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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 24/122
231
- Cho, Se-Hyung
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.293-302
- 2014
- 원문 바로보기
Simultaneous time monitoring observations of <TEX>$H_2O$</TEX> <TEX>$6_{16}-5_{23}$</TEX>, SiO J = 1-0, 2-1, 3-2, and <TEX>$^{29}SiO$</TEX> <TEX>${\upsilon}=0$</TEX>, J = 1-0 lines are carried out in the direction of the Mira variable star TX Cam with the Korean VLBI Network single dish radio telescopes. For the first time, the <TEX>$H_2O$</TEX> maser emission from TX Cam is detected near the stellar velocity at five epochs from April 10, 2013 (<TEX>${\phi}=3.13$</TEX>) to June 4, 2014 (<TEX>${\phi}=3.89$</TEX>) including minimum optical phases. The intensities of <TEX>$H_2O$</TEX> masers are very weak compared to SiO masers. The variation of peak antenna temperature ratios among SiO <TEX>${\upsilon}=1$</TEX>, J = 1-0, J = 2-1, and J = 3-2 masers is investigated according to their phases. The shift of peak velocities of <TEX>$H_2O$</TEX> and SiO masers with respect to the stellar velocity is also investigated according to observed optical phases. The <TEX>$H_2O$</TEX> maser emission occurs around the stellar velocity during our monitoring interval. On the other hand, the peak velocities of SiO masers show a spread compared to the stellar velocity. The peak velocities of SiO J = 2-1, and J = 3-2 masers show a smaller spread with respect to the stellar velocity than those of SiO J = 1-0 masers. These simultaneous observations of multi-frequencies will provide a good constraint for maser pumping models and a good probe for investigating the stellar atmosphere and envelope according to their different excitation conditions.
232
- Na, Sung-Ho
- Journal of the Korean astronomical society = 천문학회지
- 47, n.1
- pp.41-41
- 2014
- 원문 바로보기
The equivalent phase lag <TEX>${\varepsilon}_{lmpq}$</TEX> of Earth tide suggested by Lambeck have been found reasonable. Due to a mistake in his calculation, the author falsely claimed that those are too large. However, the main contents of the article are valid and not affected by this mistake.
233
- Hanna, Magdy
- Journal of the Korean astronomical society = 천문학회지
- 47, n.3
- pp.99-104
- 2014
- 원문 바로보기
We present the rst period variation study for the Algol eclipsing binary V346 Cyg by constructing the (O-C) residual diagram using all the available precise minima times. We conclude that the period variation can be explained by a sine-like variation due to the presence of a third body orbiting the binary in about <TEX>$68.89{\pm}4.69$</TEX> years, together with a long-term orbital period decrease (<TEX>$dP/dt=-1.23{\times}10^{-7}day/yr$</TEX>) that can be interpreted to be due to slow mass loss from the <TEX>${\delta}$</TEX>-Scuti primary component. The sinusoidal variation may also be explained by using the the Applegate (1992) mechanism involving cyclic magnetic activity due to star-spots on the secondary component. The present preliminary solution needs more precise photometric observations to be confirmed.
234
- Lee, Sang-Sung
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.303-309
- 2014
- 원문 바로보기
We present results of our investigation of the radio intrinsic brightness temperatures of compact radio jets. The intrinsic brightness temperatures of about 100 compact radio jets at 2, 5, 8, 15, and 86 GHz are estimated based on large VLBI surveys conducted in 2001-2003 (or in 1996 for the 5 GHz sample). The multi-frequency intrinsic brightness temperatures of the sample of jets are determined by a statistical method relating the observed brightness temperatures with the maximal apparent jet speeds, assuming one representative intrinsic brightness temperature for a sample of jets at each observing frequency. By investigating the observed brightness temperatures at 15 GHz in multiple epochs, we find that the determination of the intrinsic brightness temperature for our sample is affected by the flux density variability of individual jets at time scales of a few years. This implies that it is important to use contemporaneous VLBI observations for the multi-frequency analysis of intrinsic brightness temperatures. Since our analysis is based on the VLBI observations conducted in 2001-2003, the results are not strongly affected by the flux density variability. We find that the intrinsic brightness temperature <TEX>$T_0$</TEX> increases as <TEX>$T_0{\propto}{\nu}^{\xi}_{obs}$</TEX> with <TEX>${\xi}=0.7$</TEX> below a critical frequency <TEX>${\nu}_c{\approx}9GHz$</TEX> where the energy loss begins to dominate the emission. Above <TEX>${\nu}_c$</TEX>, <TEX>$T_0$</TEX> decreases with <TEX>${\xi}=-1.2$</TEX>, supporting the decelerating jet model or particle cascade model. We also find that the peak value of <TEX>$T_0{\approx}3.4{\times}10^{10}$</TEX> K is close to the equipartition temperature, implying that the VLBI cores observable at 2-86 GHz may be representing jet regions where the magnetic field energy dominates the total energy in jets.
