• Journal of The Korean Astronomical Society
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• v.46 no.6
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• pp.253-259
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• 2013

We present near-infrared light curves of HBC 722 after its the September 2010 outburst. We have been monitoring its near-infrared light curves since November 2010 with Korean Astronomy and Space Science Institute Infrared Camera System (KASINICS). HBC 722 exhibits large changes in optical and near-infrared brightness since its outburst. The J, H, and $K_s$ light curves over about 2.5 years show that in all observed bands HBC 722 progressively became fainter until around April 2011, down to J ~10.7, H ~9.9, $K_s$ ~9.3, but it is getting brighter again. Large scatter in the obtained light curve prevents us from finding whether there is any short timescale variation as reported in other optical observations. The near-infrared color of HBC 722 is becoming bluer since its outburst. The pre-outburst Spectral Energy Distribution (SED) of HBC 722 is consistent with that of a slightly reddened Class II YSO with the exception of the extraordinary IR-excess in the far-infrared region.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.147.2-147.2
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• 2011

We have initiated a long-term identification campaign of supernova remnant candidates in X-ray regime. In the short-listed unidentified sources from the ROSAT All Sky Survey, we have chosen the brightest candidate, G308.3-1.4, as our pilot target for a dedicated investigation with Chandra X-ray Observatory. Our observation has revealed an incomplete shell-like X-ray structure which well-correlated with the radio feature. Together with the spectral properties of a shocked heated plasma, we confirm that G308.3-1.4 is indeed a supernova remnant. A bright X-ray point source which locates close to the remnant center is also uncovered in this observation. Its spectral behavior conform with those observed in a rare class of neutron stars. The properties of its optical/infrared counterpart suggests the evidence for a late-type companion star. Interestingly, possible excesses in B-band and H-alpha have been found which indicate this can be an accretion-powered system. With the further support from the putative periodicity of ~1.4 hrs, this source can possibly provide the direct evidence of a binary system survived in a supernova explosion for the first time.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.76-76
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• 2011

The SPICA (SPace Infrared Telescope for Cosmology & Astrophysics) project is a next-generation astronomical mission optimized for mid- and far-infrared observation with a cryogenically cooled 3m-class telescope. Due to its high angular resolution and unprecedented sensitivity, SPICA will enable us to resolve many key issues from the star-formation history of the universe to the planetary formation. As an international collaboration, KASI proposed the near-infrared instrument which is composed of two parts; (1) science observation with the capability of imaging and spectroscopy covering $0.7{\mu}m$ to $5{\mu}m$ (FPC-S) (2) fine guiding to stabilize and improve the attitude (FPC-G). Here, we present the current status of SPICA/FPC.

• Journal of The Korean Astronomical Society
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• v.25 no.1
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• pp.1-9
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• 1992

We present new approach to analysis of velocity data of globular clusters. Maximum likelihood method is applied to get model parameters such as central potential, anisotropy radius, and total mass fractions in each mass class. This method can avoid problems in conventional binning method of chi-square. We utilize three velocity components, one from line of sight radial velocity and two from proper motion data. In our simplified scheme we adopt 3 mass-component model with unseen high mass stars, intermediate visible stars, and low mass dark remnants. Likelihood values are obtained for 124 stars in M13 for various model parameters. Our preferred model shows central potential of $W_o=7$ and anisotropy radius with 7 core radius. And it suggests non-negligible amount of unseen high mass stars and considerable amount of dark remnants in M13.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.58.2-58.2
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• 2016

FU Orionis 형 별들은 폭발 현상(outburst)을 일으키며 급작스럽게 변광 하는 전주계열(PMS) 변광성의 한 부류(class)이다. 원형(prototype)인 FU Orioins를 비롯하여 이와 비슷한 분광 특성을 갖는 이 그룹은 FUors로 알려져 왔다. 이와 같은 유형의 별들이라도 주변 환경 및 원반의 활동에 따라서 광학 분광선들의 모양이나 특징은 다르게 나타난다. 2013년 2월부터 2016년 3월까지 보현산 천문대의 BOES 분광기로 6개의 FUors (FU Ori, V1057 Cyg, V1515 Cyg, HBC 722, V582 Aur, 2MASS J06593158-0405277)에 대한 고분산 스펙트럼을 얻었다. 발머선을 포함한 여러 파장대의 선들을 비교 분석 하였으며 주요 분광선의 변화 양상을 나타내고 그 변화 원인을 유추하고자 한다.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.118-118
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• 2011

