• 천문학회보
• /
• 제38권1호
• /
• pp.69.2-69.2
• /
• 2013

The direct detection of gravitational wave has a very important meaning as a basis for verification of the theory of relativity. Several laser interferometer detectors have attempted to detect GW directly (e.g. LIGO, VIRGO), but positional accuracy of GW detector is too wide (about 10~100sq deg) to find which objects emit GW. One of the main sources of GW is gamma-ray burst which can be detected even in electromagnetic wave. Then to verify Gamma-ray burst object as a GW source, we proceed EM follow-up observation with wide field of view. A first program initiating EM follow-ups to possible transients GW events has been developed and exercised by LIGO and VIRGO community in association with several partners. Using QUEST optical data, we tested the method of cross-convolution recommended by EM follow-up community. We will describe the results of that test.

• 천문학회보
• /
• 제41권1호
• /
• pp.31.3-31.3
• /
• 2016

Exploring a universe with gravitational waves (GWs) was only theoretical expectation for long time. In September 2015, the Laser Interferometer GW Observatory (LIGO) first detected GWs emitted from the collision of two stellar-mass black holes in cosmological distance (1.3 billion light years) on Earth. This confirms the existence of black-hole binary mergers, and further, opens a new field of GW astronomy. We begin our discussion with a list of important GW sources that can be detectable on Earth by large-scale laser interferometers such as LIGO. Focusing on compact objects such as neutron stars and black holes, we then discuss possible research in the context of GW astronomy. By coordinating with existing observatories, searching for electromagnetic waves or particles from astronomical objects, around the world, multi-messenger astronomy for the universe's most cataclysmic phenomena (e.g. gamma-ray bursts) will be available in the near future.

• 천문학회보
• /
• 제36권1호
• /
• pp.34.2-34.2
• /
• 2011

In this talk we explain U-loop emergence, in which U-shaped field lines emerge into the solar surface against gravitational force. In principle, they hardly emerge because mass tends to accumulate at the bottom of U-loops, thereby decreasing buoyancy. A key is found to be the shape of U-loops, that is, if U-loops have a shallow dip whose depth is of the order of the photospheric gravitational scale height, then a diverging flow is generated via a siphon-like mechanism by which the mass accumulated at the dip of the loops is drained out to enhance buoyancy. This successfully makes U-part of the loops emerge against gravity. We also discuss the relation between U-loop emergence and the so-called flux cancellation observed on the Sun in which opposite polarity regions apparently approach together and disappear.

• 천문학회보
• /
• 제44권1호
• /
• pp.62.3-62.3
• /
• 2019

After first identification of electromagnetic counterpart of gravitational wave source (GW170817), era of multi-messenger astronomy has begun. For specifying coordinate, magnitude, and host galaxy information, optical follow-up observation of GW source becomes important. With following engineering run and O3 run of LIGO and VIRGO starting in March 2019, we present searching strategy for optical counterpart of GW source using KMTNet. 24 hours monitoring system and large field of view (4 square-degree) of KMTNet are advantage to discover a transient like GW event. By performing tiling observation of high probability area in GW localization map, we expect to observe early light-curve of GW optical counterpart. After identification, follow-up observation with various KMTNet bands and other telescopes like Gemini and UKIRT will also be performed. We will study collision mechanism, progenitor, and characteristics of host galaxy using observation data of GW source.

• 천문학회보
• /
• 제44권1호
• /
• pp.58.2-58.2
• /
• 2019

Recent observation of the neutron star merger event, GW170817, through both gravitational wave (GW) and electromagnetic wave (EM) observations opened a new way of exploring the universe, namely, multi-messenger astronomy (MMA). One of the keys to the success of MMA is a rapid identification of EM counterpart through optical/NIR observations. We will present the strategy for prioritization of GW source host galaxy candidates to be observed with narrow-field optical telescopes. Our method relies on recent simulation results regarding plausible properties of GW source host galaxies and the low latency localization map from LIGO/Virgo. We will show the test results for both NS merger and BH merger events using previous events and possible future events and describe observing strategy with our facilities for GW events during the ongoing LIGO/Virgo O3 run.

• 천문학회보
• /
• 제46권1호
• /
• pp.61.2-61.2
• /
• 2021

SkyMapper is the largest-aperture optical wide-field telescope in Australia and can be used for transient detection in the Southern sky. Reference images from its Southern Survey cover the sky at δ <+10 deg to a depth of I ~ 20 mag. It has been used for surveys of extragalactic transients such as supernovae, optical counterparts to gravitational-wave (GW) and fast radio bursts. We adopt an ensemble-based machine learning technique and further filtering scheme that provides high completeness ~98% and purity ~91% across a wide magnitude range. Here we present an important use-case of our robotic transient search, which is the follow-up of GW event triggers from LIGO/Virgo. We discuss the facility's performance in the case of the second binary neutron star merger GW190425. In time for the LIGO/Virgo O4 run, we will have deeper reference images for galaxies within out to ~200 Mpc distance, allowing rapid transient detection to i ~ 21 mag.

