The first results of BVRI CCD photometry of the cluster IC 166, obtained at the new telescope IAC80 at the Observatorio del Teide (Tenerife, Spain) are presented. Using the Daophot crowded field photometric package, different color-magnitude diagrams were constructed and some cluster properties (reddening, distance and age) studied.

The present paper deals with the results of electrophotometric observations of 59 components of 19 trapezia in the Stroemgren and Crawford six-colour photometric system.

From MAMA measurements of Tautenburg and OCA Schmidt plates we obtained proper motions and photographic UBVR photometry for ca. 45 000 stars up to B = 19 mag within a 17 square degree region in the Pleiades. An accuracy of 0.6 mag and 2 mas/year was estimated for magnitudes and proper motions, respectively. A sample of 554 cluster members was separated by use of both astrometric and photometric information on stars.

In a series of emission-line star survey programs we have conducted wide and deep survey observations for Hα emission stars in the Orion star-forming region. The first result for the Kiso area A-0904 (5°x5°, centered at α = 5h40m and δ = +0°) was presented in Paper I (Wiramihardja et al., 1989), followed by Paper II (Kogure et al., 1989) for the area A-0903 (α = 5h20m, δ = −5° and A-0976 (α = 5h40m, δ = −5°). In Paper IV the results for the areas A-1047 (α = 5h20m, δ = −10° and A-1048 (α = 5h40m, δ = −10°) are given.

Statistical distances to the known galactic symbiotic stars are derived from the calibration of the absolute K magnitude of galactic bulge symbiotic giants versus spectral type. The resulting space distributions of S, D and yellow symbiotic stars are studied.

It is well-known that the velocities and distributions of stars perpendicular to the Galactic plane indicate the presence of unseen or missing mass in the local disk of the Milky Way. In spite of an abundance of papers on this subject, no consensus seems to have been reached on not only the amount of dark matter, but even on a “correct” method of analysis.

We investigate the kinematics of the thick disk population using photometric and astrometric sample surveys towards two opposite directions at intermediate latitude. A multivariate discriminant analysis (MDA) is used to distinguish the ‘Thick Disk’ from other populations with the help of the Besançon model of population synthesis. The data constrain the asymmetric drift of the thick disk population, which is found to be 40±10 km/s and does not depend on the galactic radius.

All models of the visual Galaxy are verified only in fields with galactic latitude |b| > 20°. At lower galactic latitudes, all the broad-band photometric systems and the majority of medium-band photometric systems fail to classify stars due to interstellar reddening. For the Vilnius photometric system the interstellar reddening is not an obstacle.

The aim of our stellar population study is to investigate the kinematical and chemical characteristics of the thin disk, thick disk and halo of the Galaxy. We have selected 51 stars in 2 astrometric and photometric surveys at l = 42°, b = +79° (Soubiran 1992) and l = 167°, b = +47° (Ojha et al. 1994), on the basis of the Reduced Proper Motion Diagram. They were observed with the 193cm telescope at Observatoire de Haute-Provence, with the CARELEC spectrograph (dispersion of 66Å/mm, FWHM of 3.0Å, range λλ4600 – 5500Å), together with 43 comparison stars with known fundamental parameters. The derivation of Teff, logg and [Fe/H] was done differentially using a grid of synthetic spectra and the comparison stars, as described in Cayrel et al. (1991). Twenty of the target stars were found to be more deficient than −0.5. In the (V, [Fe/H]) distribution, the halo stars are clearly separated from the other stars with a mean of (V, [Fe/H]) ≃ (−210km/s, – 1.4dex). Because of the small size of the sample, it was not possible to discriminate the thick disk from the thin disk. We have taken 200 more spectra, and with these new observations, we hope to be able to deconvolve the 3 populations in the (U, V, W, [Fe/H]) space as we did previously with the (U, V) velocity (Soubiran 1993).

The iron abundance of 160 disk and halo F-G-dwarfs is determined from 6-m spectra of 60 stars and published equivalent width data. Kurucz's (1979) model atmospheres and WIDTH6 programme are used for iron abundance determination. We have shown that FeI lines are formed under non-LTE conditions (Bikmaev et al.,1990), and so used Fell lines for iron abundance determination, following Bikmaev (1991). The use of the FeII lines and high quality homogeneous spectroscopic data decreases systematic and accidental errors and allows us to obtain qualitatively new results (Bikmaev, 1994). The distribution of the sample of stars is a non-monotonous function of metallicity: at least 3 groups of stars are seen, corresponding to the three Galaxy populations - disk ([Fe/H]=+0.1 to −0.3), thick disk ([Fe/H]=−0.7 to −0.8) and halo ([Fe/H]=−1.3 to −2.0). In contrast with previous studies, a sharp boundary in the kinematic characteristics (the eccentricity of space orbits and angular velocity) was found at [Fe/H]=−0.9, the boundary between disk and halo stars. These kinematic properties demand a relatively long time between halo and disk formation. The average metallicity of the thick disk stars is very close to the metallicity of the Large Magellanic Cloud. Perhaps an explanation is merging during the approach of the LMC to the Galaxy several billion years ago.

The availability of photometric and astrometric star counts on large fields well distributed in the Galaxy allows us to measure the characteristics of the thick disc population. We use a total of 19 data sets in UBV towards a dozen directions in order to measure the scale height, scale length, local density and metallicity of the intermediate population.

