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1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 7/119
61
- 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.
62
- Morgan, Hannah L.
- Journal of the Korean astronomical society = 천문학회지
- 53, n.6
- pp.117-123
- 2020
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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-2 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.
63
- Gould, Andrew
- Journal of the Korean astronomical society = 천문학회지
- 53, n.5
- pp.99-102
- 2020
- 원문 바로보기
I show that when the observables (π<sub>E</sub>, t<sub>E</sub>, θ<sub>E</sub>, π<sub>s</sub>, µ<sub>s</sub>) are well measured up to a discrete degeneracy in the microlensing parallax vector π<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, θ<sub>E</sub> is the angular Einstein radius, and (π<sub>s</sub>, µ<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.
64
- Hyung, Siek
- Journal of the Korean astronomical society = 천문학회지
- 53, n.2
- pp.35-42
- 2020
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We analyze high dispersion emission lines of the symbiotic nova AG Pegasi, observed in 1998, 2001, and 2002. The Hα and Hβ 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°, 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.
65
- Lee, Byeong-Cheol
- Journal of the Korean astronomical society = 천문학회지
- 53, n.1
- pp.27-34
- 2020
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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 ±3 days and 613±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 ± 0.2M<sub>⊙</sub> (HD 60292) and 1.8 ± 0.2M<sub>⊙</sub> (HD 112640), we obtain minimum planetary companion masses of 6.5 ± 1.0M<sub>Jup</sub> and 5.0 ± 1.0M<sub>Jup</sub>, and periods of 495.4 ± 3.0 days and 613.2 ± 5.8 days, respectively.
66
- Kim, Yun Hak
- Journal of the Korean astronomical society = 천문학회지
- 53, n.6
- pp.161-168
- 2020
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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 ± 0.39 × 10-3 and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of θE = 0.52 ± 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, tE ≃ 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 Mh = 0.55+0.36-0.29 M⊙ hosting a giant planet with Mp = 5.53+3.62-2.87 MJup, at a distance of DL = 5.67+1.11-1.52 kpc. The projected star-planet separation is a⊥ = 3.92+1.10-1.32 au. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is μrel ~ 7 mas yr-1, 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.
67
- Gould, Andrew
- Journal of the Korean astronomical society = 천문학회지
- 53, n.1
- pp.9-26
- 2020
- 원문 바로보기
At q = 1.81 ± 0.20 × 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 ×10<sup>-5</sup>. The event was observed by Spitzer, yielding a microlens-parallax π<sub>E</sub> measurement. Combined with a measurement of the Einstein radius θ<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>⊙</sub> and planet M<sub>planet</sub> = 7.59<sup>+0.75</sup><sub>-0.69</sub> M<sub>⊕</sub>, system distance D<sub>L</sub> = 3.38<sup>+0.22</sup><sub>-0.26</sub> kpc and projected separation a<sub>⊥</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.
68
- Barbier, Hugo
- Journal of the Korean astronomical society = 천문학회지
- 53, n.3
- pp.69-75
- 2020
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We study the photometric phase curves for the planets of our solar system which can be considered as a prototypical non-compact planetary system. We focus on modeling the small variations caused by three effects: reflection, ellipsoidal, and Doppler beaming. Theoretical predictions for these photometric variations are proposed, considering a hypothetical external observer. Unlike similar studies of multi-planetary systems, the physical and geometrical parameters for each planet of the solar system are well-known. Therefore, we can accurately evaluate the relationships that shape the planetary light curves for a fictitious external observer. Our results suggest that, for all planets, the ellipsoidal effect is very weak while the Doppler beaming effect (DBE) is, in general, dominant. In fact, the DBE seems to be the principal cause of variations of the light curves for the planets of the solar system. However, for Mercury and Venus the Doppler beaming and reflection effects have similar amplitudes. The phase curves obtained for the planets of the solar system show new interesting features of interest for the study of other non-compact planetary systems.
69
- Kim, Yoo Jung
- Journal of the Korean astronomical society = 천문학회지
- 53, n.1
- pp.1-7
- 2020
- 원문 바로보기
The recent study of Chae et al. (2017) found a one-to-one correspondence between plasma blobs outflowing along a ray formed after a coronal mass ejection (CME) and small X-ray flares. In the present work, we have examined the spatial configuration and the eruption process of the flares that are associated with the blobs by analyzing EUV images and magnetograms taken by the SDO/AIA and HMI. We found that the main flare and the successive small flares took place in a quadrupolar magnetic configuration characterized by predominant magnetic fields of positive polarity, two minor magnetic fragments of negative polarity, and a curved polarity inversion line between them, which suggests that the formation process of the blobs may be similar to that of the parent CME. We also found that the successive flares resulted in a gradual change of the quadrupolar magnetic configuration, and the relevant migration of flaring kernels. The three-dimensional geometry and the property of the current sheet, that is often supposed to be embedded in an observed post-CME ray, seem to keep changing because of mutual feedback between the successive flares and the temporal change of the magnetic field configuration. Our results suggest that the observed post-CME rays may not reflect the characteristics of the current sheet responsible for the impulsive phase of the flare.
70
- Minh, Young Chol
- Journal of the Korean astronomical society = 천문학회지
- 53, n.3
- pp.77-85
- 2020
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In the molecular cloud G33.92+0.11A, massive stars are forming sequentially in dense cores, probably due to interaction with accreted gas. Cold dense gas, which is likely the pristine gas of the cloud, is traced by DCN line and dust continuum emission. Clear chemical differences were observed in different source locations and for different velocity components in the same line of sight. Several distinct gas components coexist in the cloud: the pristine cold gas, the accreted dense gas, and warm turbulent gas, in addition to the star-forming dense clumps. Filaments of accreted gas occur in the northern part of the A1 and A5 clumps, and the velocity gradient along these features suggests that the gas is falling toward the cloud and may have triggered the most recent star formation. The large concentration of turbulent gas in the A2 clump seems to have formed mainly through disturbances from the outside.