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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 17/123
161
- Seo, Hyunjong
- Journal of the Korean astronomical society = 천문학회지
- 50, n.1
- pp.7-20
- 2017
- 원문 바로보기
We carry out the study of <TEX>$850{\mu}m$</TEX> sources in a part of the XMM-LSS field. The <TEX>$850{\mu}m$</TEX> imaging data were obtained by the SCUBA-2 on the James Clerk Maxwell Telescope (JCMT) for three days in July 2015 with an integration time of 6.1 hours, covering a circular area with a radius of 15'. We choose the central area up to a radius of 9'.15 for the study, where the noise distribution is relatively uniform. The root mean square (rms) noise at the center is 2.7 mJy. We identify 17 sources with S/N > 3.5. Differential number count is estimated in flux range between 3.5 and 9.0 mJy after applying various corrections derived by imaging simulations, which is consistent with previous studies. For detailed study on the individual sources, we select three sources with more reliable measurements (S/N > 4.5), and construct their spectral energy distributions (SEDs) from optical to far-infrared band. Redshift distribution of the sources ranges from 0.36 to 3.28, and their physical parameters are extracted using MAGPHYS model, which yield infrared luminosity <TEX>$L_{IR}=10^{11.3}-10^{13.4}L_{\odot}$</TEX>, star formation rate <TEX>$SFR=10^{1.3}-10^{3.2}M_{\odot}yr^{-1}$</TEX> and dust temperature <TEX>$T_D=30-53K$</TEX>. We investigate the correlation between <TEX>$L_{IR}$</TEX> and <TEX>$T_D$</TEX>, which appears to be consistent with previous studies.
162
- Lee, Hee-Jae
- Journal of the Korean astronomical society = 천문학회지
- 50, n.3
- pp.41-49
- 2017
- 원문 바로보기
We conduct BVRI and R band photometric observations of asteroid (5247) Krylov from January 2016 to April 2016 for 51 nights using the Korea Microlensing Telescope Network (KMTNet). The color indices of (5247) Krylov at the light curve maxima are determined as <TEX>$B-V=0.841{\pm}0.035$</TEX>, <TEX>$V-R=0.418{\pm}0.031$</TEX>, and <TEX>$V-I=0.871{\pm}0.031$</TEX> where the phase angle is <TEX>$14.1^{\circ}$</TEX>. They are acquired after the standardization of BVRI instrumental measurements using the ensemble normalization technique. Based on the color indices, (5247) Krylov is classified as a S-type asteroid. Double periods, that is, a primary period <TEX>$P_1=82.188{\pm}0.013h$</TEX> and a secondary period <TEX>$P_2=67.13{\pm}0.20h$</TEX> are identified from period searches of its R band light curve. The light curve phases with <TEX>$P_1$</TEX> and this indicate that it is a typical Non-Principal Axis (NPA) asteroid. We discuss the possible causes of its NPA rotation.
163
- Lee, Hyun-Uk
- Journal of the Korean astronomical society = 천문학회지
- 50, n.3
- pp.51-59
- 2017
- 원문 바로보기
The presence of blue stragglers pose challenges to standard stellar evolution theory, in the sense that explaining their presence demands a complex interplay between stellar evolution and cluster dynamics. In the meantime, mass transfer in binary systems and stellar collisions are widely studied as a blue straggler formation channel. We explore properties of the Galactic open clusters where blue stragglers are found, in attempting to estimate the relative importance of these two favored processes, by comparing them with those resulting from open clusters in which blue stragglers are absent as of now. Unlike previous studies which require a sophisticated process in understanding the implication of the results, this approach is straightforward and has resulted in a supplementary supporting evidence for the current view on the blue straggler formation mechanism. Our main findings are as follows: (1) Open clusters in which blue stragglers are present have a broader distribution with respect to the Z-axis pointing towards the North Galactic Pole than those in which blue stragglers are absent. The probability that two distributions with respect to the Z-axis are drawn from the same distribution is 0.2%. (2) Average values of <TEX>$log_10(t)$</TEX> of the clusters with blue stragglers and those without blue stragglers are <TEX>$8.58{\pm}0.232$</TEX> and <TEX>$7.52{\pm}0.285$</TEX>, respectively. (3) The clusters with blue stragglers tend to be relatively redder than the others, and are distributed broader in colors. (4) The clusters with blue stragglers are likely brighter than those without blue stragglers. (5) Finally, blue stragglers seem to form in condensed clusters rather than simply dense clusters. Hence, we conclude that mass transfer in binaries seems to be a relatively important physical mechanism of the generation of blue stragglers in open clusters, provided they are sufficiently old.