We have analyse star-count data in the direction of the Galactic Poles using a model of stellar population synthesis (Robin & Crézé (1986), Bienaymé, Robin & Crézé (1987)). The HR diagram for disc stars in the model is computed for a given star formation rate history and initial mass function (Haywood, 1994). In a paper submitted to A&A (Haywood et al.), we give a detailed investigation of the effects of these two functions on the simulated star-counts, and compare these with observed V, B-V data from V=5 to 22. We have obtained new constraints on the SFR, which we show has remained constant (to within a factor <3) since the disc formation, and on the IMF in the intermediate mass range (1-2 M⊙). Finally, we also obtain new constraint on the increase of vertical velocity dispersion with age. We state that if the disc does not containt any dynamically important dark mass, then this relation saturates at value smaller than 21 km.s−1.

A long standing issue in Astronomy is the amount of unseen matter in the Galactic disk. This has been addressed many times since Oort (1960) showed that about half the local disk mass is in unseen material. Oort's method infers the disk mass via the vertical change in density and velocity dispersion of appropriate tracer stars. Recently, Kuijken and Gilmore (1989) analysed a sample of K dwarfs at the South Galactic Pole and found in fact no compelling evidence for dark matter in the disk — a conclusion also reached by Bienaymé, Robin and Crézé (1987) based on faint star count data. However, Bahcall, Flynn and Gould (BFG, 1992), analysed K giants at the South Galactic Pole, and while they corroborated the Oort result, they could state at only the 85% confidence level that at least some disk matter is ‘missing’. Here we describe the Flynn and Fuchs (1994) analysis of a sample of nearby K-giants, which they combine with the BFG sample. The combined sample can be well fit without dark matter in the disk. The fit can be improved using a small amount of disk dark matter: our best fit has a disk surface density of Σ⊙ = 53 ± 13 M⊙ pc−2, compared to Σ⊙ = 49 ± 9 M⊙ pc−2 for the known disk matter. We conclude the disk is relatively light and the dark halo makes a significant contribution to the rotation curve at the sun.

An investigation has been made to determine the relationship between kinematic and chemical properties of stars covering nearly all population types in the Galaxy. For this purpose, a sample has been taken of about 1150 high-galactic-latitude F–K stars down to V = 14.0, for which photoelectric seven-color data in the Vilnius medium-band system were collected at the Maidanak Observatory in Uzbekistan, Central Asia. Combining the obtained photometric material with the proper motion and radial velocity data enabled us to compute kinematic parameters of the sample stars and then to make plots of the galactic orbital eccentricities, angular momenta, and velocity dispersions versus [Fe/H], with much attention drawn to the region where the transition between the thin disk and halo occurs.

The chemical composition of 11 suspected RHB stars in the galactic field was recently analyzed using high-resolution spectra obtained with the 6-meter telescope of the Special Astrophysical Observatory, North Caucasus. We summarize here some of the main conclusions obtained from comparison of the abundances of the RHB stars with available abundances of giants and dwarfs (hereafter G and D).

The discussions about stellar populations and their spatial distribution can be best advanced by studies of special and well defined star types. The study of subdwarf B stars provides great promise: it is relatively easy both to find sdB stars and to determine their physical parameters.

The total mass of the Milky-Way dark corona and its contribution to the total mass of the Galaxy, is estimated by combining the limits imposed by the Local Group as probably bound and the constraints on the local escape velocity. The results: total mass of the Milky Way about 1.6 TM⊙ (dark corona over 1.5 TM⊙; T = 1012), local escape velocity about 600 kms−1.

CCD photometry of the halo cluster Pall in Thuan-Gunn system is presented. The color - magnitude diagrams (Fig. 1) show a well defined red horizontal branch, lower giant branch and main-sequence down to about two magnitudes below the main-sequence turnoff. The giant branch is absent and the brightest stars are horizontal-branch stars. The horizontal branch is composed of red stars only. The age of the cluster, determined by comparison with the isochrones of Bell and Vanden Berg (1987) is consistent with an age between 12 – 14 Gyr. and a metallicity [Fe/H] = −0.79. The observed luminosity function shows a deficiency of stars from about 0.5 mag below turnoff up to g = 21 mag. A distance modulus of (m – M)g0 = 15.35 ± 0.1 magnitude has been derived. An estimate of the cluster structural parameters gives rc = 1.7 pc and c = 1.46. A mass estimate of 1.6 × 103M⊙ and mass-to-light ratio 1.77 has been obtained, using King's (1966) method.

The FOCAP multi-object system on the Anglo-Australian Telescope (AAT) has been used to observe 35 faint stars (V > 18, Mv > + 4.6) and 83 stars with V < 18 in 47 Tuc. The large sample of stars well below the turnoff permits us to examine abundance variations in relatively unevolved stars for the first time. Our spectral resolution (2.7Å) is greater than that used in previous studies.

This poster reports the isolation of a new, complete sample of 24 faint halo B stars. These B stars were selected as blue- and ultraviolet-excess objects in the US survey at high Galactic latitudes (Usher and Mitchell 1990), and were given preliminary classifications using low-resolution spectrophotometry. The new sample is complete over 206 square degrees of sky to faint magnitude completeness limits in the range B = 16.5 and B = 18.3.

Stromgren color indices for the US B stars have been derived from the spectrophotometry through numerically convolved filters (Howell 1986). The colors have been used to help define the red completeness limit of the sample at (b – y) = −0.01, at the B9.5/A0 classification boundary. In addition, surface gravity and temperature estimates useful for separating the hotter B stars from sdB stars have been provided by atmospheric model fitting to the existing spectra (cf. Saffer et al. 1994).