We have estimated the fractal dimension of the molecular clouds in the Antigalactic Center based on the 12CO (J = 1- 0) and 13CO (J = 1- 0) database obtained using the 14m telescope at Taeduk Radio Astronomy Observatory. Using a developed code within IRAF, we were able to identify slice-clouds, and determined the dispersions of two spatial coordinates as well as perimeters and areas. The fractal dimension of the target region was estimated to be D = 1.34 for low resolution 12CO (J = 1 - 0) database, and D = 1.4 for higher resolution 12CO (J = 1 - 0) and 13CO (J = 1 - 0) database, where P ∝ AD/2. The sampling rate (spatial resolution) of observed data must be an important parameter when estimating fractal dimension. Our database with higher resolution of 1 arcminute, which is corresponding to 0.2 pc at a distance of 1.1 kpc, gives us the same estimate of fractal dimension to that of local dark clouds. Fractal dimension is apparently invariant when varying the threshold temperatures applied to cloud identification. According to the dispersion pattern of longitudes and latitudes of identified slice-clouds, there is no preference of elongation direction.

We present results of a H13CN J=1-0 mapping survey of molecular clouds toward the Galactic Center (GC) region of -1.6° ≤ l ≤ 2° and -0.23° ≤ b ≤ 0.30° with 2' grid resolution. The H13CN emissions show similar distribution and velocity structures to those of the H12CN emissions, but are found to better trace the feature saturated with H12CN (1-0). The bright components among multi-components of H12CN line profiles usually appear in the H13CN line while most of the dynamically forbidden, weak H12CN components are seldom detected in the H13CN line. We also present results of other complementary observations in 12CO (J=1-0) and 13CO (J=1-0) lines to estimate physical quantities of the GC clouds, such as fractional abundance of HCN isotopes and mass of the GC cloud complexes. We confirm that the GC has very rich chemistry. The overall fractional abundance of H12CN and H13CN relative to H2 in the GC region is found to be significantly higher than those of any other regions, such as star forming region and dark cloud. Especially cloud complexes nearer to the GC tend to have various higher abundance of HCN. Total mass of the HCN molecular clouds within |l|≤ 6° is estimated to be ~2 ×10 7 M⊙ using the abundances of HCN isotopes, which is fairly consistent with previous other estimates. Masses of four main complexes in the GC range from a few 10 5 to ~ 10 7 M⊙ All the HCN spectra with multi-components for the four main cloud complexes were investigated to compare the line widths of the complexes. The largest mode (45 km s-1) of the FWHM distributions among the complexes is in the Clump 2. The value of the mode tends to be smaller at the farther complexes from the GC.

We conducted a deep CCD observations in V band to obtain stellar density distribution and to determine the distances toward two molecular clouds with anomalous velocity in the Galactic anti-center region. Star count method based on the linear programming technique was applied to the CCD photometric data. We found two prominent peaks at distances of around 1.4 and 2.7 kpc. It is found that the first peak coincides well with stellar density enhancement of B8-A0 stars and the second one with the outer Perseus arm. The effect of the choice of the luminosity function is discussed. The stellar number density distribution is used to derive the distances to the molecular clouds and the visual extinctions caused by the clouds. We found that two molecular clouds are located almost at the same distance of about 1.1 ± 0.1 kpc, and the peak extinctions caused by the clouds are about 2.2 ± 0.3 mag in V band.

