The 6th Taipei Astrophysics Workshop
- Prospects in Astronomy and Astrophysics in the New Millennium
May 16-19, 2000
ASIAA, Taipei, Taiwan

Abstracts

Hsiang-Kuang Chang, Dept. of Physics, National Tsing Hua Univ.

Magnetic Inclination of PSR B0656+14 Inferred from Its Thermal X-ray Emissions

The angle between rotation and magnetic axes of a pulsar has long been an important factor, but so far ill-determined, in accounting for its various appearances as observed in different energy bands. We devise a method to infer that angle, and the angle between observer's line of sight and the rotation axis as well, for pulsars whose X-ray spectrum has a good two-blackbody model fit. We present the result for PSR B0656+14 and discuss its implications on models for high-energy emissions from pulsars.

TBA

Wenping Chen, Natl Center Univ.

Census of Kuiper-Belt Objects

Thus far some two hundred large (size more then 100 km) Kuiper-belt objects (KBOs) have been identified by direct imaging. Even smaller bodies, though expected to be more numerous on theoretical grounds, are much too faint to image directly. A KBO can reveal its existence, nevertheless, if it happens to block out the light from a background star. The Taiwan-America Occultation Survey (TAOS) project, a collaboration of the Lawrence Livermore Laboratory (USA), Academia Sinica, National Central University (both of Taiwan), and other institutes, aims to measure the frequency of such chance stellar occultations. Our experiment provides the only means to conduct the census of the Kuiper-belt population down to a few kilometer sizes. We are setting up an array of small (50~cm), wide-field (f/1.9) telescopes in Taiwan to monitor continuously the brightness of several thousand stars at a rate of 5 Hz. These robot telescopes will operate in a coincidence mode, so the sequence and timing of any candidate occultation event can be recorded and distinguished agaist a false detection. Other scientific byproducts, such as variable star studies, will conceivably also derive from this huge TAOS database, some 10,000 GB worth of photometrical measurements per year.

Kwong-Sang Cheng, Dept. of Physics, Univ. of Hong Kong

We use a three dimension magnetospheric model to study the multi-waveband emission from pulsars. The observed light curves in various waveband and their phase-resolved spectra provide very important information about gamma-ray pulsars.

Eugene Chiang, Caltech

Dynamics of Eccentric Planetary Rings

The boundaries of several of the Uranian and Saturnian rings can be fitted by Keplerian ellipses. The pair of ellipses that outline a given ring are nearly perfectly aligned with each other. Apsidal alignment is surprising because the quadrupole moment of the central planet induces differential precession on extremely short timescales. Rigid precession of an eccentric ring has remained a problem in ring dynamics for over 20 years. I will propose that rigid precession is maintained by a balance of forces due to ring self-gravity, planetary oblateness, and interparticle collisions. Remarkably, collisional forces felt by material in the last 100m of a 10km wide ring can increase equilibrium masses up to a factor of 100. I will derive new ring surface densities that accord with Voyager radio measurements. Prospects for the Cassini Saturn orbiter will be summarized.

TBA

Wenchien Chou, ASIAA

Dynamics of the Parker-Jeans Instability in a Galactic Gaseous Disk

Linear analysis and non-linear 3D simulation of magnetohydrodynamics of a gas layer are carried out in local co-rotating coordinates, taking into account the effect of self-gravitational force and shearing rotation. The gas is subject to the Jeans instability when there is no magnetic field, or to the Parker-Jeans instability when a magnetic field is present. We study the evolution of these instabilities in several cases which vary in factors such as the rotational speed, shearing rate, strength of magnetic fields, external pressure, external gravitational force, and directions of perturbations. We find that the growth rate of the instabilities and the shape of the dense blobs that aggregate in the nonlinear stage depend sensitively on these factors. When we adopt typical parameters of nearby molecular clouds, we find that the gas forms coherent long filaments with a separation of about 5pc. This agrees with observation. This suggests that molecular clouds with a coherent filamentary structure may be attributed to the Parker-Jeans instability of a gaseous disk under the influence of rotation. This study sheds light on how interstellar/intergalactic gas aggregates to form molecular clouds and seeds of stars, and thus on the star forming process at its very early stage.

