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天文館

臺北天文館學報(出版品)

臺北天文館學報 第2期(English)

JTAM VOL. 2 (2004)


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FieldAuthorTitle
CosmologyHo Pei-Li, Chen Lin-Wen, Stephane Leon, Jean Guibert, Yan Chi-HungAlignment of Galaxy Clusters in the Shapley Supercluster(pdf檔案)
CosmologyTan Sze-Yeong, Ip Wing-HuenData Mining for Gravitational Lenses(pdf檔案)
GalaxiesWu Szu-Ying, Sun Wei-ShinNuclear Dust Features in Radio and Normal Galaxies(pdf檔案)
GalaxiesChen An-Chen, Sun Wei-ShinPhotometric Study of AGN Host Galaxies(pdf檔案)
Nebulae and Stellar ClustersWu Chih-Kang, Fu Hsieh-HaiThe Photometry, Kinematics and Dynamics of Young Open Cluster NGC 6910(pdf檔案)
StarsYang Sheng-Zhi, Chou YiThe Long Term Monitoring of Orbital Modulation for Low Mass X-Ray Binary 4U 1820-30(pdf檔案)
InstrumentationHuang Yu-Jen, Chen Wen-Ping, Zhang Zhi-WeiOccultation Detection and Field Selection for the TAOS Project(pdf檔案)
InstrumentationKinoshita Daisuke, Chen Chin-Wei, Lin Hung-Chin, Lin Zhong-Yi,
Huang Kui-Yun, Chang Yung-Shin, Chen Wen-Ping
Characteristics and Performance of the CCD Photometric System at Lulin Observatory(pdf檔案)

Title: Alignment of Galaxy Clusters in the Shapley Supercluster

Author: Ho Pei-Li, Chen Lin-Wen, Stephane Leon, Jean Guibert, Yan Chi-Hung

Keywords: Shapley supercluster, galaxy overdensity region, alignment of galaxy clusters

Abstract:
   Using a sample of ~104 galaxies in a 20°×20° sky centered on the core of the Shapley Supercluster, we identify 164 galaxy clusters/groups out of 220 detected galaxy overdensity regions in this area, including 103 previously unknown galaxy systems and 37 cluster merger candidates which consist of more than one overdensity region. Cross-checking with the FLASH redshift survey catalogue, we have further estimated the redshifts of these sources, followed by a series of statistical analysis to study the formation history of the supercluster. The clusters/groups in the Shapley Supercluster show a tendency of alignment with their nearest neighbors, and the alignment signal is stronger for the merger candidates. In addition, we note that clusters/groups with larger ellipticity are better aligned with their nearest clusters, which suggests the apparent ellipticities of clusters and their alignment angles are anti-correlated. Both results indicate that the Shapley Supercluster was formed in accordance with the anisotropic accreting scenario of galaxy clusters formation along the large scale filaments. The signal of cluster alignment with the core of the Shapley Supercluster (A3558) is however weak, only marginally detected in a few Abell clusters in the vicinity of core, thus more galaxy velocity data are required to further constrain the collapse region of the Shapley Supercluster.

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Title: Data Mining for Gravitational Lenses

Author: Tan Sze-Yeong, Ip Wing-Huen

Keywords: gravitational lensing, moments analysis, merging galaxies, arc fitting

Abstract:
   The discovery of gravitational lensing events are very import in the study of cosmology. Unlike the traditional method of discovering the strong lenses which based on direct visual inspection on over-dense region of galaxy clusters or photometry of caustic sources, our method is based on morphology. Since our method is shape-motivated, it will not only relief the task of astronomers but also capable of detecting the "dark lenses".
   We have defined a shape parameter to select the candidates efficiently. Through error analysis the arcs produced by lenses can be identified .The algorithm developed in this work has been tested on two of the gravitational lensing events found in the RCS and proved to be successful.

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Title: Nuclear Dust Features in Radio and Normal Galaxies

Author: Wu Szu-Ying, Sun Wei-Shin

Keywords: dust features, radio galaxies, normal galaxies, HST

Abstract:
   We have carried out a statistical study of a large sample of radio galaxies in order to understand how frequently we can detect nuclear optical jets, circum-nuclear dust disks, dust lanes, or dust filaments, and to further find out what the relationships are between the existence of dust features and their radio properties. A total of 46 nearby radio galaxies are selected based on their HST/WFPC2 observations, from which radio jets have been detected but without known optical jets. Galaxy model subtractions did not reveal any prominent optical features in or near the nuclei for the sample galaxies. However, among these galaxies, 22 (48%) reveal dark features such as dust disks, lanes, or even filaments. In several sample galaxies, we confirm the main morphological results published by previous authors; while in others, such as in PKS2152-69, we present our new findings of dust features. We also discuss the dust properties along with their radio properties. Further study will be conducted in order to learn more about the physics and the relationships between nuclear dust and the ambient medium.