The structure and environments of the molecular clouds near the SNR HB3(G132.7±1.3) HB3(G132.7±1.3) are studied. The molecular complex which is located at the southern rim of HB3 was proposed by former investigators as the one interacting with HB3. This complex region of 2∘×2∘atl=133∘ 2∘×2∘atl=133∘ has been observed at 12CO,13CO,J=1−0ata1′ 12CO,13CO,J=1−0ata1′ , resolution with the 14-m radio telescope at Taeduk Radio Astronomy Observatory. We have reached to the following four conclusions. The possibility that these molecular complex and HB3 are interacting with each other cannot be supported with any of our data. The morphologies of the two show no similarities. Neither particular features for the interaction are found in the CO lines. The hypothetical 'Molecular wall' which was expected to exist on the northwestern rim of HB3 as a cause for the noncircular morphology of HB3 is turned out to be nonexistent in CO. The molecular complex which resembles a 'bar' at a low resolution is now resolved into a U-shaped shell. It seems that the U-shape is consist of two independent components. No peculiarities, such as unseen masses or bright stars capable of forming HlI regions, are found within the U-shape region. The total mass included in the complex is estimated to be Mtotal=2.9\~8.4×105M⨀ Mtotal=2.9\~8.4×105M⨀ , which is in good agreement with previous observations within errors. Considering about 12 clumps distinguishable within the complex, the total mass implies that masses of each of clumps are on the order of 104M⨀ 104M⨀ , which makes these good objects for further studies in relation to star-formation. Especially the clumps associated with W3 are worthy for more high resolution observations for better understanding of astrophysical phenomenon ongoing in them.

We have studied the IR properties of molecular clouds in the region of the supershell GS234-02 using IRAS and COBE data. The mean values of dust color temperature and optical depth at 240μm are derived to be 15.4±1.5 K and 9.0±5.7×10-4, respectively, which agree well with those determined by Sodroski et al.(1994) for the outer Galaxy. Mean IRAS colors, R12/100= 0.074, R25/100= 0.052, R60/100= 0.219, indicate that the abundance of PAHs is enhanced but other particles are nearly the same as those of the solar neighborhood. We found the anticorrelation between R100/140 and R140/240. It cannot be explained by the thermal emission of traditional big grains. The anticorrelation implies that, at high ISRF, T100/140 underestimates the equilibrium temperature, while T140/240 overestimates it and, at low ISRF, vice versa. Therefore we propose to use the intensity ratio, R100/240 as a dust thermometer.

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.

We have reviewed three different techniques to estimate molecular cloud mass, and discussed the uncertainties involved. We found that determination of the most important parameter, the 13CO 13CO abundance, is not very sensitive to the real LTE conditions, and that any possible error in deriving LTE column density may not introduce an error in the total gas column density, as far as the visual extinction is established for the object cloud. The virial technique always endows the largest mass estimate as there are several uncertainties, even if the cloud is in virial equilibrium. The strong indicator of the cloud perturbation is the centroid velocity dispersion. The mass using CO luminosity is based on the empirical law, but weakly dependent on the virial assumption, thus it still gives a larger mass estimate. The mass discrepancy is likely to be inevitable, and a factor of two or three difference between mass estimates could easily be attributed to the uncertainties mentioned above. The LTE mass estimate may be the most reliable one if we use the relation visual extinction and 13CO 13CO column density of the object cloud, and the intercept is included.

We present two codes which estimates virial mass and LTE mass using IMFORT interface within IRAF (Image Reduction and Analysis Facility). It is discussed that threshold value (temperature or CO integrated intensity), which defines a reasonable cloud boundary and size, is the most important parameter determining accurate results. Several virial masses are to be obtained using the vir task, as well as three velocity dispersions including the centroid velocity dispersion, a turbulence indicator. LTE mass is to be estimated by using task lte as well as three by-product images. The 13CO 13CO abundance and threshold temperature of 13CO 13CO and 12CO 12CO peak temperatures are the most critical parameters in LTE technique.

We have searched for the 2 mm transitions of H 2 C O H + ( 2 02 − 1 01 ) and H 2 13 C O ( 2 02 − 1 01 , 2 12 − 1 11 , a n d 2 11 − 1 10 ) toward the dense interstellar molecular clouds Orion A, TMC-1 and L134N using the FCRAO 14 m telescope. None of the transitions have been detected except the H 2 13 C O transitions toward Orion-KL. We set upper limits for the abundances of the protonated formaldehyde ion ( H 2 C O H + ) , which are close to the abundances expected from ion-molecule chemistry.