Yaoquan Chu, Univ. of Sci. & Tech. Of China, Hefei

The LAMOST project

In China, we now start to build a new spectroscopic survey telescope. It will be a meridian reflecting Schmidt telescope. The optical system is horizontal. The primary mirrors is spherical and segmented. It faces towards the north. In its spherical center there is a plane mirror which is segmented too. The different shape of reflecting Schmidt plate is realized by active optics. The clear aperture is 4m and f-ration is 5. The angular field of view is 5 square degree, 4000 objects can be observed simultaneously by using optical fibre. The science goal is to make a 20000 square degrees spectroscopic survey, including ten million galaxies and stars, many variable objects and the identification of numerous objects found by radio, x-ray, IR and other survey in this sky areas.

Wei Cui, MIT

Probing Relativistic Effects around Black Holes and Neutron Stars

I will review the basic ideas recently proposed for studying general relativistic effects around stellar-mass black holes and neutron stars, based on X-ray observations of binary systems that contain such objects.

Longlong Feng, Center for Astrophysics, Univ. of Sci. and Tech. Of China

Non-Gaussianity and the recovery of the mass power spectrum from Lyman-alpha forest

The non-Gaussianity of the cosmic density field could be the dominant source of error and inevitably leads to the information loss in power spectrum analysis. In this article, the effect of non-Gaussianity on the reconstruction of the initial mass field from the Lyman-alpha forest is investigated. It is shown that the non-Gaussianities such as skewness, kurtosis and scale-scale correlation can not be completely removed by the conventional algorithm of Gaussianization. To eliminate the effect of non- Gaussianity, two methods are proposed. The first is to perform the Gaussianization scale-by-scale using the discrete wavelet transform (DWT) decomposition. We show that the non-Gaussian features of the Lyman-alpha forest basically will no longer exist in the scale-by-scale Gaussianized mass field. The second method is to choose a proper orthonormal basis (representation) to suppress the effect of the non-Gaussian correlations. In the quasilinear regime of cosmic structure formation, the DWT power spectrum is efficient for suppressing the non-Gaussian contamination. These two methods significantly improve the recovery of the mass power spectrum from the Lyman-alpha forest.

Howard K.C. Yee, Univ. of Toronto

High-Redshift Galaxy clusters: Cosmology and Galaxy Evolution

High redshift galaxy clusters provide powerful constraints to cosmological models and scenarios of galaxy formation and evolution. I will describe a large 100sq deg optical imaging survey using the new generation of wide-field mosaic CCDs at CFHT and CTIO to generate a complete sample of rich galaxy clusters at redshift between 0.4 and 1.4. This survey will produce by far the largest high-redshift cluster sample. Some preliminary results and their implications will be presented. Also, future plans for detailed studies of amny aspcts of cluster properties, dynamics, and evolution will be discussed.

TBA

Shuang-Nan Zhang, Univ. of Alabama in Huntsville

Uncovering the Masks around the Black Holes in X-ray Binaries

We present our recent results on extensive analysis and modeling of X-ray data on several black hole X-ray binaries, obtained from several space borne high energy astrophysical instruments. Our results allow us to determine the properties of the black holes and the detailed structure of the accretion disks around them. In particular the angular momenta of the black holes are estimated for the first time and a three-layered atmospheric structure around the black holes has been discovered recently.

Dr. Zhou Xu, Beijing Astronomical Observatory

Large Field Multicolor Studies of Abell 566

Abell566 is a nearby galaxy of Z=0.1. The CCD images of BATC large field multicolor photometric system can cover the whole galaxy cluster and give spectral energy distribution (SED) of all the sources in field of Abell 566. By using BATC data on field of Abell566, following main study result on Abell 566 are: (1) Base on characteristic of morphology and spectral energy distribution, we have successfully separated the member galaxies of galaxy cluster Abell566 from field star and field galaxies. The estimated total number of the member galaxies is more than 700. That include about 400 galaxies have high reliability of membership. Before our work, the total number of member galaxies only 100 to 200 galaxies and only very few of them are identified. (2) The special distribution of red and blue galaxies are very different. The red galaxy include elliptical and early type spiral galaxies. The blue galaxies are the galaxies of other types. The red galaxies are much more condensed in center of the cluster than blue galaxies. (3) By a galaxy evolutionary model attribute by Arimoto, we analyzed the evolutionary relation among the member galaxies of the galaxy cluster.