• Journal of The Korean Astronomical Society
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• v.34 no.4
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• pp.297-299
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• 2001

We have constructed the foundations to a series of theoretical diagnostic methods to probe the jet phenomenon in young stars as observed at various optical forbidden lines. We calculate and model in a self-consistent manner the physical and radiative processes which arise within an inner disk-wind driven magneto centrifugally from the circumstellar accretion disk of a young sun-like star. Comparing with real data taken at high angular resolution, our approach will provide the basis of systematic diagnostics for jets and their related young stellar objects, to attest the emission mechanisms of such phenomena. This work can help bring first-principle theoretical predictions to confront actual multi-wavelength observations, and will bridge the link between many very sophiscated numerical simulations and observational data. Analysis methods discussed here are immediately applicable to new high-resolution data obtained with HST and Adaptic Optics.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.46.2-46.2
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• 2021

Presolar silicon carbide (SiC) grains form around in the envelopes of asymptotic giant branch (AGB) stars by satisfying C/O>1 which is an optimal condition for SiC grains to condense in the stellar outflows. Ruthenium (Ru) isotopes are locked into the SiC grains during the condensation of SiC grains. We investigate the isotopic compositions of Ru in the stellar winds by using the NuGrid data, which are obtained by nucleosynthesis calculations during the stellar evolution. We compare the isotopic compositions of Ru obtained from the NuGrid data with measurements and the predictions obtained from different codes. Our results present a piece of evidence that SiC grains in the presolar system came from low-mass and low-metallicity AGB stars, also confirming that they were not from massive stars. We also suggest a new scenario in which the total stellar yields are also considered because SiC grains can condense during the collapse of molecular clouds.

• Journal of The Korean Astronomical Society
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• v.30 no.1
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• pp.13-25
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• 1997

Sobolev approximation can be adopted to a macroscopic supersonic motion comparatively larger than a random (thermal) one. It has recently been applied not only to the winds of hot early type stars, but also to envelopes of late type giants and/or supergiants. However, since the ratio of wind velocity to stochastic one is comparatively small in the winds of these stars, the condition for applying the Sobolev approximation is not fulfilled any more. Therefore the validity of the Sobolev approximation must be checked. We have calculated exact P Cygni profiles with various velocity ratios, $V_\infty/V_{sto}$, using the accelerated lambda iteration method, comparing with those obtained by the Sobolev approximation. While the velocity ratio decrease, serious deviations have been occured over the whole line profile. When the gradual increase in the velocity structure happens near the surface of star, the amount of deviations become more serious even at the high velocity ratios. The investigations have been applied to observed UV line profile of CIV in the Copernicus spectrums $of\;\zeta\;Puppis\;and\;NV\;of\;\tau\;Sco$. In case of $\tau$ Sco which has an expanding envelope with the gradual velocity increase in the inner region, The Sobolev approximation has given the serious deviations in the line profiles.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.55.2-55.2
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• 2018

Neutron stars (NS) are rapidly spinning compact objects. Their rotation energy is released by particles, electromagnetic waves, and even gravitational waves. The source of the energy is of course the rotation, so by studying the rotational properties of neutron stars, we can gain some insights into matter under extreme conditions. In particular, it is known that the braking index n is sensitive to the moment of inertia and/or NS winds. The neutron star PSR B0540-69 exhibits interesting timing behavior; previous measurements of the braking index for this pulsar may suggest a change in time. In order to see if the change is real, We investigate the timing properties of B0540-69 using recent ~1000-days Swift satellite data.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.66.4-67
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• 2016

Our recent investigation (Lee et al. 2015) suggests that the presence of double red clump in the Milky Way bulge is another manifestation of multiple populations observed in halo globular clusters. The origin of Helium enhancement in the 2nd generation population (G2), however, is not yet fully understood. Here we investigate the origin of this super-Helium-rich population in the framework of self-enrichment scenario. We find that chemical enrichments and pollutions by asymptotic giant branch stars and winds of massive rotating stars can naturally reproduce the observed Helium enhancement. The Helium to metal enrichment ratio appears to be ${\Delta}Y/{\Delta}Z=6$ for G2, while the standard ratio, ${\Delta}Y/{\Delta}Z=2$, is appropriate for G1, which is probably enriched mostly by typeII supernovae.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.42.3-42.3
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• 2020

