• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.56.1-56.1
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• 2018

Astronomy education and research can benefit from a high performance telescope that is easily accessible in campus. Such a facility allows hands-on education of observations, small research projects, test of new instruments, and time-domian study of astronomical phenomena. Recently, SNU reconstructed a 40-year old observatory (also known as 구천문대), and established the new SNU Astronomical Observatory (SAO) on that site. On 2018 March 27, the 1-m optical telescope was successfully installed at SAO. Since then, this telescope has been producing wonderful images, with the best seeing value recorded being as small as 0.85 arcsec. This poster will give an overview of the 1-m telescope, and its performance based on test observations during the 2018A semester.

• Journal of The Korean Astronomical Society
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• v.23 no.2
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• pp.85-96
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• 1990

High resolution $^{12}CO$ observations of the region containing the planetary nebula Hb12 were made with the Nobeyama Radio Telescope. These observations reveal that there is no significant CO emission from Hb 12 itself. Near Hb 12, however, the observed regions show a structure of clustered dark clouds whose physical parameters suggest that these clumps would be further fragmented or collapesed. Also found with the high resolution observations is that a few isolated clumps are located away from the main CO feature extended possibly from the galactic plane. For more detail morphologies and velocity structures of the clumps, especially in relation to the large CO complex to which these are likely to be associated, more observations are substantiated.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.51.4-51.4
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• 2019

We started a systematic observational study of the 22 GHz water and 44 GHz class I methanol masers in 87 high-mass young stellar objects (HM-YSOs) as a KaVA large program (LP). The primary goal is to understand dynamical evolution of HM-YSOs and their circumstellar structures by measuring spatial distributions and 3-dimensional velocity fields of multiple maser species. In the first-year observations (2016-2017), we made snap-shot imaging surveys of 25 water and 19 methanol maser sources. In the second-year observations (2018-2019), we have carried out monitoring observations of 19 water and 3 methanol maser sources that were selected on the basis of the first-year survey results. By combining follow-up observations with VERA (distances), JVN/EAVN (6.7 GHz methanol masers), and ALMA cycles 3 and 6 (thermal lines/continuum), we will provide novel information on physical properties (density, temperature, size, mass), 3D dynamical structures of disk/jet/outflow/infalling envelope, and relationship between evolutionary of HM-YSOs. In this presentation, we will report the current status and future plans of our KaVA large program.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.100.1-100.1
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• 2012

Lunar limb profiles are needed for analyses of lunar occultations and solar eclipses. The lunar limb profile data by C.B. Watts (1963) have been used for such analyses, but it has been found that there are many kinds of errors in the data by Watts, which seriously affected the results obtained from the analyses of the observations. Recently very precise lunar topographic data were obtained by the Japanese lunar explorer Kaguya and NASA's Lunar Reconnaissance Orbiter. I obtained lunar limb profiles for any lunar librations from them. I will show how well the lunar limb profiles fit to observed ones from lunar grazing occultations. By combining the accurate lunar limb profiles with observations of lunar occultations we can detect errors in the Hipparcos stellar reference frame. By analyzing Baily's beads timing observations of past total and annular solar eclipses using the accurate lunar limb profiles we will be able to detect solar diameter variations.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.65.5-66
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• 2017

In the history of astronomy, observed data were interpreted very frequently based upon data measured at laboratories. For example, all the spectroscopic observations were understood via spectroscopic measurements on nuclei, atoms, and molecules. Recently, computational astrophysics plays a role of bridging experimental data to observations, in particular via numerical modeling of complex astronomical phenomena. This presentation focuses on computational nuclear astrophysics that connects experimental data on nuclei to high-energy observation data obtained by X-ray and gamma-ray telescopes. As an example case, X-ray burst will be discussed. In this phenomenon, observed X-ray light curves and spectra can be modeled by stellar evolution calculations that take nuclear reactions of rare isotopes as input information. This presentation also works as an introduction to the following presentation that will provide more detailed discussion on the experimental aspect of X-ray burst.

