Schmidt telescopes are ideal for many types of survey work, and this includes surveying the solar system. Schmidt cameras have the advantages of speed and wide fields for rapid coverage of large areas of the sky, and good image quality over the entire field. The small focal ratios also have the effect of enhancing low surface-brightness features. This is an advantage for studying cornetary tails and comae.

Current work in the field of small solar system objects can be divided into three different areas: searching for new objects, recovering lost objects, and astrornetry of known objects. Each of these areas requires its own techniques.

Photographic imaging of the plasma- and dust-tails of bright comets requires fast (f<4.0), wide-field (F0V>5°) optics for the proper recording of these large, low surface brightness features. Schmidts and astrographs are well-suited to this task and a large number of these instruments around the world will be turned toward Halley's Comet in 1985-1986 in support of the Large-Scale Phenomena Discipline of the International Halley Watch (IHW). This “worldwide network” should provide imagery with a time resolution never before realized in the study of a comet, and major breakthroughs in the understanding of highly-variable, elusive plasma processes in comets are expected. The imagery will also provide support for the GIOTTO, VEGA, AND PLANET-A deep space probes to the comet.

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 combined Poisson-Boltzman equation for the gravitational potential is solved numerically for a detailed Galaxy model. The main result - obtained by comparing the calculated densities with observations of F dwarfs and K giants - is that about half of the mass density in the vicinity of the Sun has not yet been observed.

The use of Schmidt Telescopes for the determination of space density gradients is discussed. Space densities can be determined by a three colour photometry for main sequence stars with M< 8. 0 and later type giants of population I and for metal poor stars in higher galactic latitudes with M< 7. 0. A general synthesis of the present available results is not yet possible. But the determination of a density gradient for later type giants along a galactic radius, the distribution of metal poor stars in a galactic meridian and around the galactic centre seems to be possible with the existing observational material.

Stellar content contributing to near IR radiation do not show radial differentiation in the Galaxy. Late-type giants and supergiants supply about 70% of the total volume emissivity at the K band, in the solar vicinity within 1 kpc, and also at the distance of several kpc in the Scutum region.

The aim of this survey is to locate samples of very distant field halo stars, to study the kinematics and metal abundance distribution in the outer regions of the galactic halo. Field halo K giants were chosen for the study, as they are intrinsically bright stars whose evolution is well understood. Halo K giants, near the tip of the giant branch and between 10 and 40 kpc from the sun, will have apparent magnitudes in the range 13 < V < 18, and colours (B-V) > 0.9.

In the 1950’s Haro (Haro and Luyten 1962) developed a survey method in which three images, roughly corresponding to U,B, and V, are exposed on one plate. The images are separated by several arc seconds by moving the telescope between exposures. Exposure times are chosen so an unreddened star of spectral type AO to A5 shows three images roughly equal in size and density. The plates are examined by eye to find stars by their colors. A red star shows a strong central image flanked by two weaker images, while a blue star shows a weak central image flanked by two stronger ones. This method allows surveys for stars and galaxies with very red or very blue colors to be carried out with any telescope, and in particular with the Schmidt telescopes at Tonantzintla and at Palomar which were not equipped with objective prisms.

Space distribution and kinematics of stars are determined by the initial distribution, i.e. the distribution of spatial positions and kinematical data just after the birth, and dynamical effects the stars experienced during their life. Evidence is presented that the space distribution of A type stars perpendicular to the galactic plane might be a result of periodic star formation having a characteristic time of 108<τ<6x108 years.

I am now engaged in an objective-prism program directed toward the discovery of new peculiar and interesting stars in most of the northern sky. The plates utilized are 20-min. blue exposures taken with the Warner & Swasey Observatory’s Burrell Schmidt telescope, now located on Kitt Peak. The dispersion of the spectra is 108 A/mm at Hγ, the limiting magnitude about mpg =10.5, and the plate quality generally excellent. This paper discusses the history and status of the project and gives examples of the variety of objects being found.

As a region of recent star formation and intense stellar activity the Orion Complex extending over several square degrees is of paramount importance in the study of early evolution and activity in the stellar chromospheres of low mass stars. Although red stars form a rather inhomogeneous group, including foreground K-M dwarfs, distant K-M giants, carbon stars and a variety of reddened objects, in principle these can be separated from a combination of photometric, spectroscopic and kinematic data. The proximity of the Orion Complex and its relatively high galactic latitude mean that future astrometric and radial velocity work will yield useful kinematical information on all member stars, including the enigmatic pre-main sequence stars on the lower part of the HR diagram. For these stars, differences in spectroscopic properties, photometric behaviour, kinematics and the interstellar environment contain the key to some of the problems, presently insurmountable, in the early evolution of the entire Orion Complex.