235
- Lee, Youngung
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.319-325
- 2014
- 원문 바로보기
We map two molecular clouds located in the exact anticenter region emitting in the (J = 1-0) transition of <TEX>$^{12}CO$</TEX> and <TEX>$^{13}CO$</TEX> using the 3-mm SIS mixer receiver on the 14-m radio telescope at Taeduk Radio Astronomy Observatory. The target clouds with anomalous velocities of <TEX>$V_{LSR}{\sim}-20km\;s^{-1}$</TEX> are distinguished from other clouds in this direction. In addition, they are located in the interarm region between the Orion Arm and the Perseus Arm. Sizes of the clouds are estimated to be about 8.6 and 10.8 pc, respectively. The total mass is estimated to be about <TEX>$4{\times}10^3$</TEX> <TEX>$M_{\odot}$</TEX> using CO luminosity of the clouds. Several cores are detected, but no sign of star formation is found according to the IRAS point sources. Their larger linewidths, anomalous velocities, and their location at the interarm region make these clouds more distinguished, though their physical properties are similar to the dark clouds in the solar neighborhood in terms of mass and size.
236
- Cho, Il-Hyun
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.255-258
- 2014
- 원문 바로보기
Using sunspot number data from 270 historical stations for the period 1981-2013, we investigate their personal reduction coefficients (k) statistically. Chang & Oh (2012) perform a simulation showing that the k varies with the solar cycle. We try to verify their results using observational data. For this, a weighted mean and weighted standard deviation of monthly sunspot number are used to estimate the error from observed data. We find that the observed error (noise) is much smaller than that used in the simulation. Thus no distinct k-variation with the solar cycle is observed contrary to the simulation. In addition, the probability distribution of k is determined to be non-Gaussian with a fat-tail on the right side. This result implies that the relative sunspot number after 1981 might be overestimated since the mean value of k is less than that of the Gaussian distribution.
237
- Gould, Andrew
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.279-291
- 2014
- 원문 바로보기
I show that the WFIRST microlensing survey will enable detection and precision orbit determination of Kuiper Belt Objects (KBOs) down to <TEX>$H_{vega}=28.2$</TEX> over an effective area of <TEX>${\sim}17deg^2$</TEX>. Typical fractional period errors will be <TEX>${\sim}1.5%{\times}10^{0.4(H-28.2)}$</TEX> with similar errors in other parameters for roughly 5000 KBOs. Binary companions to detected KBOs can be detected to even fainter limits, <TEX>$H_{vega}=29$</TEX>, corresponding to R~30.5 and effective diameters D~7 km. For KBOs H~23, binary companions can be found with separations down to 10 mas. This will provide an unprecedented probe of orbital resonance and KBO mass measurements. More than a thousand stellar occultations by KBOs can be combined to determine the mean size as a function of KBO magnitude down to H~25. Current ground-based microlensing surveys can make a significant start on finding and characterizing KBOs using existing and soon-to-be-acquired data.
238
- Minh, Young Chol
- Journal of the Korean astronomical society = 천문학회지
- 47, n.5
- pp.179-185
- 2014
- 원문 바로보기
We study the physical and chemical properties of the molecular clump hosting a young stellar cluster, IRAS 20160+3636, which is believed to have formed via the 'collect and collapse' process. Physical parameters of the UC H II region associated with the embedded cluster are measured from the radio continuum observations. This source is found to be a typical Galactic UC H II region, with a B0.5 type exciting star, if it is ionized by a single star. We derive a CN/HCN abundance ratio larger than 1 over this region, which may suggest that this clump is being affected by the UV radiation from the H II region.
239
- Li, Xue-Bao
- Journal of the Korean astronomical society = 천문학회지
- 47, n.2
- pp.43-47
- 2014
- 원문 바로보기
Many advanced ground-based solar telescopes improve the spatial resolution of observation images using an adaptive optics (AO) system. As any AO correction remains only partial, it is necessary to use post-processing image reconstruction techniques such as speckle masking or shift-and-add (SAA) to reconstruct a high-spatial-resolution image from atmospherically degraded solar images. In the New Vacuum Solar Telescope (NVST), the spatial resolution in solar images is improved by frame selection and SAA. In order to overcome the burden of massive speckle data processing, we investigate the possibility of using the speckle reconstruction program in a real-time application at the telescope site. The code has been written in the C programming language and optimized for parallel processing in a multi-processor environment. We analyze the scalability of the code to identify possible bottlenecks, and we conclude that the presented code is capable of being run in real-time reconstruction applications at NVST and future large aperture solar telescopes if care is taken that the multi-processor environment has low latencies between the computation nodes.
240
- Lee, Byeong-Cheol
- Journal of the Korean astronomical society = 천문학회지
- 47, n.2
- pp.69-76
- 2014
- 원문 바로보기
We report the detection of an exoplanet candidate in orbit around <TEX>${\sigma}$</TEX> Persei from a radial velocity (RV) survey. The system exhibits periodic RV variations of <TEX>$579.8{\pm}2.4$</TEX> days. The purpose of the survey is to search for low-amplitude and long-period RV variations in giants and examine the origin of the variations using the fiber-fed Bohyunsan Observatory Echelle Spectrograph installed at the 1.8-m telescope of Bohyunsan Optical Astronomy Observatory in Korea. We present high-accuracy RV measurements of <TEX>${\sigma}$</TEX> Per made from December 2003 to January 2014. We argue that the RV variations are not related to the surface inhomogeneities but instead a Keplerian motion of the planetary companion is the most likely explanation. Assuming a stellar mass of <TEX>$2.25{\pm}0.5$</TEX> <TEX>$M_{\odot}$</TEX>, we obtain a minimum planetary companion mass of <TEX>$6.5{\pm}1.0$</TEX> <TEX>$M_{Jup}$</TEX>, with an orbital semi-major axis of <TEX>$1.8{\pm}0.1$</TEX> AU, and an eccentricity of <TEX>$0.3{\pm}0.1$</TEX> around <TEX>${\sigma}$</TEX> Per.