• Publications of The Korean Astronomical Society
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• v.11 no.1
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• pp.57-73
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• 1996

As a continuing effort to develop an automatic control system for small telescope, we developed the software for telescope control and CCD observations under DOS operating system. For accurate pointing of the telescope in short amount of time, we modelled the angular speed of the telescope by aquadratic function of time (constant acceleration) for the first 15 second and then linear function of time (zero acceleration) aftwewards. By changing the telescope speed from 'slew' to 'fine' before the telescope reaches the desired position, we could achieve the accuracy of a few arcsecond. The CCD control software was written for model CCD-10 of CCD Technology. This CCD can be used for guiding purposes. We also conducted the study for remote control of the telescope using telephone line. Although it cannot be used for real observations at the present form, we succeded in remotely pointing the telescope to desired direction. As faster communication technologies become widely available, simple observations can be made remotely in the near future. Finally we report some observational results made with the present control system.

• Publications of The Korean Astronomical Society
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• v.25 no.4
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• pp.155-165
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• 2010

In this study, we investigate the changes in the equatorial lodge degrees and polar distance degrees of determinative stars in the ancient Chinese archives. Confirmed is the fact that the coordinate values of those determinative stars defined in B.C. 104 had been used until the 8th century but were modified by the observations of Li Chunfeng (李淳風) in the early 7th century and Yixing (一行) in 723 A.D. The results of this study are compared with those in History of Chinese Astronomical Observations of Pan Nai. By applying the results of comtemporary astrodynamical calculations, their reliability is checked, and the corrected catalogues of Shi Shi (石氏) and Yixing are provided. The positional accuracy of those observations is estimated to be one degree.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.169-173
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• 2017

We provide a new physical insight on the hot molecular clouds near the nucleus of the obscured AGNs. We performed near-infrared spectroscopic observations of heavily obscured AGNs in order to reveal physical characteristics of molecular clouds, especially focused on the CO fundamental ro-vibrational absorption around $4.7{\mu}m$. We have made systematic moderate-resolution spectroscopic observations toward 30 representative (U)LIRGs using the AKARI/IRC, and some of the ULIRGs showed the strong CO absorption feature. For three bright (U)LIRGs that show a steep red continuum with the deep CO absorption feature, IRAS 08572+3915, UGC 05101, and IRAS 01250+2832, we have also made high-resolution spectroscopic observations using the Subaru/IRCS. We have successfully detected many absorption lines up to highly excited rotational levels, and these lines are very deep and extremely broad. The derived physical conditions of molecular clouds are extreme; the gas temperature is as high as several 100 to a 1000 K, the $H_2$ column density is larger than $10^{22}cm^{-2}$, and the gas density is greater than $10^7cm^{-3}$. Such hot and dense molecular clouds must exist around the central engine of the AGN.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.43.1-43.1
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• 2010

We have carried out 43-GHz VLBI test observations of the Korean VLBI Network (KVN), which has obtained the first fringes at 22/43-GHz in 2009 (a talk by Sohn, Bong Won). In collaboration with VERA (VLBI Exploration of Radio Astrometry) in Japan, we have observed Active Galactic Nuclei (AGNs) and Orion-KL at 43GHz on 22nd and 23rd December, 2009, in order to evaluate the baseline- and image-sensitivity of KVN and KVN+VERA. In this talk we report the preliminary results of the VLBI test observations of the Korean VLBI Network at 43GHz.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.106.2-106.2
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• 2012

A Jupiter-family comet, 17P/Holmes, underwent an outburst on 2007 October 23. Since there has been no more dramatic comet outburst than the 17P/Holmes event in the history of modern astronomical observations, active observations were made soon after the outburst. However, little is known about the activity before the outburst because of the accidental event. In addition, since the nucleus has been veiled by the thick dust cloud by the 2007 outburst, the physical status of the nucleus was unknown. In this presentation, we investigated the contrast between before and after the outburst through the imaging observations in both optical and mid-infrared wavelengths. We thus analyzed data taken by Akari infrared telescope, Subaru 8-m telescope, University of Hawaii 2.2-m telescope and Nishi-Harima Astronomical Observatory 2-m Nayuta telescope. As the result, we found that the nucleus was significantly activated through the outburst. The surface fractional active area was 0.3% in the pre-outburst data while 10% in the past-outburst data. We expect that 17P/Holmes shows strenuous activity in the next return in 2013-2014.