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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 49/122
481
- SHEN ZHI-QIANG
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.261-266
- 2005
- 원문 바로보기
This paper reviews the progress in the VLBI (Very Long Baseline Interferometry) studies of Sgr A<TEX>$\ast$</TEX>, the best known supermassive black hole candidates with a dark mass concentration of <TEX>$4 {\times} 10^6 M_{\bigodot}$</TEX> at the center of the Milky Way. The emphasis is on the importance of the millimeter and sub-millimeter VLBI observations in the detection of Sgr A<TEX>$\ast$</TEX>'s intrinsic structure and search for the structural variation.
482
- UMETSU KEIICHI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.191-195
- 2005
- 원문 바로보기
We used Subaru observations of A1689 (z = 0.183) to derive an accurate, model-independent mass profile for the entire cluster, r<TEX>$\le$</TEX>2Mpc/h, by combining magnification bias and distortion measurements. The projected mass profile steepens quickly with increasing radius, falling away to zero at r<TEX>${\~}$</TEX>1.0Mpc/h, well short of the anticipated virial radius. Our profile accurately matches onto the inner profile, r <TEX>$\le$</TEX>200kpc/ h, derived from deep HST / ACS images. The combined ACS and Subaru information is well fitted by an NFW profile with virial mass, <TEX>$(1.93 \pm 0.20) {\times}10^{15} M_{\bigodot}$</TEX>, and surprisingly high concentration, <TEX>$C_{vir} = 13.7^{+1.4}_{-1.1}$</TEX>, significantly larger than theoretically expected (<TEX>$C_{vir} {\le}4$</TEX>), corresponding to a relatively steep overall profile. These results are based on a reliable sample of background galaxies selected to be redder than the cluster E/SO sequence. By including the faint blue galaxy population a much smaller distortion signal is found, demonstrating that blue cluster members significantly dilute the true signal for r <TEX>$\le$</TEX> 400kpc/ h. This contamination is likely to affect most weak lensing results to date.
483
- SATO BUN'EI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.315-318
- 2005
- 원문 바로보기
We have carried out a precise Doppler survey of G-type giants aiming to unveil the properties of planetary systems in intermediate-mass stars (<TEX>$1.5-5M_{\bigodot}$</TEX>). G-type giants are promising targets for Doppler planet searches around massive stars, because they are slow-rotators and have many sharp absorption lines in their spectra and their surface activities are relatively low in contrast to their younger counterparts on the main-sequence (B-A stars). We are now monitoring radial velocities of about 300 late G-type (including early K-type) giants using HIgh Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory. We have achieved a Doppler precision of about 6-7 m/s over a time span of 3 years using an iodine absorption cell. We found that most of the targets have radial velocity scatters of <TEX>${\sigma}{\~} 10-20 m\;s^{-1}$</TEX> over 1-3 years, with the most stable reaching levels of 6-8 m <TEX>$s^{-1}$</TEX>. Up to now, we have succeeded in discovering the first extrasolar planet around a G-type giant star HD 104985, and also found several candidates showing significant radial velocity variations, suggesting the existence of stellar and substellar companions. Observations have continued to establish their variability.
484
- Kim, Sung-Eun
- Journal of the Korean astronomical society = 천문학회지
- 38, n.3
- pp.365-370
- 2005
- 원문 바로보기
We have made a multi-wavelength study of the X-ray bright giant shell complex 30 Doradus in the Large Magellanic Cloud (LMC). This is the one of the largest H II complexes in the Local Group. The Australia Telescope Compact Array (ATCA) and the Parkes 64-m single dish observations reveal that the distribution and internal motions of H I gas show the effects of fast stellar winds and supernova blasts. The hot emitting gas within the 30 Doradus complex and the entire giant H II complex are encompassed by an expanding H I shell. We investigate the dynamical age of this H I shell and compare to the age of starbursts occurred in the 30 Doradus nebula using the radiative transfer model and the infrared properties.
485
- Bong, Su-Chan
- Journal of the Korean astronomical society = 천문학회지
- 38, n.4
- pp.445-462
- 2005
- 원문 바로보기
In a companion paper, we have presented so-called Spatio-Spectral Maximum Entropy Method (SSMEM) particularly designed for Fourier-Transform imaging over a wide spectral range. The SSMEM allows simultaneous acquisition of both spectral and spatial information and we consider it most suitable for imaging spectroscopy of solar microwave emission. In this paper, we run the SSMEM for a realistic model of solar microwave radiation and a model array resembling the Owens Valley Solar Array in order to identify and resolve possible issues in the application of the SSMEM to solar microwave imaging spectroscopy. We mainly concern ourselves with issues as to how the frequency dependent noise in the data and frequency-dependent variations of source size and background flux will affect the result of imaging spectroscopy under the SSMEM. We also test the capability of the SSMEM against other conventional techniques, CLEAN and MEM.
