• 천문학회지
• /
• 제29권2호
• /
• pp.269-278
• /
• 1996

We present the color-magnitude diagrams (CMD) of more than 24,000 stars in the field of an intermediate age open cluster M11, based on wide field CCD imaging. The morphology of the CMDs varies strikingly as the distance from the center of the cluster increases. From the surface number density analysis, we confirm the mass segregation effect in this cluster: the bright, massive stars are centrally more concetrated than the faint, low mass stars. The slope of the field-corrected surface density with respect to magnitude progressively increases as the radius increases, up to r = 5'. Most of the field stars in or near the cluster main sequence band and in the bright part of the red stars in the CMDs appear to be nearly at the same distance as M11, and they are considered to be the major component of disk stars in the Sagittarius-Carina arm.

• 한국임상약학회지
• /
• 제8권2호
• /
• pp.139-142
• /
• 1998

The effects of MeOH extracts from 28 herbal medicines on monoamine oxidase (MAO) activity were investigated. MAO was purified from mouse brain and its activity was determined by fluoro-photometry using kynuramine as a substrate. Three MeOH extracts, Coptis japonica, Cinnamomum cassia and Poncirus trifoliate from the herbal medicines showed a strong inhibitory effect with less than $100\;{\mu}g/ml$ in their inhibitory amounts of $50\%$ ($IC_{50}$ values) on MAO activity. Four MeOH extracts including Evodia officinalis exhibited a mild inhibition of MAO activity with $100-200\;{\mu}g/ml$ in their $IC_{50}$ values.

• 천문학논총
• /
• 제30권2호
• /
• 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.

• 천문학회보
• /
• 제44권2호
• /
• pp.49.1-49.1
• /
• 2019

I present the mean metallicity distribution of stars in the Milky Way based on photometry from the Sloan Digital Sky Survey. I utilize an empirically calibrated set of stellar isochrones developed in previous work to estimate the metallicities of individual stars to a precision of 0.2 dex for reasonably bright stars across the survey area. I also obtain more precise metallicity estimates using priors from the Gaia parallaxes for relatively nearby stars. Close to the Galactic mid-plane (|Z| < 2 kpc), a mean metallicity map reveals deviations from the mirror symmetry between the northern and southern hemispheres, displaying wave-like oscillations. The observed metallicity asymmetry structure is almost parallel to the Galactic mid-plane, and coincides with the previously known asymmetry in the stellar number density distribution. This result reinforces the previous notion of the plane-parallel vertical waves propagating through the disk, which have been excited by a massive halo substructure such as the Sagittarius dwarf galaxy plunging through the Milky Way's disk. This work provides evidence that the Gaia phase-space spiral may continue out to |Z| ~ 1.5 kpc.

• 천문학회보
• /
• 제39권2호
• /
• pp.83.1-83.1
• /
• 2014

Kepler-47 is the first multi-body circumbinary planetary system detected by the Kepler space telescope. The two planets were detected by the transit method. In the discovery paper the authors report about the presence of an additional transit-like signal in their dataset which cannot be explained by a four-body (binary + 2 planets) system. Therefore it is likely that the unexplained signal could be due to a third planet. In this talk I will present recent results from a dynamical investigation of the five-body system (binary + 3 planets). We have applied the MEGNO technique to detect regions of quasi- or near quasi-periodic orbits of a hypothetical third planet. Quasi-periodic regions exists for a third planet and the long-term stability has been tested. Although the existence of a third planet is most likely to be confirmed from transit photometry we calculate transit-timing variation (TTV) signals due to the third planet which also can be used to infer its presence.

• 천문학논총
• /
• 제19권1호
• /
• pp.27-31
• /
• 2004

Through time-series CCD photometry using a 155mm refractor, we found a new $\delta$ Scuti type variable star, HD 235428, near a known bright $\delta$ Scuti type star, DQ Cep. We performed follow-up observations using a 61cm telescope at Sobaeksan Optical Astronomy Observatory. Four frequencies have been derived by multiple-frequency analysis, which are 15.804, 5.498, 15.351 and 24.516cycle $day^{-1}$, respectively. V-amplitude of HD 235428 is ${\Delta} V$ = 0.026.

