We present high resolution (HPBW = 5 arcsec) continuum and molecular-line observations of the circumstellar environment of the emission-line star LkHα 234 made with the Owens Valley Millimeter-Wave Interferometer. These 98 GHz observations have revealed an unresolved continuum source coincident with the star and a 10 000 by 17000 A.U. ridge of enhanced CS(2-1) emission which peaks ∼ 4″ east of the star. The resulting spectral dependence for the radio continuum emission of ν1.5 is most easily interpreted as arising from a partially ionized stellar wind. Attempts are made to describe the properties of the CS emission in terms of a rotating molecular disk which would link LkHα 234 with large scale mass loss activity in the cloud. However, it appears most likely that the CS emission is arising from a dense (n(H2) ∼ 106 cm −3) condensation of gas adjacent to, but not dynamically associated with, the star.

This paper examines the distribution of pulsars in the Galaxy and compares it with the distribution of supernova remnants. The dispersion measure has been used as a distance indicator to obtain the distribution in luminosity, z-distance and period of the pulsars. The z-distance distribution is similar within the uncertainties to that of the supernova remnants. An estimate of the total number of pulsars in the Galaxy with a peak luminosity ≥ 1 fu(dm)2 gives 5 × 105 within a factor of 10. The data is consistent with the hypothesis that pulsars are formed at the same rate as supernovae, if the pulsars are assumed to have a timescale of 107yr.

Determining the locations of the major snowlines in protostellar environments is crucial to fully understand the planet formation process and its outcome. Despite being located far enough from the central star to be spatially resolved with ALMA, the CO snowline remains difficult to detect directly in protoplanetary disks. Instead, its location can be derived from N2H+ emission, when chemical effects like photodissociation of CO and N2 are taken into account. The water snowline is even harder to observe than that for CO, because in disks it is located only a few AU from the protostar, and from the ground only the less abundant isotopologue H218O can be observed. Therefore, using an indirect chemical tracer, as done for CO, may be the best way to locate the water snowline. A good candidate tracer is HCO+, which is expected to be particularly abundant when its main destructor, H2O, is frozen out. Comparison of H218O and H13CO+ emission toward the envelope of the Class 0 protostar IRAS2A shows that the emission from both molecules is spatially anticorrelated, providing a proof of concept that H13CO+ can indeed be used to trace the water snowline in systems where it cannot be imaged directly.

Numerical simulations of supersonic jets are able to explain the structures observed in many VLA images of radio sources. The improvements achieved in classical simulations (see Hardee, these proceedings) are in contrast with the almost complete lack of relativistic simulations the reason being that numerical difficulties arise from the highly relativistic flows typical of extragalactic jets. For our study, we have developed a two-dimensional code which is based on (i) an explicit conservative differencing of the special relativistic hydrodynamics (SRH) equations and (ii) the use of an approximate Riemann solver (see Martí et al. 1995a,b and references therein).

The study of cosmological evolution of the sizes of extragalactic radio sources started about a quarter century back. From the very first angular size-redshift (θ-z) plots (Miley 1968, 1971; Legg 1970) and angular size-flux density (θ-S) plots (Swarup 1975; Kapahi 1975) it became evident that some sort of cosmic epoch-dependent evolution in the size distribution for the population of extragalactic radio source needs to be proposed; the sources at earlier epochs appeared on the average to have smaller physical sizes. However, a suitable luminosity-linear size (P-l) correlation among the radio source population could also explain the observations, without invoking a size evolution with redshift. The only reliable way to disentangle these two separate effects is to investigate the size distribution in the luminosity-redshift plane, where one could examine not only the l-z relation for a given luminosity class, but could also check for a P-l correlation in a given redshift bin.

Pulse arrival times of pulsars have a high – though limited – degree of predictability: they show both discrete ‘glitches’, and continuous deviations from an analytic extrapolation of earlier data spans; they are ‘noisy’. This noise shows a strong dependence on a pulsar’s spindown age. Both types of noise can be understood as due to a loose coupling of the charged component of a pulsar’s moment of inertia to a neutral superfluid component, of relative moment of inertia usually below 1%, but reaching 10% in extreme cases. Differential spin rates δΩ/Ω of the two components are ≲ 10−3, usually only ≲ 10−5.

