During the last decades, the heliospheric studies significantly contributed to our understanding of how the Sun’s magnetic acitivity affects the space weather of Earth in the short term and its climate change in the intermediate term. It now seems quite timely or urgent to extend this expersise to resolve two outstanding problems: 1) how the solar magnetic activity have affected the habitability of Earth and other planets in the long term, and 2) how the magnetic acivity of a star affects the habitability of an exoplanet orbiting around the star. Resolving these two problems are intimately related to revealing of the fundamental principle and diversity of dynamo process in a variety of stars, planets and satellites. A useful tool for these scientific goals is comparative heliospheric studies: comparing Earth and Mars, comparing the present Sun-Earth system and the past system, comparing solar magnetic activity and stellar magnetic activity. Comparing flares between the Sun and other stars has become very active in the last decade, and comparing prominence eruptions between the Sun and stars is becoming popular, as prominnece eruptions are regarded as a signature of coronal mass jections that can be observed from the ground. In this talk, I will review the recent observations of flares and prominence eruptions on EK Dra that is regarded as a “young Sun”, in comparison with those on the Sun. We conclude that detecting prominence eruptions on a magnetically active star is much more difficult to detect flares, and would require high S/N spectroscopy as well as a reasonable model of radiation on the star during the eruptions.

I report on methods for the estimation of stellar parameters and elemental abundances, including [Fe/H], [C/Fe], and [Mg/Fe], for very large samples of stars in the disk and halo of the Milky Way, making use of a combination of narrow-band photometry from the J-PLUS and S-PLUS surveys and broad-band photometry from Gaia DR3. The techniques employed can achieve estimates with precisions that are commensurate with that obtained from low- and medium-resolution spectroscopy. I summarize the identification of on the order of 0.5 million carbon-enhanced metal-poor (CEMP) stars for future exploration of the chemo-dynamical properties of CEMP-no and CEMP-s stars in the halo and disk systems of the Galaxy.

The Dark Energy Spectroscopic Instrument (DESI) collaboration is conducting a five-year redshift survey of 40 million extra-galactic sources over 14,000 square degrees of the northern sky up to the redshift of 4 with the Mayall 4-meter telescope at Kitt Peak National Laboratory. One of its primary goals is to measure the cosmic expansion history precisely and accurately through the measurements of baryon acoustic oscillations (BAO). In this talk, I will present the analysis of the DESI First Year Baryon Acoustic Oscillations using the distributions of galaxies and quasars over the redshift range of 0.1-2, the estimates of the relevant systematics, and their intriguing cosmological implications, including the time-evolving dark energy.

Previously, offsets between galaxies and mass during cluster collisions were regarded as a promising indicator for evaluating the self-interaction cross-section of dark matter. However, past investigations based on these offsets have been hindered by significant biases regarding the phase and geometry of the merger. I will introduce a reliable constraint on the self-interaction of dark matter using a novel and effective approach with observations of cluster collisions featuring double radio relics. By utilizing the distance between relics relative to the distance between halos as a gauge for dark matter characteristics, we have established an upper limit of 0.33 cm^2 g^-1 for the self-interaction cross-section with 68% confidence. This marks the first robust outcome derived from colliding clusters, accounting for ambiguities such as mass variability, viewing angle, collision velocity, merger phase, impact parameter, and gas slope.

Photons looping around photon shells in black hole spacetimes form a sequence of higher order images -- the photon ring. Unlike in the case of the direct image, the size and shape of the photon ring reflects properties of spacetime, aka "clean geometry" with only limited impact of the configuration of the emitting source, aka "dirty astrophysics". Thus, they enable unprecedented robust observational tests of strong gravity, possibly including estimates of black hole spin, or constraining deviations from the Kerr metric. For at least 1 black hole in the Universe, M87*, the photon ring can be characterized with space radiointeferometry at mm wavelengths. I will talk about the ongoing plans and efforts to do it in the next decade with the proposed NASA Black Hole EXplorer (BHEX) space VLBI mission.