486
- Kim Sang-Chul
- Journal of the Korean astronomical society = 천문학회지
- 38, n.4
- pp.429-435
- 2005
- 원문 바로보기
We present BV CCD photometry for the open clusters Czernik 24 and Czernik 27. These clusters have never been studied before, and we provide, for the first time, the cluster parameters; reddening, distance, metallicity and age. Czernik 24 is an old open cluster with age <TEX>$1.8{\pm}0.2Gyr$</TEX>, metallicity <TEX>$[Fe/H]=-0.41{\pm}0.15dex$</TEX>, distance modulus <TEX>$(m-M)_0=13.1{\pm}0.3mag$</TEX> (<TEX>$d=4.1{\pm}0.5kpc$</TEX>), and reddening <TEX>$E(B-V)=0.54{\pm}0.12mag$</TEX>. The parameters for Czernik 27 are estimated to be <TEX>$age=0.63{\pm}0.07Gyr$</TEX>, <TEX>$[Fe/H]=-0.02{\pm}0.10dex$</TEX>, <TEX>$(m-M)_0=13.8{\pm}0.2mag$</TEX> (<TEX>$d=5.8{\pm}0.5kpc$</TEX>), and <TEX>$E(B-V)=0.15{\pm}0.05mag$</TEX>. The metallicity and distance values for Czernik 24 are consistent with the relation between the metallicity and the Galactocentric distance of other old open clusters. We find the metallicity gradient of 51 old open clusters including Czernik 24 to be <TEX>${\Delta}[Fe/H]/{\Delta}R_{gc}=-0.064 {\pm}0.009dex\;kpc^{-1}$</TEX>.
487
- AWADALLA N. S.
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.43-57
- 2005
- 원문 바로보기
The authors have assembled a sample of 80 W UMa binary systems (42 W-subtype and 38 A-subtype) whose light curves have all been solved by means of the recent W-D code and combined with up-to-date radial velocity solutions. The absolute parameters (masses, radii and luminosities) have been derived (without any constraint on the physical parameters). The main results of this paper are: (1) the mass-luminosity relations for both W&A-subtypes. as well as for all W UMa contact binaries have been shown, (2) the mass-radius relations have been found for both subtypes, (3) some remarks on the evolution status have been presented.
488
- SUH KYUNG-WON
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.267-270
- 2005
- 원문 바로보기
We investigate the spectral energy distributions (SEDs) of low mass-loss rate O-rich asymptotic giant branch (AGB) stars using the infrared observational data including the Infrared Space Observatory (ISO) data. Comparing the results of detailed radiative transfer model calculations with observations, we find that the dust formation temperature is much lower than 1000 K for standard dust shell models. We find that the superwind model with a density-enhanced region can be a possible alternative dust shell model for LMOA stars.
489
- Lee, Ho-Gyu
- Journal of the Korean astronomical society = 천문학회지
- 38, n.4
- pp.385-414
- 2005
- 원문 바로보기
We have searched for infrared emission from supernova remnants (SNRs) included in the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) field. At the positions of 100 known SNRs, we made 3.6, 4.5, 5.8, and <TEX>$8.0{\mu}m$</TEX> band images covering the radio continuum emitting area of each remnant. In-depth examinations of four band images based on the radio continuum images of SNRs result in the identification of sixteen infrared SNRs in the GLIMPSE field. Eight SNRs show distinct infrared emission in nearly all the four bands, and the other eight SNRs are visible in more than one band. We present four band images for all identified SNRs, and RGB-color images for the first eight SNRs. These images are the first high resolution (<2') images with comparative resolution of the radio continuum for SNRs detected in the mid-infrared region. The images typically show filamentary emission along the radio enhanced SNR boundaries. Most SNRs are well identified in the 4.5 and <TEX>$5.8{\mu}m$</TEX> bands. We give a brief description of the infrared features of the identified SNRs.
490
- TATEMATSU KEN'ICHI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.279-282
- 2005
- 원문 바로보기
We report the millimeter-wave radio observations of molecular cloud cores in Taurus. The observed line is the <TEX>$N_2H^+$</TEX> emission at 93 GHz, which is known to be less affected by molecular depletion. We have compared starless (IRAS-less) cores with star-forming cores. We found that there is no large difference between starless and star-forming cores, in core radius, linewidth, core mass, and radial intensity profile. Our result is in contrast with the result obtained by using a popular molecular line, in which starless cores are larger and less condensed. We suggest that different results mainly come from whether the employed molecular line is affected by depletion or not. We made a virial analysis, and found that both starless and star-forming cores are not far from the critical equilibrium state, in Taurus. Together with the fact that Taurus cores are almost thermally supported, we conclude that starless Taurus cores evolve to star formation without dissipating turbulence. The critical equilibrium state in the virial analysis corresponds to the critical Bonnor-Ebert sphere in the Bonnor-Ebert analysis (Nakano 1998). It is suggested that the initial condition of the molecular cloud cores/globules for star formation is close to the critical equilibrium state/critical Bonnor-Ebert sphere, in the low-mass star forming region.