The Third Catalogue of Nearby Stars (CNS3) was analyzed. A study of the stellar luminosity function in the solar neighborhood with CNS3 was described. The luminosity function for main sequence stars derived from CNS3 was compared with that from CNS2 and that based on the method of photometric parallaxes. The results from CNS3 for stars with Mv <15.5 were well defined. Luminosity functions for the giants and A, F, G, K and M type main sequence stars are also given, based on CNS3.

Pointed observations with ISO have been made, or are planned, towards 58 supernova remnants (SNRs) in the galaxy and Magellanic clouds. The main emphasis is on detailed studies of gas, dust and synchrotron emission from selected regions within 24 well studied galactic remants. First results are available for Cas A (Lagage et al. 1996, 1997; Tuffs et al. 1997; Unger et al. 1997), the Cygnus Loop (deCourchelle et al 1997; Fischera et al. 1997), RCW103 (Oliva et al. 1997; Wright et al. 1997), and W44 and 3C391 (Reach and Rho 1996). These are providing insights into issues such as the yield and composition of condensates in supernova ejecta, the processing of grains by adiabatic and radiative shocks, and the measurement of cold gas, inaccessible to optical observations, both from cool regions in radiative shocks and from unshocked ejecta. In this progress report these points are illustrated with reference to Cas A, the prototype of an ejecta-dominated remnant of a massive core-collapse supernova, and the Cygnus Loop and RCW103 as prime examples of radiative shocks delineating the interaction of fast blast waves with diffuse atomic and dense molecular clouds, respectively.

The Solar System is characterized by a large variety of objects, with sizes ranging from more than a hundred thousand km down to less than a /mi. All solar-system IR spectra are the sum of two components: at short wavelengths, the reflected sunlight provides information upon the albedo and the chemical composition of the body; at longer wavelengths (typically above 3 to 5 /um), the thermal emission provides information on the temperature of the surface or the atmosphere, and on the vertical distribution of atmospheric constituents.

Olson’s light curves of the Algol-type binary WW And, showing evidence of harbouring an accretion disk, were re-analysed. Two approaches were attempted to find a solution: the first one, the Roche geometry model assuming the system consisting of two stars, and the second one, including also the existence of an accretion disk around the hotter component. In both cases the Monte Carlo method was employed to search for the best solution. We found that adding an additional parameter, namely the third light, the data can be satisfactorily reproduced with only a marginal underfilling of the Roche lobe of the cool star, for the Roche geometry. A thorough search within the semidetached configuration, incuding an accretion disk around the hotter component, was performed. Although such a fit is slightly worse (as measured by the rms error) than that for the Roche geometry, it can explain the observed spectroscopic features. Absolute parameters of the components of this interacting binary are presented for both models.

There is no reason to believe that the prospects expressed in Part III are the ultimate ones for development of evidences about stellar evolutionary information. Instead, (and just as for all other domains of science) technology advances and the availability of funds and manpower will remain important discriminants for new knowledge. As it happened, a presentation of some significant and imminent and distant hardware programs was given at the JD8 and it has been chosen (out of sequence with its order in Kyoto)to end this report.

Comets, the most pristine members of our solar system, are faint at large heliocentric distances (rh > 3 au) and therefore difficult to observe. Data reduction of these faint objects (periodic comets) is time consuming and hence most often just preliminary results can be discussed. Only the orbits of short periodic comets can be predicted and most of those that have been accessible for ISO have been covered within the guaranteed time programme. About 10 proposals were accepted by the selection for open time proposals. A target of opportunity team was formed. The outstanding comet Hale-Bopp (C/1995 01), one of the brightest and therefore most active comets of this century, was suggested and accepted as TOO. The important results from the ISO cometary programme are derived from its observations. In addition to the observations of "classic" comets the newly detected (Jewitt and Luu, 1993) transneptunian objects, probably objects from the Kuiper belt, are observed in an attempt to determine their physical properties.

Directly measuring stellar evolution may be accomplished in at least two distinctly different ways. The first approach will be observing it in real time as the phenomenon is taking place; the examples will include explosive events in recurrent novae, stellar oscillations in Cepheid and RR Lyrae variables, and mass flow in and out of interacting binaries. The second approach will be to observe a number of stars that are believed to belong to the same class at different stages of their evolutionary paths.

In this talk, I will focus on the first method of direct observations. The most direct method will probably be to observe images of the events thatwe wish to investigate. The same astronomical phenomena can and should alsobe studied using high-time and spectroscopic resolution data; however, thisis already being done with increasingly better spectral-and-temporal resolutions and will probably be reported elsewhere in this Joint Discussion. It is also noted that over the past two decades multiwavelength observations, using various telescopes on the ground and in space, have come to play a crucial role in astronomy, although I am not addressing this subject in this paper. I will talk primarily about imaging using interferometry that will soon become possible due to the advances in technology.

This has been an exciting meeting in which we saw all the different instruments on ISO revealing strikingly novel results that challenged conventional perceptions with unexpected findings or confirmed long-held astrophysical views which previously had to be taken on faith.

Most of the mass near the Sun takes the form of stars less luminous than the Sun. A central problem of Galactic astronomy is the determination of how much mass these stars contain.

The only thoroughly reliable way of detecting mass is through its gravitational field. Classically this has been done by studying the Galaxy’s rotation curve and the Oort limit, both of which remain active areas of research. In the last few years an exciting new way of probing the Galaxy’s gravitational field has been opened up by large surveys for microlensing events. These surveys are yielding important information about the numbers of low-mass objects both in the disk and above it. Another truly dynamical probe for low-luminosity objects is provided by studies of clusters. JD 10 reviewed what we have learned about the density of low-luminosity stars from each of these approaches.