164
- Chae, Jongchul
- Journal of the Korean astronomical society = 천문학회지
- 50, n.2
- pp.21-27
- 2017
- 원문 바로보기
The autoregressive method provides a univariate procedure to predict the future sunspot number (SSN) based on past record. The strength of this method lies in the possibility that from past data it yields the SSN in the future as a function of time. On the other hand, its major limitation comes from the intrinsic complexity of solar magnetic activity that may deviate from the linear stationary process assumption that is the basis of the autoregressive model. By analyzing the residual errors produced by the method, we have obtained the following conclusions: (1) the optimal duration of the past time for the forecast is found to be 8.5 years; (2) the standard error increases with prediction horizon and the errors are mostly systematic ones resulting from the incompleteness of the autoregressive model; (3) there is a tendency that the predicted value is underestimated in the activity rising phase, while it is overestimated in the declining phase; (5) the model prediction of a new Solar Cycle is fairly good when it is similar to the previous one, but is bad when the new cycle is much different from the previous one; (6) a reasonably good prediction of a new cycle can be made using the AR model 1.5 years after the start of the cycle. In addition, we predict the next cycle (Solar Cycle 25) will reach the peak in 2024 at the activity level similar to the current cycle.
165
- Kim, Sujin
- Journal of the Korean astronomical society = 천문학회지
- 50, n.4
- pp.125-129
- 2017
- 원문 바로보기
We investigate the solar cycle variation of microwave and extreme ultraviolet (EUV) intensity in latitude to compare microwave polar brightening (MPB) with the EUV polar coronal hole (CH). For this study, we used the full-sun images observed in 17 GHz of the Nobeyama Radioheliograph from 1992 July to 2016 November and in two EUV channels of the Atmospheric Imaging Assembly (AIA) <TEX>$193{\AA}$</TEX> and <TEX>$171{\AA}$</TEX> on the Solar Dynamics Observatory (SDO) from 2011 January to 2016 November. As a result, we found that the polar intensity in EUV is anti-correlated with the polar intensity in microwave. Since the depression of EUV intensity in the pole is mostly owing to the CH appearance and continuation there, the anti-correlation in the intensity implies the intimate association between the polar CH and the MPB. Considering the report of Gopalswamy et al. (1999) that the enhanced microwave brightness in the CH is seen above the enhanced photospheric magnetic field, we suggest that the pole area during the solar minimum has a stronger magnetic field than the quiet sun level and such a strong field in the pole results in the formation of the polar CH. The emission mechanism of the MPB and the physical link with the polar CH are not still fully understood. It is necessary to investigate the MPB using high resolution microwave imaging data, which can be obtained by the high performance large-array radio observatories such as the ALMA project.
166
- Choi, Changsu
- Journal of the Korean astronomical society = 천문학회지
- 50, n.3
- pp.71-78
- 2017
- 원문 바로보기
We present the characteristics and the performance of the new CCD camera system, SNUCAM-II (Seoul National University CAMera system II) that was installed on the Lee Sang Gak Telescope (LSGT) at the Siding Spring Observatory in 2016. SNUCAM-II consists of a deep depletion chip covering a wide wavelength from <TEX>$0.3{\mu}m$</TEX> to <TEX>$1.1{\mu}m$</TEX> with high sensitivity (QE at > 80% over 0.4 to <TEX>$0.9{\mu}m$</TEX>). It is equipped with the SDSS ugriz filters and 13 medium band width (50 nm) filters, enabling us to study spectral energy distributions (SEDs) of diverse objects from extragalactic sources to solar system objects. On LSGT, SNUCAM-II offers <TEX>$15.7{\times}15.7$</TEX> arcmin field-of-view (FOV) at a pixel scale of 0.92 arcsec and a limiting magnitude of g = 19.91 AB mag and z=18.20 AB mag at <TEX>$5{\sigma}$</TEX> with 180 sec exposure time for point source detection.
