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통합검색

통합검색

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한국천문학회지

1968년 ~ 2021년까지 1,130 건한국천문학회지를 격월간 확인하실 수 있습니다.

  • The Korean Astronomical Society (The Korean Astronomical Society)
  • 계간 (Quarterly)
  • ISSN : 1225-4614 (ISSN : 1225-4614)
  • DB구축현황 : 1,130건 (DB Construction : 1,130 Articles)
안내사항
총 게시글 1,130 페이지 1/113
1
  • Park, Nuri
  • Journal of the Korean astronomical society = 천문학회지
  • 54, n.1
  • pp.9-16
  • 2021
  • 원문 바로보기
The Ozone Dynamics Investigation Nano-Satellite (ODIN) is a CubeSat design proposed by Chungnam National University as contribution to the CubeSat Competition 2019 sponsored by the Korean Aerospace Research Institute (KARI). The main objectives of ODIN are (1) to observe the polar ozone column density (latitude range of 60° to 80° in both hemispheres) and (2) to investigate the chemical dynamics between stratospheric ozone and ozone depleting substances (ODSs) through spectroscopy of the terrestrial atmosphere. For the operation of ODIN, a highly efficient power system designed for the specific orbit is required. We present the conceptual structural design of ODIN and an analysis of power generation in a sun synchronous orbit (SSO) using two different configurations of 3U solar panels (a deployed model and a non-deployed model). The deployed solar panel model generates 189.7 W through one day which consists of 14 orbit cycles, while the non-deployed solar panel model generates 152.6 W. Both models generate enough power for ODIN and the calculation suggests that the deployed solar panel model can generate slightly more power than the non-deployed solar panel model in a single orbit cycle. We eventually selected the non-deployed solar panel model for our design because of its robustness against vibration during the launch sequence and the capability of stable power generation through a whole day cycle.
2
  • Kim, Minjun
  • Journal of the Korean astronomical society = 천문학회지
  • 54, n.1
  • pp.1-8
  • 2021
  • 원문 바로보기
We report X-ray timing and spectral properties of the pulsar PSR J0205+6449 measured using NuSTAR and Chandra observatories. We measure the pulsar's rotation frequency &#957; = 15.20102357(9) s-1 and its derivative <TEX>$\dot{\nu}=-4.5(1){\times}10^{-11}\;s^{-2}$</TEX> during the observation period, and model the 2-30 keV on-pulse spectrum of the pulsar with a power law having a photon index &#915;psr = 1.07 &#177; 0.16 and a 2-30 keV flux F2-30 keV = 7.3&#177;0.6 &#215; 10-13 erg cm-2 s-1. The Chandra 0.5-10 keV data are analyzed for an investigation of the pulsar's thermal emission properties. We use thermal and non-thermal emission models to fit the Chandra spectra and infer the surface temperature T&#8734; and luminosity Lth of the neutron star to be T&#8734; = 0.5 - 0.8 MK and Lth = 1 - 5 &#215; 1032 erg s-1. This agrees with previous results which indicated that PSR J0205+6449 has a low surface temperature and luminosity for its age of 800-5600 yrs.
3
  • Mun, Jae Yeon
  • Journal of the Korean astronomical society = 천문학회지
  • 54, n.1
  • pp.17-35
  • 2021
  • 원문 바로보기
We study galaxies undergoing ram pressure stripping in the Virgo cluster to examine whether we can identify any discernible trend in their star formation activity. We first use 48 galaxies undergoing different stages of stripping based on H i morphology, H i deficiency, and relative extent to the stellar disk, from the VIVA survey. We then employ a new scheme for galaxy classification which combines H i mass fractions and locations in projected phase space, resulting in a new sample of 365 galaxies. We utilize a variety of star formation tracers, which include g - r, WISE [3.4]-[12] colors, and starburstiness that are defined by stellar mass and star formation rates to compare the star formation activity of galaxies at different stripping stages. We find no clear evidence for enhancement in the integrated star formation activity of galaxies undergoing early to active stripping. We are instead able to capture the overall quenching of star formation activity with increasing degree of ram pressure stripping, in agreement with previous studies. Our results suggest that if there is any ram pressure stripping induced enhancement, it is at best locally modest, and galaxies undergoing enhancement make up a small fraction of the total sample. Our results also indicate that it is possible to trace galaxies at different stages of stripping with the combination of H i gas content and location in projected phase space, which can be extended to other galaxy clusters that lack high-resolution H i imaging.
