모달창 닫기
- 홈으로 이동
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 24/122
231
- Ann, Hong Bae
- Journal of the Korean astronomical society = 천문학회지
- 47, n.1
- pp.1-13
- 2014
- 원문 바로보기
We analyze the dependence of disk morphology (arm class, Hubble type, bar type) of nearby spiral galaxies on the galaxy environment by using local background density (<TEX>${\Sigma}_n$</TEX>), projected distance (<TEX>$r_p$</TEX>), and tidal index (T I) as measures of the environment. There is a strong dependence of arm class and Hubble type on the galaxy environment, while the bar type exhibits a weak dependence with a high frequency of SB galaxies in high density regions. Grand design fractions and early-type fractions increase with increasing <TEX>${\Sigma}_n$</TEX>, <TEX>$1/r_p$</TEX>, and T I, while fractions of flocculent spirals and late-type spirals decrease. Multiple-arm and intermediate-type spirals exhibit nearly constant fractions with weak trends similar to grand design and early-type spirals. While bar types show only a marginal dependence on <TEX>${\Sigma}_n$</TEX>, they show a fairly clear dependence on <TEX>$r_p$</TEX> with a high frequency of SB galaxies at small <TEX>$r_p$</TEX>. The arm class also exhibits a stronger correlation with <TEX>$r_p$</TEX> than <TEX>${\Sigma}_n$</TEX> and T I, whereas the Hubble type exhibits similar correlations with <TEX>${\Sigma}_n$</TEX> and <TEX>$r_p$</TEX>. This suggests that the arm class is mostly affected by the nearest neighbor while the Hubble type is affected by the local densities contributed by neighboring galaxies as well as the nearest neighbor.
232
- Jeong, Eui-Jun
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.209-214
- 2014
- 원문 바로보기
In this study we develop a set of solar proton event (SPE) forecast models with NOAA scales by Multi Layer Perceptron (MLP), one of neural network methods, using GOES solar X-ray flare data from 1976 to 2011. Our MLP models are the first attempt to forecast the SPE scales by the neural network method. The combinations of X-ray flare class, impulsive time, and location are used for input data. For this study we make a number of trials by changing the number of layers and nodes as well as combinations of the input data. To find the best model, we use the summation of F-scores weighted by SPE scales, where F-score is the harmonic mean of PODy (recall) and precision (positive predictive value), in order to minimize both misses and false alarms. We find that the MLP models are much better than the multiple linear regression model and one layer MLP model gives the best result.
233
- Cho, Se-Hyung
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.293-302
- 2014
- 원문 바로보기
Simultaneous time monitoring observations of <TEX>$H_2O$</TEX> <TEX>$6_{16}-5_{23}$</TEX>, SiO J = 1-0, 2-1, 3-2, and <TEX>$^{29}SiO$</TEX> <TEX>${\upsilon}=0$</TEX>, J = 1-0 lines are carried out in the direction of the Mira variable star TX Cam with the Korean VLBI Network single dish radio telescopes. For the first time, the <TEX>$H_2O$</TEX> maser emission from TX Cam is detected near the stellar velocity at five epochs from April 10, 2013 (<TEX>${\phi}=3.13$</TEX>) to June 4, 2014 (<TEX>${\phi}=3.89$</TEX>) including minimum optical phases. The intensities of <TEX>$H_2O$</TEX> masers are very weak compared to SiO masers. The variation of peak antenna temperature ratios among SiO <TEX>${\upsilon}=1$</TEX>, J = 1-0, J = 2-1, and J = 3-2 masers is investigated according to their phases. The shift of peak velocities of <TEX>$H_2O$</TEX> and SiO masers with respect to the stellar velocity is also investigated according to observed optical phases. The <TEX>$H_2O$</TEX> maser emission occurs around the stellar velocity during our monitoring interval. On the other hand, the peak velocities of SiO masers show a spread compared to the stellar velocity. The peak velocities of SiO J = 2-1, and J = 3-2 masers show a smaller spread with respect to the stellar velocity than those of SiO J = 1-0 masers. These simultaneous observations of multi-frequencies will provide a good constraint for maser pumping models and a good probe for investigating the stellar atmosphere and envelope according to their different excitation conditions.
234
- Na, Sung-Ho
- Journal of the Korean astronomical society = 천문학회지
- 47, n.1
- pp.41-41
- 2014
- 원문 바로보기
The equivalent phase lag <TEX>${\varepsilon}_{lmpq}$</TEX> of Earth tide suggested by Lambeck have been found reasonable. Due to a mistake in his calculation, the author falsely claimed that those are too large. However, the main contents of the article are valid and not affected by this mistake.
235
- Hanna, Magdy
- Journal of the Korean astronomical society = 천문학회지
- 47, n.3
- pp.99-104
- 2014
- 원문 바로보기
We present the rst period variation study for the Algol eclipsing binary V346 Cyg by constructing the (O-C) residual diagram using all the available precise minima times. We conclude that the period variation can be explained by a sine-like variation due to the presence of a third body orbiting the binary in about <TEX>$68.89{\pm}4.69$</TEX> years, together with a long-term orbital period decrease (<TEX>$dP/dt=-1.23{\times}10^{-7}day/yr$</TEX>) that can be interpreted to be due to slow mass loss from the <TEX>${\delta}$</TEX>-Scuti primary component. The sinusoidal variation may also be explained by using the the Applegate (1992) mechanism involving cyclic magnetic activity due to star-spots on the secondary component. The present preliminary solution needs more precise photometric observations to be confirmed.