Interferometer have already been commercialized and utilized in various fields, but it is too weeak to enviromental condition, its performance remains significantly limited. Therefore, research continues to apply advanced measurement techniques in various fields, such as optical measurement technology for gravitational wave detectors and large-aperture optical measurement technology. In this talk, I will introduce about birefringence sensor for test mass of gravitational wave detector and interferometric sensor for lareg-scale optics. In addition scattered light analysis from large scale optics will be introduced. 

본 세미나에서는 달 탐사를 위한 인공지능 기반 3차원 컴퓨터 비전 융합 기술을 소개합니다. 먼저, 연구실에서 수행해온 자율주행을 위한 3차원 시각인지 기법에 대한 대표 연구 성과를 살펴보고, 최신 인공지능 기법과 3차원 구조 복원 및 모델링 기술의 동향을 소개합니다. 이러한 기술들을 활용하여 달 궤도선 탑재체로 촬영한 영상을 통해 달의 3차원 지형을 복원하는 방법을 소개합니다. 특히, 기존 인공지능 및 컴퓨터 비전 분야의 태스크와 달 탐사를 위한 태스크의 차이점과 도전 과제를 분석하고, 이를 극복하기 위한 방안을 공유합니다. 이를 통해 인공지능과 컴퓨터 비전 기술이 달 탐사에 어떻게 혁신적인 변화를 가져올 수 있는지 논의하고자 합니다.

Planetary soft landing is a critical challenge in space exploration, requiring precision and robustness to ensure the safety and success of lander missions. Convex programming, known for its global optimality and computational efficiency, offers significant advantages for designing landing trajectories and control strategies under complex constraints and uncertainties. In this presentation, we explore the application of convex programming to develop algorithms for soft landing on planetary surfaces. We introduce our approaches that utilize first-order methods and distributed optimization to enhance computational speed and scalability. The first-order methods are particularly advantageous as they are simpler and can be efficiently implemented on Graphics Processing Units (GPUs), leveraging their parallel processing capabilities to handle large-scale problems more effectively. Furthermore, we discuss the use of various testbeds, including indoor flight test facilities and rocket test beds, which play a pivotal role in validating our proposed algorithms and ensuring their reliability and effectiveness in real-world scenarios. This talk highlights how cutting-edge optimization techniques, combined with advanced computational resources and rigorous testing, pave the way for safer and more efficient planetary landings.

Barred galaxies are a common type of galaxies in the local universe, observed in over 60% of disk galaxies. The bar structure plays a significant role in determining galaxy substructures such as spiral arms, rings and central dust structures. It is also a crucial driver of the secular evolution of galaxies, redistributing the mass of gas, stars, and even dark matter: it drives gas into the central regions of galaxies, builds a pseudo- or boxy/peanut bulge, and can even elongate the dark matter halo. According to theoretical studies, in an isolated system, a bar structure rapidly forms when a stellar disk is unstable and grows by interacting with the dark matter halo. However, observations do not find evidence for the growth of bar structures in terms of their length, strength, and pattern speed, which induces tension between the distribution of dark matter in simulations and observations. Furthermore, galaxy interactions that induce barred galaxies add complexity to our understanding of barred galaxies. In this talk, I will introduce our recent and ongoing work on barred galaxies using photometry from SDSS, PS1, HST, DESI, and CFHT and spectroscopy from Gemini, CALIFA, MUSE, and JWST. Our work spans the methods to detect barred galaxies to their evolution in the context of their main properties: length, strength, and pattern speed. Lastly, I will introduce the important role of the KASI’s next projects, including K-DRIFT, LSST, and the DARWIN project, in the study of barred galaxies.

