We present UBV CCD photometry of the double cluster NGC 1850 located at the NW edge of the bar of the Large Magellanic Cloud. The color-magnitude diagram shows that NGC 1850 has a prominent population of massive core-He burning stars which is incomparably richer than any other known star clusters. The reddening is estimated from the (U-B) - (B-V) diagram to be E(B - V) = 0.15±0.05. We have estimated the ages of NGC 1850 and a very compact blue star cluster (NGC 1850A) located at ~30" west of NGC 1850 using isochrones based on the convective overshooting models: 80 ±10 Myrs and 5 ± 2 Myra, respectively. Several evidence suggest that it is probably the compact cluster NGC 1850A that is responsible for the arc-shaped nebulosity (Henize N 103B) surrounding the east side of NGC 1850.

More than 22,300 stars in NGC 6752 were measured over the region of 5' < r < 23' in B and V AAT plates. The most of these are main sequence(MS) stars and about 130 blue horizontal branch(BHB) stars were detected. The C-M diagram of all measured stars shows gaps appearing at V≈15.m2 and 16.m2 along the red giant branch(RGB) and their appearance shown by Lee & Cannon(1980) is found to be independent of measured region. The bimodal distribution of BHB stars is confirmed again and a wide gap shown by Lee & Cannon(1980) at V≈16m is clearly seen for stars in the outer part (8' < r < 13') in the cluster. It is noted, however, that this gap is occupied by about a dozen of BHB staIs located in the inner region (5' < r < 8'). The number ratio of bright BHB star (V < 15m) to faint BHB stars (V > 15m) decreases with increasing radial distance from the cluster center. Three faintest BHB stars were found, and two stars (V≈18.m5) of there are located in the inner region of r≈6' and the other faintest one (V≈19.m3) located in the outer part of r≈13'. Also a bluest star of (B - V) ≈ -0.5 at V≈17.m2 is found but it is located at the outer part of r≈13' in NE region. Therefore, the membership of the faintest BHB star and bluest star is suspected. The luminosity function(LF) and mass function(MF) for NGC 6752 were derived for MS stars. The LF for stars of Mv< 6m in the outer part of r > 8' shows a consistency with that derived by Penny & Dickens(1986).

The UBVIKC CCD photometry was performed in the central region(~ 20' × 20') of the extremely young open cluster IC1805. Member stars were selected in the (B-V)-(U-B) and (V-I)-(B-V) color-color planes. Applying recent stellar evolutionary models, we derived the age, age-spread, and initial mass function(IMF) of the cluster. IC1805 was found to be an extremely young(tage ~ 1.5Myr) and has a flat IMF with the slope of Γ=-1.0±0.2.

We present UBVRI CCD photometry of the Type Ie supernova SN 19941 in M51 which was discovered on April 2, 1994 (UT). UBVRI CCD photometry of SN 1994 I were obtained for the period of the first two months from April 4, 1994, using the Seoul National University Observatory 60 cm telescope. The light curves of SN 19941 show several interesting features: (a) SN 19941 reaches the maximum brightness at B-band on April 8.23 (B = 13.68 mag), at V-band on April 9.10 (V = 12.89 mag), and at I-band on April 10.32 (I = 12.48 mag); (b) The light curves around the maximum brightness are much narrower than those of other types of supernovae; (c) The light curves after the peak decline more steeply than those of other types of supernovae; and (d) The colors get redder from (V-R) ≈ 0.2 mag ((V - I) ≈ 0.3 mag, (B - V) ≈ 0.7 mag) on April 4 to (V-R)≈ 0.6 mag ((V-1) ≈0.9 mag, (B-V) ≈ 1.3 mag) on April 18. Afterwards (V - R) colors get bluer slightly (by ~0.005 mag/day), while (V-I) colors stay almost constant around (V-1) ≈ 1.0 mag. The color at the maximum brightness is (B-V)=0.9 mag, which is ~1 mag redder than the mean color of typical Type la supernovae at the maximum brightness. The light curves of SN 1994I are similar to those of the Type Ie supernova SN 1962L in NGC 1073. Adopting the distance modulus of (m-M)0 = 29.2 mag and the reddening of E(B - V) = 0.45 mag [Iwamoto et al. 1994, preprint for ApJ], we derive absolute magnitudes at the maximum brightness of SN 1994I, Mv(max) = -17.7 mag and MB(max) = -17.4 mag. This result shows that SN 1994I was ~2 mag fainter at the maximum brightness compared with typical Type Ia supernovae. A narrower peak and faster decline after the maximum in the light curve of SN 1994I compared with other types of supernovae indicate that the progenitor of SN 1994I might be a lower mass star compared with those of other types of supernovae.

