Galactic mass modeling has a long history. The first mass models were designed to represent the galactic attraction force in the radial direction. Considerable progress in galactic mass modeling was made during the fifties when Kuzmin (1952) introduced nonhomogeneous ellipsoids and Schmidt (1956) used a number of ellipsoids to represent various galactic populations. Further progress in galactic mass modeling has followed with the improvement of the system of the galactic constants and with the improvement of our knowledge of the structure of the galactic populations, in particular with the discovery of a massive corona around the Galaxy. In this report we present a new mass model of the Galaxy. It has been constructed using the most recent data available. A preliminary version of this model has been discussed earlier by Einasto, Jôeveer and Kaasik (1976).

The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 AU have been applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments, in the same way as other earlier determinations based on the same method. However, we have combined the spacecraft data with daily full sun averages of the H Lya 1216 A line obtained by the Solar Mesospheric Explorer (SME) satellite, to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a 1 year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are [H] = 0,12 cm-3 and [He] = .016 cm-3, giving a density ratio close to the cosmic abundance value, in contrast to some earlier results indicating a depletion of atomin hydrogen. We have obtained estimates of galactic background emissions in the signals of both spacecraft.

The solar chemical composition has recently undergone a drastic revision, in particular in terms of the C, N, O and Ne abundances that have been lowered by almost a factor of two. In this invited review I will describe the different compounding reasons for this change (3D model atmospheres, non-LTE line formation, improved atomic/molecular data) and discuss some astrophysical implications thereof, which fall under both good (solar neighborhood) and bad (helioseismology) news. The most recent literature regarding the solar O abundance is surveyed and a critical evaluation whether or not these support the low solar abundance scale is presented. Finally I venture to make some predictions to what the real solar O abundance may be.

Milky Way dwarf companions and satellites of distant spirals seem to show a preference for polar orbits. We suggest that five out of six M31 dwarf spheroidal companions as well as two dwarf irregulars may also be located near a polar plane.

We briefly discuss preliminary results from a statistical approach to study correlations between star formation histories and orbits of Local Group dwarf galaxies, such as a possible correlation between star formation episodes and galaxy separations.

We have acquired about 1200 hr of both spectroscopic and photometric measurements of the β Cep star ν Eri with 22 telescopes around the world, detecting and identifying seven independent pulsation modes. They are the radial fundamental mode, an l = 1, g1 triplet, an l = 1, p1 doublet and an l = 1, p2 singlet. Seismic model calculations by two independent teams suggest that it is not possible to explain the pulsational behaviour of ν Eri with standard stellar models. Some modifications of the input physics are required.

The basic characteristics of the stellar populations in galaxies are determined by the history of star formation and by the initial mass spectrum with which the stars are formed. Many attempts have been made to model the history of star formation in galaxies using various quasi-theoretical descriptions of star formation, but star formation remains a very poorly understood process and no theoretical understanding with any real predictive power has yet been attained. However, recent work suggests the importance for star formation of some mechanisms that have so far not been very extensively studied, and I shall mention some of these possible processes here, undeveloped though these ideas still are at present.

First, I shall review briefly the observational evidence concerning the history of star formation in galaxies of different Hubble type. Most of the information we have for galaxies other than our own comes from their colors, which can be compared with the predictions of models constructed with various assumed histories of star formation. Ever since the work of Tinsley (1968), it has been clear that most of the observed variation of color with Hubble type can be understood in terms of differing time scales for star formation, the reddest galaxies (E and SO) having formed the bulk of their stars at a relatively early stage, while the much bluer Sc galaxies have formed their stars much more gradually and at a rate that has remained nearly constant up to the present time. Recent studies of normal elliptical galaxies, reviewed by Faber in this volume, confirm that they have no detectable present star formation.

Probing the atmospheres of Be stars by means of Optical Long Baseline Interferometry (OLBI) is a method still in its infancy. Published observational results in this field can be counted on one hand. In this paper we introduce the principles of OLBI as they apply to observations of Be stars and review results from existing long baseline interferometers. Regular operation of OLBI is most effective when carried out in conjunction with standard techniques such as photometry and spectroscopy. With the next generation of synthetic arrays combining sub-milliarcsecond resolution and a spectral resolution better than 10000, OLBI should be able to address the direct detection of pulsation and magnetic fields.

