We examine the morphology and luminosity distribution of a strongly warped spiral galaxy PGC 20348 by conducting a detailed BVI CCD surface photometry using BOAO 1.8m telescope. The radial surface brightness shows a break at warp radius rω with a shallow gradient in the inner disk and a steeper gradient in the outer disk. The luminosity of east side of the disk is ~0.5 mag fainter than the west side at r > rω. The reason for the asymmetric luminosity distribution is thought to be the asymmetric flarings that result in the formation of a large diffuse region at the edge of the east disk and a smaller diffuse region at the west disk. The vertical luminosity profiles show a thick disk component whose scale heights increase with increasing galactocentric distances. The warp of PGC 20348 seems to be made by the tidal interactions with the two massive companion galaxies since the flarings and radial increase of disk scale heights are thought to be general properties of tidally perturbed disks. According to the colors of the two clumps inside the diffuse region at the edge of the east disk, they seem to be sites of active star formation triggered by tidal forces from the companion galaxies.

Numerical simulations based on the smoothed particle hydrodynamics (SPH) is performed to investigate the dynamical properties of barred galaxies that have nuclear rings. The nuclear ring morphology depends on the relative strength of bar potentials. Nuclear rings form between the two ILRs and align perpendicular to the bars unless the bar potentials are strong enough to allow the x1 orbits near the ILRs. Shock dissipation plays a critical role in the formation of nuclear rings.

We have studied the central parts of M82, which is a well-known infrared luminous, starburst galaxy, by analyzing archival data from the Infrared Space Observatory (ISO). M82 was observed at 11 positions covering ±45" from the center along the major axis. We analyzed 4 emission lines, [ArIII] 8.99 μm, H2 17.034 μm, [FeII] 25,98 μm, and [SiII] 34,815 μm from SWSO2 data. The integrated flux distributions of these lines are quite different. The H2 line shows symmetric twin peaks at ~18" from the center, which is a general characteristic of molecular lines in starburst or barred galaxies. This line appears to be associated with the rotating molecular ring at around ~200 pc just outside the inner spiral arm. The relative depletion of the H2 line at the center may be due to the active star formation activity which dissociates the H2 molecules. The other lines have peaks at the center and the distributions are nearly symmetric. The line profiles are deconvolved assuming that both intrinsic and instrumental profiles are Gaussian. The velocity dispersion outside the core is found to be ~50 km s-1. The central velocity dispersion is much higher than 50 km s-1, and different lines give different values. The large central velocity dispersion (σ) is mostly due to the rotation, but there is also evidence for a high σ for [ArIII] line. We also generated position-velocity maps for these four lines. We found very diverse features from these maps.

Open clusters are useful tools to investigate the structure and evolution of the Galactic disk. We have started a long-term project to obtain UBVI CCD photometry of open clusters which were little studied before, using the Doyak 1.8 m telescope of Bohyunsan Optical Astronomy Observatory in Korea. The primary goals of this project are (1) to make a catalog of UBVI photometry of open clusters, (2) to make an atlas of open clusters, and (3) to survey and monitor variable stars in open clusters. Here we describe this project and report the first results based on preliminary analysis of the data on four open clusters in the survey sample: Be 14, Cr 74, Biu 9, and NGC 2355. Isochrone fitting of the color-magnitude diagrams of the clusters shows that all of them are intermediate age to old (0.3-1.6 Gyrs) open clusters with moderate metallicity.

We have studied the response of molecular clouds in the Galactic disk to a rotating bar by conducting Smoothed Particle Hydrodynamics (SPH) simulations for the Galaxy in order to understand the dynamical structures of the Galactic Center (GC) molecular clouds, and their implications. In our study it was found that the structures of GC molecular clouds could be induced by the combined effects of rotating bar potential, the hydrodynamic collisions and gravitational miss collisions between the clouds.

On the basis of observational constraints, particularly the relationship between metal abundance and cumulative stellar mass, a simple two-zone disk-halo model for the chemical evolution of our Galaxy was investigated, assuming different chemical processes in the disk and halo and the infall rates of the halo gas defined by the halo evolution. The main results of the present model calculations are: (i) The halo formation requires more than 80% of the initial galactic mass and it takes a period of 2 ∼ 3 × 10 9 yrs. (ii) The halo evolution is divided into two phases, a fast collapse phase ( t = 2 ∼ 3 × 10 8 yrs) during which period most of the halo stars ( ∼ 95 are formed and a later slow collapse phase which is characterized by the chemical enrichment due to the inflow of external matter to the halo. (iii) The disk evolution is also divided into two phases, an active disk formation phase with a time-dependent initial mass function (IMF) up to t ≈ 6 × 10 9 yrs and a later steady slow formation phase with a constant IMF. It is found that at the very early time t ≈ 5 × 10 8 yrs, the metal abundance in the disk is rapidly increased to ∼ 1 / 3 of the present value but the total stellar mass only to ∼ 10 of the present value, finally reaching about 80% of the present values toward the end of the active formation phase.

Photoelectric drift scans of nearby galaxies, M106, M31 and M33 have been made at diurnal rate with the 61cm Cassegrain Reflector at Sobacksan Observing Station. Luminosity profiles of M106 and M31 show the asymmetries between east and west sides of the galaxies and the near side of each galaxy exhibits a larger B-V color than the far side. B-V color distribution in the central part of MI06 shows somewhat unusual feature of a blue center with red surrounding regions, and this is an opposite trend to the ordinary color distribution of most of external galaxies. B-V color of M31 is nearly constant in the central part of the galaxy while U-B color decreases as the distance from the center increases.