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1968년 ~ 2025년까지 1,227 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- 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 44/123
431
- Seo, Y.M.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.119-122
- 2007
- 원문 바로보기
From the HCN observations of dense molecular cloud L694-2, Lee et al.(2007) determined internal distributions of density and velocity for the cloud. The density profile collaborates roughly with the Bonnor- Ebert gas sphere, but the velocity field departs significantly from the result of numerical simulations that are started from the BE sphere. Taking L694-2 as an example of collapsing clouds, we have performed a series of collapse simulations and determined initial configurations for the cloud in such a way that the resulting density and velocity profiles both match with the empirically deduced ones. Among many trial configurations the cloud which is initially uniform in density and bound by an expanding envelop depicts most closely the empirically obtained profiles of both density and velocity.
432
- Kim, Hyo-Sun
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.179-182
- 2007
- 원문 바로보기
Dynamical friction plays an important role in reducing angular momenta of objects in orbital motions. While astronomical objects usually follow curvilinear orbits, most previous studies focused on the linear-trajectory cases. Here, we present the gravitational wake due to, and dynamical friction on, a perturber moving on a circular orbit in a uniform gaseous medium using a semi-analytic method. The circular orbit causes the density wakes to bend along the orbit into asymmetric configurations, resulting in the drag forces in both opposite (azimuthal) and lateral (radial) directions to the perturber motion, although the latter does not contribute to the orbital decay much. For a subsonic perturber, the bending of a wake is only modest and the resulting drag force in the opposite direction is remarkably similar to the linear-trajectory counterpart. On the other hand, a supersonic perturber is able to overtake its own wake, possibly multiple times, creating a high-density trailing tail. Despite the dramatic changes in the wake morphologies, the azimuthal drag force is in surprisingly good agreement with the formulae of Ostriker for the linear-trajectory cases, provided <TEX>$V_pt=2R_p,\;where\;V_p\;and\;R_p$</TEX> are the velocity and orbital radius of the perturber, respectively.
433
- Kim, Hyo-Sun
- Journal of the Korean astronomical society = 천문학회지
- 40, n.1
- pp.17-28
- 2007
- 원문 바로보기
We present wide-field <TEX>$JHK_s$</TEX>-band photometric observations of the three compact H II regions G48.9-0.3, G49.0-0.3, and G49.2-0.3 in the active star-forming region W51B. The star clusters inside the three compact H II regions show the excess number of stars in the <TEX>$J-K_s$</TEX> histograms compared with reference fields. While the mean color excess ratio <TEX>$(E_{J-H}/E_{H-K_s})$</TEX> of the three compact H II regions are similar to <TEX>${\sim}2.07$</TEX>, the visual extinctions toward them are somewhat different: <TEX>${\sim}17$</TEX> mag for G48.9-0.3 and G49.0-0.3; <TEX>${\sim}23$</TEX> mag for G49.2-0.3. Based on their sizes and brightnesses, we suggest that the age of each compact H II region is <TEX>${\leq}2\;Myr$</TEX>. The inferred total stellar mass, <TEX>${\sim}1.4{\times}10^4M_{\odot}$</TEX>, of W51B makes it one of the most active star forming regions in the Galaxy with the star formation efficiency of <TEX>${\sim}10%$</TEX>.
434
- Kim, Sung-Soo S.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.153-155
- 2007
- 원문 바로보기
We have analyzed H and <TEX>$K_s$</TEX>-band images of the Arches cluster obtained using the NIRC2 instrument on Keck with the laser guide star adaptive optics (LGS AO) system. With the help of the LGS AO system, we were able to obtain the deepest ever photometry for this cluster and its neighborhood, and derive the background-subtracted present-day mass function (PDMF) down to <TEX>$1.3M_{\bigodot}$</TEX> for the 5'-9' annulus of the cluster. We find that the previously reported turnover at <TEX>$6M_{\bigodot}$</TEX> is simply due to a local bump in the mass function (MF), and that the MF continues to increase down to our 50 % completeness limit (<TEX>$1.3M_{\bigodot}$</TEX>) with a power-law exponent of <TEX>${\Gamma}$</TEX> = -0.91 for the mass range of 1.3 < M/<TEX>$M_{\bigodot}$</TEX> < 50. Our numerical calculations for the evolution of the Arches cluster show that the <TEX>${\Gamma}$</TEX> values for our annulus increase by 0.1-0.2 during the lifetime of the cluster, and thus suggest that the Arches cluster initially had <TEX>${\Gamma}$</TEX> of <TEX>$-1.0{\sim}-1.1$</TEX>, which is only slightly shallower than the Salpeter value.
435
- Lee, Jeong-Eun
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.107-111
- 2007
- 원문 바로보기
The original environment of the solar system can be inferred by studying the oxygen isotope ratios in the Sun as well as in primitive meteorites and comets. The oxygen isotopic fractionation measured in primitive meteorites is mass-independent, which can be explained by the isotopic-selective photodissociation of CO. The isotopic-selective photodissociation model in a collapsing cloud by Lee et al. (2007) imply the birth of the Sun in a stellar cluster with an enhanced radiation field, which is consistent with the inferred presence of <TEX>$^{60}Fe$</TEX>.
436
- Selim, H.H.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.2
- pp.49-60
- 2007
- 원문 바로보기
This paper deals with the theory for rotational motion of a two-layer Earth model (an inelastic mantle and liquid core) including the dissipation in the mantle-core boundary(CMB) along with tidal effects produced by Moon and Sun. An analytical solution being derived using Hori's perturbation technique at a second order Hamiltonian. Numerical nutation series will be deduced from the theory.