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.

We developed an Automatized Differential Photometry System (ADPS) to achieve high time resolution and high efficiency in the photometric observations of short period variable stars. This ADPS has been introduced to the CCD camera system attached to the 6lcm Reflector at Sobaeksan Astronomy Observatory. Several new algorithms were devised for the controlling the telescope. the star recognition in a CCD frame and the aperture photometry, etc..As the result, the differential photometric observation was fully automatized without any manual control, and much faster data acquisition could be achieved over the conventional photoelectric differential photometry.

The Automated Eichner Iris Photometer(AEIP) at the Korea Basic Science Center was tested for its function and the proper procedure for photographic photometry. The AEIP requires about three hours for reaching the electrical stability. When the iris is controlled automatically, the repeatability of density unit (DU) is accurate in the uncertainty of (0.0028∼0.0048 0.0028∼0.0048 )DU. The iris reading is found to be accurate within the mean error of 0.m05 0.m05 , which could be reduced to 0.m02 0.m02 by the manual control. To check the applicability of the AEIP. each two photographic plates for UBV colors which were taken by Dupuy and Zukauskas(l976) for the open cluster Byur 2, were measured by using the AEIP. and the photographic magnitudes and colors of the stars in Byur 2 were determined. discussing the previous results.

We have conducted surface photometry of a spiral galaxy NGC4419, by making use of photographic plates in U, B, V and R-bands taken by 105cm Schmidt Camera at Kiso Observatory. Two dimensional surface brightness distributions as well as luminosity profiles along the major axis are examined in detail to decipher the morphological properties of the galaxy. Analysis of the color distributions of NGC4419 shows that B-V and U-B colors remain constant throughout the galaxy with a weak trend of blue bulge in B-V color. The blue bulge might indicate an active star formation in the nucleus of NGC4419. For a quantitative analysis of the luminosity distribution of NGC4419, the observed luminosity profiles are decomposed into bulge and disk components, assuming the bulge component to follow de Vaucouleurs γ 1 / 4 − l a w while the disk component is assumed to be exponential. The fitting generally fails at the central part and at the shoulder near r = 15' where bulge and disk components overlap. The failure at the central part cannot be attributed wholly by the seeing disk since the core-radius of the central plateau is much larger than the width of point spread function. The failure at shoulder could be due to the luminosities from the spiral arms.

We have conducted BVI photographic surface photometry of four spiral galaxies NGC1087, NGC2715, NGC2844 and NGC3593, by making use of the Kiso Schmidt plates. Detailed examination of the morphological properties of the galaxies using isophotal maps and luminosity profiles showed that all the program galaxies have some peculiarities in their luminosity distributions. NGC1087 and NGC2715 have extremely small nuclei with inner rings which contain several bright HII regions. NGC2844 has a very large bulge whose luminosity dominates over the disk luminosity in all the radii. The I-band luminosity profile of NGC3593 shows shallower gradient than B- and V-band profiles. We were able to successfully decompose the luminosity profile into a bulge following de Vaucouleurs γ 1 / 4 − l a w and an exponential disk only for NGC 3953. Other galaxies have more complicated luminosit profiles.

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.