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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 53/122
521
- IZUMIURA HIDEYUKI
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.81-84
- 2005
- 원문 바로보기
We are undertaking an extra-solar planet search around G-type giant stars by means of Doppler technique using an iodine absorption cell installed to the high dispersion echelle spectrograph for the 188 cm reflector at Okayama Astrophysical Observatory (Okayama Planet Search Program, OPSP). Having detected the first planet candidate (Sato et al. 2003)the search has been proved very promising. Taking advantage of this success, we are trying to develop OPSP to an international collaborative work. We here report the current status of our efforts for establishing such collaborations, namely, those with Chinese and Korean astronomers. We also propose to establish an East-Asian network to search for extra-solar planets around G-type giant stars with the transit detecting technique as well as the Doppler technique, asking other persons/groups to join us to enjoy the planet search.
522
- KAIFU NORIO
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.325-328
- 2005
- 원문 바로보기
I report here about the future direction of cooperation of astronomy in East Asia region, which has been a long-years subject of the EAMA since 1990. During this EAMA-6 we had many positive discussions and remarkable progress toward the promotion of our cooperation. We also had an 'East Asian Observatory' WG meeting yesterday with many attendants, and actively discussed this important subject in some detail. The following report is to summarize the fruitful products we had in the EAMA-6 discussions and in past EAMA activities, and to propose a direction and some action items toward the bright future of astronomy in East Asia.
523
- LYO A-RAN
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.241-244
- 2005
- 원문 바로보기
We have analysed near-infrared JHKL observations of the members of the <TEX>$\approx$</TEX>9 Myr-old <TEX>$\eta$</TEX> Chamaeleontis cluster. Using (J - H)/(K - L) and (H - K)/(K - L) IR colour-colour diagrams for the brightest 15 members of the cluster, we find the fraction of stellar systems with near-IR excess emission was 0.60 <TEX>$\pm$</TEX> 0.13 (2<TEX>$\sigma$</TEX>). For the CTT and WTT star population, we also find a strong correlation between the IR excess and Ha emission which is also known as an accretion indicator. The (K - L) excess of these stars appears to indicate a wide range of star-disk activity; from a CTT star with high levels of accretion, to CTT - WTT transitional objects with evidence for some on-going accretion, and WTT stars with weak or absent IR excesses. Among the brightest 15 members, four stars (RECX 5, 9, 11 and ECHA J0843.3-7905) with IR excesses <TEX>${\Delta}$</TEX>(K - L) > 0.4 mag and strong or variable optical emission were identified as likely experiencing on-going mass accretion from their circumstellar disks which we confirmed their accretion disks from the optical high-resolution echelle spectroscopic study. The result-ing accretion fraction of 0.27 <TEX>$\pm$</TEX> 0.13 (2<TEX>$\sigma$</TEX>) suggests that the accretion phase, in addition to the disks themselves, can endure for at least <TEX>${\~}$</TEX>10 Myr.
524
- KAWASAKI WATARU
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.141-144
- 2005
- 원문 바로보기
Based on optical galaxy data, we executed a systematic search for galaxy clusters around the 15 steady unidentified EGRET GeV gamma-ray sources in high Galactic-latitude sky ([b] > <TEX>$30^{\circ}$</TEX>). We found a strong correlation with 3.7<TEX>$\sigma$</TEX> level between close cluster pairs (merging cluster candidates) and the unidentified EGRET sources, though, in contrast, no correlation with single clusters. This result implies that merging clusters of galaxies are a possible candidate for the origin of high galactic-latitude, steady unidentified EGRET gamma-ray sources.
525
- KANG HYESUNG
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.225-232
- 2004
- 원문 바로보기
Shocks are ubiquitous in astrophysical environments and cosmic-rays (CRs) are known to be accelerated at collisionless shocks via diffusive shock acceleration. It is believed that the CR pressure is important in the evolution of the interstellar medium of our galaxy and most of galactic CRs with energies up to <TEX>${\~}\;10^{15}$</TEX> eV are accelerated by supernova remnant shocks. In this contribution we have studied the CR acceleration at shocks through numerical simulation of 1D, quasi-parallel shocks for a wide range of shock Mach numbers and shock speeds. We show that CR modified shocks evolve to time-asymptotic states by the time injected particles are accelerated to moderately relativistic energies, and that two shocks with the same Mach number, but with different shock speeds, evolve qualitatively similarly when the results are presented in terms of a characteristic diffusion length and diffusion time. We find that <TEX>$10^{-4} - 10^{-3}$</TEX> of the particles passed through the shock are accelerated to form the CR population, and the injection rate is higher for shocks with higher Mach number. The time asymptotic value for the CR acceleration efficiency is controlled mainly by shock Mach number, and high Mach number shocks all evolve towards efficiencies <TEX>${\~}50\%$</TEX>, regardless of the injection rate and upstream CR pressure. We conclude that the injection rates in strong quasi-parallel shocks are sufficient to lead to significant nonlinear modifications to the shock structures, implying the importance of the CR acceleration at astrophysical shocks.