437
- Kim, Kyoo-Hyun
- Journal of the Korean astronomical society = 천문학회지
- 39, n.3
- pp.57-71
- 2006
- 원문 바로보기
We investigated the structural parameters of a sample of 30 dwarf galaxies(15 dEs and 15 dS0s) in the Virgo Cluster using i-band images from the Sloan Digital Sky Survey Data Release 4. Among 28 galaxies for which surface brightness profiles were derived from ellipse fittings, 23 galaxies had a single component that was adequately described by a generalized <TEX>$S\acute{e}rsic$</TEX> function with a shape parameter ranging from n=0.5 to 2, while 5 galaxies(2 dEs and 3 dS0s) had bulge and disk components that were fitted by a generalized <TEX>$S\acute{e}rsic$</TEX> function and an exponential function, respectively. Since the majority of dwarf galaxies in the present sample had a single component, it seems likely that genuine dS0 galaxies that have disk and bulge components are quite rare in the Virgo Cluster. The similarity in structural parameters of genuine dS0 galaxies in the Virgo Cluster with those of Magellanic-type galaxies implies that the progenitors of dwarf lenticular galaxies in the Virgo Cluster were most likely Magellanic-type galaxies if dS0s are harassed late-type spirals.
438
- Kim, Sang-Chul
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.115-123
- 2006
- 원문 바로보기
We present <TEX>$JHK_S$</TEX> near-infrared CCD photometric study for the Galactic open clusters NGC 1641 and NGC 2394. These clusters have never been studied before, and we provide, for the first time the cluster parameters; reddening, distance, metallicity and age. NGC 1641 is an old open cluster with age <TEX>$1.6{\pm}0.2$</TEX> Gyr, metallicity <TEX>$[Fe/H]=0.0{\pm}0.2$</TEX> dex, distance modulus<TEX>$(m-M)_0=10.4{\pm}0.3\;mag(d=1.2{\pm}02\;kpc)$</TEX>, and reddening <TEX>$E(B-V)=0.10{\pm}0.05$</TEX> mag. The parameters for the other old open cluster NGC 2394 are estimated to be <TEX>$age=1.1{\pm}0.2$</TEX> Gyr, <TEX>$[Fe/H]=0.0{\pm}0.2$</TEX> dex, <TEX>$(m-M)_0=9.1{\pm}0.4\;mag(d=660{\pm}120\;pc)$</TEX>, and <TEX>$E(B-V)=0.05{\pm}0.10$</TEX> mag. The metallicities and distance values for these two old open clusters are consistent with the relation between the metallicities and the Galactocentric distances of other old open clusters. We find the metallicity gradient of 53 old open clusters including NGC 1641 and NGC 2394 to be <TEX>${\Delta}[Fe/H]/{\Delta}R_{gc}=-0.067{\pm}0.009\;dex\;kpc^{-1}$</TEX>.
439
- Chi Seung-Youp
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.9-17
- 2006
- 원문 바로보기
In an attempt to investigate star formation activity and statistical properties of clumps of high Galactic latitude clouds (HLCs), we mapped the Polaris Flare region, PF121.3+25.5, in <TEX>$^{12}CO\;and\;^{13}CO$</TEX> J = 1 - 0 using SRAO 6-m telescope and also observed its 12 <TEX>$^{13}CO$</TEX> peak positions in CS J = 2 - 1 with TRAO 14-m telescope. <TEX>$^{13}CO$</TEX> integrated intensity map shows clearly its clumpy structure and the locations of clumps well agree with <TEX>$^{12}CO$</TEX>morphology. CS line is not detected toward the 12 <TEX>$^{13}CO$</TEX> peak positions, so we can conclude there are no dense <TEX>$(\sim10^4\;cm^{-3})$</TEX> in this region. We decomposed 105 clumps from <TEX>$^{13}CO$</TEX> map using GAUSSCLUMPS algorithm. The mass of clumps ranges from <TEX>$7.8\;M_{\odot}\;to\;7.4{\times}10^{-2}\;M_{\odot}$</TEX> with a total mass of <TEX>$66.4\;M_{\odot}$</TEX> The mass spectrum follows a power law, dN/dM <TEX>${\propto}\;M^{-\alpha}$</TEX> with a power index of <TEX>${\alpha}=1.91{\pm}0.13$</TEX>. The virial masses of clumps are in the range of <TEX>$10{\sim}100M_{LTE}$</TEX> and so these clumps are considered to be gravitationally unbound.
440
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.125-128
- 2006
- 원문 바로보기
In order to determine the precise effective temperature and surface gravity of warm stars, all synthetic spectral lines in the wavelength range of <TEX>$4000-5700{\AA}$</TEX> with T=6000-7750 K, and log g=3.5, 4.0, and 4.5 for [M/H]=0.0, <TEX>$V_{rot}$</TEX>=10 km <TEX>$s^{-1}$</TEX>, and <TEX>$V_{tubl}$</TEX>=2 km <TEX>$s^{-1}$</TEX> were calculated using the SYNSPEC package(Hubeny, et al., 1995) and the Kurucz(1995) model. Then, the depth-ratios for all line pairs were investigated and we selected two and six depth-ratios appropriate for the surface gravity and temperature indicators, respectively. We plotted six grids with X- and Y-axes for the depth-ratios of surface gravity and temperature, respectively, for the simultaneous estimation of these two atmospheric parameters. This method was applied to the spectum of <TEX>$\delta$</TEX> Scu for the determination of its temperature and surface gravity simultaneously.