecules s-1. Nonstationary phenomena like tail rays and so-called tail disconnections are very briefly reviewed. A movie of plasma envelopes observed in the light of OH+ in comet 1995 01 (Hale-Bopp) is presented on the attached CD-ROM.

We present new narrow-band images of the Extended Emission-Line Region (EELR) in NGC 3516 in light of [O III] λ 4959, Hα + [N II] λλ 6548, 84, [O I] λ 6364, He is/c λ 6678 and [Fe VII] + [Ca V] λ 6087. The observations were carried with the 2-m reflector of the Bulgarian National Astronomical Observatory and the Focal Reducer of the Max-Plank-Institut for Aeronomy. Our [O III] and Hα + [N II] images confirm previously reported EELR features. In contrast, the image in the high-excitation [Fe VII] + [Ca V] line shows a different structure. We identify a biconical morphology over a kiloparsec scale with peak intensities 5.9 × 10−16 ergs cm−2 s−1 arcsec−2 and 3.5 × 10−16 ergs cm−2 s−1 arcsec−2 to north and south of the nucleus, respectively. The total flux of the [Fe VII] + [Ca V] emission in 5″ and 24″ circular apertures centered at the nucleus is (9.97 ± 0.38) × 10−14 ergs cm−2 s−1 and (1.53 ± 0.15) × 10−13 ergs cm−2 s−1, respectively, which is in good agreement with measurements of Boksenberg & Netzer (1977) through the 5″ aperture. The cone axis lies at PA ∼ −10°. The continuum images (Veilleux et al., 1993, Miyaji et al., 1992) indicate a “bar” aligned along PA ∼ −10°. The velocity extrema regions revealed by Veilleux et al. (1993) are coincident with the peak intensities in our [Fe VII] + [Ca V]. We suppose that our image in [Fe VII] + [Ca V] outlines a Coronal-Line Region (CLR) of NGC 3516, which extends far beyond the classical NLR of the galaxy. Korista & Ferland (1989) have recently shown theoretically that the CLR in Seyferts may be a result of a low-density interstellar medium exposed to and photoionized by a “bare” active nucleus. A typical ISM with Ne ∼ 1–5 cm−3 may produce such an extended CLR as that observed by us.

In this note we discuss observations of two eruptive prominences. We find evidence for twisting motions in the early stages of the eruption. This twisting may be caused by a mechanism recently discussed by Parker (1974) and by Jockers (1976) wherein a magnetic flux tube, part of which has expanded because of reduction of external pressure, readjusts the magnetic torque along its axis.

Preliminary results from the JPA instrument on Giotto indicate that Comet Halley, even on the flanks, has a bow shock which moves backwards and forwards over the spacecraft. To understand the structure properly will require more detailed investigation of the relationships between three particle populations, cometary ions, solar wind ions and electrons.

By combining observations of Comet Kohoutek (1973 f) made in the Southwest US, Alaska and Hawaii, a cometary tail movie has been made. Parts of the movie were shown at the conference and some frames of the movie are reproduced in Fig. 1, In this paper we give some details of the observations and describe what we see on the movie.Observers who contributed to the movie are listed in Table 1 with their institutions, instruments, and site locations. In all but one case, fast Schmidt cameras were used; high-speed optics are needed for this work because the interval between successive pictures should not exceed 15 minutes if plasma tail motions are to be properly visualized. The 36 cm f/2 Schmidt camera of the Joint Observatory for Cometary Research (JOCR) is clearly well-suited because of its flat field of about 8 x 10°.

The process of mass loading of the solar wind by cometary ions, which forms comet tails, has been observed throughout the coma of comet Halley. Three distinct regimes were found where the nature of the energy and momentum coupling between solar wind and cometary ions is different. Outside the bow shock, where there is little angular scattering of the freshly ionised particles, the coupling is described by the simple pickup trajectory and the energy is controlled by the angle between the flow and the magnetic field. Just inside the bow shock, there is considerable scattering accompanied by another acceleration process which raises some particle energies well above the straightforward pickup value. Finally, closer to the nucleus, the amount of scattering decreases and the coupling is once more controlled by the magnetic field direction.

The three-dimensional positive ion analyzer aboard the Giotto spacecraft has been used to study the interaction between protons and alpha-particles in the solar wind and positive ions from comet Halley. Although the first impression of the overall structure is that the plasma flow evolves smoothly as the nucleus is approached, three sharp transitions of relatively small amplitude can be identified on both the inbound and outbound legs of the trajectory. The outermost one, at about one million km from the nucleus, appears to be a multiple crossing of a weak bow shock. The innermost one, at 80,000 km, is the boundary where the flowing plasma becomes depleted. On a microscopic scale, the turbulence created by the interaction between the two ion populations extends to a distance of several million km from the nucleus. At Giotto's closest approach to the nucleus, the plasma produced around the spacecraft by dust and gas impacts was much more energetic than had been expected.