We investigate the observational properties of Wolf-Rayet stars, suggest the constraint of their mass-loss rate and apply our results to the observed progenitor candidates of Type Ib/Ic supernovae (iPTF13bvn and SN 2017ein). For this purpose, we adopt the WR star models with various mass-loss rates and wind terminal velocities. We obtain the high resolution spectra of those models at the pre-supernova phase using the radiative transfer code CMFGEN. We verify the optically faint property of SN Ic progenitors and show that the optical faintness is mainly originated by the high effective temperature at the photosphere. We also show that a simple analytic model for WR winds using a constant opacity can roughly predict the photospheric parameters. We show that the change of the mass-loss rate and the terminal wind velocity critically affects the optical luminosity. We find the optical luminosities of SN Ic progenitor models with our fiducial mass-loss rate prescription are fainter than the detection limits. We also suggest the mass-loss rate of WR stars may not exceed 2 times of our fiducial value by comparing our predictions with the detection limit of SN Ib/Ic progenitors. The directly observed progenitor candidate of iPTF13bvn can be explained by our SN Ib progenitor models. We find that the SN 2017ein progenitor candidate is too bright and too blue to be a SN Ic progenitor.

• The Journal of Dong Guk Oriental Medicine
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• v.5
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• pp.281-306
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• 1996

A study on the effect of the Sun-Moon-Stars(日月星辰) in Huang Ti Nei Ching("黃帝內經") on the formation of the Yunqi theory(運氣理論) have revealed following conclusions. 1. There was a record of Stars(星辰) written by Gabgol-Character(甲骨文字) in the Yin(殷) Dynasty. But the very first documentary records of Stars(星辰) is Shu Jing("書經"). Ancient astronomy had the tendency of astrology of combined with theory of the Five Elements(五行) and finally effects the theory of formation of Huang Ti Nei Ching("黃帝內經"). 2. Shu Jing("書經") said that Junrak(錢樂) made an Armillary sphere(運天儀) in the Sung(宋) Dynasty. And in the Jin(秦) and the Han(漢) Dynasty, they already observed the stars. The Sunkiokhyung(璿機玉衡) which is machinery of star-observing, became to be called an Armillary sphere (運天儀) by the pass of times. 3. As of the theory of the Cosmos-structure(宇宙-構造論) in Ohanunhangdaeron("五運行大論"), Guiyugu(鬼兒區) announced the Hypothesis of Covering Heaven(蓋天說) but Kibak(岐伯) supported the Hypothesis of chaosheven's(蓋天說) and in the theory of atmosphere(大氣論) in Ohanunhangdaeron("五運行大論") said that the earth was in Great Empty(太虛) and it was floating in the universe by the Great Chi(大氣). 4. The knowledge about the Five stars(五星) in Huang Ti Nei Ching("黃帝內經") is presented in the section of Gemgwejineonron("金?眞言論"), Gigoupyondaeron("氣交變大論"), Youkwonjeonggidaeron("六元正紀大論").ln the method of identifying the Five stars(五星) presented the criteria of the brightness, the altitude, the colours and the orbit etc. 5. The jupiter which has twelve year's revolution cycle was the basis of determination on the Twelve constellation(12辰), the Twelve field of heaven(12次), the Twelve Houses in the ecliptic(黃道 12宮), the Twelve Earth's Branches(12支) and the Twelve fields of Earth(12分野) and also it became the origin of the duodecimals(12進法). 6. The saturn having about twenty-eight year's revolution cycle became the criterion in identifying the Twenty Eight Constellations(28宿) which was used as the coordinates of the Celestial sphere (天球). 7. By the Percussional movement(歲差運動), the position of polaris and the Vernal-Antumal equinox(春秋分点) were shifted. Therefore the ancient the Heaven Gate-Earth Door(天門-地戶) changed from the position of Sil-Byuk(室壁), Yik-Jin(翼軫). And the precisional movements brought about the concept of the WunHoyYunSe(元會運世) that is a method of dividing a period. Also the precisional movement gave three dimension(三次元) foundation interpreted the Sixty JiaZi (六十甲子) which is revolving through sixty years uniformally. 8. The Hypothesis of the Nine Houses and Eight Winds(九宮八風論) which is one field of the astrology of ancient polaris-nine Houses divination plate(太一九宮占盤) brought about the concept of deficiency and excess and the concept of the Wind Vice(風邪). In the Calendar System(曆法) presented in Huang Ti Nei Ching("黃帝內經") the tropical year of the Sun-Moon-Stars(日月星辰) and the revolution and the rotation of the earth give explanations the changes of Yin-Yang(陰陽) by the use of the ten Celestial branches(十干) and the twelve Earth branches(十二支).

