간행물
천문학회지 KCI 등재 SCOPUS Journal of The Korean Astronomical Society
- 발행기관 한국천문학회
- 자료유형 학술지
- 간기 반년간
- ISSN 1225-4614 (Print)2288-890X (Online)
- 수록기간 1968 ~ 2024
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
- 십진분류KDC 440DDC 520
권호리스트/논문검색
제56권 제1호 (2023년 1월) 10건
1.
2023.01
구독 인증기관 무료, 개인회원 유료
Minchul Kam, Sascha Trippe, Do-Young Byun, Jongho Park, Sincheol Kang, Naeun Shin, Sang-Sung Lee, Taehyun Jung
The Crab nebula is widely used as a polarization angle calibrator for single-dish radio observations because of its brightness, high degree of linear polarization, and well-known polarization angle over a wide frequency range. However, the Crab nebula cannot be directly used as a polarization angle calibrator for single-dish observations with the Korean VLBI Network (KVN), because the beam size of the telescopes is smaller than the size of the nebula. To determine the polarization angle of the Crab nebula as seen by KVN, we use 3C 286, a compact polarized extragalactic radio source whose polarization angle is well-known, as a reference target. We observed both the Crab nebula and 3C 286 with the KVN from 2017 to 2021 and find that the polarization angles at the total intensity peak of the Crab nebula (equatorial coordinates (J2000) R.A. = 05h34m32.3804s and Dec = 22◦00′44.0982′′) are 154.2◦ ±0.3◦, 151.0◦ ±0.2◦, 150.0◦ ±1.0◦, and 151.3◦ ±1.1◦ at 22, 43, 86, and 94 GHz, respectively. We also find that the polarization angles at the pulsar position (RA = 05h34m31.971s and Dec = 22◦00′52.06′′) are 154.4◦ ±0.4◦, 150.7◦ ±0.4◦, and 149.0◦ ± 1.0◦ for the KVN at 22, 43, and 86 GHz. At 129 GHz, we suggest to use the values 149.0◦ ± 1.6◦ at the total intensity peak and 150.2◦ ± 2.0◦ at the pulsar position obtained with the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30-meter Telescope. Based on our study, both positions within the Crab nebula can be used as polarization angle calibrators for the KVN single-dish observations.
4,000원
2.
2023.01
구독 인증기관 무료, 개인회원 유료
Hye-Eun Jang, Young Sun Lee, Wako Aoki, Tadafumi Matsuno, Wonseok Kang, Ho-Gyu Lee, Sang-Hyun Chun, Miji Jeong, Sung-Chul Yoon
We report the result of a high-resolution spectroscopic study on seven magnesium (Mg) enhanced stars. The high Mg abundances in these stars imply that they were born in an environment heavily affected by the nucleosynthesis products of massive stars. We measure abundances of 16 elements including Mg and they show various abundance patterns implying their diverse origin. Three of our program stars show a very high Mg to Si ratio ([Mg/Si] ≈ 0.18–0.25), which might be well explained by fall-back supernovae or by supernovae with rapid rotating progenitors having an initial mass higher than about 20 𝑀⊙. Another three of our program stars have high light to heavy s-process element ratios ([Y/Ba] ≈ 0.30–0.44), which are consistent with the theoretical prediction of the nucleosynthesis in rapidly rotating massive stars with an initial mass of about 𝑀 = 40 𝑀⊙. We also report a star having both high Y ([Y/Fe] = 0.2) and Ba ([Ba/Fe] = 0.28) abundance ratios, and it also shows the highest Zn abundance ratio ([Zn/Fe] = 0.27) among our sample, implying the nucleosynthesis by asymmetric supernova explosion induced by very rapid rotation of a massive progenitor having an initial mass between 20 𝑀⊙ ≲ 𝑀 ≲ 40 𝑀⊙. A relative deficiency of odd-number elements, which would be a signature of the pair-instability nucleosynthesis, is not found in our sample.
4,300원
3.
2023.01
구독 인증기관 무료, 개인회원 유료
We investigate the diffusion process of Thomson-scattered line photons in both real space and frequency space through a Monte Carlo approach. The emission source is assumed to be monochromatic and point-like embedded at the center of a free electron region in the form of a sphere and a slab. In the case of a spherical region, the line profiles emergent at a location of Thomson optical depth τTh from the source exhibit the full width of the half maximum σλ ≃ τ 1.5 Th . In the slab case, we focus on the polarization behavior where the polarization direction flips from the normal direction of the slab to the parallel as the slab optical depth τTh increases from τTh ≪ 1 to τTh ≫ 1. We propose that the polarization flip to the parallel direction to the slab surface in optically thick slabs is attributed to the robustness of the Stokes parameter Q along the vertical axis with respect to the observer’s line of sight whereas randomization dominates the remaining region as τTh increases. A brief discussion on the importance of our study is presented.
