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- 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 35/123
341
- Hanna, Magdy A.
- Journal of the Korean astronomical society = 천문학회지
- 44, n.3
- pp.97-108
- 2011
- 원문 바로보기
The photometric light curves of the W-type W UMa eclipsing contact binary system BB Pegasi have been found to be extremely asymmetric over all the observed 63 years in all wavelengths UBVR. The light curves have been characterized by occultation primary minima. Hence, the morphology of these light curves has been studied in view of these different asymmetric degrees. The system shows a distinct O'Connell effect, as well as depth variation. A 22.96 years of stellar dark spots cycle has been determined for the system. Almost the same cycle (22.78 yr) has been found for the depth variation of MinI and MinII. We also present an analysis of mid-eclipse time measurements of BB Peg. The analysis indicates a period decrement of <TEX>$5.62{\times}10^{-8}$</TEX> day/yr, which can be interpreted in terms of mass transfer at a rate of <TEX>$-4.38{\times}10^{-8}M_{\odot}$</TEX>/yr, from the more to the less massive component. The O - C diagram shows a damping sine wave covering two different cycles of 17.0 yr and 12.87 yr with amplitudes equal to 0.0071 and 0.0013 day, respectively. These unequal durations show a non-periodicity which may be explained as a result of magnetic activity cycling variations due to star spots. The obtained characteristics are consistent with similar chromospherically active stars, when applying the Applegate's (1992) mechanism.
342
- Lee, Hyun-Chul
- Journal of the Korean astronomical society = 천문학회지
- 44, n.5
- pp.195-200
- 2011
- 원문 바로보기
We have revisited the ACS Virgo Cluster Survey (ACSVCS), a Hubble Space Telescope program to obtain ACS/WFC g and z bands imaging for a sample of 100 early-type galaxies in the Virgo Cluster. In this study, we examine 51 nucleated early-type galaxies in the ACSVCS in order to look into the relationship between the photometric and structural properties of stellar nuclei and their host galaxies. We morphologically dissect galaxies into five classes. We note that (1) the stellar nuclei of dwarf early-type galaxies (dS0, dE, and dE,N) are generally fainter and bluer with g > 18.95 and (g-z) < 1.40 compared to some brighter and redder counterparts of the ellipticals (E) and lenticular galaxies (S0), (2) the g-band half-light radii of stellar nuclei of all dwarf early-type galaxies (dS0, dE, and dE,N) are smaller than 20 pc and their average is about 4 pc, and (3) the colors of red stellar nuclei with (g - z) > 1.40 in bright ellipticals and lenticular galaxies are bluer than their host galaxies colors. We also show that most of the unusually 'red' stellar nuclei with (g-z) > 1.54 in the ACSVCS are the central parts of bright ellipticals and lenticular galaxies. Furthermore, we present multi photometric band color - color plots that can be used to break the age-metallicity degeneracy particularly by inclusion of the thermally pulsing-asymptotic giant branch (TP-AGB) phases of stellar evolution in the stellar population models.
343
- Han, Cheong-Ho
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.109-113
- 2011
- 원문 바로보기
In current microlensing planet searches that are being carried out in a survey/follow-up mode, the most important targets for follow-up observations are lensing events with high magnifications resulting from the very close approach of background source stars to the lens. In this paper, we investigate the dependence of the sensitivity to planets on detailed properties of high-magnification events. From this, it is found that the sensitivity does not monotonically increase as the impact parameter between the lens and the source trajectory decreases. Instead, it is roughly the same for events with impact parameters less than a certain threshold value. It is also found that events involving main-sequence source stars are sensitive to planets in a much wider range of separation and mass ratio, than those events involved with giant source stars. Based on these results, we propose observational strategies for maximal planet detections considering the types of telescopes available for follow-up observations.
344
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 44, n.3
- pp.73-79
- 2011
- 원문 바로보기
We collect 24 times of light maxima data from sources in the literature, unpublished data and open databases, and investigate the variations of the observed and calculated (O-C) values for light maxima of V1719 Cyg. We found no evidence of the variations in the (O-C) values. We estimate the effective temperature and surface gravity using both the Kurucz and MARCS/SSG grids for different metallicity values [A/H]=0.0 and +0.5 for V1719 Cyg. It is confirmed that the temperature is almost the same, but, in the case of surface gravity, the MARCS/SSG grid gives the value closest to that obtained from the period-gravity relation derived by using the pulsation-evolution theory. We obtain two spectra of V1719 Cyg from spectroscopic observation which permitted us to find the effective temperature and the surface gravity of the star directly. We estimate the metallicity and it is found that the abundance of iron is equal to the solar value.
345
- Kim, Ji-Hoon
- Journal of the Korean astronomical society = 천문학회지
- 44, n.5
- pp.151-160
- 2011
- 원문 바로보기
We present a study searching for globular cluster systems (GCSs) of two face-on low surface bright- ness galaxies (LSBGs), UGC 5981 and UGC 6614. Based on HSTWFPC2 images of F555Wand F814W filters, we detect 12 and 18 GC candidates for UGC 5981 and UGC 6614, respectively. Although these two LSBGs have very different bulge properties, they have very similar specific frequencies (<TEX>$S_N$</TEX>) of 0.1. However, <TEX>$S_N$</TEX> ~ 0.1 is quite small even for their late morphological types, albeit within errors. This suggests that LSBGs have had star formation histories lacking dominant initial starburst events while accumulating their stellar masses through sporadic star formation activities.
