The VI CCD photometry is made for stars in the globular cluster M22 down to V ≈ 19m, I ≈ 18m. In the color-magnitude diagram (CMD), red giant branch (RGB), asymtotic giant branch (AGB) and blue horizontal branch (BHB) are well defined. The luminosity functions (LF) of RGB, AGB and BHB stars are derived, discussing deficient gaps and bumps in the CMD. The anomalously wide RGB seen in the BV photometric system is found to disappear in the VI photometric system.

The wide field (~20'×20') CCD photometry has been performed for more than 4,000 stars over a whole region of NGC 362 which is located inside the SMC halo. The Color-Magnitude diagram (CMD) and luminosit function (LF) for red giant branch (RGB) stars are presented, discussing a distinct bump along the RGB and some blue stars appearing in the blue horizontal branch (BHB) and above BHB. The anomalous globular cluster NGC 362 with highly populated red horizontal branch (RHB) stars is compared with the another anomalous globular cluster NGC 288 with highly populated BHB stars. A metal-rich, young blue component and metal-'poor, old red component of the SMC halo stars are examined.

We present the color-magnitude diagrams (CMD) of more than 24,000 stars in the field of an intermediate age open cluster M11, based on wide field CCD imaging. The morphology of the CMDs varies strikingly as the distance from the center of the cluster increases. From the surface number density analysis, we confirm the mass segregation effect in this cluster: the bright, massive stars are centrally more concetrated than the faint, low mass stars. The slope of the field-corrected surface density with respect to magnitude progressively increases as the radius increases, up to r = 5'. Most of the field stars in or near the cluster main sequence band and in the bright part of the red stars in the CMDs appear to be nearly at the same distance as M11, and they are considered to be the major component of disk stars in the Sagittarius-Carina arm.

NGC 6716 is an intermediate-age open cluster in Sagittarius. In this paper, we present the new UBV CCD photometry of the stars in the cluster, which is deeper than previous ones. From the color-color diagram and the color-magnitude diagram, we derived a reddening EB- V = 0.17±0.03 and a distance modulus of the cluster, (V - Mv)o = 9.2±0.1. An age of the cluster is estimated as 8 × 107 yrs from the latest isochrone. Luminosity function and mass function of the cluster are derived. The gradient of the mass function of bright stars is a bit steep, Γ = -1.85±0.05, and there is no distinct bump and dip in the mass function.

The previous study of chemical evolution of the Galaxy is extended to the radial properties of the Galactic disk. The present model includes radial dependency of the time-dependent bimodal IMF, radial flow of material in the disk, and the change of type I supernova explosion rate with radial distance from the disk center as model parameters and observed gas and stellar density distributions and metallicity abundance gradient as observational constraints. The results of two models in this study explain the observed gas and stellar density distributions well, with the slope of the gas density gradient in the region of 4.5 kpc<r<12kpc as -0.136dex/kpc in model Y1 and -0.123dex/kpc in model Y2, respectively, which fit well the observed gradient of -0.l1dex/kpc. The abundance gradient reproduced in model Y1 is getting flatter with decreasing radius, while that in model Y2 is getting steeper, which fits better the observed abundance gradient. This result shows the necessity of exponentially increasing type I supernova explosion rate with decreasing radius in order to explain the observed abundance gradient in the disk. The fitness of observed density distribution and star formation rate distribution justifies the reliability of time-dependent bimodal IMF as a compound quantitative chemical evolution model of the Galaxy. The temporal variations of metallicity gradients for carbon, nitrogen and oxygen are also shown.

31 white dwarfs in 10 open clusters are examined, and their maximum mass and the upper mass limit of their progenitors are obtained as 1.22±0.02M⊙ and 7.2±0.4⊙ respectively, suggesting that the upper mass limit of white dwarfs is less than 8M⊙. The final mass of white dwarfs shows no clear correlation with the initial mass of their progenitors, and it is found that a deficient gap of initial mass exists between ~4 and ~5.2M⊙. This gap seems to correspond to the mass range for carbon detonation or deflagration. The total expected numbers of white dwarfs are 11~22 in Hyades with 7 known white dwarfs and 17 in Praesepe with 8 known white dwarfs. These known white dwrfs are all younger than the others in both clusters. But one known white dwarf in Pleiades is older one among 2~3 expected white dwarfs.