TAUMOK is a joint project of the Max Planck Institut für Astronomie Heidelberg and the Thüringer Landessternwarte Tautenburg. It is based on the concept of the “Spaltspinne” (Pitz 1993) now in operation at the Calar Alto Observatory. A first describtion of the technical concept was given by Pitz et al. (1993). TAUMOK was built at the MPIA Heidelberg in collaboration with astronomers and technicians from Tautenburg. It is now in the test phase and will have its first operation at the Tautenburg telescope in the middle of this year.

The use of a Schmidt telescope gives a very wide field for multi-object spectroscopy (TAUMOK will cover a field of 2.3°) but it also requires a series of special considerations. So, some of the details of the original “Spaltspinne” were modified to meet the site specific peculiarities. The size of the ground plate was minimized and yields a central obscuration of only 60 cm in diameter. The curved field of the Schmidt focus (deviation of up to ±400 µm from the mean focal plane) is flattened by a field lens - a solution alternative to the guiding of the fiber supporting rods on a sphere.

We present the preliminary findings of a deep imaging survey covering 17 square degrees in the Pleiades. We have identified in excess of 300 candidate cluster members in the i, i-z diagram. The survey is complete to ~ i=22, with candidates detected as faint as i=23.

This study was originally motivated from the discussion of the obliquity of the ecliptic, e, in the work of Needham (1959) and his collaborators, and the article, “An 8-th Century Meridian Line,” by Beer et al. (1961). A search in the historical records yields values of e in addition to the published values in the literatures.

The effect of tidal friction in the lunar orbit is one of the classic examples of ad hoc modelling of an unknown physical phenomenon. The two basic calculational approaches in current use are developed in some detail, and numerical tests and comparisons are presented. Although attention is normally concentrated on the acceleration in orbital longitude produced as a result of terrestrial dissipation, it is shown that the variation in Earth-Moon distance due to Earth tides is far from negligible. A significant, though minor, fraction of this variation is supplied by the radial component of the acceleration, which would exist even in the absence of tidal friction. In fact, this represents almost all the difference in the predictions of the two models.

Observations of circular polarization of molecular masers associated with late type giant and supergiant stars can be used to estimate the magnetic field strength in the masing region. Magnetic field strengths of ~ 5 mG are deduced for OH masers in circumstellar envelopes at distances of ~ 1016 cm from the star, and magnetic field strengths of ~ 50 G are deduced for SiO masers that reside above the photosphere. Extrapolation to the stellar photosphere suggests that average surface magnetic fields are on the order of 103 G.

From a new study of 113 F8-G1 IV or V primaries in an apparent-magnitude limited sample, measured with a CCD for about 20 radial velocities of accuracy 0.2-0.5 km s−1 each, we collected data for 28 binary orbits and 39 visual systems. We again found a flat distribution (or slightly decreasing toward lower masses) of secondary masses, unlike the Salpeter distribution for B2-B5 stars. But we find that the different distributions for these field stars and for open clusters of various ages can all be explained by a capture mechanism of binary formation.

Project STAR (Science Teaching through its Astronomical Roots) emerged from growing concern about the decreasing enrollment in science classes, and lack of understanding of science and math concepts (Figure 1). Using astronomy as a focus, Project STAR is trying not simply to increase the enrollment in high school science courses, but also to improve the students’ understanding of science and its role in making sense of the world.

The educational approach of Project STAR is based on three principles:

• Mastery of a few ideas is more important for students than cursory exposure to many concepts.

• Students learn best through hands-on activities.

• Students enter the classroom with certain preconceptions, or “naive theories,” about how physical systems work, without a sense of whether their understandings are accurate (often they are not).

High resolution IUE spectra of Feige 24 reveal sharp C IV absorption features at both the stellar velocity and the velocity of the interstellar lines. Dupree and Raymond have shown that the ionization zone created by Feige 24 itself accounts for the interstellar components of C IV and Si IV, and that the density of hot white dwarfs in the galaxy implies that similar ionized zones around hot white dwarfs make a significant contribution to the C IV column densities observed toward distant O and B stars. Typical white dwarf velocities of around 30 km/s and C IV ionization zone diameters less than 1 pc imply that the crossing time is comparable to the ionization time, so that non-equilibrium ionization models are required. Models of the resulting elongated trails are presented.