4
  • Kim, Yonggi
  • Journal of the Korean astronomical society = 천문학회지
  • 53, n.2
  • pp.43-48
  • 2020
  • 원문 바로보기
We report an analysis of two poorly studied eclipsing binary stars, GSC 04396-00605 and GSC 04395-00485 (recently named V455 Dra and V454 Dra, respectively). Photometric data of the two stars were obtained using the 1-m Korean telescope of the LOAO operated by KASI while monitoring the cataclysmic variable DO Dra in the frame of the Inter-Longitude Astronomy (ILA) project. We derived periods of 0.434914 and 0.376833 days as well as initial epochs JD 2456480.04281 and JD 2456479.0523, respectively, more accurate than previously published values by factors 9 and 6. The phenomenological characteristics of the mean light curves were determined using the New Algol Variable (NAV) algorithm. The individual times of maxima/minima (ToM) were determined using the newly developed software MAVKA, which outputs accurate parameters using 'asymptotic parabola' approximations. The light curves were approximated using phenomenological and physical models. In the NAV algorithm, the phenomenological parameters are well determined. We derived physical parameters using the Wilson-Devinney model. In this model, the best-fit parameters are highly correlated, thus some of them were fixed to reasonable values. For both systems, we find evidence for the presence of a cool spot and estimate its parameters. Both systems can be classified as overcontact binaries of EW type.
5
  • Morgan, Hannah L.
  • Journal of the Korean astronomical society = 천문학회지
  • 53, n.6
  • pp.117-123
  • 2020
  • 원문 바로보기
We investigate the plausibility of mass return, from stellar mass loss processes within the central ~100 pc region of the Milky Way (the inner nuclear bulge), as a mass supply mechanism for the Circumnuclear Disk (CND). Gas in the Galactic disk migrates inward to the Galactic centre due to the asymmetric potential caused by the Galactic bar. The inward migration of gas stops and accumulates to form the central molecular zone (CMZ), at 100-200 pc from the Galactic center. It is commonly assumed that stars have formed in the CMZ throughout the lifetime of the Galaxy and have diffused inward to form a 'r<sup>-2</sup> stellar cusp' within the inner nuclear bulge. We propose that the stars migrating inward from the CMZ supply gas to the inner nuclear bulge via stellar mass loss, resulting in the formation of a gas disk along the Galactic plane and subsequent inward migration down to the central 10 pc region (CND). We simulate the evolution of a gas distribution that initially follows the stellar distribution of the aforementioned stellar cusp, and illustrate the potential gas supply toward the CND.
6
  • Lee, Byeong-Cheol
  • Journal of the Korean astronomical society = 천문학회지
  • 53, n.1
  • pp.27-34
  • 2020
  • 원문 바로보기
We report the detection of exoplanet candidates in orbits around HD 60292 and HD 112640 from a radial velocity (RV) survey. The stars exhibit RV variations with periods of 495 &#x00B1;3 days and 613&#x00B1;6 days, respectively. These detections are part of the Search for Exoplanets around Northern Circumpolar Stars (SENS) survey using the fiber-fed Bohyunsan Observatory Echelle Spectrograph installed at the 1.8-m telescope of the Bohyunsan Optical Astronomy Observatory in Korea. The aim of the survey is to search for planetary or substellar companions. We argue that the periodic RV variations are not related to surface inhomogeneities; rather, Keplerian motions of planetary companions are the most likely interpretation. Assuming stellar masses of 1.7 &#x00B1; 0.2M<sub>&#x2299;</sub> (HD 60292) and 1.8 &#x00B1; 0.2M<sub>&#x2299;</sub> (HD 112640), we obtain minimum planetary companion masses of 6.5 &#x00B1; 1.0M<sub>Jup</sub> and 5.0 &#x00B1; 1.0M<sub>Jup</sub>, and periods of 495.4 &#x00B1; 3.0 days and 613.2 &#x00B1; 5.8 days, respectively.
7
  • Hyung, Siek
  • Journal of the Korean astronomical society = 천문학회지
  • 53, n.2
  • pp.35-42
  • 2020
  • 원문 바로보기
We analyze high dispersion emission lines of the symbiotic nova AG Pegasi, observed in 1998, 2001, and 2002. The H&#x03B1; and H&#x03B2; lines show three components, two narrow and one underlying broad line components, but most other lines, such as H<sub>I</sub>, He<sub>I</sub>, and He<sub>II</sub> lines, show two blue- and red-shifted components only. A recent study by Lee & Hyung (2018) suggested that the double Gaussian lines emitted from a bipolar conical shell are likely to form Raman scattering lines observed in 1998. In this study, we show that the bipolar cone with an opening angle of 74&#x00B0;, which expands at a velocity of 70 km s<sup>-1</sup> along the polar axis of the white dwarf, can accommodate the observed double line profiles in 1998, 2001, and 2002. We conclude that the emission zone of the bipolar conical shell, which formed along the bipolar axis of the white dwarf due to the collimation by the accretion disk, is responsible for the double Gaussian profiles.