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Title: Photometric Study of AGN Host Galaxies

Author: Chen An-Chen, Sun Wei-Shin

Keywords: Active Galactic Nucleus, Host Galaxy, Surface Brightness, Color Index, Decomposition of Intensity Profile

Abstract:
   We have obtained multi-band (BVR) photometry of a sample of 41 active galaxies, including type 1 Seyfert, type 2 Seyfert galaxies, and low ionization nuclear emission region (LINER). In order to study the physical properties of AGN host galaxies. the intensity profiles in each band are obtained. We calculate the colors of the nuclei and the effective radii using average B-V, and V-R value. We find that the Seyfert 1 galaxies have bluer nucleus color. We also caculate the nucleus-to-galaxy ratio, and find that the Seyfert 1 galaxies have higher ratio.

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Title: The Photometry, Kinematics and Dynamics of Young Open Cluster NGC 6910

Author: Wu Chih-Kang, Fu Hsieh-Hai

Keywords: open cluster, star count, King model

Abstract:
   Based on the Johnson UBV CCD photometry of a young open cluster NGC 6910 with 1.0-m telescope at Lulin Observatory of National Central University, the magnitude, extinction, reddening, distance and age of clusters are derived. The USNO-B1.0 catalogue is used for star counting method of King model.
   In the photometric calibration, it shows the standard errors 0.056 mag in U, 0.028 mag in B and 0.021 mag in V. The reddening E(B-V) is determined to be 1.11±0.16 mag. The age of NGC 6910 is estimated, using well isochrones fit, to be 4~10 Myrs and its distance modulus is 10.88.
   The magnitudes and coordinates in the USNO-B1.0 catalogue are derived from the POSS-I 103a-O blue sensitive plates. The analysis of the star counting is based on the images within the area 1°×1° centered at the cluster. The results show that the radial distribution of the stellar number density for NGC 6910 is consistent with the King’s model. The best fit gives core radius (rc) 2.48 pc, tidal radius (rt) 26.13 pc and k=12.50 stars/pc2. By adopting the Oort’s constants A = 14.4±0.8 km s-1 kpc-1, B = -12.4±0.6 km s-1 kpc-1 (Feast and Whitelock 1997), the mass of NGC 6910 is estimated to be about 6400 M⊙.

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Title: The Long Term Monitoring of Orbital Modulation for Low Mass X-Ray Binary 4U 1820-30

Author: Yang Sheng-Zhi, Chou Yi

Keywords: Low Mass X-Ray Binary, hierarchical triple system, superhump

Abstract:
   We report our analysis results of the orbital modulation for the ultra-compact low mass X-ray binary 4U 1820-30 in globular cluster NGC 6624 monitored by the Rossi X-ray Timing Explorer (RXTE) from 1998 to 2002. Clear phase drift from -0.20 to -031 as well as phase jitter of 0.034 are detected during the 1998-2000 observation period. Combined with the observation results since 1976, the orbital phase evolution is in fact better described as a cubic function rather than the quadratic model proposed by the historical reports. The cubic fitting yields the first discovered = (1.87±0.96) x 10-13 per year. We conclude that the previous period derivatives were probably underestimated due to the significant . On the other hand, the CLEAN algorithm was also applied to search the possible side bands made by a hierarchical third star (triple model) or the tidally driven modulations of the accretion disk (superhump). However, no significant (2σ upper limit) sideband was detected in our data sets.

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Title: Occultation Detection and Field Selection for the TAOS Project

Author: Huang Yu-Jen, Chen Wen-Ping, Zhang Zhi-Wei

Keywords: Solar System, Kuiper-belt Objects, Observational Technique, Statistical Analysis

Abstract:
   The Taiwan-America Occultation Survey (TAOS) aims to conduct a census of the Kuiper-belt objects (KBOs). Rather than direct imaging, the TAOS project monitors stellar light curves for chance stellar occultation by KBOs.
   Stellar occultation events by KBOs are expected to be extremely rare and each event would last in less than a second. The TAOS project makes use of a special CCD readout scheme to achieve stellar photometry sampled at a few hertzs, and requires coincidence detection by multiple telescopes to accredit an event. We report our effort to develop an image acquisition simulator program, written with MATLAB, which provides useful guidance for photometry pipelines, and for analysis of multiple-telescope data by nonparametric rank statistics. A specific application of our simulator is target field selection. We parameterize for each star field a "detectability" --- the likelihood number of occultation events detectable given the stellar distribution in a field --- with which one target field can be prioritized against another.

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Title: Characteristics and Performance of the CCD Photometric System at Lulin Observatory

Author: Kinoshita Daisuke, Chen Chin-Wei, Lin Hung-Chin, Lin Zhong-Yi, Huang Kui-Yun, Chang Yung-Shin, Chen Wen-Ping

Keywords: CCD, calibration, transformation coefficients

Abstract:
   The Lulin One-meter Telescope at Lulin Observatory in Taiwan started the open-use observations in January 2003. In order to evaluate the performance of the CCD photometric system and the characteristics and quality of the site, we have obtained the data of photometric standards as well as calibration data from February to November 2004. We report the results of our analysis including gain, readout noise, dark current and linearity of the CCD, transformation coefficients, total throughtputs, night sky brightnesses and limiting magnitudes for UBVRI bands.

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