• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.1
• /
• pp.54.3-55
• /
• 2016

DEEP-South Scheduling and Data reduction System (DS SDS) consists of two separate software subsystems: Headquarters (HQ) at Korea Astronomy and Space Science Institute (KASI), and SDS Data Reduction (DR) at Korea Institute of Science and Technology Information (KISTI). HQ runs the DS Scheduling System (DSS), DS database (DB), and Control and Monitoring (C&M) designed to monitor and manage overall SDS actions. DR hosts the Moving Object Detection Program (MODP), Asteroid Spin Analysis Package (ASAP) and Data Reduction Control & Monitor (DRCM). MODP and ASAP conduct data analysis while DRCM checks if they are working properly. The functions of SDS is three-fold: (1) DSS plans schedules for three KMTNet stations, (2) DR performs data analysis, and (3) C&M checks whether DSS and DR function properly. DSS prepares a list of targets, aids users in deciding observation priority, calculates exposure time, schedules nightly runs, and archives data using Database Management System (DBMS). MODP is designed to discover moving objects on CCD images, while ASAP performs photometry and reconstructs their lightcurves. Based on ASAP lightcurve analysis and/or MODP astrometry, DSS schedules follow-up runs to be conducted with a part of, or three KMTNet telescopes.

• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.2
• /
• pp.44.4-45
• /
• 2018

(4179) Toutatis (Toutatis hereafter) is one of the Near-Earth Asteroids which has been studied most rigorously not only via ground-based photometric, spectroscopic, polarimetric, and radar observations, but also via the in-situ observation by the Chinese Chang'e-2 spacecraft. However, one of the most fundamental physical properties, the geometric albedo, is less determined. In order to derive the reliable geometric albedo and further study the physical condition on the surface, we made photometric observations of Toutatis near the opposition (i.e., the opposite direction from the Sun). We thus observed it for four days on 2018 April 7-13 using three 1.6-m telescopes, which consist of the Korean Microlensing Telescope Network (KMTNet). Since the asteroid has a long rotational period (5.38 and 7.40 days from Chang'e-2, Zhao et al., 2015), the continuous observations with KMTNet matches the purpose of our photometric study of the asteroid. The observed data cover the phase angle (Sun-asteroid-observer's angle) of 0.65-2.79 degree. As a result, we found that the observed data exhibited the magnitude changes with an amplitude of ~0.8 mag. We calculated the time-variable geometrical cross-section using the radar shape model (Hudson & Ostro 1995), and corrected the effect from the observed data to derive the geometric albedo. In this presentation, we will present our photometric results. In addition, we will discuss about the regolith particles size together with the polarimetric properties based on the laboratory measurements of albedo-polarization maximum.

• Journal of The Korean Astronomical Society
• /
• v.52 no.3
• /
• pp.71-82
• /
• 2019

We derive the geometric albedo of a near-Earth asteroid, (4179) Toutatis, to investigate its surface physical conditions. The asteroid has been studied rigorously not only via ground-based photometric, spectrometric, polarimetric, and radar observations but also via in situ observation by the Chinese Chang'e-2 space probe; however, its geometric albedo is not well understood. We conducted V-band photometric observations when the asteroid was at opposition in April 2018 using the three telescopes in the southern hemisphere that compose the Korea Microlensing Telescope Network (KMTNet). The observed time-variable cross section was corrected using the radar shape model. We find that Toutatis has a geometric albedo $p_V=0.185^{+0.045}_{-0.039}$, which is typical of S-type asteroids. We compare the geometric albedo with archival polarimetric data and further find that the polarimetric slope-albedo law provides a reliable estimate for the albedo of this S-type asteroid. The thermal infrared observation also produced similar results if the size of the asteroid is updated to match the results from Chang'e-2. We conjecture that the surface of Toutatis is covered with grains smaller than that of the near-Sun asteroids including (1566) Icarus and (3200) Phaethon.