236
- Lee, Youngung
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.319-325
- 2014
- 원문 바로보기
We map two molecular clouds located in the exact anticenter region emitting in the (J = 1-0) transition of <TEX>$^{12}CO$</TEX> and <TEX>$^{13}CO$</TEX> using the 3-mm SIS mixer receiver on the 14-m radio telescope at Taeduk Radio Astronomy Observatory. The target clouds with anomalous velocities of <TEX>$V_{LSR}{\sim}-20km\;s^{-1}$</TEX> are distinguished from other clouds in this direction. In addition, they are located in the interarm region between the Orion Arm and the Perseus Arm. Sizes of the clouds are estimated to be about 8.6 and 10.8 pc, respectively. The total mass is estimated to be about <TEX>$4{\times}10^3$</TEX> <TEX>$M_{\odot}$</TEX> using CO luminosity of the clouds. Several cores are detected, but no sign of star formation is found according to the IRAS point sources. Their larger linewidths, anomalous velocities, and their location at the interarm region make these clouds more distinguished, though their physical properties are similar to the dark clouds in the solar neighborhood in terms of mass and size.
237
- Lee, Sang-Sung
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.303-309
- 2014
- 원문 바로보기
We present results of our investigation of the radio intrinsic brightness temperatures of compact radio jets. The intrinsic brightness temperatures of about 100 compact radio jets at 2, 5, 8, 15, and 86 GHz are estimated based on large VLBI surveys conducted in 2001-2003 (or in 1996 for the 5 GHz sample). The multi-frequency intrinsic brightness temperatures of the sample of jets are determined by a statistical method relating the observed brightness temperatures with the maximal apparent jet speeds, assuming one representative intrinsic brightness temperature for a sample of jets at each observing frequency. By investigating the observed brightness temperatures at 15 GHz in multiple epochs, we find that the determination of the intrinsic brightness temperature for our sample is affected by the flux density variability of individual jets at time scales of a few years. This implies that it is important to use contemporaneous VLBI observations for the multi-frequency analysis of intrinsic brightness temperatures. Since our analysis is based on the VLBI observations conducted in 2001-2003, the results are not strongly affected by the flux density variability. We find that the intrinsic brightness temperature <TEX>$T_0$</TEX> increases as <TEX>$T_0{\propto}{\nu}^{\xi}_{obs}$</TEX> with <TEX>${\xi}=0.7$</TEX> below a critical frequency <TEX>${\nu}_c{\approx}9GHz$</TEX> where the energy loss begins to dominate the emission. Above <TEX>${\nu}_c$</TEX>, <TEX>$T_0$</TEX> decreases with <TEX>${\xi}=-1.2$</TEX>, supporting the decelerating jet model or particle cascade model. We also find that the peak value of <TEX>$T_0{\approx}3.4{\times}10^{10}$</TEX> K is close to the equipartition temperature, implying that the VLBI cores observable at 2-86 GHz may be representing jet regions where the magnetic field energy dominates the total energy in jets.
238
- Kim, Chulhee
- Journal of the Korean astronomical society = 천문학회지
- 47, n.5
- pp.163-166
- 2014
- 원문 바로보기
In order to identify peculiar X-ray sources, we select 442 sources with no counterparts in other wavelength bands (as of the year 1999) from the ROSAT All-Sky Survey Bright Source Catalog. We cross-correlate this initial list with the NASA/IPAC Extragalactic Database, the USNO and WISE catalogs, and the HEASARC XRAY Master Catalog. Eventually, we are left with four unidentified sources with no counterparts in other wavelength bands. We present these four sources and their X-ray properties in this paper.
239
- Gould, Andrew
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.215-218
- 2014
- 원문 바로보기
One-dimensional (1-D) microlens parallaxes can be combined with heliocentric lens-source relative proper motion measurements to derive the lens mass and distance, as suggested by Ghosh et al. (2004). Here I present the first mathematical anlysis of this procedure, which I show can be represented as a quadratic equation. Hence, it is formally subject to a two-fold degeneracy. I show that this degeneracy can be broken in many cases using the relatively crude 2-D parallax information that is often available for microlensing events. I also develop an explicit formula for the region of parameter space where it is more difficult to break this degeneracy. Although no mass/distance measurements have yet been made using this technique, it is likely to become quite common over the next decade.
240
- Trippe, Sascha
- Journal of the Korean astronomical society = 천문학회지
- 47, n.1
- pp.15-39
- 2014
- 원문 바로보기
Polarization is a basic property of light and is fundamentally linked to the internal geometry of a source of radiation. Polarimetry complements photometric, spectroscopic, and imaging analyses of sources of radiation and has made possible multiple astrophysical discoveries. In this article I review (i) the physical basics of polarization: electromagnetic waves, photons, and parameterizations; (ii) astrophysical sources of polarization: scattering, synchrotron radiation, active media, and the Zeeman, Goldreich-Kylafis, and Hanle effects, as well as interactions between polarization and matter (like birefringence, Faraday rotation, or the Chandrasekhar-Fermi effect); (iii) observational methodology: on-sky geometry, influence of atmosphere and instrumental polarization, polarization statistics, and observational techniques for radio, optical, and <TEX>$X/{\gamma}$</TEX> wavelengths; and (iv) science cases for astronomical polarimetry: solar and stellar physics, planetary system bodies, interstellar matter, astrobiology, astronomical masers, pulsars, galactic magnetic fields, gamma-ray bursts, active galactic nuclei, and cosmic microwave background radiation.