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1968년 ~ 2024년까지 1,211 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 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 6/122
51
- 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.
52
- 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.
53
- Jeon, Junhyeok
- Journal of the Korean astronomical society = 천문학회지
- 55, n.4
- pp.99-110
- 2022
- 원문 바로보기
This study presents the characteristics of publications in the Journal of Korean Astronomy Society (JKAS) from 1968 to 2021. JKAS has published 763 research articles over the past 54 years. In addition, 376 proceedings were also published with research articles. There were slight increases and decreases in the number of articles published in JKAS in the 1990s and 2000s, and in 2015 there was the highest recorded number of articles published for a given year. Since then, the number of articles has tended to decrease each year, up to and including the most recent period (2020-2021), which includes the Coronavirus pandemic. However, since theory centered research is primarily conducted without being swayed by society and policies, and that the proportion of authors belonging to educational institutions, such as universities, is high, the future direction of JKAS is encouraging. There are also positive developments including sustained researchers affiliated with international institutions at greater than approximately 23%, as well as improvements in the impact factor. Therefore, it is important to not be deterred by the decreasing trends of the quantitative aspect, but to respond positively by determining a future roadmap.
54
- 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 𝜇as < 𝜃<sub>E</sub> < 26 𝜇as, which is consistent with the gap in Einstein timescales near t<sub>E</sub> ~ 0.5 days found by Mróz 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 ± 0.2) (M/38 M<sub>⊕</sub>)<sup>-p</sup>/star, with 0.9 ≲ p ≲ 1.2. There are substantially more FFPs than known bound planets, implying that the bound planet power-law index 𝛾 = 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 ± 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.
55
- Park, Jang-Ho
- Journal of the Korean astronomical society = 천문학회지
- 55, n.1
- pp.1-9
- 2022
- 원문 바로보기
We present the photometric properties of V608 Cas from detailed studies of light curves and eclipse timings. The light curve synthesis indicates that the eclipsing pair is an overcontact binary with parameters of ∆T = 155 K, q = 0.328, and f = 26%. We detected the third light ℓ<sub>3</sub>, which corresponds to about 8% and 5% of the total systemic light in V and R bands, respectively. Including our 6 timing measurements, a total of 38 times of minimum light were used for a period study. It was found that the orbital period of V608 Cas has varied in some combination of an upward parabola and two periodic variations. The continuous period increase with a rate of +3.99 × 10<sup>-7</sup> d yr<sup>-1</sup> can be interpreted as a mass transfer from the secondary component to the primary star at a rate of 1.51 × 10<sup>-7</sup> M<sub>⊙</sub> yr<sup>-1</sup>. The periods and semi-amplitudes of the two periodic variations are about P<sub>3</sub> = 16.0 yr and P<sub>4</sub> = 26.3 yr, and K<sub>3</sub> = 0.0341 d and K<sub>4</sub> = 0.0305 d, respectively. The most likely explanation of both cycles is a pair of light-traveling time effects operated by the possible presence of third and fourth components with estimated masses of M<sub>3</sub> = 2.20 M<sub>⊙</sub> and M<sub>4</sub> = 1.27 M<sub>⊙</sub> in eccentric orbits of e<sub>3</sub> = 0.66 and e<sub>4</sub> = 0.52. Because the contribution of ℓ<sub>3</sub> is very low compared to the estimated masses of two circumbinary objects, they can be inferred as very faint compact objects.
56
- Tetsuya, Magara
- Journal of the Korean astronomical society = 천문학회지
- 55, n.6
- pp.215-220
- 2022
- 원문 바로보기
To seek an atmospheric heating mechanism operating on the Sun we investigated a heating source generated by a downflow, both of which may arise in a magnetic loop dynamically formed on the Sun via flux emergence. Since an observation shows that the illumination of evolving magnetic loops under the dynamic formation occurs sporadically and intermittently, we performed a magnetohydrodynamic simulation of flux emergence to obtain a high-cadence simulated data, where temperature enhancement was identified at the footpoint of an evolving magnetic loop. Unlike a rigid magnetic loop with a confined flow in it, the evolving loop in a low plasma β atmosphere is subjected to local compression by the magnetic field surrounding the loop, which drives a strong supersonic downflow generating an effective footpoint heating source in it. This may introduce an energy conversion system to the magnetized atmosphere of the Sun, in which the free magnetic energy causing the compression via Lorentz force is converted to the flow energy, and eventually reduced to the thermal energy. Dynamic and thermodynamic states involved in the system are explained.
