Compared to low-mass star formation, very little is known about the formation process of high-mass stars that are fundamental in the evolution of galaxies. It is still much debated whether high-mass stars form in a manner qualitatively similar to low-mass stars, and there are two major competing models: accretion via disks and coalescence of low-mass (proto)stars. In this talk I will discuss some recent efforts to differentiate between the two models by observing bipolar outflows from massive protostars.

In this talk, we introduce recent Sun-Earth connection studies which have been done in solar and space weather research group at KASI. In a series of papers, we have examined the physical characteristics of geoeffective halo CMEs that produced geomagnetic storms. First, we investigated the probability of geoeffective CMEs depending on its solar surface location and speed using SOHO/LASCO CMEs from 1997 to 2003. Second, we examined the relationship between several CME physical parameters (e.g., earthward direction, density, mass, location) and geomagnetic storms for very fast halo CMEs (VCME > 1300 km/s). In particular, we suggested a new earthward direction parameter that is defined as a ratio, the shorter front from the solar center to the longer one. Third, we examined the relationship between the field orientation in a CME source region and a geomagnetic storm using a coronal flux rope model as well as its dependence on ICME classification (magnetic cloud or ejecta). Major results are as follows. 1) The most probable areas whose geoeffectiveness fraction is larger than the mean probability (0.4), are 0800 km/s). 2) The CME direction has much better correlations with the Dst index than other parameters for very fast halo CMEs. 3) The relationship between the field orientation and the geomagnetic storm for magnetic cloud is much better than that for ejecta, implying that the field orientation of the magnetic clouds is well conserved through the heliosphere. We also briefly introduce several ongoing studies: (1) earthward direction as an important geoeffective parameter, (2) solar wind effect on the propagation of IP shocks, and (3) satellite drag effect during strong solar/geomagnetic activities and the comparison between the drag derived density and the MSIS-90 model. Finally, we present some future plans in the Sun-Earth connection field.

The colors of globular clusters in most large elliptical galaxies are bimodal. This is generally taken as evidence for the presence of two cluster subpopulations that have different geneses. However, here we find that, because of the nonlinear nature of the metallicity-to-color transformation, a coeval group of old clusters with a unimodal metallicity spread can exhibit color bimodality. The models of cluster colors indicate that horizontal-branch stars are the main drivers behind the empirical nonlinearity. We show that the scenario gives simple and cohesive explanations for all the key observations and could simplify theories of elliptical galaxy formation.

계산과학이 컴퓨터의 급속한 발전에 힘 입어 이론, 실험 혹은 관찰에 이어 과학 기술을 연구, 교육하는데 있어서 중요한 방법론으로 등장하게 되었다. 이러한 계산과학의 핵심을 이루고 있는 계산과학 기술에 대해 전반적으로 고찰합니다. 계산과학 기술은 크게 기존의 과학 기술의 패러다임인 (편)미분 혹은 적분 방정식의 연장선 상에서 이해할 수 있는 유한 차분법 혹은 유한 요소법과 컴퓨터의 출현과 더불어 가능해진 확률론적 방법인 (동력학적) 몬테 카알로와 직접 모사법으로 나눌 수 있을 것입니다. 이 각각의 계산과학 기술의 특징들을 전반적으로 고찰하고자 합니다.

Cosmology concerns the study of the universe at large, its history and its future. Considering observational situations in cosmology, we are unable to obtain a model of the universe without some specifically cosmological assumptions which are completely unverifiable. Therefore, there exist limits. Cosmology itself, like all arts and sciences, is a construct of human intelligence, subject to social and linguistic conditioning and dubious means of communication. The question at issue is ultimately one for philosophic discussions.

During this year, I have studied the feature of the active region filaments. Using two different observations which are H-alpha fibrils and EUV threads, we have determined filament chirality. We found clear hemispheric pattern. Namely, filaments in the northern (southern) hemisphere have dextral (sinistral) fibrils in H-alpha observations obtained from the Big Bear Solar Observatory. On the other hand, negative (positive) closings of filament threads in EUV images observed with TRACE appear in the northern (southern) hemisphere, respectively. These indicate that positive (negative) chirality filaments are surrounded by sinistral (dextral) fibrils. Since fibrils and EUV threads are along magnetic field lines, we suggest that filament and surrounding feature have a same helicity sign.

