모달창 닫기
- 홈으로 이동
1968년 ~ 2024년까지 1,211 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 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 41/122
401
- Dib, Sami
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.157-160
- 2007
- 원문 바로보기
I present a model to explain the mass segregation and shallow mass functions observed in the central parts of starburst stellar clusters. The model assumes that the initial pre-stellar cores mass function resulting from the turbulent fragmentation of the proto-cluster cloud is significantly altered by the cores coalescence before they collapse to form stars. With appropriate, yet realistic parameters, this model based on the competition between cores coalescence and collapse reproduces the mass spectra of the well studied Arches cluster. Namely, the slopes at the intermediate and high mass ends, as well as the peculiar bump observed at <TEX>$6M_{\bigodot}$</TEX>. This coalescence-collapse process occurs on a short timescale of the order of the free fall time of the proto-cluster cloud (i.e., a few <TEX>$10^4$</TEX> years), suggesting that mass segregation in Arches and similar clusters is primordial. The best fitting model implies the total mass of the Arches cluster is <TEX>$1.45{\times}10^5M_{\bigodot}$</TEX>, which is slightly higher than the often quoted, but completeness affected, observational value of a few <TEX>$10^4M_{\bigodot}$</TEX>. The model implies a star formation efficiency of <TEX>${\sim}30$</TEX> percent which implies that the Arches cluster is likely to a gravitationally bound system.
402
- Yoo, Kye-Hwa
- Journal of the Korean astronomical society = 천문학회지
- 40, n.2
- pp.39-47
- 2007
- 원문 바로보기
A high resolution spectrum of PU Vul obtained at Bohyunsan Astronomy Observatory on April 9, 2004 is presented. At this phase, PU Vul was an emission-line star and its continuum was very weak. Emission lines of He II, H I, [Ne IV], [N II], [O III], [Ar V ] and [Fe VII] dominated the spectrum of PU Vul. Many of them exhibited hat-top profiles with strong and multi-peaked emissions on flat-tops of their profiles. Radial velocities for these lines were measured. Origins of the spectral lines are discussed in terms of the wind and the photoionization models.
403
- 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.
404
- 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.
405
- Silich, Sergiy
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.187-188
- 2007
- 원문 바로보기
This contribution to the IV Korea-Mexico meeting deals with the hydrodynamics of the matter reinserted within super star clusters (SSCs) by both stellar winds and supernova explosions, results recently printed in The Astrophysical Journal (Silich et al. 2007). The motivation of such a project arose from the persistent presence of the small mass and compact HII regions that sit right on top of many massive and compact SSCs, from which one expects a large mechanical energy power. The data used for our calculations appear only recently (see Smith et al. 2006) for the massive and compact SSC M82-A1. We presented in our paper the calculated flow, derived through analytical and semi-analytical methods, which led to almost identical results. We have found out that the only way of accommodating a compact HII region (4.5 pc in radius, in the case of M82-A1) on top of a 6.3 Myr old and massive (> <TEX>$10^6M_{\bigodot}$</TEX>) SSC with a half light radius of 3 pc, requires of two assumptions: a very low heating efficiency (< 10%) within the cluster, what leads to a bimodal solution (see Tenorio-Tagle et al. 2007) and a high pressure in the surrounding medium.
406
- 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.
407
- Sanchez-Salcedo, F.J.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.171-177
- 2007
- 원문 바로보기
In external galaxies, the velocity dispersion of the atomic hydrogen gas shows a remarkably flat distribution with the galactocentric radius. This has been a long-standing puzzle because if the gas velocity dispersion is due to turbulence caused by supernova explosions, it should decline with radius. After a discussion on the role of spiral arms and ram pressure in driving interstellar turbulence in the outer parts of galactic disks, we argue that the constant bombardment by tiny high-velocity halo clouds can be a significant source of random motions in the outer disk gas. Recent observations of the flaring of H I in the Galaxy are difficult to explain if the dark halo is nearly spherical as the survival of the streams of tidal debris of Sagittarius dwarf spheroidal galaxy suggests. The radial enhancement of the gas velocity dispersion (at R > 25 kpc) due to accretion of cloudy gas might naturally explain the observed flaring in the Milky Way. Other motivations and implications of this scenario have been highlighted.
408
- Elias, Federico
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.141-145
- 2007
- 원문 바로보기
Here we analyze if the ionized shells associated with giant HII regions represent the progenitors of the larger neutral hydrogen supershells detected in the Milky Way and other spiral and dwarf irregular galaxies. We calculate the evolutionary tracks that 12 HII shells found by Relano et al. (2005, 2007) would have if they expanded into the interstellar medium because of multiple supernovae explosions occurring inside the cavity. We find, contrary to Relano et al. (2007), that the evolutionary tracks of these HII shells are inconsistent with the observed parameters of the largest and most massive neutral hydrogen supershells. Thus, an additional energy source to the multiple supernovae explosions is required in order to explain the origin of the most massive neutral hydrogen shells.
409
- Lee, Jeong-Eun
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.83-89
- 2007
- 원문 바로보기
A new type of object called 'Very Low Luminosity Objects (VeLLOs)' has been discovered by the Spitzer Space Telescope. VeLLOs might be substellar objects forming by accretion. However, some VeLLOs are associated with strong outflows, indicating the previous existence of massive accretion. The thermal history, which significantly affects the chemistry, between substellar objects with a continuous low accretion rate and objects in a quiescent phase after massive accretion (outburst) must be greatly different. In this study, the chemical evolution has been calculated in an episodic accretion model to show that CO and <TEX>$N_2H^+$</TEX> have a relation different from starless cores or Class 0/I objects. Furthermore, the <TEX>$CO_2$</TEX> ice feature at <TEX>$15.2{\mu}m$</TEX> will be a good tracer of the thermal process in VeLLOs.
410
- Shin, Ji-Hye
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.91-97
- 2007
- 원문 바로보기
The Fokker-Planck (FP) model is one of the commonly used methods for studies of the dynamical evolution of dense spherical stellar systems such as globular clusters and galactic nuclei. The FP model is numerically stable in most cases, but we find that it encounters numerical difficulties rather often when the effects of tidal shocks are included in two-dimensional (energy and angular momentum space) version of the FP model or when the initial condition is extreme (e.g., a very large cluster mass and a small cluster radius). To avoid such a problem, we have developed a new integration scheme for a two-dimensional FP equation by adopting an Alternating Direction Implicit (ADI) method given in the Douglas-Rachford split form. We find that our ADI method reduces the computing time by a factor of <TEX>${\sim}2$</TEX> compared to the fully implicit method, and resolves problems of numerical instability.