We present test results of time-series CCD photometry to investigate the photometric precision of the BOAO (Bohyunsan Optical Astronomy Observatory) 1.8m telescope. A well-known field of the old open cluster M67, which includes two pulsating blue stragglers and two W UMa type binaries, was monitored for 3.5 hours on February 22, 1996. We have collected 148 V frames and 3 B frames. Photometric noises which consist mainly of photon noise and scintillation noise, were lowered down to about 1.9 mmag for stars of 10.m5 in M67 with exposure time of 20 seconds. From the C-M diagram for M67, a number of observational properties were derived; E(B-V) = 0.03, (V-Mv)o = 9.6, Age = 4 Gyr. We obtained light curves for four known variable stars and confirmed their variational characteristics. The pulsating blue stragglers show a low amplitude (about 0.01 mag) of light variation.

We have examined the photometric evolution of elliptical galaxies, using stellar evolutionary models covering the wide ranges of metallicity and mass, and the different IMFs (simple IMP & time-dependent bimodal IMF). The model with a time-dependent bimodal IMF can reproduce the observed integrated magnitudes and colors at all wavelengths. The computed model shows that the star formation in elliptical galaxies is still going on, although the number of newly born stars is very small. The chemical evolutionary effect is clearly seen in the C-M diagram of computed elliptical galaxies.

The BVR CCD photometry was performed for the globular cluster M13 down to V=19m over the region from the center to the west 13 arcmin and the CMD of M13 is investigated. The major photometric error in the crowded field which is due to the variation in the sky background was corrected by the median filtering method and the direct sky method. Some characteristics of the CMD of M13 obtained in the present study are as follows: Firstly, the distribution of stars on the CMD is well consistent with the mean lines of Sandage(1970) along the red giant branch(RGB), horizontal branch(HB) and asymtotic giant branch(AGB). Secondly, some gaps exists along the RGB and blue horizontal branch(BHB). Thirdly, the UV-bright stars are more concentrated at the inner region of the cluster.

The photometric evolution of cluster stars are examined for six synthetic clusters in the age range from 2.4 × 10 6 y r t o 7.6 × 10 8 y r by using the detailed evolutionary model calculation, and their results are compared with the observed integrated absolute magnitude and colors of 47 clusters. The reasonable agreements of the observed photometric parameters with the synthetic evolutionary sequences imply that there is a general form of time-dependent IMF including the noncoeval formation of stars and its detailed function is changed slightly with various environmental conditions of each primordial cloud.

New photoelectric UBV Photometry of 112 stars in open cluster M35 field was obtained. The distance modulus and age of the cluster are 9. m 3 (725pc) and 8.5 × 10 7 y r s , respectively. The internal differential reddening within the cluster is apparent.

The evolution of the Galaxy is examined by the halo-disk model, using the time-dependent bimodal IMF and contraints such as cumulative metallicity distribution, differential metallicity distribution and PDMF of main sequence stars. The time scale of the Galactic halo formation is about 3Gyr during which the most of halo stars and metal abundance are formed and ∼ 95 of the initial halo mass falls to the disk. The G-dwarf problem could be explained by the time-dependent bimodal IMF which is suppressed for low mass stars at the early phase (t < 1Gyr) of the disk evolution. However, the importance of this problem is much weakened by the Pagel's differential metallicity distribution which leads to less initial metal enrichment and many long-lived metal-poor stars with Z < 1 / 3 Z ⊙ The observational distribution of abundance ratios of C, N, O elements with respect to [Fe/H] could be reproduced by the halo-disk model, including the contribution of iron product by SNIs of intermediate mass stars. The initial enrichment of elements in the disk could be explained by the halo-disk model, resulting in the slight decrease and then the increase in the slopes of the [N/Fe]- and [C/Fe]-distributions with increasing [Fe/H] in the range of [Fe/H] < -1.