526
- RHEE MYUNG-HYUN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.1
- pp.15-39
- 2004
- 원문 바로보기
We analyse the results of mass models derived from the HI rotation! curves of spiral galaxies and find that the slope of the luminous mass-circular velocity relation is close to 4. The luminous mass-circular velocity relation with a slope of about 4 can be explained by an anti-correlation between the mass surface density of luminous matter and the mass ratio of the dark and luminous components. We also argue that the conspiracy between luminous and dark matter exists in a local sense (producing a flat or smooth rotation curve) and in a global sense (affecting the mass ratio of the dark and luminous matter), maintaining the luminous mass-circular velocity relation with a slope of about 4. We therefore propose that the physical basis of the Tully-Fisher relation lies in the luminous mass-circular velocity relation. While the slope of the luminous mass-circular velocity relation is fairly well defined regardless of the dark matter contribution, the zero-point of the relation is still to be determined. The determination of the slope of the Tully-Fisher relation needs one more step: the mean trend of the luminosity-luminous mass relation determines the overall shape (slope) of the Tully-Fisher relation. The key parameter needed to determine the zero-point of the luminous mass-circular velocity relation and the slope of the Tully-Fisher relation obviously is the luminous mass-to-light ratio.
527
- TREGILLIS I. L.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.509-515
- 2004
- 원문 바로보기
We present results from an extensive synthetic observation analysis of numerically-simulated radio galaxy (RG) jets. This analysis is based on the first three-dimensional simulations to treat cosmic ray acceleration and transport self-consistently within a magnetohydrodynamical calculation. We use standard observational techniques to calculate both minimum-energy and inverse-Compton field values for our simulated objects. The latter technique provides meaningful information about the field. Minimum-energy calculations retrieve reasonable field estimates in regions physically close to the minimum-energy partitioning, though the technique is highly susceptible to deviations from the underlying assumptions. We also study the reliability of published rotation measure analysis techniques. We find that gradient alignment statistics accurately reflect the physical situation, and can uncover otherwise hidden information about the source. Furthermore, correlations between rotation measure (RM) and position angle (PA) can be significant even when the RM is completely dominated by an external cluster medium.
528
- HWANG CHORNG- YUAN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.461-463
- 2004
- 원문 바로보기
We investigate the role of secondary electrons in galaxy clusters and in ultra-luminous infrared galaxies (ULIGs). The radio emission in galaxy clusters and ULIGs is believed to be produced by the synchrotron radiation of relativistic electrons. Nonetheless, the sources of these relativistic electrons are still unclear. Relativistic secondary electrons can be produced from the hadronic interactions of cosmic-ray nuclei with the intra-cluster media (ICM) of galaxy clusters and the dense molecular clouds of ULIGs. We estimate the contribution of the secondary electrons in galaxy clusters and ULIGs by comparing observational results with theoretical calculations for the radio emission in these sources. We find that the radio halos of galaxy clusters can not be produced from the secondary electrons; on the other hand, at least for some ULIGs, the radio emission can be dominated by the synchrotron emission of the secondary electrons.
529
- BIERMANN PETER L.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.527-531
- 2004
- 원문 바로보기
It is argued that the key task in understanding magnetic fields in the cosmos is to comprehend the origin of their order or coherence over large length scales in galaxies. Obtaining magnetic fields can be done in stars, whose lifetime is usually <TEX>$10^{10}$</TEX> rotations, while galactic disks have approximately 20 to 50 rotations in their lifetime since the last major merger, which established the present day gaseous disk. Disorder in the galactic magnetic fields is injected on the disk time scale of about 30 million years, about a tenth of the rotation period, so after one half rotation already it should become completely disordered. Therefore whatever mechanism Nature is using, it must compete with such a short time scale, to keep order in its house. This is the focal quest.
530
- KOCH PATRICK
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.471-476
- 2004
- 원문 바로보기
We propose an analytical model to estimate the influence of a merger on the thermal SZ effect. Following observations we distinguish between subsonic and transonic mergers. Using analytical velocity fields and the Bernoulli equation we calculate the excess pressure around a moving subcluster for an incompressible subsonic gas. Positive excess around the stagnation point and negative excess on the side of the subcluster lead to characteristic signatures in the SZ map, of the order of <TEX>$10\%$</TEX> compared to the unperturbed signal. For a transonic merger we calculate the change in the thermal spectral SZ function, resulting from bow shock accelerated electrons. The merger shock compression factor determines the power law tail of the new non-thermal electron population and is directly related to a shift in the crossover frequency. This shift is typically a few percent towards higher frequencies.