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- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 88/123
871
- WANG JIA LONG
- Journal of the Korean astronomical society = 천문학회지
- 29, n.2
- pp.217-221
- 1996
- 원문 바로보기
We have examined morphological change and movements of individual sunspots within a sunspot group in association with a large solar flare activity (3B/X1.5) appeared on 13 May 1981. For this purpose we measured distance among spots during the period before and after the flare activity and estimated the average velocity of their movement. Our main results are as follows: (1) The longitudinal displacement among sunspots are generally greater than the latitudinal displacement. (2) During the period the spots moved with an average velocity of 1.2 km/s in longitude and 0.86 km/s in latitude. (3) The most notable change took place in the central part placed between the two ribbons of the flare.
872
- MESZAROS A.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.43-43
- 1996
- 원문 바로보기
873
- CHUN MOO-YOUNG
- Journal of the Korean astronomical society = 천문학회지
- 29, n.2
- pp.137-156
- 1996
- 원문 바로보기
NGC 6716 is an intermediate-age open cluster in Sagittarius. In this paper, we present the new UBV CCD photometry of the stars in the cluster, which is deeper than previous ones. From the color-color diagram and the color-magnitude diagram, we derived a reddening <TEX>$E_{B- V} = 0.17\pm0.03$</TEX> and a distance modulus of the cluster, <TEX>$(V - Mv)_o = 9.2\pm0.1$</TEX>. An age of the cluster is estimated as <TEX>$8\pm10^7 yrs$</TEX> from the latest isochrone. Luminosity function and mass function of the cluster are derived. The gradient of the mass function of bright stars is a bit steep, <TEX>$\Gamma = -1.85\pm0.05$</TEX>, and there is no distinct bump and dip in the mass function.
874
- MOON YONG-JAE
- Journal of the Korean astronomical society = 천문학회지
- 29, n.2
- pp.207-215
- 1996
- 원문 바로보기
To derive coronal temperature, electron density and nonthermal velocity, we have analyzed high resolution spectra (e.g., Fe XII 338.3, Fe XII 352.1, Fe XIV 334.2, Fe XIV 353.8, Fe XV 284.2, Fe XV 321.8, Fe XV 327.0, Fe XVI 335.4, and Fe XVI 360.8) taken from AR 6615 by SERTS (Solar Extreme Ultraviolet Rocket Telescope and Spectrograph). Important findings emerging from the present study are as follows: (1) Temperature estimated from Fe XVI 335.4 and Fe XIV, 334.2 is <TEX>$\~2.4\times10^6 K$</TEX> and no systematic difference in temperature is found between the active region and its adjacent quiet region; (2) Mean electron density estimated from Fe XV is <TEX>$\~3\times10^9 cm^{-3}\;and\;\~10^{10} cm^{-3}$</TEX> from Fe XII and Fe XIV; (3) Mean density of the active region is found to be higher than that of the quiet region by a factor of 2; (4) Nonthermal velocity estimated from Fe XV and Fe XVI is <TEX>$20\times25 km\;s^{-l}$</TEX> which decreases with increasing ionization temperatures. This supports the notion that the nonthermal velocity declines outwards above the transition region.
875
- KIM YONG HA
- Journal of the Korean astronomical society = 천문학회지
- 29, n.2
- pp.245-253
- 1996
- 원문 바로보기
We have analyzed infrared (IR) images of Jupiter which was observed at the McDonald Observatory, Texas, U.S.A., during the P/SHoemaker-LEvy 9 (SL9) impact period and about one week after the last impact. The IR images were obtained on the 2.7m telescope using a NICMOS array with filters to isolate the <TEX>$1.5{\mu}m\;NH_3\; band,\;the\;2.3{\mu}m\;CH_4\;band,\;the\;2.12{\mu}m\;H_2\;S(0)$</TEX> pressure-induced absorption, and the continua at <TEX>$1.58{\mu}m\;and\;2.0{\mu}m$</TEX> (short K-band). All images except those with the <TEX>$1.58{\mu}m$</TEX> continuum filter show bright impact sites against the relatively dark Jovian disk near the impact latitude of about <TEX>$45^{\circ}$</TEX> S. This implies that dusts originated from the impacts reflect the solar radiation at high altitudes before absorbed by stratospheric <TEX>$CH_4,\;NH_3 \;or\;H_2$</TEX>. The impact sites observed with the <TEX>$2.3{\mu}m$</TEX> filter are conspicuously bright against a very dark background. The morphology of impact sites, G, L, and H at 2.3 and <TEX>$2.12{\mu}m$</TEX> filters shows clearly an asymmetric structure toward the incident direction of the comet fragments, in agreement with the studies of visible impact images obtained with the Hubble Space Telescope. Comparisons of reflectances of G, L, and H sites with simple radiative transfer models suggest that optically thick dust layers were formed at high altitudes at which methane absorption attenuates incoming sunlight only by about <TEX>$1\%$</TEX>. The dust layers in these sites seem to form at about the same altitude regardless of the magnitude of the impacts, but they appear to descend gradually after the impacts. The dust layers have optical depths of 2-5, according to the models.
