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1968년 ~ 2025년까지 1,227 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 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 25/123
241
- ALGABA, JUAN-CARLOS
- Journal of the Korean astronomical society = 천문학회지
- 48, n.5
- pp.237-255
- 2015
- 원문 바로보기
The Interferometric Monitoring of Gamma–ray Bright Active galactic nuclei (iMOGABA) program provides not only simultaneous multifrequency observations of bright gamma–ray detected active galactic nuclei (AGN), but also covers the highest Very Large Baseline Interferometry (VLBI) frequencies ever being systematically monitored, up to 129 GHz. However, observation and imaging of weak sources at the highest observed frequencies is very challenging. In the second paper in this series, we evaluate the viability of the frequency phase transfer technique to iMOGABA in order to obtain larger coherence time at the higher frequencies of this program (86 and 129 GHz) and image additional sources that were not detected using standard techniques. We find that this method is applicable to the iMOGABA program even under non–optimal weather conditions.
242
- Amin, S.M.
- Journal of the Korean astronomical society = 천문학회지
- 48, n.1
- pp.1-7
- 2015
- 원문 바로보기
The orbital period changes of the W UMa eclipsing binary AU Ser are studied using the (O-C) method. We conclude that the period variation is due to mass transfer from the primary star to the secondary one at a very low and decreasing rate <TEX>$dP/dt=-8.872{\times}10^{-8}$</TEX>, superimposed on the sinusoidal variation due to a third body orbiting the binary with period <TEX>$42.87{\pm}3.16$</TEX> years, orbital eccentricity <TEX>$e=0.52{\pm}0.12$</TEX> and a longitude of periastron passage <TEX>${\omega}=133^{\circ}.7{\pm}15$</TEX>. On studying the magnetic activity, we have concluded that the Applegate mechanism failed to describe the cycling variation of the (O-C) diagram of AU Ser.
243
- Kang, Hyesung
- Journal of the Korean astronomical society = 천문학회지
- 48, n.1
- pp.9-20
- 2015
- 원문 바로보기
We study the evolution of the energy spectrum of cosmic-ray electrons accelerated at spherically expanding shocks with low Mach numbers and the ensuing spectral signatures imprinted in radio synchrotron emission. Time-dependent simulations of diffusive shock acceleration (DSA) of electrons in the test-particle limit have been performed for spherical shocks with parameters relevant for typical shocks in the intracluster medium. The electron and radiation spectra at the shock location can be described properly by the test-particle DSA predictions with instantaneous shock parameters. However, the volume integrated spectra of both electrons and radiation deviate significantly from the test-particle power-laws, because the shock compression ratio and the flux of injected electrons at the shock gradually decrease as the shock slows down in time. So one needs to be cautious about interpreting observed radio spectra of evolving shocks based on simple DSA models in the test-particle regime.
244
- LAL, DHARAM V.
- Journal of the Korean astronomical society = 천문학회지
- 48, n.6
- pp.399-412
- 2015
- 원문 바로보기
We study the radio properties at 1.4 GHz of Seyfert galaxies with strong forbidden highionization lines (FHILs), selected from the Sloan Digital Sky Survey - a large-sized sample containing nearly equal proportion of diverse range of Seyfert galaxies showing similar redshift distributions compiled by using the Very Large Array survey images. The radio detection rate is low, 49%, which is lower than the detection rate of several other known Seyfert galaxy samples. These galaxies show low star formation rates and the radio emission is dominated by the active nucleus with ≤10% contribution from thermal emission, and possibly, none show evidence for relativistic beaming. The radio detection rate, distributions of radio power, and correlations between radio power and line luminosities or X-ray luminosity for narrow-line Seyfert 1 (NLS1), Seyfert 1 and Seyfert 2 galaxies are consistent with the predictions of the unified scheme hypothesis. Using correlation between radio and [O III] λ 5007 Å luminosities, we show that ∼8% sample sources are radio-intermediate and the remaining are radio-quiet. There is possibly an ionization stratification associated with clouds on scales of 0.1-1.0 kpc, which have large optical depths at 1.4GHz, and it seems these clouds are responsible for free-free absorption of radio emission from the core; hence, leading to low radio detection rate for these FHIL-emitting Seyfert galaxies
245
- KIM, KEE-TAE
- Journal of the Korean astronomical society = 천문학회지
- 48, n.6
- pp.365-380
- 2015
- 원문 바로보기
We map 6 massive young stellar objects (YSOs) in the CO J=2-1 line and survey 18 massive YSOs, including the six, in the HCO<sup>+</sup> J=1−0, SiO J=2−1, H<sub>2</sub>O 6<sub>16</sub> − 5<sub>23</sub> maser, and CH<sub>3</sub>OH 7<sub>0</sub> − 6<sub>1</sub> A<sup>+</sup> maser lines. We detect CO bipolar outflows in all the six mapped sources. Four of them are newly discovered (07299−1651, 21306+5540, 22308+5812, 23133+6050), while 05490+2658 is mapped in the CO J=2-1 line for the first time. The detected outflows are much more massive and energetic than outflows from low-mass YSOs with masses >20 M<sub>⊙</sub> and momenta >300 M<sub>⊙</sub> km s<sup>−1</sup>. They have mass outflow rates (3−6)×10<sup>−4</sup> M<sub>⊙</sub> yr<sup>−1</sup>, which are at least one order of magnitude greater than those observed in low-mass YSOs. We detect HCO<sup>+</sup> and SiO line emission in 18 (100%) and 4 (22%) sources, respectively. The HCO<sup>+</sup> spectra show high-velocity wings in 11 (61%) sources. We detect H<sub>2</sub>O maser emission in 13 (72%) sources and 44 GHz CH<sub>3</sub>OH maser emission in 8 (44%) sources. Of the detected sources, 5 H<sub>2</sub>O and 6 CH<sub>3</sub>OH maser sources are new discoveries. 20081+3122 shows high-velocity (>30 km s<sup>−1</sup>) H<sub>2</sub>O maser lines. We find good correlations of the bolometric luminosity of the central (proto)star with the mechanical force, mechanical luminosity, and mass outflow rate of molecular outflow in the bolometric luminosity range of 10<sup>−1</sup>−10<sup>6</sup> L<sub>⊙</sub>, and identified 3 intermediate- or high-mass counterparts of Class O objects.
246
- Trippe, Sascha
- Journal of the Korean astronomical society = 천문학회지
- 48, n.3
- pp.191-194
- 2015
- 원문 바로보기
Massive gravity provides a natural solution for the dark energy problem of cosmology and is also a candidate for resolving the dark matter problem. I demonstrate that, assuming reasonable scaling relations, massive gravity can provide for Milgrom’s law of gravity (or “modified Newtonian dynamics”) which is known to remove the need for particle dark matter from galactic dynamics. Milgrom’s law comes with a characteristic acceleration, Milgrom’s constant, which is observationally constrained to a<sub>0</sub> ≈ 1.1 × 10<sup>−10</sup> ms<sup>−2</sup> . In the derivation presented here, this constant arises naturally from the cosmologically required mass of gravitons like <graphic></graphic> , with Λ, H<sub>0</sub>, and Ω<sub>Λ</sub> being the cosmological constant, the Hubble constant, and the third cosmological parameter, respectively. My derivation suggests that massive gravity could be the mechanism behind both, dark matter and dark energy.
247
- 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.
248
- 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.
249
- 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.
250
- 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.