Three architectural traditions with astronomical associations have been identified among the ‘Great Houses’ and ‘Great Kivas’ of Chaco Canyon, New Mexico. Great Houses and one Great Kiva built during the height of construction activity (AD 1020–1100), the Bonito Phase, include front-facing south-southeast (SSE) orientations, and cardinal north-south and/or east-west (NS/EW) alignments. We present ethnographic material supporting our previous proposal that the SSE orientation is probably linked to migration traditions and ancestor veneration. We also confirm that a majority of Late Bonito Phase Great Houses (built after A.D. 1100) exhibit a third astronomical tradition: five of the principal in-canyon Great Houses built at that time were positioned at or near observing locations that could have functioned as solstice calendrical stations. Through use of these locations for public ceremonies, the Chacoan elite could demonstrate astronomical knowledge and ritual power. These findings provide support for Van Dyke's hypothesis that construction during this period was intended to reinvigorate a faltering system. One ‘Chaco halo’ Great House, Bis sa'ani, incorporates all three traditions. We suggest that temporal analysis of these traditions improves understanding of migration paths and shifting balances of power and social dominance among ancestral Pueblo culture groups.

We present first results of a new heterodyne spectrometer dedicated to high-resolution spectroscopy of molecules of astrophysical importance. The spectrometer, based on a room-temperature heterodyne receiver, is sensitive to frequencies between 75 and 110 GHz with an instantaneous bandwidth of currently 2.5 GHz in a single sideband. The system performance, in particular the sensitivity and stability, is evaluated. Proof of concept of this spectrometer is demonstrated by recording the emission spectrum of methyl cyanide, CH3CN. Compared to state-of-the-art radio telescope receivers the instrument is less sensitive by about one order of magnitude. Nevertheless, the capability for absolute intensity measurements can be exploited in various experiments, in particular for the interpretation of the ever richer spectra in the ALMA era. The ease of operation at room-temperature allows for long time integration, the fast response time for integration in chirped pulse instruments or for recording time dependent signals. Future prospects as well as limitations of the receiver for the spectroscopy of complex organic molecules (COMs) are discussed.

The orbital motion of comets is difficult to characterize accurately due to the rocket-like outgassing of material from the cometary nucleus. The resulting nongravitational accelerations often appear to be fundamentally stochastic in nature and thus pose severe modeling challenges in orbit determination, especially when the comet has been observed for many revolutions. Even so, new techniques have arisen in recent years that give new insight, not only into the motion of the comets, but also into their physical characteristics and spin states. These approaches include modeling of spin axis precession over many decades and the consideration of the seasonal variation in the thrust from discrete jets acting on a rotating nucleus. Such advances have been enabled, in part, by the increasing efforts and capabilities of comet observers worldwide as more and more comets with longer and longer observing arcs become available for study. In this review we specifically consider the application of the Rotating Jet Model to several space mission targets, indicating how this model can often be used to infer the orientation of a comet's spin axis.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Star formation is enhanced in spiral arms because of a combination of orbit crowding, cloud collisions, and gravitational instabilities. The characteristic mass for the instability is 107M⊙ in gas and 105M⊙ in stars, and the morphology is the familiar beads on a string with 1-2 kpc separation. Similar instabilities occur in resonance rings and tidal tails. Sequential triggering from stellar pressure occurs in two ways. For short times and near distances, it occurs in the bright rims and dense knots that lag behind during cloud dispersal. For long times, it occurs in swept-up shells and along the periphery of cleared regions. The first case should be common but difficult to disentangle from independent star formation in the same cloud. The second case has a causality condition and a collapse condition and is often easy to recognize. Turbulent triggering produces a hierarchy of dense cloudy structure and an associated hierarchy of young star positions. There should also be a correlation between the duration of star formation and the size of the region that is analogous to the size-linewidth relation in the gas. The cosmological context is provided by observations of star formation in high redshift galaxies. Sequential and turbulent triggering is not yet observable, but gravitational instabilities are, and they show a scale up from local instabilities by a factor of ~3 in size and ~100 in mass. This is most easily explained as the result of an increase in the ISM turbulent speed by a factor of ~5. In the clumpiest galaxies at high redshift, the clumps are so large that they should interact with each other and merge in the center, where they form or contribute to the bulge.