876
- REY SOO-CHANG
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.137-138
- 1996
- 원문 바로보기
The first large-format CCD color-magnitude diagram (CMD) in the B and V passbands is presented for the Galactic globular cluster M53 (NGC 5024). We have discovered 117 new blue straggler (BS) candidates in the field of M53. The analysis of bright BS stars (V <19.0) clearly shows a bimodal radial distribution, with a high frequency in the inner and outer regions. The distribution is similar to that found in M3, a globular cluster with similar central density and concentration.
877
- KIM SUNGSOO S.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.143-144
- 1996
- 원문 바로보기
Two-component models (normal star and degenerate star components) are the simplest realization of clusters with a mass spectrum because the high mass stars quickly evolve off leaving degenerate stars behind, while low mass stars survive for a long time as main-sequence stars. In the present study we examine the post-collapse evolution of globular clusters using two-component Fokker-Planck models that include three-body binary heating. We confirm that a simple parameter <TEX>${\epsilon}{\equiv} (E_{tot}/t_{rh})/(E_c/t_{rc})$</TEX> well describes the occurrence of gravothermal oscillations of two-component clusters. Also, we find that the degree of instability depends on the steepness of the mass function such that clusters with a steeper mass function are less exposed to instability.
878
- CHOI MINHO
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.195-196
- 1996
- 원문 바로보기
We observed CO J = 2 <TEX>$\to$</TEX> 1 and J = 3 <TEX>$\to$</TEX> 2 lines toward several star formation regions with extremely high velocity (EHV) outflows: W3 IRS5, W28 A2, GL2591, S140, and Cepheus A. The full width of the wings are 90-235 km <TEX>$s^{-1}$</TEX>. Some wings show clear break of slope in the line profile implying that the nature of the EHV outflow is different from that of the high velocity outflow. We suggest that the EHV CO wing emission is tracing CO molecules in the stellar wind or jet which drives the high velocity outflow.
879
- XIE R. X.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.331-332
- 1996
- 원문 바로보기
We present 3 rare subtypes of the FFSs observed with high temporal resolution at 4-frequency (1.42, 2.13, 2.84 and 4.2G GHz). The various FFSs occurred during the main and post-flare phase can demonstrate that coronal nonthermal electron acceleration/injection may go through the whole development process of flares, and deduce that there may exist the re-forming of loop-like structures in the post-flare phase, and the complex multi-type magnetic structures in corona.
880
- CHOE SEUNG-URN
- Journal of the Korean astronomical society = 천문학회지
- 29, n.2
- pp.93-105
- 1996
- 원문 바로보기
We have solved the radiative transfer problem using a Sobolev approximation with an escape probability method in case of the supersonic expansion of a stellar envelope to an ambient medium. The radiation from the expanding envelope turns out to produce a P-Cygni type profile. In order to investigate the morphology of the theoretical P-Cygni type profile, we have treated <TEX>$V_\infty,\;V_{sto},\;\beta$</TEX> (parameters for the velocity field), it and E(parameter for collisional effect) as model parameters. We have investigated that the velocity field and the mass loss rate affect the shapes of the P-Cygni type profiles most effectively. The secondarily important factors are <TEX>$V_\infty,\;V_{sto}$</TEX>. The collisional effect tends to make the total flux increased but not so much in magnitude. We have infered some physical parameters of 68 Cyg, HD24912, and <TEX>$\xi$</TEX> persei such as <TEX>$V_\infty,\;M$</TEX> from the model calculation, which shows a good agreenment with the observational results.