• 천문학회보
• /
• 제44권1호
• /
• pp.43.3-43.3
• /
• 2019

Magnetic fields play an important role in supporting molecular clouds against gravitational collapse. The measured magnetic field strengths in molecular clods enable us to see the effect of magnetic fields in star-forming regions. People have used the Chandrasekhar and Fermi (CF) method to estimate magnetic field strength from observational quantities of molecular cloud density, turbulent velocity and polarization angle dispersion. However, previous studies obtained just one magnetic field strength over the quite large region of a molecular cloud by using the CF method. We here suggest a way to estimate magnetic field strength distribution in Orion A region. We used 450 and 850-micron polarization data of James Clerk Maxwell Telescope (JCMT). Magnetic field strengths were estimated in two wavelengths with 4 pixel resolutions of 16, 20, 24 and 28". Through statistical analysis, we proved the difference of magnetic field strengths between two wavelengths were caused by the difference of their beam sizes. Additionally, we calculated the radii of curvature of polarization segments to select a best pixel resolution for estimating the magnetic field distribution. The pixel resolution should be larger than a radius of curvature. We selected that 20 or 24" pixel resolutions are good choices towards Orion A region.

• Geomechanics and Engineering
• /
• 제37권3호
• /
• pp.243-251
• /
• 2024

In the current work, a poro-thermoelastic half-space issue with temperature-dependent characteristics and an inclined load is examined in the framework of the three-phase-lag model (3PHL) while taking into account the effects of magnetic and gravity fields. The resulting coupled governing equations are non-dimensional and are solved by normal mode analysis. To investigate the impacts of the gravitational field, magnetic field, inclined load, and an empirical material constant, numerical findings are graphically displayed. MATLAB software is used for numerical calculations. Graphs are used to visualize and analyze the computational findings. It is found that the physical quantities are affected by the magnetic field, gravity field, the nonlocal parameter, the inclined load, and the empirical material constant.

• 한국측량학회지
• /
• 제38권2호
• /
• pp.153-163
• /
• 2020

After launching the GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) which obtains high-frequency gravity signal using a gravity gradiometer, many research institutes are concentrating on the development of GGM (Global Geopotential Model) based on GOCE data and evaluating its precision. The precision of some GGMs was also evaluated in Korea. However, some studies dealt with GGMs constructed based on initial GOCE data or others applied a part of GNSS (Global Navigation Satellite System) / Leveling data on UCPs (Unified Control Points) for the precision evaluation. Now, GGMs which have a higher degree than EGM2008 (Earth Gravitational Model 2008) are available and UCPs were fully established at the end of 2019. Thus, EIGEN-6C4 (European Improved Gravity Field of the Earth by New techniques - 6C4), GECO (GOCE and EGM2008 Combined model), XGM2016 (Experimental Gravity Field Model 2016), SGG-UGM-1, XGM2019e_2159 were collected with EGM2008, and their precisions were assessed based on the GNSS/Leveling data on UCPs. Among GGMs, it was found that XGM2019e_2159 showed the minimum difference compared to a total of 5,313 points of GNSS/Leveling data. It is about a 1.5cm and 0.6cm level of improvement compare to EGM2008 and EIGEN-6C4. Especially, the local biases in the northern part of Gyeonggi-do, Jeju island shown in the EGM2008 was removed, so that both mean and standard deviation of the difference of XGM2019e_2159 to the GNSS/Leveling are homogeneous regardless of region (mountainous or plain area). NGA (National Geospatial-Intelligence Agency) is currently in progress in developing EGM2020 and XGM2019e_2159 is the experimentally published model of EGM2020. Therefore, it is expected that the improved GGM will be available shortly so that it is necessary to verify the precision of new GGMs consistently.

• 분석과학
• /
• 제24권4호
• /
• pp.249-255
• /
• 2011

물의 흡수에 의한 전분알갱이의 swelling은 물과 친화력이 있는 새로운 부분의 노출에 의하여 구조적인 변화로써 점진적으로, 때로는 갑작스럽게 변화를 일으킨다. 이러한 이유로 인해서, 물과의 접촉 시간에 따르는 전분 알갱이의 크기 또는 모양의 변화에 관심을 가진다. 중력 장-흐름 분획법(gravitation field-flow fractionation, GrFFF)은 마이크론 범위의 크기를 가지는 입자들을 분리하는 데에 유용한 분리기술이다. 본 연구에서는 감자와 고구마 전분알갱이들의 크기와 크기 분포도를 결정하는 데에 있어서 GrFFF의 응용가능성을 검사하고자 한다. GrFFF를 이용하여 물과의 접촉 시간에 따르는 전분 알갱이들의 크기분포도 변화를 모니터하였다. GrFFF로부터 얻어진 전분알갱이들의 크기 및 크기분포는 광학현미경(optical microscopy, OM) 결과와 비교하였다. 결과적으로 감자와 고구마 전분의 swelling은 물과의 접촉시간이 증가함에 따라 전분알갱이의 크기가 증가하며, 전분의 종류가 달라지면 swelling 속도가 달라짐을 확인하였다.