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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
- 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.
482
- HIRANO NAOMI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.219-222
- 2005
- 원문 바로보기
We present the high-resolution (2'-4') images of the molecular envelopes surrounding the evolved stars, V Hya, VY CMa, and <TEX>${\pi}^1$</TEX> Gru observed with the Submillimeter Array. The CO J=2-1 and 3-2 images of the carbon star V Hya show that the circumstellar structure of this star consists of three kinematic components; there is a flattened disk-like envelope that is expanding with a velocity of <TEX>${\~}16 km\;s^{-1}$</TEX>, the second component is the medium-velocity wind having a deprojected velocity of 40-120 km <TEX>$s^{-l}$</TEX> moving along the disk plane, and the third one is the bipolar molecular jet having an extreme velocity of 70-185 km <TEX>$s^{-l}$</TEX>. The axis of this high velocity jet is perpendicular to the plane of the disk-like envelope. We found that the circumstellar structure of the S-star <TEX>${\pi}^1$</TEX> Gru traced by the CO J =2-1 resembles that of V Hya quite closely; the star is surrounded by the expanding disk-like envelope and is driving the medium-velocity wind along the disk plane. We also obtained the excellent images of VY CMa with the CO and <TEX>$^{13}CO$</TEX> J=2-1 and <TEX>$SO\;6_5-5_4$</TEX> lines. The maps of three molecular lines show that the envelope has a significant velocity gradient in the east-west direction, suggesting that the envelope surrounding VY CMa is also flattened and expanding along its radial direction. The high-resolution images obtained with the SMA show that some AGB stars are associated with the asymmetric mass loss including the equatorial wind and bipolar jet.
483
- 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.
484
- WANG Z.R.
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.289-290
- 2005
- 원문 바로보기
The 6th East Asian Meeting of Astronomy was held just at the time of 400 years after the discovery of SN (supernova) 1604 and its pre-maximum observation by the astronomers both from the East and the West in the 17th century. It has a special meaning and is interesting to look back on the historical observation of SN 1604. In this paper, we only limit to concern the Chinese observation on SN 1604.
485
- 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.
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
- KANG MEEJOO
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.33-41
- 2005
- 원문 바로보기
We have conducted observations toward the molecular cloud associated with the H II region Sh 156 in <TEX>$^{13}CO$</TEX>(J = 1-0), <TEX>$C^{18}O$</TEX>(J = 1-0), and CS(J = 2 -1) using the TRAO 14 m telescope. Combining with existing <TEX>$^{12}CO$</TEX>(J = 1- 0) data of the Outer Galaxy Survey, we delineated the physical properties of the cloud. We found that there is a significant sign of interaction between the H II region and the molecular gas. We estimated the masses of the molecular cloud, using three different techniques; the most plausible mass is estimated to be <TEX>$1.37 {\times} 10^5 M_{\bigodot}$</TEX>, using a conversion factor of <TEX>$X = 1.9 {\times} 10^{20}\;cm^{-2} (K\;km\;s^{-1})^{-1}$</TEX>, and this is similar to virial mass estimate. This implies that the cloud is gravitationally bound and in virial equilibrium even though it is closely associated with the H II region. In addition to existing outflow, we found several MSX and IRAS point sources associated with dense core regions. Thus, more star forming activities other than the existing H II region are also going on in this region.
488
- WANG YUN-CHING
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.299-302
- 2005
- 원문 바로보기
Sprites, elves and blue jets are collectively denominated as the upper atmospheric transient luminous events (TLEs). They are recently discovered optical flashes between active thunderstorms and the ionosphere. In this report, a brief introduction to the most important characteristics of TLEs is given. Since 2001, scientists from the National Cheng Kung University have been performing yearly summer campaigns from various locations in Taiwan. The main achievements of their yearly campaign are presented.
489
- 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.
490
- 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.