4,200원
4.
2023.01
구독 인증기관 무료, 개인회원 유료
We have been conducting a exoplanet search survey using Bohyunsan Observatory Echelle Spectrograph (BOES) for the last 18 years. We present the detection of exoplanet candidate in orbit around HD 18438 from high-precision radial velocity (RV) mesurements. The target was already reported in 2018 (Bang et al. 2018). They conclude that the RV variations with a period of 719 days are likely to be caused by the pulsations because the Lomb-Scargle periodogram of HIPPARCOS photometric and Hα EW variations for HD 18438 show peaks with periods close to that of RV variations and there were no correlations between bisectors and RV measurements. However, the data were not sufficient to reach a firm conclusion. We obtained more RV data for four years. The longer time baseline yields a more accurate determination with a revised period of 803 ± 5 days and the planetary origin of RV variations with a minimum planetary companion mass of 21 ± 1MJup. Our current estimate of the stellar parameters for HD 18438 makes it currently the largest star with a planetary companion.
4,000원
5.
2023.01
구독 인증기관 무료, 개인회원 유료
We measured temporal and emission properties of quiescent magnetars using archival Chandra and XMM-Newton data, produced a list of the properties for 17 magnetars, and revisited previously suggested correlations between the properties. Our studies carried out with a larger sample, better spectral characterizations, and more thorough analyses not only confirmed previously-suggested correlations but also found new ones. The observed correlations differ from those seen in other neutron-star populations but generally accord with magnetar models. Specifically, the trends of the intriguing correlations of blackbody luminosity (𝐿BB) with the spin-inferred dipole magnetic field strength (𝐵S) and characteristic age (𝜏c) were measured to be 𝐿BB ∝ 𝐵1.5 S and 𝐿BB ∝ 𝜏−0.6 c , supporting the twisted magnetosphere and magnetothermal evolution models for magnetars. We report the analysis results and discuss our findings in the context of magnetar models.
5,100원
6.
2023.01
구독 인증기관 무료, 개인회원 유료
The second generation of stars in the globular clusters (GCs) of the Milky Way (MW) exhibit unusually high N, Na, or Al, compared to typical Galactic halo stars at similar metallicities. The halo field stars enhanced with such elements are believed to have originated in disrupted GCs or escaped from existing GCs. We identify such stars in the metallicity range −3.0 < [Fe/H] < 0.0 from a sample of ∼36,800 giant stars observed in the Sloan Digital Sky Survey and Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, and present their dynamical properties. The N-rich population (NRP) and N-normal population (NNP) among our giant sample do not exhibit similarities in either in their metallicity distribution function (MDF) or dynamical properties. We find that, even though the MDF of the NRP looks similar to that of the MW’s GCs in the range of [Fe/H] < −1.0, our analysis of the dynamical properties does not indicate similarities between them in the same metallicity range, implying that the escaped members from existing GCs may account for a small fraction of our N-rich stars, or the orbits of the present GCs have been altered by the dynamical friction of the MW. We also find a significant increase in the fraction of N-rich stars in the halo field in the very metal-poor (VMP; [Fe/H] < −2.0) regime, comprising up to ∼20% of the fraction of the N-rich stars below [Fe/H] = −2.5, hinting that partially or fully destroyed VMP GCs may have in some degree contributed to the Galactic halo. A more detailed dynamical analysis of the NRP reveals that our sample of N-rich stars do not share a single common origin. Although a substantial fraction of the N-rich stars seem to originate from the GCs formed in situ, more than 60% of them are not associated with those of typical Galactic populations, but probably have extragalactic origins associated with Gaia Sausage/Enceladus, Sequoia, and Sagittarius dwarf galaxies, as well as with presently unrecognized progenitors.
4,800원
7.