• Journal of The Korean Astronomical Society
• /
• v.49 no.3
• /
• pp.73-81
• /
• 2016

We report the characterization of a massive (m_p = 3.9±1.4M_jup) microlensing planet (OGLE-2015-BLG-0954Lb) orbiting an M dwarf host (M = 0.33 ± 0.12M_⊙) at a distance toward the Galactic bulge of $0.6^{+0.4}_{-0.2}kpc$, which is extremely nearby by microlensing standards. The planet-host projected separation is a⊥ ~ 1.2AU. The characterization was made possible by the wide-field (4 deg²) high cadence (Γ = 6 hr^–1) monitoring of the Korea Microlensing Telescope Network (KMTNet), which had two of its three telescopes in commissioning operations at the time of the planetary anomaly. The source crossing time t_* = 16 min is among the shortest ever published. The high-cadence, wide-field observations that are the hallmark of KMTNet are the only way to routinely capture such short crossings. High-cadence resolution of short caustic crossings will preferentially lead to mass and distance measurements for the lens. This is because the short crossing time typically implies a nearby lens, which enables the measurement of additional effects (bright lens and/or microlens parallax). When combined with the measured crossing time, these effects can yield planet/host masses and distance.

• Journal of The Korean Astronomical Society
• /
• v.49 no.6
• /
• pp.295-306
• /
• 2016

We present the results of BV time-series photometry of the globular cluster NGC 288. Observations were carried out to search for variable stars using the Korea Microlensing Telescope Network (KMTNet) 1.6-m telescopes and a 4k pre-science CCD camera during a test observation from August to December, 2014. We found a new SX Phe star and confirmed twelve previously known variable stars in NGC 288. For the semi-regular variable star V1, we newly determined a period of 37.3 days from light curves spanning 137 days. The light-curve solution of the eclipsing binary V10 indicates that the system is probably a detached system. The pulsation properties of nine SX Phe stars were examined by applying multiple frequency analysis to their light curves. We derived a new Period-Luminosity (P-L) relation, ${\langle}M_V{\rangle}=-2.476({\pm}0.300){\log}P-0.354({\pm}0.385)$, from six SX Phe stars showing the fundamental mode. Additionally, the period ratios of three SX Phe stars that probably have a double-radial mode were investigated; $P_{FO}/P_F=0.779$ for V5, $P_{TO}/P_{FO}=0.685$ for V9, $P_{SO}/P_{FO}=0.811$ for V11. This paper is the first contribution in a series assessing the detections and properties of variable stars in six southern globular clusters with the KMTNet system.

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.2
• /
• pp.49.2-49.2
• /
• 2016

The number of discovery of asteroids with peculiar rotational states has recently increased, and hence a novel approach for lightcurve analysis is considered to be critical. In order to investigate objects such as Non-Principal Axis (NPA) rotator, we selected a NPA candidate, (5247) Kryolv as our target considering its Principal Axis Rotation (PAR) code and the visibility in early 2016. The observations of Krylov were made using Korea Microlensing Telescope Network (KMTNet) 1.6 m telescopes installed at the three southern sites with TO (Target of Opportunity) observation mode. We conducted R-band time-series photometry over a total of 51 nights from January to April 2016 with several exposures during each allocated run. The ensemble normalization photometry was employed using the AAVSO Photomtric All-Sky Survey (APASS) catalog for the standardization. We successfully confirmed its NPA spin state based on the deviation from the reduced lightcurve, and thus Krylov is recorded as the first NPA rotator of its kind in the main-belt, with its precession and rotation periods, $P{\varphi}=81.18h$ and $P_{\Psi}=67.17h$, respectively. In this paper, we present the spin direction, the 3D shape model and taxonomy of the newly confirmed NPA asteroid (5247) Krylov.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.50.1-50.1
• /
• 2017

