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한국천문학회지

1968년 ~ 2023년까지 1,187 건한국천문학회지를 격월간 확인하실 수 있습니다.

  • The Korean Astronomical Society (The Korean Astronomical Society)
  • 계간 (Quarterly)
  • ISSN : 1225-4614 (ISSN : 1225-4614)
  • DB구축현황 : 1,187건 (DB Construction : 1,187 Articles)
안내사항
총 게시글 1,187 페이지 4/119
31
  • Kim, Minsu
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.5
  • pp.149-172
  • 2022
  • 원문 바로보기
We present a new method which constructs an H&#x026A; super-profile of a galaxy which is based on profile decomposition analysis. The decomposed velocity profiles of an H&#x026A; data cube with an optimal number of Gaussian components are co-added after being aligned in velocity with respect to their centroid velocities. This is compared to the previous approach where no prior profile decomposition is made for the velocity profiles being stacked. The S/N improved super-profile is useful for deriving the galaxy's global H&#x026A; properties like velocity dispersion and mass from observations which do not provide sufficient surface brightness sensitivity for the galaxy. As a practical test, we apply our new method to 64 high-resolution H&#x026A; data cubes of nearby galaxies in the local Universe which are taken from THINGS and LITTLE THINGS. In addition, we also construct two additional H&#x026A; super-profiles of the sample galaxies using symmetric and all velocity profiles of the cubes whose centroid velocities are determined from Hermite h3 polynomial fitting, respectively. We find that the H&#x026A; super-profiles constructed using the new method have narrower cores and broader wings in shape than the other two super-profiles. This is mainly due to the effect of either asymmetric velocity profiles' central velocity bias or the removal of asymmetric velocity profiles in the previous methods on the resulting H&#x026A; super-profiles. We discuss how the shapes (&#x1D70E;<sub>n</sub>/&#x1D70E;<sub>b</sub>, A<sub>n</sub>/A<sub>b</sub>, and A<sub>n</sub>/A<sub>tot</sub>) of the new H&#x026A; super-profiles which are measured from a double Gaussian fit are correlated with star formation rates of the sample galaxies and are compared with those of the other two super-profiles.
32
  • Naeun, Shin
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.6
  • pp.207-213
  • 2022
  • 원문 바로보기
The Seoul Radio Astronomy Observatory (SRAO) operates a 6.1-meter radio telescope on the Gwanak campus of Seoul National University. We present the efforts to reform SRAO to a Very Long Baseline Interferometry (VLBI) station, motivated by recent achievements by millimeter interferometer networks such as Event Horizon Telescope, East Asia VLBI Network, and Korean VLBI Network (KVN). For this goal, we installed a receiver that had been used in the Combined Array for Research in Millimeter-wave Astronomy and a digital backend, including an H-maser clock. The existing hardware and software were also revised, which had been dedicated only to single-dish operations. After several years of preparations and test observations in 1 and 3-millimeter bands, a fringe was successfully detected toward 3C 84 in 86 GHz in June 2022 for a baseline between SRAO and KVN Ulsan station separated by 300 km. Thanks to the dual frequency operation of the receiver, the VLBI observations will soon be extended to the 1 mm band and verify the frequency phase referencing technique between 1 and 3-millimeter bands.
33
  • Jeon, Seong-Gyeong
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.3
  • pp.67-74
  • 2022
  • 원문 바로보기
In this study, we perform a statistical investigation of the kinematic classification of 4,264 coronal mass ejections (CMEs) from 1996 to 2015 observed by SOHO/LASCO C3. Using the constant acceleration model, we classify these CMEs into three groups: deceleration, constant velocity, and acceleration motion. For this, we devise three different classification methods using fractional speed variation, height contribution, and visual inspection. The main results of this study can be summarized as follows. First, the fractions of three groups depend on the method used. Second, about half of the events belong to the groups of acceleration and deceleration. Third, the fractions of three motion groups as a function of CME speed are consistent with one another. Fourth, the fraction of acceleration motion decreases as CME speed increases, while the fractions of other motions increase with speed. In addition, the acceleration motions are dominant in low speed CMEs whereas the constant velocity motions are dominant in high speed CMEs.
34
  • Kim, Sungsoo S.