2023.01
구독 인증기관 무료, 개인회원 유료
We investigate the astronomical phenomenon records of Sukjong’s 𝐶ℎ𝑢𝑛𝑏𝑎𝑛𝑔-𝐼𝑙𝑔𝑖 made by 𝑆𝑖𝑔𝑎𝑛𝑔𝑤𝑜𝑛 (Royal Educational Office of the Crown Prince) at which King Sukjong was the crown prince (i.e., 1667 January 24–1674 September 22). From the daily records of 2,799 days, we extract the astronomical records of 1,443 days and classify them into 14 categories. Then, we group the records of each category into five phenomena (Atmosphere, Eclipse, Daylight Appearance, Apparition, and Appulse) and compare them with the results of modern astronomical computations wherever possible. Except for Atmosphere group comprising records of meteorological events, such as solar halo, lunar halo, and unusual clouds, the significant findings in every other group are as follows: In Eclipse group, the solar eclipse that occurred on 1673 August 12 was unobservable in Korea, which is in contrast to the record of 𝐽𝑜𝑠𝑒𝑜𝑛𝑤𝑎𝑛𝑔 𝑗𝑜-𝑆𝑖𝑙𝑙𝑜𝑘 (Annals of the Joseon Dynasty), which states that the sun was in eclipse around sunset time, as observed at 𝑁𝑎𝑚 mountain. From the lunar eclipse records, we verify that the Joseon court did not change the date of the events observed after midnight. In Daylight Appearance group, we confirm that this phenomenon was observed during the daytime and not during twilight. We further suggest that if observation conditions are met, a celestial body brighter than −2.3 mag could be seen during the daytime with the naked-eye. In Apparition group, we find the possibilities that the Orionid meteor shower had influence on the meteor records and the seasonality on the aurora records. We also find that the Korean records in which the coma of comet C/1668 E1 was located below the horizon were overlooked in previous studies. Finally, we find that the records of Appulse group generally agree with the results of modern calculations. The records of 𝐵𝑒𝑜𝑚 (trespass in literal) and 𝑆𝑖𝑘 (eating in literal) events show average angular separations of 1.2◦ and 1.0◦, respectively. In conclusion, we believe this work helps study the astronomical records of other logs of 𝑆𝑖𝑔𝑎𝑛𝑔𝑤𝑜𝑛, such as Sunjong’s 𝐶ℎ𝑢𝑛𝑏𝑎𝑛𝑔-𝐼𝑙𝑔𝑖.
4,800원
8.
2023.01
구독 인증기관 무료, 개인회원 유료
In this paper, we describe the first multi-frequency synthesis observations of blazar 0059+581 made with the Radioastron spaceground interferometer in conjunction with the Korean VLBI Network (KVN), Medicina and Torun ground telescopes. We conducted these observations to assess the spaceground interferometer multi-frequency mode capability for the first time.
4,000원
9.
2023.01
구독 인증기관 무료, 개인회원 유료
We present the deep homogeneous 𝑈𝐵𝑉𝑅𝐼 photometric data of 135,071 stars down to 𝑉 ∼ 23 mag and 𝐼 ∼ 22 mag toward the Carina Nebula. These stars are cross-matched with those from the previous surveys in the X-ray, near-infrared, and mid-infrared wavelengths as well as the Gaia Early Data Release 3 (EDR3). This master catalog allows us to select reliable members and determine the fundamental parameters distance, size, stellar density of stellar clusters in this star-forming region. We revisit the reddening toward the nebula using the optical and the near-infrared colors of early-type stars. The foreground reddening [𝐸(𝐵 −𝑉) 𝑓 𝑔] is determined to be 0.35 ± 0.02, and it seems to follow the standard reddening law. On the other hand, the total-toselective extinction ratio of the intracluster medium (𝑅𝑉,𝑐𝑙) decreases from the central region (Trumpler 14 and 16, 𝑅𝑉,𝑐𝑙 ∼ 4.5) to the northern region (Trumpler 15, 𝑅𝑉,𝑐𝑙 ∼ 3.4). It implies that the central region is more dusty than the northern region. We find that the distance modulus of the Carina Nebula to be 11.9 ± 0.3 mag (𝑑 = 2.4 ± 0.35 kpc) using a zero-age main-sequence fitting method, which is in good agreement with that derived from the Gaia EDR3 parallaxes. We also present the catalog of 3,331 pre-main-sequence (PMS) members and 14,974 PMS candidates down to 𝑉 ∼ 22 mag based on spectrophotometric properties of young stars at infrared, optical, and X-ray wavelengths. From the spatial distribution of PMS members and PMS candidates, we confirm that the member selection is very reliable down to faint stars. Our data will have a legacy value for follow-up studies with different scientific purposes.
5,400원
10.
2023.01
구독 인증기관 무료, 개인회원 유료
A Forbush decrease (FD) is a depression of cosmic ray (CR) intensity observed by ground-based neutron monitors (NMs). The CR intensity is thought to be modulated by the heliospheric magnetic structures including the interplanetary coronal mass ejection (ICME) surrounding the Earth. The different magnitude of the decreasing in intensity at each NM was explained only by the geomagnetic cutoff rigidity of the NM station. However, sometimes NMs of almost the same cutoff rigidity in northern and southern hemispheres observe the asymmetric intensity depression magnitudes of FD events. Thus, in this study we intend to see the effects on CR intensity modulation of FD event recorded at different NMs due to different ICME propagation directions as an additional parameter in the model explaining the CR modulation. Fortunately, since 2006 the coronagraphs of twin spacecraft of the STEREO mission allow us to infer the propagation direction of ICME associated with the FD event in 3-dimension with respect to the Earth. We suggest the hypothesis that the asymmetric CR modulations of FD events are determined by the propagation directions of the associated ICMEs.
4,000원