The dynamic properties of the dust striae, observed in comets West 1976VI, and Mrkos 1957V, are reexamined in terms of the high speed emission model (HS model) proposed by Notni (1966). It is demonstrated that most striae can be well fitted to modified synchrones but this kind of fitting does not lead to a conclusive model; in most cases, the dynamic solution is not unique, and, furthermore, the derived high values of the ejection speed appear to be unrealistic, particularly for distant (or old) striae. The results suggest that the required initial velocity could be better interpreted as indicating the presence of nonradial acceleration.

Durch Einwirkung von amalgamiertem Reinstaluminium auf Reinstwasser entsteht bei Temperaturen unter 40° Bayerit, bei Temperaturen uber 80° Bohmit in groster Reinheit. Die Darstellung von Bohmit beruht auf der geringen Keimbildungsgeschwindigkeit des Bayerits bei Temperaturen uber 80°. Bei der Wiederbewasserung von Aluminiumoxyd aus Reinstbohmit und Reinstbayerit entsteht bei 100° als Endprodukt Bayerit A. Oxyde aus gefallten Hydroxyden zeigen dagegen ein deutliches „Erinnerungsvermogen” an ihre Vorgeschichte: Oxyde aus Bayerit ergeben Bayerit, Oxyde aus Bohmit neigen zum Bohmit hin. Die Ursache dieses unterschiedlichen Verhaltens ist in kleinen Verunreinigungen von der Darstellung her zu sehen. Im Widerspruch zu N. Parravano u. G. Malquori entsteht bei der thermischen Zersetzung von AlCl3 · 6 H2O ein amorphes Aluminiumoxyd. Bei der Wiederbewasserung dieses definierten amorphen Aluminiumoxyds entsteht bei 100° Bohmit, bei 20° Bayerit B.

1. Es wurden die Ev-Werte zweier Aluminiumoxydreihen gemessen. Die EV-Werte der Praparate stehen in einer uberraschend einfachen Beziehung zu den aus der mono-molekularen Schicht berechneten Oberflachen. Es gilt 2. Fur Oberflachenberechnungen sind die in feuchter Luft erhaltenen EV-Werte nicht verwendbar. Auserdem mussen die Substanzen in Form feiner Pulver vorliegen. 3. Die Ev-Werte nachtraglich indizierter, fertiger Praparate ergeben brauchbare Annaherungswerte.

Durch Bestimmung der Scheindichte, Dichte und der Benzolisothermen wahrend des Weges Hydroxyd γAl2O3 αAl2O3 wurde ein Einblick in den Aufbau und die Sekundarstruktur von Aluminiumoxyden und ihre Abhangigkeit von Ausgangsmaterialien und Erhitzung erhalten. Wahrend Bayerit aus kompakten Kristallchen besteht, ist Bohmit ein poroser Korper ohne Makroporen. Die Oxyde aus Bohmit sind infolge eines anderen porosen Aufbaus zuganglicher fur Fremdstoffe und auserdem thermisch stabiler als jene von Bayerit.

UNLIKE plasma instruments used on previous space missions to Mars, the TAUS instrument on Phobos 2 was designed so that the energy per charge and angular spectra of three species of ions could be measured separately. These species were H+ and He2+ characteristic of the solar wind, and 'heavy ions' collected in one integral channel covering the mass per charge (M/q) range 3 to infinite, which we anticipated to find predominantly in the near-martian regime. In all spacecraft orbits around Mars we found a sharp boundary, separating the shocked solar wind from the martian magnetosphere which was characterized by the absence of solar-wind-like plasma. As the plasma inside the magnetosphere, and particularly in the tail, was dominated by heavy ions with number densities orders of magnitude higher than found in the solar wind, we assumed it was mainly of martian origin. Typically, heavy ions of low tailward flow velocity were seen near the boundary of the magnetotail, whereas high-speed tailward plasma flows of such ions were detected deeper inside the tail, a region not investigated before. Near the centre of the martian magnetotail a plasma regime, comparable to the terrestrial as well as the venusian1 plasma sheet, was detected, characterized by highly supersonic tailward streams of heavy ions. The flux of planetary ions leaving Mars through its magnetotail is tentatively estimated to be of the order of a few times 1025 s-1. Such loss rates would be significant for the dissipation of the martian atmosphere on cosmological timescales.

The main emissions of the cometary plasma tail are due to CO+ (400/402 and 425/427 nm) and H2O+ (aroud 650 nm). Emissions of CO2+ at 367 nm have also been observed (Swings and Page 1950). These ions relate much more directly to the presumed mother molecules of the cometary nucleus (like H2O, CO2, CO) than most strong emissions of the neutral cometary coma (Ruebner and Giguere, 1980, see also Jockers, 1982). Therefore it is important to determine column densities of cometary ions. So far only very few measurements of ion column densities are available (Wyckhoff and Wehinger, 1976a, b; Arpigny, 1965).