We used two-dimensional hydrodynamical simulations and one-dimensional radiative transport radiation hydrodynamical simulations to investigate the properties of dense ejecta clumps (bullets) in Type Ia and core collapse supernova remnants, motivated by the observation of protrusions probably caused by clumps in Tycho…s remnant (SN 1572) and the Vela supernova remnant. The ejecta were assumed to freely expand into an ambient medium with a constant density. Ejecta clumps with an initial density contrast Co56 -> Fe56 in supernova ejecta during the first ~10 days is a possible mechanism to produce the clumping, which induces a forward shock that compresses the ejecta gas into a shell. When the flow tends toward a freely-expanding state, the thickness of the shell takes up ~ 100 in a narrow region limited by numerical resolution. The resultant interaction of the clumps with the remnant is expected at a stage as indicated by our simulations.

Opto-mechanical analysis is an essential to develop a large telescope. In order to achieve the required performance specification of the telescope it should be optimized under static, thermal and dynamic loads by the high fidelity finite element analyses integrated with optical performance analyses. In addition, the active optics support system with lightweight mirror should be considered to correct a distorted image during the telescope operation which is designed and optimized by the extensive opto-mechanical analyses. Detailed opto-mechanical analyses will be discussed in this seminar for the lightweight mirrors, active optics support system, overall telescope structure under various environments including gravity, thermal, wind and seismic loads. The overall performance of telescope will be addressed as well based on the Line of Sight (LOS) sensitivity equations.

We used two-dimensional hydrodynamical simulations and one-dimensional radiative transport radiation hydrodynamical simulations to investigate the properties of dense ejecta clumps (bullets) in Type Ia and core collapse supernova remnants, motivated by the observation of protrusions probably caused by clumps in Tycho…s remnant (SN 1572) and the Vela supernova remnant. The ejecta were assumed to freely expand into an ambient medium with a constant density. Ejecta clumps with an initial density contrast 100 relative to their surroundings are found to be rapidly fragmented and decelerated. In order to cause a pronounced protrusion on the blast wave front of the remnant as observed in the Vela remnant, a density contrast of ~1000 may be required. This result applies to moderately large clumps; smaller clumps would require an even larger density contrast. Clumps can create ring structure in the shell of the Vela remnant and we investigate the possibility that RX J0852--4622, an apparent supernova remnant superposed on Vela, is actually part of the Vela shell. The heating from the radioactive decay of Ni56 -> Co56 -> Fe56 in supernova ejecta during the first ~10 days is a possible mechanism to produce the clumping, which induces a forward shock that compresses the ejecta gas into a shell. When the flow tends toward a freely-expanding state, the thickness of the shell takes up ~ 100 in a narrow region limited by numerical resolution. The resultant interaction of the clumps with the remnant is expected at a stage as indicated by our simulations.

The frequencies of the harmonics of standing Alfven waves depend on the distribution of mass along the magnetic field line that sustains the waves. This fact is the basis of the inversion techniques (normal mode magnetospheric seismology) to estimate the plasma mass density variation along the magnetic field from the frequencies of observed ULF waves. However, the technique has not been used extensively because it is difficult to accurately determine the frequencies. Wave observations from geostationary (e.g., GOES) or near-geostationary (e.g., CRRES) satellites provide the best chance of a successful implementation of the technique because the satellites accumulate the spectral information on the harmonics with minimal variations in frequency. By using the frequencies observed by these satellites in a numerical density modeling technique, we find an equatorial mass density enhancement and much milder density variations along the field line than previously thought

I talk about the newly developed near-infrared (0.9-2.5um) imager and spectrograph ISLE for the Cassegrain focus (f/18) of the 1.88 m telescope at Okayama Astrophysical Observatory (OAO). The detector of ISLE is a HAWAII 1024 x 1024 HgCdTe array. The field of view and the pixel scale are 4.2 x 4.2 arcmin^2 and 0.25 arcsec / pixel, respectively. The pixel scale is optimized to sample the light profile of a point source under typical near-infrared seeing condition of OAO (around 1 arcsec). The spectroscopy mode of ISLE provides a capability of long-slit spectroscopy with a spectral resolution R ranging from 500 to 4800. We developed a low-noise readout electronics for the detector and achieved a readout noise lower than 10 e with single sampling readout. Applying a special readout technique, we also succeeded to suppress so-called \"reset anomaly\" of the detector significantly.