• Acta Via Serica
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• v.8 no.2
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• pp.25-52
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• 2023

The astronomic observatory of Graw Village is located on Mount Dari Lolikan, facing the village. Graw is located in the foothills of Mount Ser-i-Rash, 25 km northeast of Erbil Governorate, Iraq. This study attempts to clarify the foundations of this observatory, its components, as well as the founder and the date of its establishment. The study made efforts to clarify the benefits of this calendar to local residents in their daily lives. The database for this study is based on direct observation of the observatory station. The observation included the recording date and position of sunset and the appearance of stars throughout the year. Observation and documentation for both sunset and stars were performed over several years due to weather conditions since observation was not possible on foggy and rainy days and nights. Each observation took five to ten minutes depending on the clarity of the sky. The observatory consists of a group of stone cones. Each cone was built by stones in a specific location after careful and long observation of the sunset. Efforts were made to observe the disappearance and reappearance of the stars based on the change in the position of the Earth in relation to the sun. Graw's calendar helped to recognize important times of the year, such as the winter and summer forties, which were very important, especially when snow covered the roads, transportation stopped, crops spoiled, and pets stayed in their barn. The most important features of the winter forties are the memories, experiences, and minds of the villagers' ancestors. The forties were associated with the arrival of cold and heavier rain throughout the year, which is consistent with modern science, as the angle at which the Earth rotates increases the number and activity of weather depressions that affect the study area during this period. This observatory has a close connection with the daily life of the villagers, especially in the past centuries. It helped the people of the area in their appointments to carry out their work in the field of agriculture. The observatory was also of great importance in the field of education in the past centuries, especially in traditional religious schools. It also appears from this research that the calendar has ancient roots, which extend back thousands of years, as evidenced by the Ezidis who follow an ancient religion whose roots extend back thousands of years and who fast during both the winter and summer forties annually, with the participation of people in various regions of the world. It is not known who made this astronomic observatory but most of the oral information that has been passed down to us by word of mouth agrees on both Mullah Abdullah Al-Kurdi and Mullah Omar. Likely, this astronomic observatory was built around the late 17^th and early 18^th centuries.

• Journal of The Korean Astronomical Society
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• v.27 no.1
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• pp.81-102
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• 1994

We have decomposed the 11-cm radio continuum emission of the W51 complex into thermal and non-thermal components. The distribution of the thermal emission has been determined by analyzing HI, CO, and IRAS $60-{\mu}m$ data. We have found a good correlation between the 11-cm thermal continuum and the 60- 11m emissions, which is used to obtain the thermal and non-thermal 11-cm continuum maps of the W51 complex. Most of the thermal continuum is emanating from the compact H II regions and their low-density ionized envelopes in W51A and W51B. All the H II regions, except G49.1-0.4 in W51B, have associated molecular clumps. The thermal radio continuum fluxes of the compact H II regions are proportional to the CO fluxes of molecular clumps. This is consistent with the previous results that the total mass of stars in an H II region is proportional to the mass of the associated molecular clump. According to our result, there are three non-thermal continuum sources in W51: G49.4-0.4 in W51A, a weak source close to G49.2-0.3 in W51B, and the shell source W51C. The non-thermal flux of G49.5-0.4 at 11-cm is $\~28 Jy$, which is $\~25\%$ of its total 11-cm flux. The radio continuum spectrum between 0.15 and 300 GHz also suggests an excess emission over thermal free-free emission. We show that the excess emission can be described as a non-thermal emission with a spectral index ${\alpha}{\simeq}-1.0 (S_v{\propto}V^a)$ attenuated by thermal free-free absorptions at low-frequencies. The non-thermal source close to G49.2-0.3 is weak $(\~9 Jy)$. The nature of the source is not known and the reality of the non-thermal emission needs to be confirmed. The non~thermal shell source W51C has a 11-cm flux of $\~130Jy$ and a spectral index ${\alpha}{\simeq}-0.26$.