The Non-Principal Axis (NPA) rotators can be clues to spin evolutionary processes of asteroids because their excited spin states evolve due to either internal or external forces. The NPA rotation of (5247) Krylov was confirmed by Lee et al. (2017) based on KMTNet photometric observations during the 2016 apparition. We conducted follow-up observations in 2017 apparition using the 0.6-2.1m telescopes in the northern hemisphere to determine the spin state and shape model of this asteroid. We found that it is rotating in the Short Axis Mode (SAM) based on the determined rotation period ($P_{\psi}=374.6hr$) and precession period ($P_{\phi}=67.48hr$). The greatest and intermediate principal inertia moments are nearly the same as $I_b/I_c=0.94$, but the smallest principal inertia moments are nearly half that of the others, $I_a/I_c=0.43$. This ratio of principal inertia moments suggests that dynamically equivalent shape of this asteroid is close to that of a prolate ellipsoid. In this presentation, we will provide the physical model of (5247) Krylov to discuss its possible spin evolutionary processes that acted on its spin.

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.1
• /
• pp.55.2-56
• /
• 2016

The spin states of asteroids is regarded as an important clue to understand not only the physical property of an individual object but also the dynamical evolution of the of the population as a whole. Single asteroids can be broadly classified into two separate groups according to their rotational states; Principal Axis (PA) and Non-Principal Axis (NPA) rotators. To date, lightcurve observations have been carried out mostly for PA asteroids. However, discovery of NPA objects has recently been increased due to new observing techniques, and this is the reason why rotational properties of NPA rotators became an issue. As a DEEP-South pilot study for NPA, we selected two targets, 5247 Krolv (1982 UP6) and 14764 Kilauea (7072 P-L) considering their Principal Axis Rotation (PAR) code and visibility. Observations were made between Jan. and Feb. 2016 for 17 nights employing Korea Microlensing Telescope Network (KMTNet) 1.6 m telescopes installed at SSO and SAAO using DEEP-South TO (Target of Opportunity) mode. To obtain lightcurves, we conducted time-series photometry using Johnson-Cousins R-filter. Multi-band photometry was also made with BVRI filters at the same time, for taxonomy. Their preliminary lightcurves and approximate mineralogy will be presented.

• Journal of The Korean Astronomical Society
• /
• v.53 no.6
• /
• pp.161-168
• /
• 2020

We report the discovery of a giant exoplanet in the microlensing event OGLE-2017-BLG-1049, with a planet-host star mass ratio of q = 9.53 ± 0.39 × 10-3 and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of θE = 0.52 ± 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, tE ≃ 29 days, is too short. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. We find that the lens system has a star with mass Mh = 0.55+0.36-0.29 M⊙ hosting a giant planet with Mp = 5.53+3.62-2.87 MJup, at a distance of DL = 5.67+1.11-1.52 kpc. The projected star-planet separation is a⊥ = 3.92+1.10-1.32 au. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is μrel ~ 7 mas yr-1, thus the lens and source will be separated from each other within 10 years. After this, it will be possible to measure the flux of the host star with 30 meter class telescopes and to determine its mass.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.53.3-54
• /
• 2021

We present optical follow-up observation results of three binary black hole merger (BBH) events, GW190408 181802, GW190412, and GW190503 185404, which were detected by the Advanced Ligo and Virgo gravitational wave (GW) detectors. Electromagnetic (EM) counterparts are generally not expected for BBH merger events, however, some theoretical models suggest that EM counterparts of BBH can possibly arise in special environments. To identify EM counterparts of the three BBH merger events, we observed high-credibility regions of the sky with telescopes of the Gravitational-wave EM Counterpart Korean Observatory (GECKO), including the Korea Microlensing Telescope Network (KMTNet). Our observation started as soon as 100 minutes after the GW event alert and covered roughly 29 - 63 deg2 for each event with a depth of 22.5 mag in R-band within hours of observation. No plausible EM counterparts were found for these events. Our result gives a great promise for the GECKO facilities to find EM counterparts within few hours from GW detection in future GW observation runs.