Attempts to explain both the expansion of the universe and the condensation of galaxies must be very largely contradictory so long as gravitation is the only force field under consideration. For if the expansive kinetic energy of matter is adequate to give universal expansion against the gravitational field it is adequate to prevent local condensation under gravity, and vice versa. This is why, essentially, the formation of galaxies is passed over with little comment in most systems of cosmology. Yet the galaxies, and the clusters in which they are often found, are such an important characteristic property of the universe that it is unsatisfactory to dismiss their origin in the vague term “fluctuation phenomenon.”

In the last decade, it has become clear that the dust-enshrouded star formation contributes significantly to early galaxy evolution. Detection of dust is therefore essential in determining the properties of galaxies in the high-redshift universe. This requires observations at the (sub-)millimeter wavelengths. Unfortunately, sensitivity and background confusion of single dish observations on the one hand, and mapping efficiency of interferometers on the other hand, pose unique challenges to observers. One promising route to overcome these difficulties is intensity mapping of fluctuations which exploits the confusion-limited regime and measures the collective light emission from all sources, including unresolved faint galaxies. We discuss in this contribution how 2D and 3D intensity mapping can measure the dusty star formation at high redshift, through the Cosmic Infrared Background (2D) and [CII] fine structure transition (3D) anisotropies.

We present an overview of our work on shape and spin state determination of asteroids from photometric data sparse in time. Our results are based on simulations that were performed using realistic shape and light-scattering models and time sequences that will be provided by Pan-STARRS (Panoramic Survey Telescope and Rapid Response System). We show some typical examples of physical model reconstruction of main belt and near-Earth asteroids and discuss the lightcurve inversion of slow and fast rotators, binary asteroids and tumbling asteroids. We emphasize the scientific potential of sparse photometric data to produce models of a large number of asteroids within the next few years.

We report on an ongoing investigation into a seismic calibration of solar models designed for estimating the main-sequence age and a measure of the chemical abundances of the Sun. Only modes of low degree are employed, so that with appropriate modification the procedure could be applied to other stars. We have found that, as has been anticipated, a separation of the contributions to the seismic frequencies arising from the relatively smooth, glitch-free, background structure of the star and from glitches produced by helium ionization and the abrupt gradient change at the base of the convection zone renders the procedure more robust than earlier calibrations that fitted only raw frequencies to glitch-free asymptotics. As in the past, we use asymptotic analysis to design seismic signatures that are, to the best of our ability, contaminated as little as possible by those uncertain properties of the star that are not directly associated with age and chemical composition. The calibration itself, however, employs only numerically computed eigenfrequencies. It is based on a linear perturbation from a reference model. Two reference models have been used, one somewhat younger, the other somewhat older than the Sun. The two calibrations, which use BiSON data, are more-or-less consistent, and yield a main-sequence age t⊙ = 4.68 ± 0.02 Gy, coupled with a formal initial heavy-element abundance Z = 0.0169 ± 0.0005. The error analysis has not yet been completed, so the estimated precision must be taken with a pinch of salt.

Seismology from the ground has already provided many important results, as discussed for instance in Frandsen (1997) and in this symposium. The limitations of this approach are essentially the day-night alternance and the meteorological instabilities for photometry, the lack of photons and the broadening of spectral lines due to rotation for spectroscopy. Seismology from space is less limited, as photometry at a very high accuracy on long uninterrupted observing runs is possible.

This review is restricted to a few topics of the extensive problem under discussion; it refers to the literature since 1967 only. The literature prior to 1967 is reviewed in Zwaan, 1968; Howard, 1967; Lüst, 1965; Kiepenheuer, 1968; Jäger, 1964; and Bray and Loughead, 1964.

We describe an ongoing, large-scale, photometric and spectroscopic survey of the Large Magellanic Cloud (LMC) periphery. This survey uses Washington M, T2 + DDO51 photometry to identify distant LMC red giant branch (RGB) star candidates; multi-object spectroscopy is used to confirm the stellar surface gravities of these RGB stars and their association with the LMC (e.g., through radial velocities). The survey now encompasses hundreds of fields ranging from the LMC center with full azimuthal coverage around the LMC and out to 23° from the LMC center. We have confirmed the existence of RGB stars with (the unusual) Magellanic velocities out to the radial limit of this survey coverage. From data in a subsample of these fields, we show that this extended population of stars makes up a diffuse structure enveloping the LMC with a two-dimensional distribution resembling a classical halo with a shallow de Vaucouleurs profile and a broad metallicity spread around a typical mean value of [Fe/H] ~ −1.0.