• Journal of Astronomy and Space Sciences
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• v.9 no.1
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• pp.41-51
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• 1992

Photoelectric observations of close binary stars, AO Cam and AW Cam, were made during the 1984 observing season with the 61cm reflector at the Sobaeksan Observatory. One time of primary minimum for AO Cam and three primary epochs for AW Cam were derived from the observations of these two systems. Times of minimum light of these two binaries collected from literature were analyzed with a least square fitting method. New improved light elements for AO Cam and AW Cam were determined. The orbital period of AO Cam had been constant from Octobar, 1980 (JD 244520) to February, 1985 (JD 2446107). However, one secondary time of minimum (JD 2447864.7879) of AO Cam published recently by Mullis and Faulkner(1991) shows large deviation of about 4.6 minutes ($0^d.0032$) from the one predicted by our new light elements. Future observations of times of minima for this system are needed to test this period change. The orbital period of AW Cam has been constant as P=$0^d.77134645$ for about sixty years from the early 1930's to the present.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.41.2-41.2
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• 2016

The follow-up BVRI photometric observations of NSVS 1461538, which was discovered as an $Algol/{\beta}$ Lyr eclipsing variable by Hoffman, Harrison & McNamara (2009), were performed for three years from 2011 to 2013 by using the 61-cm telescope and CCD cameras of Sobaeksan Optical Astronomy Observatory (SOAO). New light curves have deep depths both of the primary and secondary eclipses, rounded shapes outside eclipses and a strong O'Connell effect, indicating that NSVS 1461538 is a typical W UMa close binary system rather than an $Algol/{\beta}$ Lyr type binary star. A period study with all the timings shows that the orbital period may vary in a sinusoidal way with a period of about 5.6 yr and a small semi-amplitude of about 0.008 d. The cyclical period variation was interpreted as a light-time effect due to a tertiary body with a minimum mass of $0.66M{\odot}$. The first photometric solution with the Wilson-Devinney binary model shows that the system is a W-subtype contact binary with the mass ratio ($q=m_c/m_h$) of 3.46, orbit inclination of 85.6 deg and fill-out factor of 30%. From the existing empirical relationship between parameters, the absolute dimension was estimated. The masses and radii of the component stars are $0.28M{\odot}$ and $0.71R{\odot}$ for the less massive but hotter primary star, respectively, and $0.96M{\odot}$ and $1.21R{\odot}$ for the more massive secondary, respectively. Possible evolution of the system is discussed in the mass-radius and the mass-luminosity planes.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.279-282
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• 2005

We report the millimeter-wave radio observations of molecular cloud cores in Taurus. The observed line is the $N_2H^+$ emission at 93 GHz, which is known to be less affected by molecular depletion. We have compared starless (IRAS-less) cores with star-forming cores. We found that there is no large difference between starless and star-forming cores, in core radius, linewidth, core mass, and radial intensity profile. Our result is in contrast with the result obtained by using a popular molecular line, in which starless cores are larger and less condensed. We suggest that different results mainly come from whether the employed molecular line is affected by depletion or not. We made a virial analysis, and found that both starless and star-forming cores are not far from the critical equilibrium state, in Taurus. Together with the fact that Taurus cores are almost thermally supported, we conclude that starless Taurus cores evolve to star formation without dissipating turbulence. The critical equilibrium state in the virial analysis corresponds to the critical Bonnor-Ebert sphere in the Bonnor-Ebert analysis (Nakano 1998). It is suggested that the initial condition of the molecular cloud cores/globules for star formation is close to the critical equilibrium state/critical Bonnor-Ebert sphere, in the low-mass star forming region.

• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.211-222
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• 2005

Results of 6 nights of CCD VR photometry of the nova-like variable V603 Aquilae (Nova Aquilae 1918) obtained at the Mallorcian 35-cm telescope in July 2004 are reported. The ephemeris for the superhump maximum is Max.HJD=2453213.60546(96)+0.14813(10)E. The waves with $3.^d9,\;1.^d4,\;0.^d135$ are statistically significant, which may be interpreted as the negative superhump-orbital, the beat periods (negative superhump- positive superhump) and the negative superhump with low amplitude, respectively. Another possible time-scale is $0.^d8,$ which has no coincidence with the beat periods. Quasi-periodic oscillations with an effective period of 18 minutes have been detected, which are close to 15.6 minutes reported by some authors. Their effective semi-amplitudes are $^m.045\;and\;0^m.051$ for V and R, respectively. This corresponds to the 0.12 mag excess in the color index V-R as compared with the mean color, which can be understood as the pulsed emission in the hotter inner parts of the accretion disk, similar to that observed in TT Ari and MV Lyr.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.74.1-74.1
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• 2012