• 천문학논총
• /
• 제19권1호
• /
• pp.33-37
• /
• 2004

Through time-series CCD photometry using a 130mm refractor of Busan Science Academy, we found a new $\delta$ Scuti type variable star, esc 03665-00576. We performed following observations using a 1.8m telescope of Bohyunsan Optical Astronomy Observatory. Three frequencies have been derived by multiple-frequency analysis, which are 10.968, 7.156 and 15.182cycle $day^{-1}$, respectively. V-amplitude of esc 03665-00576 is ${\Delta}V$= 0.04.

• 천문학회보
• /
• 제41권1호
• /
• pp.60.3-60.3
• /
• 2016

보현산천문대가 준공되던 1996년부터 2000년까지 약 5년간 1.8m 망원경과 CCD 카메라를 이용하여 10개 이상의 산개성단에 대한 시계열 측광관측을 수행하였다. 이로부터 변광 진폭이 비교적 큰 식쌍성뿐만 아니라, 여러 개의 주기가 중첩되어 광도변화가 불규칙하면서도 진폭이 작아서 이전에 관측하기 어려웠던 산개성단내 맥동변광성들을 많이 발견하는 성과를 거두었다. 또한 2001년부터 현재까지 맥동변광성의 국제공동관측에 참여하고 있다. Delta Scuti형 맥동변광성이나 맥동백색왜성의 경우는 다수의 맥동주기를 검출하여 별의 내부구조를 추정할 수 있는 성진연구가 활발한데, 이를 위해서는 경도가 다른 여러 천문대에서 공동으로 관측함으로써 24시간 연속 자료를 얻는 것이 매우 중요하다. 우리나라가 위치한 경도대에는 2m급의 천체망원경이 드물기 때문에, 보현산천문대에서 얻은 관측 자료가 맥동변광성의 국제공동연구에 크게 기여하였다. 이번 발표에서는 보현산천문대 1.8m 망원경으로 얻은 변광천체의 시계열 측광관측 연구에 대해 돌이켜 보고, 앞으로의 연구 계획을 제시하고자 한다.

• 천문학회보
• /
• 제39권1호
• /
• pp.81.1-81.1
• /
• 2014

Kepler-47 is the first multi-body circumbinary planetary system detected by the Kepler space telescope. The two planets were detected by the transit method. In the discovery paper the authors report about the presence of an additional transit-like signal in their dataset which cannot be explained by a four-body (binary + 2 planets) system. Therefore it is likely that the unexplained signal could be due to a third planet. In this talk I will present recent results from a dynamical investigation of the five-body system (binary + 3 planets). We have applied the MEGNO technique to detect regions of quasi- or near quasi-periodic orbits of a hypothetical third planet. Quasi-periodic regions exists for a third planet and the long-term stability has been tested. Although the existence of a third planet is most likely to be confirmed from transit photometry we calculate transit-timing variation (TTV) signals due to the third planet which also can be used to infer its presence.

• 천문학회보
• /
• 제43권1호
• /
• pp.41.1-41.1
• /
• 2018

We introduce a current status and future plans of Korea Microlensing Telescope Network (KMTNet) microlensing experiments, which include an observational strategy, pipeline, event-finder, and collaborations with Spitzer. The KMTNet experiments were initiated in 2015. From 2016, KMTNet observes 27 fields including 6 main fields and 21 subfields. In 2017, we have finished the DIA photometry for all 2016 and 2017 data. Thus, it is possible to do a real-time DIA photometry from 2018. The DIA photometric data is used for finding events from the KMTNet event-finder. The KMTNet event-finder has been improved relative to the previous version, which already found 857 events in 4 main fields of 2015. We have applied the improved version to all 2016 data. As a result, we find that 2597 events are found, and out of them, 265 are found in KMTNet-K2C9 overlapping fields. For increasing the detection efficiency of event-finder, we are working on filtering false events out by machine-learning method. In 2018, we plan to measure event detection efficiency of KMTNet by injecting fake events into the pipeline near the image level. Thanks to high-cadence observations, KMTNet found fruitful interesting events including exoplanets and brown dwarfs, which were not found by other groups. Masses of such exoplanets and brown dwarfs are measured from collaborations with Spitzer and other groups. Especially, KMTNet has been closely cooperating with Spitzer from 2015. Thus, KMTNet observes Spitzer fields. As a result, we could measure the microlens parallaxes for many events. Also, the automated KMTNet PySIS pipeline was developed before the 2017 Spitzer season and it played a very important role in selecting the Spitzer target. For the 2018 Spitzer season, we will improve the PySIS pipeline to obtain better photometric results.