SiCfiller/SiC ceramic composites were prepared using a SiC powder and a liquid polycarbosiane (PCS) ceramic precursor. Ultra-fine SiC powder (d50: 170nm), prepared by mechanical alloying process, was used to prepare aqueous SiC slurries with the solid loading of 66 - 70 vol%. By the optimization of dispersion condition and the oxidation treatment of the SiC powder, SiC slurry up to 70 vol% solid loading was successfully prepared. The maximum green density of SiC compact after drying the slurry was 78%. Precursor-impregnation & pyrolysis process (PIP) was performed using SMP-10 liquid PCS precursor. The weight of the SiC composites increased almost linearly up to 4 PIP cycles and the mass gain became less efficient afterwards. The 4-point flexural strength of the SiC composites were 204 and 265MPa at 25 and 2,000℃, respectively under argon atmosphere. The result clearly indicates the excvellent thermal stability of the SiC cpmposites fabricated using the PCS precursor.

When you look at the sky on a clear night, you probably enjoy the twinkling of stars. However, if you are an astronomer, you might find it extremely annoying. Almost as soon as telescopes were invented, astronomers realized that the quality of images was limited by atmospheric turbulence, which distorts short exposure and blurs long exposure astronomical images. Even if we have 8-10 meter class telescopes now, without AO, the telescope's angular resolution would be limited by the atmospheric turbulence “seeing” -the size of the blurred image is almost two orders of magnitude worse than what the telescopes could achieve. To overcome this limitation, the first concept of adaptive optics (AO) was proposed by H. W. Babcock in 1953 for ground-based telescopes. However, the technology for AO components was not mature enough then. From the late-1980s, astronomers became interested in applying the AO technique to astronomy. As of today, AO has rapidly been developed over the past 70 years and has become a state-of-the-art technique. The wavefront aberration induced by atmospheric turbulence can be measured by a wavefront sensor and compensated for by a wavefront corrector, thereby deblurring the images in part or entirely. This presentation introduces astronomical science that can be achieved with modern AO technologies. We also present recent technology trends for the AO system, such as types of wavefront sensors (WFSs) and wavefront correctors. In the wavefront sensors section, we present Shack-Hartmann WFS, pyramid WFS, and curvature WFS. In the wavefront corrector section, we introduce wavefront correctors such as deformable mirrors and a spatial liquid modulator. Lastly, we introduce modern AO systems with multiple laser and nature guide stars for various applications.

Understanding ice composition is crucial in star and planet formation. To investigate ices in young stellar objects (YSOs), we can utilize ALMA, JWST, and the upcoming SPHEREx mission. ALMA observations reveal sublimated complex organic molecules, while JWST provides detailed ice absorption spectra. SPHEREx will perform all-sky ice mapping. We emphasize burst accretion, where episodic increases in accretion rates cause ices to sublimate, revealing their composition. YSOs gain mass through episodic accretion, causing luminosity variability. Catching burst events by monitoring YSOs allows for detailed ice composition studies. Identifying bursting YSOs at different evolutionary stages will enable us to track ice evolution from early star formation to planet formation, enhancing our understanding of surface chemistry.

Observations reveal the organization of the interstellar medium into filament networks. In molecular clouds, the densest filaments are identified as the precise birthplaces of solar-mass stars, while high-mass stars form in the hubs where the filaments merge. To understand the formation process of star-clusters, it is thus essential to describe the formation and evolution of filaments and hubs and their fragmentation into pre-stellar cores, the progenitor of stars. I will present theoretical and observational studies indicating the formation of filamentary molecular clouds at the edge of expanding bubbles. I will then show observational results suggesting the role of filament coalescence and hub-filament systems in the formation process of stars from low to high masses. I will also discuss our new study proposing the formation of the Sun along a dense molecular filament. We suggest that the host filament may play an important role in shielding the young solar system from a nearby supernova explosion while intercepting the required amount of supernova ejecta to explain the observations of primitive material found in meteorites. 

