• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.241-242
• /
• 1996

The UBV observations of the close binary system CW Cephei were made from August 198:3 to December 1984 during 25 nights using the 61cm Boller and Chivens reflector at the Sobaeksan Astronomy Observatory. The new UBV light curves were analyzed with the recent Wilson-Devinney binary model. Our photometric solution for CW Cep were well consistent with those of Clausen &. Gimenez (1991). Using our photometric solution and Popper & Hill (1991) spectroscopic one, each absolute masses and radii of components for CW Cep were derived as 13.63 M$\bigodot$ and 5.83 R$\bigodot$ for the primary, and 12.18 M$\bigodot$ and 5.14 R$\bigodot$ for the secondary, respectively.

• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.143-144
• /
• 1996

Two-component models (normal star and degenerate star components) are the simplest realization of clusters with a mass spectrum because the high mass stars quickly evolve off leaving degenerate stars behind, while low mass stars survive for a long time as main-sequence stars. In the present study we examine the post-collapse evolution of globular clusters using two-component Fokker-Planck models that include three-body binary heating. We confirm that a simple parameter ${\epsilon}{\equiv} (E_{tot}/t_{rh})/(E_c/t_{rc})$ well describes the occurrence of gravothermal oscillations of two-component clusters. Also, we find that the degree of instability depends on the steepness of the mass function such that clusters with a steeper mass function are less exposed to instability.

• Publications of The Korean Astronomical Society
• /
• v.9 no.1
• /
• pp.9-20
• /
• 1994

We observed the molecular transitions of $^{12}CO(1-0)$, $^{13}CO(1-0)$, $C^{18}O(1-0)$, CS(2-1), $HCO^+(1-0)$, and HCN(1-0) toward the high-latitude mole cular cloud MBM12. We derived total $H_2$ column densities for the two velocity components using the optically thin $C^{18}O$ transition. Molecular abundances have been derived for the observed species at the core of this cloud, which appear to be less than an order of magnitude in fractional abundances relative to $H_2$, compared to typical cold dark clouds.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.51.4-52
• /
• 2017

We present the derived kinematic characteristics of low-${\alpha}$ thin-disk and high-${\alpha}$ thick-disk stars in the Milky Way, investigated with a sample of about 33,900 G- and K-type dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Based on the level of ${\alpha}$-element enhancement as a function of [Fe/H], we separate our sample into thin- and thick-disk stars and then derive mean velocity, velocity dispersion, and velocity gradients for the U, V and W velocity components, respectively, as well as the orbital eccentricity distribution. There are notable gradients in the V velocity over [Fe/H] in both populations: -23 km s-1 dex-1 for the thin disk and +44 km s-1 dex-1 for the thick disk. The velocity dispersion of the thick disk decrease with increasing [Fe/H], while the velocity.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.45.1-45.1
• /
• 2010

Using SOHO particle and EUV detection and radio spectrograms from both ground-based and spaceborne instruments, we have studied the first phase of major solar energetic particle (SEP) events associated with wide and fast coronal mass ejections (CMEs) centered at different solar longitudes. Observations support the idea that acceleration of SEPs starts in the helium-rich plasma of the eruption's core well behind the CME leading edge, in association with coronal shocks and magnetic reconnection caused by the CME liftoff; and those "coronal" components dominate during the first ~1.5 hour of the SEP event, not yet being hidden by the CME-bow shock in solar wind. At magnetic connection to the eruption's periphery, onset of SEP emission is delayed for a time of the lateral expansion that is visualized by global coronal (EIT) wave. The first, "coronal" phase of SEP acceleration is followed by a second phase associated with CME-driven shock wave in solar wind, which accelerates high-energy ions from a helium-poor particle population until the interplanetary shock slows down to below 1000 km/s. Based on these and other SOHO observations, we discuss what findings can be expected from STEREO in the SOHO era perspective.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.39.2-39.2
• /
• 2010

We have investigated the evolution of the galaxy morphology in the hierarchical universe taking advantage of Semi-Analytic Model (SAM). It is well known that the galaxy morphology is related to the dynamical and the chemical evolution. This implies that we need to understand overall physical processes in the galaxy to reproduce its morphology. Thus we implemented gradual hot gas stripping of satellite galaxies in a galaxy cluster and recycling of stellar mass losses into our model in order to describe star formation rate of galaxies accurately. To morphologically classify galaxies, the evolution of disc and bulge components is traced carefully. We compute our models based on the dark matter halo merger trees generated by N-body simulations as well as the Extended Press-Schechter (EPS) formalism. We present morphological differences caused by the use of different merger trees.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.1
• /
• pp.59.1-59.1
• /
• 2017

Massive Population III black hole binary systems are one of the suggested candidate sources of the recently detected gravitational wave radiation (GWR). GWR detection from a black hole binary system requires a sufficiently short orbital separation at the time of their formation, such that they would undergo coalescence within the Hubble time. This condition cannot be simply fulfilled by a short initial period, because binary interactions such as mass transfer and common envelope evolution can largely change the orbital parameters and the masses of stellar components. Here, we discuss the possibility of black hole binary mergers from massive Pop III binary systems, using a new grid of Pop III binary evolutionary models with various initial primary masses ($20M_{\odot}{\leq}M{\leq}100M_{\odot}$) and initial separations, for different initial mass ratios (q = 0.5 - 0.9).

• Journal of The Korean Astronomical Society
• /
• v.37 no.4
• /
• pp.217-222
• /
• 2004

High ambient interstellar pressure is suggested as a possible factor to explain the ubiquitous ob-served growth-rate discrepancy for supernova-driven super bubbles and stellar wind bubbles. Pressures of P / k ${\~} 10^5\;cm^{-3}$ K are plausible for regions with high star formation rates, and these values are intermediate between the estimated Galactic mid-plane pressure and those observed in starburst galaxies. High-pressure components also are commonly seen in Galactic ISM localizations. We demonstrate the sensitivity of shell growth to the ambient pressure, and suggest that super bubbles ultimately might serve as ISM barometers.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.149.2-149.2
• /
• 2011

We performed the cross-correlation analysis on energy-dependent light curves of the Z-type source GX 5-1. We observed X-ray delays of a few hundred seconds between hard (16-30 keV) and soft (2-5 keV) X-ray light curves. During these phenomena, the centroid frequency of horizontal branch oscillation (HBO) was found to shift to lower or higher frequency indicating towards the dynamical movement of a Compton cloud or an inner disk front. Both eastern and western approaches were used to unfold the X-ray continuum and systematic changes were observed in soft and hard X-ray spectral components. Simultaneous energy spectral and power density spectral study shows that the production of HBOs is closely related to the Comptonizing region rather than the accretion disk. We discuss the results in the context of re-condensation of coronal material in the inner accretion disk region.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.69.1-69.1
• /
• 2013

We are developing Adaptive Optics (AO) system for 1m telescope at Gwacheon National Science Museum Observatory. The beam spot of the Gwacheon 1m telescope. The tip-tilt correction system consists of a CMOS sensor, a tip-tilt mirror and a feed back loop. The beam spot location at the CMOS sensor indicates the tip-tilt components of the incoming light. The tip-tilt mirror is controlled by DAC output voltage calculated by proportional-integral-derivative (PID) controller. This system successfully corrects the tip-tilt motion of the spot.