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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4期(English)

JTAM VOL. 4 (2006)


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FieldAuthorTitleReceived DateAccepted Date
Solar SystemWing-Huen IpA Brief History of the Study of Cometary Plasma Tails(pdf檔案)Invited Articles--
X-rayChao-Yang Tsai, Yi ChouLong-term monitoring for the timing properties of the accretion-powered millisecond pulsar SAX J1808.4-3658(pdf檔案)2006.08.092006.10.05
Star γ-rayPei-Chun Hsu, Kouichi Hirotani, Hsiang Kuang ChangParticle Acceleration in Pulsar Magnetosphere(pdf檔案)2006.10.012006.10.26
Stars NebulaeFong-Yi Huang, Wen-Ping Chen, Wen-Shan HsiaoYoung stellar population in the Lupus 3 molecular cloud(pdf檔案)2006.10.312006.12.15
Solar SystemChien-Cheng Lin, Wen-Ping Chen, Zhi-Wei Zhang, Soumen MondalProbability of Stellar Occultation by KBOs in the TAOS Project(pdf檔案)2006.10.232006.12.12
----Abstracts of CAST Symposium 2006(pdf檔案)----


Title: A Brief History of the Study of Cometary Plasma Tails

Author: Wing-Huen Ip

Keywords: --

Abstract:
   A short description is given to the historical development and future prospect of the study of cometary plasma physics. It traces the beginning of cometary research at the dawn of the space age to the present time. It is also suggested that we will soon be able to study commentary activities and dynamical behaviors in other solar systems by space-born observatories.

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Title: Long-term monitoring for the timing properties of the accretion-powered millisecond pulsar SAX J1808.4-3658

Author: Chao-Yang Tsai, Yi Chou

Keywords: Low mass X-ray binary, Accretion-powered millisecond pulsar, Kilo-Hertz Quasi periodic oscillation, Burst Quasi periodic oscillation

Abstract:
   We present our analysis results of the spin and orbital properties of the first discovered accretion-powered millisecond pulsar SAX J1808.4-3658 observed by Rossi X-ray Timing Explorer (RXTE) during its 1998 and 2002 outbursts. The event arrival times are initially folded with an ephemeris consist of the neutron star spin frequency evolution plus the effect from the circular orbital motion and the parameters are then further refined according to the variation of the pulse phase. We obtain the binary barycenter neutron star spin frequency of ν = 400.975210324(2) Hz , the orbital period of Porb = 7249.158(1)s and the projected radius = 62.811(2) lt-ms from 2002 data. For the 1998 outburst, we get consistent projected radius of = 62.814(2) lt-ms but significantly different orbital period (Porb = 7249.1558(9)s ), which indicates that the orbital period derivative is ~ (7 ± 4) × 10-8yr-1. No pulsation is significant detected for 2000 and 2005 outbursts due to their low fluxes. In addition, the pulse phase variation of 1998 outburst shows a large spin-down rate of = -3.15(1) × 10-12 Hz s-1, about a factor of 100 larger than the theoretical expectation value (~10-14 Hz s-1), whereas no clear spin frequency derivative during 2002 outburst.

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Title: Particle Acceleration in Pulsar Magnetosphere

Author: Pei-Chun Hsu, Kouichi Hirotani, Hsiang Kuang Chang

Keywords: gamma-rays: theory, methods: numerical, pulsars: general

Abstract:
   We investigate a pair creation cascade in the magnetosphere of a rapidly rotating neutron star. The charge depletion due to global flows of charged particles causes a large electric field along the magnetic field lines. Electrons and positrons are accelerated by this field to radiate gamma-rays via curvature process. Some of the gamma-rays collide with the X-rays emitted from the stellar surface to materialize as pairs in the gap. The replenished charges partially screen the original electric field. To take in to account of these physical processes self-consistently, we solve the set of the Poisson equation for the electro-static potential and the Boltzmann equations for electrons, positrons, and gamma-ray photons simultaneously. In this paper, we first examine the time-dependent nature of particle accelerators by solving the non-stationary Boltzmann equations on the two-dimensional poloidal plane in which both the rotational and magnetic axes reside. Evaluating the temperature of the heated polar cap surface, which is located near the magnetic pole, by the bombardment of gap-accelerated particles, and applying the scheme to millisecond pulsar parameters, we demonstrate that the solution converges to a stationary solution of which pair-creation cascade is maintained by the heated polar-cap emission, in a wide range of three-dimensional parameter space (period, period derivative, magnetic inclination angle). We also present the deathlines of millisecond pulsars.

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Title: Young stellar population in the Lupus 3 molecular cloud

Author: Fong-Yi Huang, Wen-Ping Chen, Wen-Shan Hsiao

Keywords: star formation, T Tauri stars

Abstract:
   We report a pilot study to identify emission-line stars by use of the image database of the hydrogen-alpha survey by the United Kingdom Schmidt Telescope. The Lupus dark clouds are among the nearest star-forming regions. We analyzed a 30' × 30' field of the UK Schmidt Hα images centered around the 2 Herbig Ae stars of the Lupus 3 cloud. A list of 46 candidate T Tauri stars have been identified, among which 22 are new identifications. Seven out of these 22 Hα stars are not associated with molecular clouds, and have 2MASS colors suggestive of being classical T Tauri stars. At least two of the candidates have been spectroscopically confirmed to be T Tauri stars, while the rest are late-type dwarfs. This suggests that star formation in Lupus 3 is not limited to association with clouds, and thus the star formation history of the region should be reassessed. The UKST H-alpha database proves to be very useful, particularly in combination with 2MASS and optical spectroscopy, in study of the young stellar population in star-forming regions.

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Title: Probability of Stellar Occultation by KBOs in the TAOS Project

Author: Chien-Cheng Lin, Wen-Ping Chen, Zhi-Wei Zhang, Soumen Mondal

Keywords: Kuiper Belt objects, occultation

Abstract:
   The TAOS project aims to estimate the number of Kuiper-belt objects (KBOs) by detecting chance stellar occultation. The detected rate of such occultation events depends on the actual occurrence rate and the detectability. For the former, the relevant parameters include the distributed population of the KBOs (our goal), the surface number density and angular size distribution of background stars, and the relative shadow speed. The detectability of any event depends on the instruments and circumstances, such as the CCD integration time, sampling rate, moon phase, sky variations, diffraction effect, etc., and requires an extensive simulation to explore the parameter space. Here we report the computation of the probability of KBO occultation from a geometric consideration. With a density of 1000 stars and 104 to 106 KBOs deg-2, a relative velocity about 0".001 s-1, one would expect about 10-8 events per hour of observations.

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Title: Abstracts of CAST Symposium 2006

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