167
- Cho, K.S.
- Journal of the Korean astronomical society = 천문학회지
- 50, n.2
- pp.29-39
- 2017
- 원문 바로보기
We investigate two abnormal CME-Storm pairs that occurred on 2014 September 10 - 12 and 2015 March 15 - 17, respectively. The first one was a moderate geomagnetic storm (<TEX>$Dst_{min}{\sim}-75nT$</TEX>) driven by the X1.6 high speed flare-associated CME (<TEX>$1267km\;s^{-1}$</TEX>) in AR 12158 (N14E02) near solar disk center. The other was a very intense geomagnetic storm (<TEX>$Dst_{min}{\sim}-223nT$</TEX>) caused by a CME with moderate speed (<TEX>$719km\;s^{-1}$</TEX>) and associated with a filament eruption accompanied by a weak flare (C9.1) in AR 12297 (S17W38). Both CMEs have large direction parameters facing the Earth and southward magnetic field orientation in their solar source region. In this study, we inspect the structure of Interplanetary Flux Ropes (IFRs) at the Earth estimated by using the torus fitting technique assuming self-similar expansion. As results, we find that the moderate storm on 2014 September 12 was caused by small-scale southward magnetic fields in the sheath region ahead of the IFR. The Earth traversed the portion of the IFR where only the northward fields are observed. Meanwhile, in case of the 2015 March 17 storm, our IFR analysis revealed that the Earth passed the very portion where only the southward magnetic fields are observed throughout the passage. The resultant southward magnetic field with long-duration is the main cause of the intense storm. We suggest that 3D magnetic field geometry of an IFR at the IFR-Earth encounter is important and the strength of a geomagnetic storm is strongly affected by the relative location of the Earth with respect to the IFR structure.
168
- Lee, Ki-Won
- Journal of the Korean astronomical society = 천문학회지
- 50, n.6
- pp.191-200
- 2017
- 원문 바로보기
We analyze the time data recorded in Korean astronomical almanacs for the years from 1913 to 1945, which belong to the period in which Japan occupied Korea (1910-1945). These almanacs, published by Japanese scholars, differ from previous almanacs in terms of organization, content, and calendrical methods. In this study, we first extract twelve kinds of time data from the almanacs at the following times: solar terms, rising and setting of the Sun and Moon, transit of the Sun, phases of the Moon (i.e., new Moon, first quarter Moon, full Moon, and last quarter Moon), and eclipses of the Sun and Moon. Then, we compare the time data with that obtained from modern calculations. Even though all time data in the almanacs are tabulated in units of minutes, we calculate the data in units of seconds and determine the root mean square (RMS) deviation values for each kind of time data to estimate the accuracy of the data. Our findings are as follows: First, the kind and tabulation method of time data changes several times. For instance, solar transit time is listed only for six years from 1937 to 1942. Second, the times of two equinoxes and those of a new Moon are considerably close to midnight. Third, there are some typographical errors in the almanacs, particularly in the times of moonrise and moonset. Fourth, the contact times for lunar eclipses represent the times of the umbra and not of the penumbra, which is different from the times for solar eclipses. Finally, the RMS deviation values are approximately 0.5 min on average in all kinds of time data, even though they show slightly large differences in the times related to the Moon. In conclusion, we believe that this study is useful for investigating the time data in the almanacs of other East Asian countries that were published during the same period, such as China, Japan, and Manchuria.