It is known that the diffuse H${\alpha}$ halos around bright H II regions are more extended than the dust-scattered halos around point sources and the line ratios [S II] ${\lambda}$6716/H${\alpha}$ and [N II] ${\lambda}$6583/H${\alpha}$ observed outside of bright H II regions are generally higher than those in H II regions. These observational facts have been regarded as evidence against the dust-scattering origin of the diffuse H${\alpha}$ emission and the effect of dust-scattering has been neglected in studying the diffuse H${\alpha}$ emission. In this paper, we find, however, that dust-scattered halos of H II regions should be more extended than those of point sources and is in good agreement with the observed H${\alpha}$ profiles around H II regions. We also found that the observed line ratios [S II]/H${\alpha}$, [N II]/H${\alpha}$, and He I ${\lambda}$5876/H${\alpha}$ in the diffuse regions can be well reproduced with the dust-scattered halos around H II regions which are photoionized by late O- and/or early B-type stars in the interstellar medium with the abundances close to those of the warm neutral medium. Therefore, we conclude that the diffuse H${\alpha}$ emission may originate mostly from the dust-scattering.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.42.2-42.2
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• 2017

The Large Magellanic Cloud (LMC) is a unique target to study the detail structures of molecular clouds and star-forming regions, due to its proximity and face-on orientation from us. Most part of the astrophysical subjects for the LMC have been investigated, but the magnetic field is still veiling despite its role in the evolution of the interstellar medium (ISM) and in the main force to influence the star formation process. Measuring polarization of the background stars behind interstellar medium allows us to describe the existence of magnetic fields through the polarization vector map. In this presentation, I introduce the near-infrared polarimetric results for the $39^{\prime}{\times}69^{\prime}$ field of the northeastern region of the LMC and the N159/N160 star-forming complex therein. The polarimetric observations were conducted at IRSF/SIRPOL 1.4 m telescope. These results allow us to examine both the global geometry of the large-scale magnetic field in the northeastern region and the close structure of the magnetic field in the complex. Prominent patterns of polarization vectors mainly follow dust emission features in the mid-infrared bands, which imply that the large-scale magnetic fields are highly involved in the structure of the dust cloud in the LMC. In addition, local magnetic field structures in the N159/N160 star-forming complex are investigated with the comparison between polarization vectors and molecular cloud emissions, suggesting that the magnetic fields are resulted from the sequential formation history of this complex. I propose that ionizing radiation from massive stellar clusters and the expanding bubble of the ionized gas and dust in this complex probably affect the nascent magnetic field structure.

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.123-125
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• 2007

NGC 1333 is a nearby star forming region, and IRAS 4A and IRAS 4BI are low-mass Class 0 protostars. IRAS 4A is a protobinary system. The NGC 1333 IRAS 4 region was observed in the 22 GHz water maser with a high resolution (0.08") using the Very Large Array. Two groups of masers were detected: one near A2 and the other near BI. Most of the masers associated with A2 are located very close (< 100 AU) to the radio continuum source. They may be associated with the circumstellar disk. Since no maser was detected near AI, the A2 disk is relatively more active than the Al disk. Most of the masers in the BI region are distributed along a straight line, and they are probably related with the outflow. As in many other water maser sources, the IRAS 4 water masers seem to trace selectively either the disk or the outflow. Considering the outflow lifetimes, the disk-outflow dichotomy is probably unrelated with the evolutionary stage of protostars. A possible explanation may be that both the outflow-maser and the disk-maser are rare phenomena and that detecting both kinds of maser around a single protostar may be even rarer.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.46.1-46.1
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• 2017

Class I methanol masers are found to be good tracers of the interaction between outflows from massive young stellar objects with their surrounding media. Although polarization observations of Class II methanol masers have been able to provide information about magnetic fi elds close to the central (proto)stars, polarization observations of Class I methanol masers are rare, especially at 44 and 95GHz. We present the results of linear polarization observations of 39 Class I methanol maser sources at 44 and 95GHz. These two lines are observed simultaneously with one of the 21m Korean VLBI Network telescopes in single-dish mode. Approximately 60% of the observed sources have fractional polarizations of a few percent in at least one transition. This is the fi rst reported detection of linear polarization of the 44GHz methanol maser. We also observed 7 targets with the KVN in VLBI mode. We will present its preliminary results, too.