8
  • Gould, Andrew
  • Journal of the Korean astronomical society = 천문학회지
  • 53, n.5
  • pp.99-102
  • 2020
  • 원문 바로보기
I show that when the observables (&#x03C0;<sub>E</sub>, t<sub>E</sub>, &#x03B8;<sub>E</sub>, &#x03C0;<sub>s</sub>, &#x00B5;<sub>s</sub>) are well measured up to a discrete degeneracy in the microlensing parallax vector &#x03C0;<sub>E</sub>, the relative likelihood of the different solutions can be written in closed form P<sub>i</sub> = KH<sub>i</sub>B<sub>i</sub>, where H<sub>i</sub> is the number of stars (potential lenses) having the mass and kinematics of the inferred parameters of solution i and B<sub>i</sub> is an additional factor that is formally derived from the Jacobian of the transformation from Galactic to microlensing parameters. Here t<sub>E</sub> is the Einstein timescale, &#x03B8;<sub>E</sub> is the angular Einstein radius, and (&#x03C0;<sub>s</sub>, &#x00B5;<sub>s</sub>) are the (parallax, proper motion) of the microlensed source. The Jacobian term B<sub>i</sub> constitutes an explicit evaluation of the 'Rich Argument', i.e., that there is an extra geometric factor disfavoring large-parallax solutions in addition to the reduced frequency of lenses given by H<sub>i</sub>. I also discuss how this analytic expression degrades in the presence of finite errors in the measured observables.
9
  • Gould, Andrew
  • Journal of the Korean astronomical society = 천문학회지
  • 53, n.1
  • pp.9-26
  • 2020
  • 원문 바로보기
At q = 1.81 &#x00B1; 0.20 &#x00D7; 10<sup>-5</sup>, KMT-2018-BLG-0029Lb has the lowest planet-host mass ratio q of any microlensing planet to date by more than a factor of two. Hence, it is the first planet that probes below the apparent 'pile-up' at q = 5-10 &#x00D7;10<sup>-5</sup>. The event was observed by Spitzer, yielding a microlens-parallax &#x03C0;<sub>E</sub> measurement. Combined with a measurement of the Einstein radius &#x03B8;<sub>E</sub> from finite-source effects during the caustic crossings, these measurements imply masses of the host M<sub>host</sub> = 1.14<sup>+0.10</sup><sub>-0.12</sub> M<sub>&#x2299;</sub> and planet M<sub>planet</sub> = 7.59<sup>+0.75</sup><sub>-0.69</sub> M<sub>&#x2295;</sub>, system distance D<sub>L</sub> = 3.38<sup>+0.22</sup><sub>-0.26</sub> kpc and projected separation a<sub>&#x22A5;</sub> = 4.27<sup>+0.21</sup><sub>-0.23</sub> AU. The blended light, which is substantially brighter than the microlensed source, is plausibly due to the lens and could be observed at high resolution immediately.
10
  • Kim, Yun Hak
  • Journal of the Korean astronomical society = 천문학회지
  • 53, n.6
  • pp.161-168
  • 2020
  • 원문 바로보기
We report the discovery of a giant exoplanet in the microlensing event OGLE-2017-BLG-1049, with a planet-host star mass ratio of q = 9.53 &#x00B1; 0.39 &#x00D7; 10<sup>-3</sup> and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of &#x03B8;<sub>E</sub> = 0.52 &#x00B1; 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, t<sub>E</sub> &#x2243; 29 days, is too short. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. We find that the lens system has a star with mass M<sub>h</sub> = 0.55<sup>+0.36</sup><sub>-0.29</sub> M<sub>&#x2299;</sub> hosting a giant planet with M<sub>p</sub> = 5.53<sup>+3.62</sup><sub>-2.87</sub> M<sub>Jup</sub>, at a distance of D<sub>L</sub> = 5.67<sup>+1.11</sup><sub>-1.52</sub> kpc. The projected star-planet separation is a<sub>&#x22A5;</sub> = 3.92<sup>+1.10</sup><sup>-1.32</sup> au. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is &#x03BC;<sub>rel</sub> ~ 7 mas yr<sup>-1</sup>, thus the lens and source will be separated from each other within 10 years. After this, it will be possible to measure the flux of the host star with 30 meter class telescopes and to determine its mass.