169
- Ann, Hong Bae
- Journal of the Korean astronomical society = 천문학회지
- 50, n.4
- pp.111-124
- 2017
- 원문 바로보기
The environmental dependence of the morphology of dwarf galaxies in isolated satellite systems is analyzed to understand the origin of the dwarf galaxy morphology using the visually classified morphological types of 5836 local galaxies with <TEX>$z{\leq}0.01$</TEX>. We consider six sub-types of dwarf galaxies, dS0, dE, <TEX>$dE_{bc}$</TEX>, dSph, <TEX>$dE_{blue}$</TEX>, and dI, of which the first four sub-types are considered as early-type and the last two as late-type. The environmental parameters we consider are the projected distance from the host galaxy (<TEX>$r_p$</TEX>), local and global background densities, and the host morphology. The spatial distributions of dwarf satellites of early-type galaxies are much different from those of dwarf satellites of late-type galaxies, suggesting the host morphology combined with <TEX>$r_p$</TEX> plays a decisive role on the morphology of the dwarf satellite galaxies. The local and global background densities play no significant role on the morphology of dwarfs in the satellite systems hosted by early-type galaxies. However, in the satellite system hosted by late-type galaxies, the global background densities of dE and dSph satellites are significantly different from those of <TEX>$dE_{bc}$</TEX>, <TEX>$dE_{blue}$</TEX>, and dI satellites. The blue-cored dwarf satellites (<TEX>$dE_{bc}$</TEX>) of early-type galaxies are likely to be located at <TEX>$r_p$</TEX> > 0.3 Mpc to keep their cold gas from the ram pressure stripping by the hot corona of early-type galaxies. The spatial distribution of <TEX>$dE_{bc}$</TEX> satellites of early-type galaxies and their global background densities suggest that their cold gas is intergalactic material accreted before they fall into the satellite systems.
170
- Kim, Sang Chul
- Journal of the Korean astronomical society = 천문학회지
- 50, n.3
- pp.79-92
- 2017
- 원문 바로보기
We present a BV I optical photometric study of the old open cluster Ruprecht 6 using the data obtained with the SMARTS 1.0 m telescope at the CTIO, Chile. Its color-magnitude diagrams show the clear existence of the main-sequence stars, whose turn-off point is located around <TEX>$V{\approx}18.45mag$</TEX> and <TEX>$B-V{\approx}0.85mag$</TEX>. Three red clump (RC) stars are identified at V = 16.00 mag, I = 14.41 mag and B - V = 1.35 mag. From the mean <TEX>$K_s-band$</TEX> magnitude of RC stars (<TEX>$K_s=12.39{\pm}0.21mag$</TEX>) in Ruprecht 6 from 2MASS photometry and the known absolute magnitudes of the RC stars (<TEX>$M_{K_S}=-1.595{\pm}0.025mag$</TEX>), we obtain the distance modulus to Ruprecht 6 of <TEX>$(m-M)_0=13.84{\pm}0.21mag$</TEX> (<TEX>$d=5.86{\pm}0.60kpc$</TEX>). From the (<TEX>$J-K_s$</TEX>) and (B - V ) colors of the RC stars, comparison of the (B - V ) and (V - I) colors of the bright stars in Ruprecht 6 with those of the intrinsic colors of dwarf and giant stars, and the PARSEC isochrone fittings, we derive the reddening values of E(B - V ) = 0.42 mag and E(V - I) = 0.60 mag. Using the PARSEC isochrone fittings onto the color-magnitude diagrams, we estimate the age and metallicity to be: <TEX>$log(t)=9.50{\pm}0.10(t=3.16{\pm}0.82Gyr)$</TEX> and <TEX>$[Fe/H]=-0.42{\pm}0.04dex$</TEX>. We present the Galactocentric radial metallicity gradient analysis for old (age > 1 Gyr) open clusters of the Dias et al. catalog, which likely follow a single relation of <TEX>$[Fe/H]=(-0.034{\pm}0.007)R_{GC}+(0.190{\pm}0.080)$</TEX> (rms = 0.201) for the whole radial range or a dual relation of <TEX>$[Fe/H]=(-0.077{\pm}0.017)R_{GC}+(0.609{\pm}0.161)$</TEX> (rms = 0.152) and constant ([Fe/H] ~ -0.3 dex) value, inside and outside of RGC ~ 12 kpc, respectively. The metallicity and Galactocentric radius (<TEX>$13.28{\pm}0.54kpc$</TEX>) of Ruprecht 6 obtained in this study seem to be consistent with both of the relations.