An important orthogonal approach to determining the density of low-luminosity stars involves seperately determining the luminosity function and the mass-luminosity relation for stars of a given spectral class (e.g. main-sequence stars) and then combining them to obtain the mass function. The development of infrared detectors and the refurbishment of the The Hubble Space Telescope have recently yielded important advances in each of these areas. A major difficulty with this line of research is the fact that, in the neighbourhood of M = 0.08 Mʘ, the main-sequence mass-luminosity relation is (i) steep and non-linear, and (ii) dependent not only on the masses of the faintest stars, but also on their ages, metallicities, rotation rates, binarity etc. Moreover, cool low-luminosity stars have extremely complex spectra, which are difficult to simulate with radiative transfer calculations. Similar difficulties are encountered in the determination of the mass-luminosity relation for white dwarfs. JD 10 reviewed the current status of these very difficult problems.

The radial distribution of mass in a disk galaxy is strongly constrained by its rotation curve. The separate contributions from the individual stellar populations and dark matter (DM) are not easily disentangled, however, especially since there is generally no feature to indicate where the component dominating the central attraction switches from luminous to dark matter. Here I summarize three recent thesis projects at Rutgers University which all suggest that DM has a low density in the inner parts of bright galaxies, and that most of the mass therefore resides in the disk. In addition, I present some preliminary work on the Milky Way. If we are able to determine the M/L of a typical disk stellar population, it should provide a useful constraint on the numbers of low mass stars.

During galaxy formation non-baryonic dark matter is not expected to pack down into a thin disk. Hence the mass-to-light ratio ϒd of the Galactic disk is a key number as the mass-to-light ratio of a purely baryonic system. If ϒd proves to be large, it suggests that the large values of ϒ that are detected elsewhere in the Universe are due to dark baryonic matter rather than some exotic form of matter. Conversely, a small value ϒd lends credence to the idea that most of the mass in the Universe is non-baryonic by suggesting that baryonic systems are well endowed with luminous stars.

The aim of this paper is to summarise the dynamical constraints on the contribution of low luminosity stars. Important restrictions come from disk stability and the Oort Limit. These are reviewed elsewhere in these Proceedings in the contributions from Sellwood and Binney. Here, our attention is concentrated on two further pieces of evidence - constraints from (1) the stochastic heating of wide binaries and from (2) microlensing.

What is known about the masses of main-sequence stars from the analysis of binary orbits? Double-lined eclipsing binaries are the main source of very precise stellar masses and radii (e.g. Andersen 1997), contributing more than 100 determinations with better than 2% precision over the range 0.6 to 20 Mʘ. For lower-mass stars we are forced to turn to nearby systems with astrometric orbits (e.g. Henry et al. 1993). Not only is the number of good mass determinations from such systems smaller, but also the precision is generally poorer. We are approaching an era when interferometers should have a major impact by supplying good astrometric orbits for dozens of double-lined systems. Already we are beginning to see the sorts of results to expect from this (e.g. Torres et al. 1997).

Figure 1. Mass vs. absolute V magnitude for eclipsing binaries (circles) and nearby astrometric binaries (squares)

Figure 1 is an updated version of a diagram presented by Henry et al. (1993, their Figure 2). It shows the general run of mass determinations from about 10 Mʘ down to the substellar limit near 0.075 Mʘ. Ninety of the points in Figure 1 are for eclipsing binary masses from Andersen’s review (1991) and are plotted as open circles. The results for eclipsing binaries published since 1991 are plotted as 30 filled circles, adopting the same limit of 2% for the mass precision. In most cases the uncertainties are similar to the size of the symbols. Especially noteworthy is the pair of new points for CM Draconis (Metcalfe et al. 1996) with masses near 0.25 Mʘ. Together with the points for YY Geminorum near 0.6 Mʘ, these are the only M dwarfs that have precise mass determinations. For the most part we are forced to rely on nearby stars with astrometric orbits, to fill in the M dwarf region of the diagram. We have used filled squares in Figure 1 for 29 such systems from Henry et al. (1993), updated using 14 new parallaxes from Hipparcos and 4 from the new Yale Parallax Catalog (1995). Gliese 508 is not included, because it is now known to be a triple, while Gliese 67AB, 570BC, and 623AB are not included because there are not yet any direct measurements of the V magnitude difference for these systems.

Most of what we know about the Luminosity and mass function of low-mass stars has been derived from analysis of ground-based photometric and astrometric Surveys. A major uncertainty in the Interpretation of such surveys lies in the appropriate correction for unresolved binaries and in the use of a reliable colour-magnitude relation. various new surveys are now uncovering large numbers of objects which should rapidly ameliorate these ambiguities.

The recent discovery of brown dwarfs and planets has highlighted the importance of low-luminosity stars. once we understand their spectra and colours and have statistically significant samples, it will be important to use them to reliably constrain theories of star formation and chemical evolution as well as to use them as a probe of galactic structure and to reliably ascertain their contribution to baryonic dark matter. In this brief review ishall focus on ground-based field searches. Hambly (1997) reviews the very successful searches that have recently been carried out in nearby clusters.

Until the 1970s, most work on the faint-star luminosity function was based on proper-motion searches primarily by dutch researchers, in particular Luyten (e.g. 1938, 1979). The Last 20 years have seen a switch from astrometric to photometric surveys employing plate-scanning machines or CCD cameras. Combined with substantial increases in computing power these technologies have led to the discovery of large numbers of very low-luminosity Stars.