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.67.2-67.2
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• 2019

We present the results of KVN and ALMA observations toward WX Psc (IRC+10011) which is a long-period variable OH/IR star. The SiO masers of v=1 and v=2, J=5-4, and the SiO thermal emission of v=0, J=5-4 were observed together with H2O v2=1 (232.6 GHz) and continuum emission at ALMA Band 6 in October 2017 (Cycle 5). This observation aims to investigate the physical association between the inner and outer parts of the circumstellar envelope (CSE) swept by the stellar winds, which is very crucial to understand the asymmetric outward motions developed during the evolutionary phases from the asymptotic giant branch (AGB) stars to the planetary nebulae (PNe). The strong SiO maser features and thermal emissions are detected together with the continuum emission in ALMA observation, which imply the elongated morphology of the CSE of WX Psc. While the spatial resolution of about 20 mas in ALMA observation cannot clearly resolve the detailed characteristics of the inner part of the CSE, the Korean VLBI Network (KVN) observations show the spatial distributions of the v=1 J=1-0, J=2-1, J=3-2 SiO masers emitted from the inner regions of CSE, which are the complementary to the ALMA results. Therefore, we expect these results reveal how the bipolar features of the 22 GHz H2O maser are connected to the innermost region of CSE through the dust condensation region, which is closely related to the enormous mass ejection of the evolved stars.

• Bulletin of the Korean Space Science Society
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• 1992.10a
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• pp.19-22
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• 1992

We have computed the model spectra for the novae that formed dust grains shortly after their explosions. And the results are closely compared with recent infrared observational data. The amorphous carbon grains appear to be the major component for the carbon-rich novae. And the silicate grains which reside in Mira variables are found to be the best candidate material for the oxygen-rich novae. In novae, the winds from the central stars are very strong and fast so the emergent spectra are highly dependent on the time scales of dust formation. We find optically thin dustemission for oxgen-rich novae because they have longer time-scales of dust formation and the dust shells with larger radii.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.93.2-93.2
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• 2014

Planetary nebulae (PN) are the last stages of evolution of intermediate mass (1-8 Msolar) stars. Their shapes are thought to result from interactions between the present-day, fast (emerging white dwarf) and previously ejected, slow (red giant) stellar winds. The observation of young, bright PN, NGC7027 and BD+30 3639, was made on July 7, 2014 using the 2.7m Harlan J. Smith telescope at the McDonald Observatory. IGRINS with high spatial (0.27") and high spectral ($7.5km\;s^{-1}$) resolution will provide more nebular lines and excitation/abundances to constrain the morphology and kinematics of the Nebula and the PDRs. Combined with other archival data (X-ray, 2MASS, WISE, Spitzer, Herschel) for PN, high-resolution IR spectroscopy will yield insight into poorly understood aspects of PN morphologies and the late stages of binary star evolution.