A classification of possible motions of triple systems is presented emphasizing the transient phenomena occurring in addition to the final (asymptotic) outcome and clarifying the discrepancies between the astronomical and mathematical formulations. A conjectured possible instability is described and it is shown that systems with negative total energy and low angular momentum may lead to instability and to the formation of binaries. The ejected or escaping star may have high velocity if the triple close approach preceding the escape is sufficiently close. The computational results of several systematic series of such escapes are applied to various stellar configurations.

The present status of the fundamental problem of partitioning the phase-space into stable and unstable regions is reviewed and a recently developed technique, applicable to stellar dynamics is described. Recently discovered families of periodic orbits and previously established classical configurations are shown to weaken the general instability conjecture.

The possible existence of triple systems in states of dissolution offer intriguing observational challenges regarding the discovery of these projected temporary trapezium type systems.

The Berkeley EUV telescope flown on the Apollo Soyuz mission in July, 1975 established the existence of a measurable flux of EUV radiation (100 ≤ λ ≤ 1000 Å) originating from sources outside the solar system. White dwarfs, flare stars and cataclysmic variables were discovered to be relatively intense compact sources of EUV photons. Moreover, this and other subsequent experiments have strongly suggested the presence of a truly diffuse component of the EUV radiation field possibly due to thermal emission from hot (T > 105 K) interstellar gas located in the general vicinity of the sun (r ≃ 100 parsecs.) Closer to the HI, 912 Å edge, the effect of a few hot O and B stars has been shown to be very important in establishing the interstellar flux density. All these results imply that the local ISM is immersed in a non-negligible EUV radiation field which, because of the strong coupling between EUV photons and matter, will play a crucial role in determining its physical structure. Conversely, of course, the local ISM is expected to leave a strong imprint on the EUV field reaching the terrestrial observer.

The objective of this review will be to assemble and critically analyze the available information on the local ISM derived from the limited EUV observations carried out so far. These include measurements of the spectra of bright EUV sources that reveal clear evidence of H photo absorption at λ > 400 Å and of the He ionization edge at 228 Å. The EUV diffuse background is found to convey interesting information on the density, temperature and possible location of the hot ISM component that can be profitably compared with similar data on far uv absorption lines, principally OVI. The results discussed in this context will be shown to be quite useful in illuminating the path that future EUV sensitive observatories such as EUVE and Columbus might profitably follow in the near future.

High resolution imaging with HST-wfpc2 of seven of the most luminous evolved cool stars shows that the three OH/IR stars NML Cyg, VX Sgr and S Per have circumstellar nebulae while no ejecta was detected for the M-type supergiant μ Cep and the yellow hypergiants ρ Cas, HR 8752 and HR 5171a.

Mean orbital elements are obtained from their instantaneous, osculating counterparts by removal of the short periodic perturbations. They can be computed by means of different theories, analytical or numerical, depending on the problem and accuracy required. The most advanced contemporary analytical theory (Knežević 1988) accounts only for the perturbing effects due to Jupiter and Saturn, to the first order in their masses and to degree four in eccentricity and inclination. Nevertheless, the mean elements obtained by means of this theory are of satisfactory accuracy for majority of the asteroids in the main belt (Knežević et al. 1988), for the purpose of producing large catalogues of mean and proper elements, to identify asteroid families, to assess their age, to study the dynamical structure of the asteroid belt and chaotic phenomena of diffusion over very long time spans. In the vicinity of the main mean motion resonances, however, especially 2:1 mean motion resonance with Jupiter, these mean elements are of somewhat degraded accuracy.

A global, monthly snow depth data set has been generated from weather satellite (Nimbus 7) observations using passive microwave remote-sensing techniques. In this paper we analyzed five years of data, 1980–1984, to compute the snow-load excitation of the annual wobble of the Earth's rotation axis. A uniform sea-level decrease has been assumed in order to conserve water mass. The result shows dominant seasonal cycles. The prograde component of the annual excitation is Ψ+ = (5.0 milliarcsec, −110*) and the retrograde component Ψ− = (5.0 milliarcsec, −31*). These computed values are compared with previous groundwater estimates, as well as the inferred values from ILS and LAGEOS polar motion measurements. The importance of accurate data is stressed and future plans proposed.

Based on a simple thermodynamical argument, we proposed a cloudy model with a warm dust cloud deep in the photosphere. We showed, for the first time, that a single grid of model photospheres (800 ≲ Teff ≳ 2600 K) offers a natural explanation not only for the division of dwarfs cooler than M into the two distinct types L and T but also for the changes of the spectra and colors along the L – T spectral sequence.