346
- Lee, Jeong-Eun
- Journal of the Korean astronomical society = 천문학회지
- 44, n.2
- pp.67-72
- 2011
- 원문 바로보기
We report the results of our high resolution optical spectroscopic monitoring campaign (<TEX>${\lambda}$</TEX> = 3800 ~ 8800 <TEX>${\AA}$</TEX>, R = 30000 - 45000) of the new FU Orionis-type object HBC 722. We observed HBC 722 with the BOES 1.8-m telescope between November 26 and December 29, 2010, and FU Orionis itself on January 26, 2011. We detect a number of previously unreported high-resolution K I and Ca II lines beyond 7500 <TEX>${\AA}$</TEX>. We resolve the H<TEX>${\alpha}$</TEX> and Ca II line profiles into three velocity components, which we attribute to both disk and outflow. The increased accretion during outburst can heat the disk to produce the relatively narrow absorption feature and launch outflows appearing as high velocity blue and red-shifted broad features.
347
- Tadross, A.L.
- Journal of the Korean astronomical society = 천문학회지
- 44, n.1
- pp.1-11
- 2011
- 원문 바로보기
A sample of 145 JHK-2MASS observations of NGC open star clusters is studied, of which 132 have never been studied before. Twelve are classified as non-open clusters and 13 are re-estimated self-consistently, after applying the same methods in order to compare and calibrate our reduction procedures. The fundamental and structural parameters of the 120 new open clusters studied here are derived using color-magnitude diagrams of JHK Near-IR photometry with the fitting of solar metallicity isochrones. We provide here, for the first time, a catalog of the main parameters for these 120 open clusters, namely, diameter, distance, reddening and age.
348
- Kyeong, Jae-Mann
- Journal of the Korean astronomical society = 천문학회지
- 43, n.1
- pp.1-8
- 2010
- 원문 바로보기
JHK near-infrared photometry of star clusters in the dwarf irregular/dwarf starburst galaxy NGC 1569 are presented. After adopting several criteria to exclude other sources (foreground stars, background galaxies, etc.), 154 candidates of star clusters are identified in the near-infrared images of NGC 1569, which include very young star clusters. Especially, from analysis based on theoretical background, we found ten very young star clusters near the center of NGC 1569. The total reddening values toward these clusters are estimated to be <TEX>$A_V$</TEX>=1-9 mag from comparison with the theoretical estimates given by the Leitherer et al. (1999)'s star cluster model.
349
- Kook, Seung-Hwa
- Journal of the Korean astronomical society = 천문학회지
- 43, n.5
- pp.141-152
- 2010
- 원문 바로보기
UBV I CCD photometry is obtained for the open clusters NGC 4609 and Hogg 15 in Crux. For NGC 4609, CCD data are presented for the first time. From new photometry we derive the reddening, distance modulus and age of each cluster - NGC 4609 : E(B-V ) = <TEX>$0.37{\pm}0.03$</TEX>, <TEX>$V_0-M_V=10.60{\pm}0.08$</TEX>, log <TEX>$\tau$</TEX>= 7.7 <TEX>$\pm$</TEX> 0.1; Hogg 15 : E(B - V ) = 1.13 <TEX>$\pm$</TEX> 0.11, <TEX>$V_0-M_V$</TEX> = 12.50 <TEX>$\pm$</TEX> 0.15, log <TEX>$\tau$</TEX> <TEX>$\lesssim$</TEX> 6.6. The young age of Hogg 15 strongly implies that WR 47 is a member of the cluster. We also determine the mass function of these clusters and obtain a slope <TEX>$\Gamma$</TEX> = -1.2 (<TEX>$\pm$</TEX>0.3) for NGC 4609 which is normal and a somewhat shallow slope (<TEX>${\Gamma}=-0.95{\pm}0.5$</TEX>) for Hogg 15.
350
- Im, Myung-Shin
- Journal of the Korean astronomical society = 천문학회지
- 43, n.3
- pp.75-93
- 2010
- 원문 바로보기
We present the characteristics of the Seoul National University 4k Camera (SNUCAM) and report its performance on the 1.5m telescope at the Maidanak observatory in Uzbekistan. SNUCAM is a CCD camera with a pixel scale of 0.266' in <TEX>$4096{\times}4096$</TEX> format, covering <TEX>$18.1'{\times}18.1'$</TEX> field of view on the 1.5m. The camera is currently equipped with Bessell UBVRI, <TEX>$H{\alpha}$</TEX>, SDSS ugriz, and Y-band filters, allowing us to carry out a variety of scientific programs ranging from exoplanet studies to survey of quasars at high redshift. We examine properties of SNUCAM such as the bias level and its temporal variation, the dark current, the readout noise, the gain, the linearity, the fringe patterns, the amplifier bias, and the bad pixels. From our observations, we also constructed the master fringe frames in I-, z-, and Y-band. We outline some of the current scientific programs being carried out with SNUCAM, and demonstrate that SNUCAM on the 1.5m can deliver excellent images that reach to the <TEX>$5-{\sigma}$</TEX> detection limits of R~25.5 mag and z~22.7 mag in 1 hour total integration.