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.3
  • pp.75-86
  • 2022
  • 원문 바로보기
The lunar surface progressively darkens and reddens as a result of sputtering from solar wind particles and bombardment of micrometeoroids. The extent of exposure to these space weathering agents is frequently calculated as the location in a diagram of reflectance at 750 nm vs. 950 nm/750 nm color (R-C). Sim & Kim (2018) examined the R-C trends of pixels within ~3,500 craters, and revealed that the length (L) and skewness (s) of R-C trends can be employed as a secondary age or maturity indicator. We broaden this research to general lunar surface areas (3,400 tiles of 0.25&#x00B0; &#x00D7; 0.25&#x00B0; size) in 218 mare basalt units, whose ages have been derived from the size-frequency distribution analysis by Hiesinger et al. (2011). We discover that L and s rise with age until ~3.2 Gyr and reduce rather rapidly afterward, while the optical maturity, OMAT, reduces monotonically with time. We show that in some situations, when not only OMAT but also L and s are incorporated in the estimation utilizing 750 & 950 nm photometry, the age estimation becomes considerably more reliable. We also observed that OMAT and the lunar cratering chronology function (cumulative number of craters larger than a certain diameter as a function of time) have a relatively linear relationship.
35
  • Kim, Jinkyu
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.4
  • pp.87-97
  • 2022
  • 원문 바로보기
Polarimetric measurements of the lunar surface from lunar orbit soon will be available via Wide-Field Polarimetric Camera (PolCam) onboard the Korea Pathfinder Lunar Orbiter (KPLO), which is planned to be launched in mid 2022. To provide calibration data for the PolCam, we are conducting speckle polarimetric measurements of the nearside of the Moon from the Earth's ground. It appears that speckle imaging of the Moon for scientific purposes has not been attempted before, and there is need for a procedure to create a 'lucky image' from a number of observed speckle images. As a first step of obtaining calibration data for the PolCam from the ground, we search for the best sharpness measure for lunar surfaces. We then calculate the minimum number of speckle images and the number of images to be shift-and-added for higher resolution (sharpness) and signal-to-noise ratio.
36
  • Chang, Heon-Young
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.5
  • pp.139-148
  • 2022
  • 원문 바로보기
We explore the latitudinal distribution of sunspots and pursue to establish a correlation between the statistical parameters of the latitudinal distribution of sunspots and characteristics of solar activity. For this purpose, we have statistically analyzed the daily sunspot areas and latitudes observed from May in 1874 to September in 2016. As results, we confirm that the maximum of the monthly averaged International Sunspot Number (ISN) strongly correlates with the mean number of sunspots per day, while the maximum ISN strongly anti-correlates with the number of spotless days. We find that both the maximum ISN and the mean number of sunspots per day strongly correlate with the the average latitude, the standard deviation, the skewness of the the latitudinal distribution of sunspots, while they appears to marginally correlate with the kurtosis. It is also found that the northern and southern hemispheres seem to show a correlated behavior in a different way when sunspots appearing in the northern and southern hemispheres are examined separately.
37
  • Kyung-Won, Suh
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.6
  • pp.195-205
  • 2022
  • 원문 바로보기
We investigate infrared properties of OGLE4 Mira variables in our Galaxy. For each object, we cross-identify the AllWISE, 2MASS, Gaia, and IRAS counterparts. We present various IR two-color diagrams (2CDs) and period-magnitude and period-color relations for the Mira variables. Generally, the Mira variables with longer periods are brighter in the IR fluxes and redder in the IR colors. In this work, we also revise and update the previous catalog of AGB stars in our Galaxy using the new sample of OGLE4 Mira variables. Now, we present a new catalog of 74,093 (64,609 O-rich and 9,484 C-rich) AGB stars in our Galaxy. A group of 23,314 (19,196 O-rich and 4,118 C-rich) AGB stars are identified based on the IRAS PSC and another group of 50,779 (45,413 O-rich and 5,366 C-rich) AGB stars are identified based on the AllWISE source catalog. For all of the AGB stars, we cross-identify the IRAS, AKARI, MSX, AllWISE, 2MASS, OGLE4, Gaia, and AAVSO counterparts and present various infrared 2CDs. Comparing the observations with the theory, we find that basic theoretical dust shell models can account for the IR observations fairly well for most of the AGB stars.