The Johnstone Plasma Analyser on Giotto operated almost continuously for two days before the encounter with comet Halley. Throughout this period it made observations of the proton and alpha particle distributions in the solar wind with 8 seconds time resolution. As the comet was approached, fluctuations were observed in all the primary bulk parameters, i.e. density, temperature and flow velocity, of both distributions at levels above the usual solar wind turbulence. We present here a survey of the data from a distance of 5 106 km from the nucleus up to the cometary foreshock at 1.4 106 km. Early in this period the variance was higher than in the solar wind on a similar day but the activity may have been associated with a crossing of the heliospheric current sheet. From a distance of 2.7 106 km the power level gradually increased, as the mass loading of the solar wind increased, to levels well above normal solar wind turbulence. We estimate that up to 16% of the free energy associated with the implanted cometary ion distribution went into the wave energy, similar to the proportion which has been estimated by quasilinear theory. Although the solar wind convection time through the mass-loaded region is short compared with the development time for a shell distribution in the cometary ions estimated from numerical simulation, the observations indicate that the cometary ion distribution is still basically ring-like.

Gaseous material expanding form the nucleus of comet Halley into space form the neutral coma around the comet. Ionisation in the solar UV radiation removes particles from the coma and injects them into the solar wind plasma. These freshly created ions are accelerated by the interplanetary electric field on cycloidal trajectories with gyrocenters moving with the speed of the magnetic field lines. In the solar wind frame of reference these particles move along the magnetic field lines with a fixed pitchangle. Pitchangle scattering and energy diffusion reduce quickly the initial energy anisotropy which is associated with the narrow pick-up structures. First observations of heavy cometary pick-up ions (water group ions) at the bowshock are presented. The evolution of the distribution function in the vicinity of the shock and radial density profiles are discussed.

The main emissions of the cometary plasma tail are due to CO+ (400/402 and 425/427 nm) and H2O+ (aroud 650 nm). Emissions of CO2 + at 367 nm have also been observed (Swings and Page 1950). These ions relate much more directly to the presumed mother molecules of the cometary nucleus (like H2O, CO2, CO) than most strong emissions of the neutral cometary coma (Huebner and Giguere, 1980, see also Jockers, 1982). Therefore it is important to determine column densities of cometary ions. So far only very few measurements of ion column densities are available (Wyckhoff and Wehinger, 1976a, b; Arpigny, 1965).

The dynamic properties of the dust striae, observed in comets West 1976VI, and Mrkos 1957V, are reexamined in terms of the high speed emission model (HS model) proposed by Notni (1966). It is demonstrated that most striae can be well fitted to modified synchrones but this kind of fitting does not lead to a conclusive model; in most cases, the dynamic solution is not unique, and, furthermore, the derived high values of the ejection speed appear to be unrealistic, particularly for distant (or old) striae. The results suggest that the required initial velocity could be better interpreted as indicating the presence of nonradial acceleration.

The bow shock of a comet is formed by the interaction of three different particle populations; solar wind ions, cometary ions and electrons. We follow the behaviour of the solar wind protons through the Giotto inbound shock crossing at comet P/Halley. A foreshock boundary is seen at ~ 1.4 106 km where the level of solar wind fluctuations increases substantially. The shock itself is seen some 2.5 105 km closer. It is a complex structure with high-amplitude waves in the cometary ion foot of the shock preceding a permanent drop in the solar wind speed. The width of the shock structure is ~ 40,000 km. There is evidence for a further excursion back into the cometary ion foot after the initial shock crossing. The cometary ion density is inferred from the solar wind speed changes and is compared with measurements.

The interaction of comets with the solar wind depends on the ionization of the heavy cometary neutrals (mostly H2O and its dissociation products O, OH) which flow out from the nucleus, and the coupling of these newly produced cometary ions with the solar wind through its embedded magnetic field. The 'pick-up' of these heavy ions slows the solar wind such that a shock may form. As expected, the structure of such a shock transition is highly complex because the gyroradius of a heavy cometary ion is much larger than that of a solar wind proton. Here we present a comparative study of the solar wind electrons and protons and the cometary pick-up ions measured by Giotto at the inbound crossing of the bow shock at comet Halley. We find a highly structured shock transition starting with a cometary ion 'foot' seen at a distance on the order of the cometary ion gyroradius upstream from a sharp decrease in the solar wind proton speed. The total solar wind thermal and magnetic pressure is dominated by the relatively small population of cometary ions throughout the shock region.

The two-dimensional force-free field equations are studied. The solar photosphere is considered as flat and infinitely extended and the magnetic field component perpendicular to the photosphere is prescribed as the field of a submerged line dipole, i.e. with two magnetic polarities divided by a straight infinitely long neutral line. In addition the shear of the field lines along the neutral line, i.e. the difference of the coordinate parallel to the neutral line of the two foot-points of a field line, is prescribed as a function f of the distance to the neutral line times a nonnegative constant γ. The function f is zero at the neutral line, goes through a maximum and drops to zero at large distances from the neutral line. The case γ = 0 corresponds to the current-free field. An approximate solution is obtained by a test function method. It is shown that for certain choices of the function f there exists a maximum value of γ beyond which a steady continuation of the solution is impossible. This forces the field to jump to a state of lower energy. The potential field, for instance, is such a lower energy state. Since the shear was prescribed as a boundary condition, the jump of the magnetic field will always be accompanied by a field line reconnection. Even though the field calculated does not closely resemble the flare geometry it is speculated that discontinuities like this one may also occur in more realistic field configurations and may actually trigger the flare.