• Publications of The Korean Astronomical Society
• /
• v.14 no.1
• /
• pp.9-22
• /
• 1999

Current searches for gravitational microlensing events are being carried out only by a photometric method. In this review paper, we demonstrate that the nature of Galactic lenses can be significantly better constrained with the additional astrometric observations of microlensng events. First, by astromerically observing lensing events, one can resolve the lens parameter degeneracy, and thus the lens mass can be determined with improved precision. Second, by being free from the blending problem, astrometric observations of lensing events will allow one to improve the uncertainties in the determined Einstein time scales. Third, the lens brightness, which could not be measured photometrically, can be measured from the astrometric observations of lensing events, and thus the nature of lens matter can be better constrained. Finally, with the help of astrometric followup observations of a binary-lens event, one can uniquely determine the solution of lens parameters, allowing one to obtain important astronomical information about the source star and the lens itself.

• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.385-386
• /
• 1996

A wide-field CCD detector for solar eclipse observations is discussed. The CCD is supposed to be of a moderate size, and the image of the corona is obtained by scanning the field of view. Results of the 1995 solar eclipse observation are shown which have been made with a prototype of the scanning CCD detector.

• Publications of The Korean Astronomical Society
• /
• v.32 no.1
• /
• pp.175-177
• /
• 2017

In order to reveal physical conditions of molecular gas in active galaxies (active galaxies mean both starbursts and AGNs in this paper), we carried out systematic observations (R = 19 ~ 120) of CO fundamental band at $4.7{\mu}m$ in absorption with AKARI. We also made follow-up CO absorption observations at higher spectral resolution (R = 5000 ~ 1000) with Subaru. Recently, Herschel made extensive observations of highly-excited CO lines in emission in the far-infrared. The two data sets (absorption and emission) sometimes provide us with apparently inconsistent results. One case is starburst galaxies: Subaru observations showed low temperature of molecular gas toward the starburst NGC 253, while Herschel detected highly excited CO lines in the starburst. This suggests that warm molecular clouds are more deeply embedded than newly formed star clusters. The other case is obscured AGNs; Herschel detected highly excited CO lines in emission in nearby AGNs, while AKARI and Subaru observations showed CO absorption only in some of the obscured AGNs. This could reflect the difference of nature of molecular tori in these AGNs. We propose the combination of the absorption and emission observations as an effective tool to reveal geometry of warm molecular clouds in active galaxies.

• The Bulletin of The Korean Astronomical Society
• /
• v.6
• /
• pp.13.1-13.1
• /
• 1981

• The Bulletin of The Korean Astronomical Society
• /
• v.28 no.2
• /
• pp.57-57
• /
• 2003

• The Bulletin of The Korean Astronomical Society
• /
• v.9
• /
• pp.4.2-4.2
• /
• 1984

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.241-245
• /
• 2015

In this work we present the results of light curve analysis for two cataclysmic variables detected recently in the SDSS project: SDSS J090350.73+330036.1 and J150240.98+333423.9. Photometric observations of the first were obtained during a superoutburst in May 2010. Our observations clearly indicate the presence of superhumps in the light curves, suggesting SDSS J090350.73+330036.1 is an SU UMa dwarf nova. We determined the period of the superhumps. We also carried out fitting using a spiral-arm model in order to determine parameters of the accretion disk, hot line, and other components of this system. Photometric observations of the second, J150240.98+333423.9, were obtained during the post-maximum decline, during April-June 2012. Photometric variability of this system has been studied in an inactive state. We obtained its parameters via a combined model fitted to the observed light curves by ${\chi}^2$ minimization.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.44.2-44.2
• /
• 2013

We probe the feasibility of high-frequency radio observations of very rapid flux variations in compact active galactic nuclei (AGN). Our study assumes observations at 230 GHz with a small 6-meter class observatory, using the SNU Radio Astronomical Observatory (SRAO) as example. We find that 33 radio-bright sources are observable with signal-to-noise ratios larger than ten. We derive statistical detection limits via exhaustive Monte Carlo simulations assuming (a) periodic, and (b) episodic flaring flux variations on time-scales as small as tens of minutes. We conclude that a wide range of flux variations is observable. This makes high-frequency radio observations - even with small observatories - a powerful probe of AGN intra-day variability; especially, those observations complement observations at lower radio frequencies with larger observatories like the Korean VLBI Network (KVN).

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.60.1-60.1
• /
• 2019

In this talk, I will briefly review the discovery and early-time interferometric observations of the Galactic Center radio source and then go through recent major updates including the improvement in the array capabilities, developments of the scattering and intrinsic structure modeling, and high-frequency astrometric observations of this source. Introduction of the 1.3 mm VLBI observations in 2017 and 2018 (e.g. array configuration and signal-to-noise ratios), as well as the related multi-wavelength campaign (including GMVA and EAVN observations), will be also presented.

• Publications of The Korean Astronomical Society
• /
• v.32 no.1
• /
• pp.5-9
• /
• 2017

This paper provides an overview of the AKARI mission, which was the first Japanese satellite dedicated to infrared astronomy. The AKARI satellite was launched in 2006, and performed both an all-sky survey and pointed observations during its 550 days in the He-cooled mission phases (Phases 1 and 2). After the He ran out, we continued near-infrared observations with mechanical cryocoolers (Phase 3). Due to a failure of its power supply, AKARI was turned off in 2011. The AKARI data are unique in terms of the observed wavelengths as well as the sky coverage, and provide a unique legacy resource for many astronomical studies. Since April 2013, a dedicated new team has been working to refine the AKARI data processing. The goal of this activity is to provide processed datasets for most of the AKARI observations in a Science Ready form, so that more users can utilize the AKARI data in their astronomical research. The data to be released will include revised All-Sky Point Source Catalogues, All-Sky Image Maps, as well as high-sensitivity images and spectra obtained by pointed observations. We expect that the data will be made public by in the Spring of 2016.