The dark energy equation of state parameter w is measured with sufficient accuracy to discover that w must be larger than one in the flat CDM universes, namely dark energy is not the cosmological constant. A series of large-volume galaxy redshift surveys samples up to redshift ~0.8 produced by the Sloan Digital Sky Survey are used in the analysis, and the expansion history of the universe was measured using an extended version of the Alcock-Paczynski test (Park et al. 2019). The test exploits the fundamental fact that gravity is an isotropic force and the statistical pattern of galaxy clustering can be used as a standard shape that is conserved with time. The new analysis of the SDSS data indicates that the expansion of the universe is indeed accelerating but the acceleration is a little slower than expected in the flat LCDM universe. The dark energy equation of state parameter is measured to be w = −0.903±0.023, a 4.2σ deviation from −1! This finding of a new "w tension" inevitably leads us to discard the cosmological constant as the source for the accelerated expansion and consider alternative quintessence models. We are now making a more accurate measurement of w using the upcoming DESI survey data to test if w is constant or evolving.

The atmospheres of planetary objects contain natural dust particles, and planetary scientists call them aerosols or haze particles. The chemical and physical properties of the haze particles in the atmospheres of Jupiter, Saturn, and Titan have been revealed by Cassini and Juno: the Saturn and Jupiter space missions, respectively. Cassini arrived at the Saturnian system in 2006, and Juno at the Jovian system in 2016. We analyzed infrared spectra from these missions in order to extract haze spectra from raw spectra, which are heavily entangled by molecular lines, especially by strong CH4 emission and absorption lines. We first analyzed the 3.0-3.5 and 2.0-2.5 mm spectra of Titan observed by Cassini/VIMS, a near-IR camera and spectrometer. Surprisingly, we found that the haze spectra of Titan are very different from the typical spectra of ‘tholins’, which have been laboratory-made and claimed by Carl Sagan for the haze particles in the atmospheres of Titan, Saturn, and Jupiter for more than 40 years. The derived haze spectra of Titan are, instead, very similar to the typical spectra of aromatic hydrocarbons at high altitudes and aliphatic hydrocarbons at low altitudes. The tholins were even considered to be one of the important components of interstellar dust particles. We also analyzed the Cassini/VIMS 3.0-3.5 mm spectra of Saturn to extract Saturnian haze spectra. We found that the polar haze is dominated by aromatic hydrocarbons while the haze at lower latitudes mostly consists of aliphatic hydrocarbons. This spectral variation in the di?erent latitudinal regions suggests that newly created haze particles at the high altitudes in the auroral regions of Saturn undergo an aging process mainly during latitudinal advection/di?usion from the polar atmosphere to the low altitude and low latitudinal regions, while in the atmosphere of Titan, the aging process mainly occurs during the vertical precipitation process of haze. Recently, we analyzed the 2.0-2.5 mm spectra of Jupiter’s polar regions observed by Juno/JIRAM, another camera and spectrometer very similar to Cassini/VIMS. We were able to extract the haze spectra of the polar regions of Jupiter; and found that the spectra are roughly similar to those of Titan suggesting similar chemical and physical processes of haze particles in the atmosphere of Jupiter.

Very long baseline radio interferometry (VLBI) with ground-based observatories is limited by the size of Earth, the geographic distribution of antennas, and the transparency of the atmosphere. In this whitepaper, we present Capella, a tentative design of a space-only VLBI system. Using four small (<500 kg) satellites in two orthogonal polar low-Earth orbit planes, and single-band heterodyne receivers operating at frequencies around 690 GHz, the interferometer is able to achieve angular resolutions of approximately 7 microarcsec. Within a total observing time of three days, a near-complete uv plane coverage can be reached. All key components required for Capella - radio telescope, receiver, sampler, recorder, atomic frequency standard, positioning system, data downlink, and pointing control system - are already available, some of them off-the-shelf; the science payload of each satellite has a mass of about 230 kg and consumes about 550 W of power. The data from the telescopes can be correlated on the ground using dedicated versions of existing Fourier transform (FX) software correlators; in addition to the steps required by VLBI data correlation and calibration in general, dedicated routines will be needed to handle the effects of orbital motion, including relativistic corrections. With the specifications assumed in this whitepaper, Capella will be able to address a range of science cases, including: photon rings around supermassive black holes; the acceleration and collimation zones of plasma jets emitted from the vicinity of supermassive black holes; the chemical composition of accretion flows into active galactic nuclei through observations of molecular absorption lines; mapping supermassive binary black holes; the magnetic activity of stars; and nova eruptions of symbiotic binary stars - and, like any substantially new observing technique, has the potential for unexpected discoveries. 