The most direct approach to the suggested relationship of Bok globules to star formation is to search for actual spots of star birth in or around them. But no protostellar objects have hitherto been found by infrared and/or radio observations. Optically relevant to this are the discoveries of some Herbig-Haro objects and pre-main sequence stars associated with cometary globules inside the Gum Nebula (Reipurth 1983).

An automatic spectral classification technique for objective-prism spectra is being developed.The procedure of selecting standard stars is described.The applicability of a linear polynomial regression model for choosing and calibrating the spectral criteria for Teff, Mv, [Fe/H] is demonstrated.

Radial velocity measurements with an objective-prism mounted on a Schmidt telescope.

A 62 cm diameter objective-prism is mounted on the CNRS-University of Liège Schmidt telescope at the Haute Provence Observatory. The field is 4 x 4° and the limiting magnitude is 12.5 on IllaJ hyper-sensitised plates. The dispersion is 200 A mm-1 at 4220 A. The plates are measured with a special machine and data are reduced by means of a computer with a correlation method. Stars of all spectral types are measured. The probable error is of some 4 km sec -1 over a mean of at least 3 plates. Already several lists of radial velocities of stars belonging to field situated at -30° of galactic latitude have been published. We have also started radial velocity observations for the Hipparcos Program.

Combined photoelectric – photographic UBV-photometry for NGC 2384 is discussed. The results achieved so far are summarized and indicate that this cluster is young enough to be used as spiral arm tracer out to a distance of 3.27 kpc. The colour excess E(B-V) is 0.31, the apparent distance modulus is 13m.50 and its earliest spectral type is BO.

Survey methods used at Asiago for finding supernovae and new variable stars are reviewed. Some by-products of the supernova searching are indicated. It is shown that the use of infrared emulsions is particularly effective for the discovery of new Mira-stars in Milky Way fields.

Objective-prism spectral surveys open the possibility to search for faint emission-line objects with the aim to complete their statistics and to pick out most interesting individual objects for further study. In the years 1964 - 1970 the Hamburg Hα Spectral Survey of the Northern Milky Way was accomplished using the Schmidt camera (80/120 cm, f= 240 cm) in Bergedorf with the following parameters: area 1 32° - 214°, -10°<b<+10°, 160 fields. Kodak 103aE + RG1, exp. 60min, widen. 10", 4° prism (580 Å/mm at Hγ ). As a main result the list of about 140 faint objects classified as planetary nebulae or possible planetary nebulae (Kohoutek,1965, 1969a,1972), and the identification of about 1500 new stars having Hα in emission (Kohoutek, Wehmeyer, in preparation) can be reported. The best known examples of this survey are K 3-50, a prototype of a compact H II region, and the symbiotic variable HBV 475 = V 1329 Cyg (Kohoutek, 1969b), which is also classified as a protoplanetary nebula.

The number of stars counted along a particular line of sight depends on the spatial distribution of stars, the luminosity function, and the absorption. Thus star count programs are designed to constrain or determine one or more of these functions. Early efforts to understand the structure of our Galaxy, including the fundamentals of stellar statistics, were largely based on work that involved star counts. Since then a growing appreciation has developed for the variety of forms the density function D(r) and the luminosity function Φ(M) can take, especially the recognition of different stellar populations, each with different density and luminosity functions. In the simplest formulation two distinct populations are considered: disk and halo. This suggests two distinct formation histories, but uncertainty in the picture remains (Eggen, Lynden-Bell and Sandage 1962; Ostriker and Thuan 1975; Saio and Yoshii 1979; Jones and Wyse 1983).

Our model of stellar population synthesis allows to derive synthetic star counts and distribution of colors, ages, and spectral types of stars in any given direction of observations. Here we compare results of the model with the distribution of stars in space and in absolute magnitude of stars of Gilmore and Reid. We find a small disagreement between observations of GR and predictions of our model in the space density of stars of 4 < Mv < 5. Ue show that this discrepancy can well be explained by a contamination of their sample of assumed main sequence stars by red giants and subgiants.

An automated method of general star counts has been developed for the purpose of deriving the distributions of extinction of large dark clouds. The result of the application to the Southern Coalsack is given.