We executed a simultaneous survey of 22 GHz water maser and 44 GHz methanol maser toward 290 shocked $H_2$ emitting regions, which were identified from the galactic plane survey at $H_2$ 2.122 micrometer (UKIRT Widefield Infrared Survey for $H_2$; UWISH2). The primary goal of this observation is to characterize the H2 emission sources whether they are sincerely due to the outflows of young stellar objects or other shocked emission from older/evolved objects. We discovered 15 water maser sources and 15 methanol maser sources which provide the detection rate of around 5 percents. Most of detected sources have IRAS sources, infrared dark clouds, and/or submilimeter sources in the beam size of KVN single dish. In this poster, we will present the detailed results of our survey observation and discuss about the star formation rate in the galactic plane.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.109.2-109.2
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• 2011

We have carried out a multi-epoch, simultaneous 22GHz $H_2O$ and 44GHz class I $CH_3OH$ maser survey of 109 low-mass protostars. $H_2O$ maser emission was detected in 23 sources, while $CH_3OH$ maser emission in 12 sources. Eight of the $CH_3OH$ detected sources are new detections. For comparison, only four low-mass protostars have been previously found to emit the maser emisison. We investigate difference between the properties of the two masers, such as relative velocity with respect to molecular gas and variability. We also compare the isotropic luminosities of both masers with the bolometric luminosity of the central star.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.45.3-46
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• 2021

Supernovae classes have been defined phenomenologically, based on spectral features and time series data, since the specific details of the physics of the different explosions remain unrevealed. However, the number of these classes is increasing as objects with new features are observed, and the next generation of large-surveys will only bring more variety to our attention. We apply the machine learning technique of multi-label classification to the spectra of supernovae. By measuring the probabilities of specific features or 'tags' in the supernova spectra, we can compress the information from a specific object down to that suitable for a human or database scan, without the need to directly assign to a reductive 'class'. We use logistic regression to assign tag probabilities, and then a feed-forward neural network to filter the objects into the standard set of classes, based solely on the tag probabilities. We present STag, a software package that can compute these tag probabilities and make spectral classifications.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.47.1-47.1
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• 2018

The NISS (Near-infrared Imaging Spectrometer for Star formation history) onboard NEXTSat-1 have successfully developed by KASI. The capability of both imaging and spectroscopy is a unique function of the NISS. At first, it have realized the low-resolution spectroscopy (R~20) with a wide field of view of $2{\times}2deg$. in a wide near-infrared range from 0.95 to $2.5{\mu}m$. The major scientific mission is to study the cosmic star formation history in local and distant universe. It will also demonstrate the space technologies related to the infrared spectro-photometry in space. Now, the NISS is ready to launch in late 2018. After the launch, the NISS will be operated during 2 years. As an extension of the NISS, the SPEHREx (Spectro-Photometer for the History of the Universe Epoch of Reionization, and Ices Explorer) is the NASA MIDEX (Medium-class Explorer) mission proposed together with KASI (PI Institute: Caltech). It will perform the first all-sky infrared spectro-photometric survey to probe the origin of our Universe, to explore the origin and evolution of galaxies, and to explore whether planets around other stars could harbor life. Compared to the NISS, the SPHEREx is designed to have much more wide FoV of $3.5{\times}11.3deg$. as well as wide spectral range from 0.75 to $5.0{\mu}m$. After passing the first selection process, the SPHEREx is under the Phase-A study. The final selection will be made in the end of 2018. Here, we report the status of the NISS and SPHEREx missions.

• Journal of The Korean Astronomical Society
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• v.52 no.1
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• pp.11-21
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• 2019

Intensive Monitoring Survey of Nearby Galaxies (IMSNG) is a high cadence observation program monitoring nearby galaxies with high probabilities of hosting supernovae (SNe). IMSNG aims to constrain the SN explosion mechanism by inferring sizes of SN progenitor systems through the detection of the shock-heated emission that lasts less than a few days after the SN explosion. To catch the signal, IMSNG utilizes a network of 0.5-m to 1-m class telescopes around the world and monitors the images of 60 nearby galaxies at distances D < 50 Mpc to a cadence as short as a few hours. The target galaxies are bright in near-ultraviolet (NUV) with $M_{NUV}$ < -18.4 AB mag and have high probabilities of hosting SNe ($0.06SN\;yr^{-1}$ per galaxy). With this strategy, we expect to detect the early light curves of 3.4 SNe per year to a depth of R ~ 19.5 mag, enabling us to detect the shock-heated emission from a progenitor star with a radius as small as $0.1R_{\odot}$. The accumulated data will be also useful for studying faint features around the target galaxies and other science projects. So far, 18 SNe have occurred in our target fields (16 in IMSNG galaxies) over 5 years, confirming our SN rate estimate of $0.06SN\;yr^{-1}$ per galaxy.