New observational methods often trigger new discoveries in astronomy. To explore the universe in an innovative way, we are constructing a multiple telescope, the 7-dimensional telescope (7DT) in Chile. 7DT is made of twenty, 0.5-m diameter wide-field telescope, and the first ten units started the operation in October, 2023, with the expected completion of the full system in 2024. With 7DT, we will perform the 7-dimensional sky survey (7DS), a wide-field, time series, spectral mapping of the southern sky. The survey aims to (i) understand the spectral variability of astronomical sources through time-series spectral mapping such as active galactic nuclei; (ii) provide a spectral map of the sky that can be used to study spatially resolved stellar population of galaxies, cosmology, etc; and (iii) rapidly identify electromagnetic counterparts of gravitational-wave sources for successful multi-messenger astronomy. In this talk, we will introduce 7DT and 7DS and outline the unsolved problems that 7DS will tackle. We will also early images and the data taken with 7DT as well as its current performance, which demonstrate the scientific promises of 7DS. We will also briefly discuss the synergies between 7DT and KASI’s initiatives such as SPHEREx, KMTNet, and the Vera Rubin Observatory.

Gaia DR3 provides state-of-art data of proper motions (transverse velocities), parallaxes (distances), radial velocities, and luminosities for nearby stars. Statistical analyses of binary stars show that Newton-Einstein standard gravity holds for the orbit size less than about 1000 astronomical units (au) or the internal acceleration greater than about 6 nanometer per second squared. However, binary orbital motions exhibit a gradual systematic anomaly from 1000 to 5000 au and a pseudo-Newtonian gravity with Newton’s constant boosted by a factor of 1.4 holds for > 5000 au. Remarkably, this behavior agrees with the prediction of Milgromian (modified Newtonian dynamics) gravity. Consistent results are obtained from three independent methods of statistical analysis, the ``acceleration plane analysis”, the “normalized velocity profile analysis”, and the “stacked velocity profile analysis” based on various samples of binaries. These results indicate that general relativity breaks down in the low acceleration limit because its nonrelativistic limit becomes Newtonian. A paradigm shift is under way in astrophysics, cosmology, and theoretical physics. Implications of the results and future prospect are discussed.

지난 40년간 방위산업 전문기업으로 대한민국 자주국방에 기여해온 한화시스템의 사업영역인 우주영역 인식 분야에 대한 기술개발 현황 중 우주감시시스템의 운용목적, 우주감시시스템의 개발현황, 우주방호 레이저에 대한 개발 현황을 소개합니다.

소형발사체 스타트업 페리지의 Blue Whale 1 발사체 개발 현황과 발사 계획을 소개하며, 이를 응용한 독특한 우주관측 임무를 제안한다.

뉴스페이스 시대의 우주산업 시장과 한국의 우주 감시를 포함한 우주산업 전략을 고찰하고, LIG넥스원의 위성 분야의 사업현황과 계획을 소개하며, 천문연과의 협업분야를 제안함.

Comparisons of quiescent galaxies in the distant universe with their counterparts in the local volume show that the structure of galaxies continues to change well after they stop forming stars. Very compact galaxies, that have the stellar mass of the Milky Way and the size of the Milky Way bulge, seem to disappear between redshifts z~2 and z~0. The average size of quiescent population increases by a factor of a few over the same redshift interval. In contrast to the existing surveys of high-redshift universe, at intermediate redshift (0.2 < z < 1)