57
- Park, Woojin
- Journal of the Korean astronomical society = 천문학회지
- 55, n.1
- pp.11-22
- 2022
- 원문 바로보기
We introduce the Transformable Reflective Telescope (TRT) kit that applies an aluminum profile as a base plate for precise, stable, and lightweight optical system. It has been utilized for optical surface measurements, developing alignment and baffle systems, observing celestial objects, and various educational purposes through Research & Education projects. We upgraded the TRT kit using the aluminum profile and truss and isogrid structures for a high-end optical test device that can be used for prototyping of precision telescopes or satellite optical systems. Thanks to the substantial aluminum profile and lightweight design, mechanical deformation by self-weight is reduced to maximum 67.5 ㎛, which is an acceptable misalignment error compared to its tolerance limits. From the analysis results of non-linear vibration simulations, we have verified that the kit survives in harsh vibration environments. The primary mirror and secondary mirror modules are precisely aligned within 50 ㎛ positioning error using the high accuracy surface finished aluminum profile and optomechanical parts. The cross laser module helps to align the secondary mirror to fine-tune the optical system. The TRT kit with the precision aluminum mirror guarantees high quality optical performance of 5.53 ㎛ Full Width at Half Maximum (FWHM) at the field center.
58
- Yeung, Paige
- Journal of the Korean astronomical society = 천문학회지
- 55, n.4
- pp.111-121
- 2022
- 원문 바로보기
Based on the light an exoplanet blocks from its host star as it passes in front of it during a transit, the mid-transit time can be determined. Periodic variations in mid-transit times can indicate another planet's gravitational influence. We investigate 83 transits of TrES-1 b as observed from 6-inch telescopes in the MicroObservatory robotic telescope network. The EXOTIC data reduction pipeline is used to process these transits, fit transit models to light curves, and calculate transit midpoints. This paper details the methodology for analyzing transit timing variations (TTVs) and using transit measurements to maintain ephemerides. The application of Lomb-Scargle period analysis for studying the plausibility of TTVs is explained. The analysis of the resultant TTVs from 46 transits from MicroObservatory and 47 transits from archival data in the Exoplanet Transit Database indicated the possible existence of other planets affecting the orbit of TrES-1 and improved the precision of the ephemeris by one order of magnitude. We now estimate the ephemeris to be (2 455 489.66026 BJD<sub>TDB</sub> ± 0.00044 d) + (3.0300689 ± 0.0000007) d × epoch. This analysis also demonstrates the role of small telescopes in making precise midtransit time measurements, which can be used to help maintain ephemerides and perform TTV analysis. The maintenance of ephemerides allows for an increased ability to optimize telescope time on large ground-based telescopes and space telescope missions.
59
- Son, Suyeon
- Journal of the Korean astronomical society = 천문학회지
- 55, n.2
- pp.37-57
- 2022
- 원문 바로보기
Using I-band images of 35 nearby (z < 0.1) type 1 active galactic nuclei (AGNs) obtained with Hubble Space Telescope, selected from the 70-month Swift-BAT X-ray source catalog, we investigate the photometric properties of the host galaxies. With a careful treatment of the point-spread function (PSF) model and imaging decomposition, we robustly measure the I-band brightness and the effective radius of bulges in our sample. Along with black hole (BH) mass estimates from single-epoch spectroscopic data, we present the relation between BH mass and I-band bulge luminosity (M<sub>BH</sub>-M<sub>I,bul</sub> relation) of our sample AGNs. We find that our sample lies offset from the M<sub>BH</sub>-M<sub>I,bul</sub> relation of inactive galaxies by 0.4 dex, i.e., at a given bulge luminosity, the BH mass of our sample is systematically smaller than that of inactive galaxies. We also demonstrate that the zero point offset in the M<sub>BH</sub>-M<sub>I,bul</sub> relation with respect to inactive galaxies is correlated with the Eddington ratio. Based on the Kormendy relation, we find that the mean surface brightness of ellipticals and classical bulges in our sample is comparable to that of normal galaxies, revealing that bulge brightness is not enhanced in our sample. As a result, we conclude that the deviation in the M<sub>BH</sub>-M<sub>I,bul</sub> relation from inactive galaxies is possibly because the scaling factor in the virial BH mass estimator depends on the Eddington ratio.
60
- Kim, Dowoon
- Journal of the Korean astronomical society = 천문학회지
- 55, n.2
- pp.59-66
- 2022
- 원문 바로보기
Stellar magnetic activity is important for formulating the evolution of the star. To represent the stellar magnetic activity, the S index is defined using the Ca II H+K flux measure from the Mount Wilson Observatory. Mg II lines are generated in a manner similar to the formation of Ca II lines, which are more sensitive to weak chromospheric activity. Mg II flux data are available from the International Ultraviolet Explorer (IUE). Thus, the main purpose of this study was to analyze the magnetic activity of stars. We used 343 high-resolution IUE spectra of 14 main-sequence G stars to obtain the Mg II continuum surface flux and Mg II line-core flux around 2,800 Å. We calculated S index using the IUE spectra and compared it with the conventional Mount Wilson S index. We found a color (B - V ) dependent association between the S index and the Mg II emission line-core flux. Furthermore, we attempted to obtain the magnetic activity cycles of these stars based on the new S index. Unfortunately, this was not successful because the IUE observation interval of approximately 17 years is too short to estimate the magnetic activity cycles of G-type stars, whose cycles may be longer than the 11 year mean activity cycle of the sun.