We construct a simple photometric evolution model of galaxies based on the evolutionary population synthesis. In our models an exponentially decreasing SFR with a power law IMF is used to compute the UBV colors of galaxies from ellipticals to late type spirals. It is shown that the integrated colors of galaxies with different Hubble type can be explained by one parameter, SFR.

New uvby photoelectric photometry was carried out for a δ Scuti variable, HR1170. By applying the Fourier method and the linear least square method, three frequencies were derived: f 1 = 10.06134 c / d ( P 1 = 0. d 0994 ). f 2 = 11.91754 c / d ( P 2 = 0. d 0839 ). f 3 = 18.96776 c / d ( P 3 = 0. d 0527 ). From the observed pulsational constants and from the phase difference and amplitude ratios for color(b-y) and magnitude y. three different pulsation modes (n, l) of f 1 ( 0 , 0 ) , f 2 ( 1 , 2 ) , f 3 ( 3 , 2 ) are deduced, indicating the existence of nonradial mode in HR1170. Some physical parameters indicate that HR1170 is evolving at the stage of H-shell burning.

Applying five morphological parameters defined along the main sequence (MS), red giant branch (RGB) and horizontal branch (HB) in the C-M diagram (CMD), and the transition period-luminosity relation for RR Lyrae variables, some basic physical quantities such as helium abundance, age, mass and luminosity are determined for 21 well observed globular clusters with combination of evolutionary models and atmospheric models properly chosen by the numerical test. The dependences of these quantities on the age and chemical abundance are investigated.

The ages of field stars given in the catalogue of Cayrel de Strobel et al. (1985) are derived by the five different methods with combination of theoretical isochrones. By using these ages and metal abundances homogenized by Lee and Choe (1988), the age-metallicity relations are obtained. For disk stars of [Fe/H] > -0.9, the present age-metallicity relations are nearly consistent with those given by Twarog (1980) and Carlberg et al. (1985).

We have examined how sensitively the extinction value determined by the method of star-count depends on such factors as the plate limit, the size of counting reseau, the non-linearity in the number distribution of stars with magnitude, and the angular resolution demanded by the given problem. We let the Poisson distribution portray the statistical nature of the countings, and chose the region containing the globule Barnard 361 as an example field. Uncertainties due to various combinations of the factors are presented in graphic forms: (1) Dynamic range in the extinction measurements is evaluated as a function of reseau size for varying plate limits. (2) Statistical errors involved in the star-count are analized in terms of the signal-to-noise ratio, the plate limit and the reseau size. (3) Systematic error due to the non-linearity in the number distribution are thoroughly analized. (4) Finally, a methodology is presented for correcting the systematic error in the observed radial density gradient. These graphs are meant to be used in selecting proper size of the reseau and in estimating errors inherent to the star-count analysis.

Combining the luminosity functions of main sequence stars in 3 associations and 22 open clusters, the initial luminosity function and mass function for these clusters are derived. For stars of m > 0.6 m ⊙ , they are well consistent with those for the field stars.

The temperature calibration of stars by photometric parameters and spectral type is discussed, using the catalogue data of Cayrel de Strobel et al. (1985) and Morel et al. (1976). The H-R diagrams and the mass-luminosity relation of stars in this catalogue are presented in the [log(L/M)-log T e ]-and [ M b o l -log(L/M)]-planes, respectively, discussing the age of main sequence (MS) stars and giant stars. The age-metallicity relation of the nearby stars suggests the initial rapid enrichment of metal abundance.

Using many homogeneous data of DDO and UBV colors for all luminosity classes and physical quantities known from spectroscopic observations, new calibration schemes with DDO photometric parameters are presented for metal abundance, effective temperature and surface gravity of stars. And an intrinsic color relation is derived for the reddening estimate.