38
  • Shin, Suhyun
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.4
  • pp.131-138
  • 2022
  • 원문 바로보기
We report the discovery of four quasars with M<sub>1450</sub> &#x2273; -25.0 mag at z ~ 5 and supermassive black hole mass measurement for one of the quasars. They were selected as promising high-redshift quasar candidates via deep learning and Bayesian information criterion, which are expected to be effective in discriminating quasars from the late-type stars and high-redshift galaxies. The candidates were observed by the Double Spectrograph on the Palomar 200-inch Hale Telescope. They show clear Ly&#x03B1; breaks at about 7000-8000 &#x212B;, indicating they are quasars at 4.7 < z < 5.6. For HSC J233107-001014, we measure the mass of its supermassive black hole (SMBH) using its C <sub>IV</sub> &#x03BB;1549 emission line. The SMBH mass and Eddington ratio of the quasar are found to be ~10<sup>8</sup> M<sub>&#x2299;</sub> and ~0.6, respectively. This suggests that this quasar possibly harbors a fast growing SMBH near the Eddington limit despite its faintness (L<sub>Bol</sub> < 10<sup>46</sup> erg s<sup>-1</sup>). Our 100% quasar identification rate supports high efficiency of our deep learning and Bayesian information criterion selection method, which can be applied to future surveys to increase high-redshift quasar sample.
39
  • Kim, Changmin
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.2
  • pp.23-36
  • 2022
  • 원문 바로보기
We present a method to determine nitrogen abundance ratios with respect to iron ([N/Fe]) from molecular CN-band features observed in low-resolution (R ~ 2000) stellar spectra obtained by the Sloan Digital Sky Survey (SDSS) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Various tests are carried out to check the systematic and random errors of our technique, and the impact of signal-to-noise (S/N) ratios of stellar spectra on the determined [N/Fe]. We find that the uncertainty of our derived [N/Fe] is less than 0.3 dex for S/N ratios larger than 10 in the ranges T<sub>eff</sub> = [4000, 6000] K, log g = [0.0, 3.5], [Fe/H] = [-3.0, 0.0], [C/Fe] = [-1.0, +4.5], and [N/Fe] = [-1.0, +4.5], the parameter space that we are interested in to identify N-enhanced stars in the Galactic halo. A star-by-star comparison with a sample of stars with [N/Fe] estimates available from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) also suggests a similar level of uncertainty in our measured [N/Fe], after removing its systematic error. Based on these results, we conclude that our method is able to reproduce [N/Fe] from low-resolution spectroscopic data, with an uncertainty sufficiently small to discover N-rich stars that presumably originated from disrupted Galactic globular clusters.
40
  • Gould, Andrew
  • Journal of the Korean astronomical society = 천문학회지
  • 55, n.5
  • pp.173-194
  • 2022
  • 원문 바로보기
We complete the survey for finite-source/point-lens (FSPL) giant-source events in 2016-2019 KMTNet microlensing data. The 30 FSPL events show a clear gap in Einstein radius, 9 &#x1D707;as < &#x1D703;<sub>E</sub> < 26 &#x1D707;as, which is consistent with the gap in Einstein timescales near t<sub>E</sub> ~ 0.5 days found by Mr&#x00F3;z et al. (2017) in an independent sample of point-source/point-lens (PSPL) events. We demonstrate that the two surveys are consistent. We estimate that the 4 events below this gap are due to a power-law distribution of free-floating planet candidates (FFPs) dN<sub>FFP</sub>/d log M = (0.4 &#x00B1; 0.2) (M/38 M<sub>&#x2295;</sub>)<sup>-p</sup>/star, with 0.9 &#x2272; p &#x2272; 1.2. There are substantially more FFPs than known bound planets, implying that the bound planet power-law index &#x1D6FE; = 0.6 is likely shaped by the ejection process at least as much as by formation. The mass density per decade of FFPs in the Solar neighborhood is of the same order as that of 'Oumuamua-like objects. In particular, if we assume that 'Oumuamua is part of the same process that ejected the FFPs to very wide or unbound orbits, the power-law index is p = 0.89 &#x00B1; 0.06. If the Solar System's endowment of Neptune-mass objects in Neptune-like orbits is typical, which is consistent with the results of Poleski et al. (2021), then these could account for a substantial fraction of the FFPs in the Neptune-mass range.