CJAA, 2001, Vol.1, No.3

2001, Vol.1, No.3 (June 20, 2001) Contents

LETTER A Large Glitch in the Crab Pulsar Na Wang, Xin-Ji Wu, R. N. Manchester, Jin Zhang, A. G. Lyne and Aili Yusup ......................................................... p.195 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) RESEARCH PAPERS A DWT Power Spectrum Analysis of PSCz Galaxies Xiao-Hu Yang, Long-Long Feng and Yao-Quan Chu .......................... p.200 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Doppler Effect and Spectral Energy Distribution of Blazars Guang-Zhong Xie, Ben-Zhong Dai, Dong-Cheng Mei and Jun-Hui Fan ........ p.213 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) Soft X-ray Properties of Ultraluminous IRAS Galaxies Xiao-Yang Xia, Th. Boller, Zu-Gan Deng, G. Börner ...................... p.221 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) Periodic Variations of the Jet Flow Lorentz Factor in 3C 273 Shan-Jie Qian, Xi-Zhen Zhang, T. P. Krichbaum, J. A. Zensus, A. Witzel, A. Kraus, S. Britzen, H. Ungerechts and U. Lisenfeld ........ p.236 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Optical Variability of 3C 273 Rui-Guang Lin .......................................................... p.245 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) L183, a Quiescent Core? Jian-Jun Zhou, Xing-Wu Zheng and Yu-Xi Chen ............................ p.250 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Peak Luminosity of Type Ia Supernovae and its Implications for the Cosmic Expansion Rate Xiao-Feng Wang, Zong-Wei Li and Li Chen ................................ p.257 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Third Peak of the 1998 Leonid Meteor Shower Yue-Hua Ma and You-Wen He .............................................. p.271 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Figure and Dynamical Parameters of Io Inferred from Internal Structure Models Hong Zhang and Cheng-Zhi Zhang ......................................... p.275 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) Orbit Determination Using Satellite-to-Satellite Tracking Data Ying-Chun Liu and Lin Liu .............................................. p.281 Abstract \| \| PDF \| PS (.gz) \| PS (.zip)
Abstract
A Large Glitch in the Crab Pulsar Na Wang, Xin-Ji Wu, R. N. Manchester, Jin Zhang, A. G. Lyne and Aili Yusup E-mail: wangna@bac.pku.edu.cn Abstract Using a new pulsar timing system at the 25-m radio telescope of Urumqi Astronomical Observatory, we have detected a large glitch in the Crab pulsar which occurred in 2000 July. The size of the glitch is $\Delta\nu/\nu \sim 2.4\times 10^{-8}$ , with a relative increment in frequency derivative $\Delta\dot{\nu}/\dot{\nu} \sim 5\times 10^{-3}$ . The observing system is introduced and the observed properties of the glitch are discussed. Key words: Stars:neutron --- pulsars:general PDF \| gzipped PS file \| zipped PS file \| Back to Contents
A DWT Power Spectrum Analysis of PSCz Galaxies Xiao-Hu Yang, Long-Long Feng and Yao-Quan Chu E-mail: xhyang@mail.ustc.edu.cn Abstract The power spectrum estimator based on the Discrete Wavelet Transformation (DWT) is applied to detect the clustering power in the IRAS Point Source Catalog Redshift Survey (PSCz). Comparison with mock samples extracted from N-body simulation shows that the DWT power spectrum estimator could provide a robust measurement of banded fluctuation power over a range of wavenumbers 0.1 $\sim$ 2.0 h Mpc^-1. We have fitted three typical CDM models (SCDM, $\tau$ CDM) using the Peacock-Dodds formula including non-linear evolution and redshift distortion. We find that, our results are in good agreement with other statistical measurements of the PSCz. Key words: large-scale structure of Universe --- Methods: N-body simulations PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Doppler Effect and Spectral Energy Distribution of Blazars Guang-Zhong Xie, Ben-Zhong Dai, Dong-Cheng Mei and Jun-Hui Fan E-mail: gzxie@public.km.yn.cn Abstract The relativistic beaming model is adopted to discuss quantitatively the observational differences between radio-selected BL Lac objects (RBLs) and X-ray-selected BL Lac objects (XBLs), and between BL Lac objects and flat spectrum radio quasars (FSRQs). The main results are the following: (1) In the Doppler corrected color-color ( $\alpha^{\rm in}_{\rm ro} - \alpha^{\rm in}_{\rm ox}$ ) diagram, XBLs and FSRQs occupy separated regions, while RBLs bridge the gap between them. These properties suggest that similar intrinsic physical processes operate in all the objects under a range of intrinsic physical conditions. (2) Our results are consistent with the results of Sambruna, Maraschi and Urry (1996) from other methods. We show the ( $\alpha_{xox}$ ) introduced by Sambruna to be a good index for describing the energy distribution because it represents the intrinsic energy distribution and includes the Doppler correction. (3) The Doppler effect of relativistic beaming is the main mechanism, and the physical differences (such as magnetic fields, electron energies) are also important complementary factors for understanding the relation between XBLs and RBLs; Key words: Blazars: general --- quasars: general --- radiation mechanism: nonthermal PDF \| gzipped PS file \| zipped PS file \| Back to Contents
Soft X-ray Properties of Ultraluminous IRAS Galaxies Xiao-Yang Xia, Th. Boller, Zu-Gan Deng, G. Börner E-mail: xyxia@bac.pku.edu.cn Abstract We report on the results of cross-correlation of a sample of 903 Ultraluminous IRAS galaxies (ULIRGs) with the ROSAT-All Sky Survey Bright Source Catalogue and the ROSAT archived pointing observations. The sample of ULIRGs has been compiled from the recently released PSCz redshift survey. In total, 35 ULIRGs are securely detected by the ROSAT All-Sky Survey and pointing observations, five of which are blazars. The statistical properties of these sources in the soft X-ray band are determined and compared with their properties in other wavebands. We find that the ratio of the soft X-ray to the far-infrared flux spans about five orders of magnitude and reaches values of about unity. This ratio is a good indicator of the main energy source of ULIRGs. Those with soft X-ray to far-infrared flux exceeding 0.01 are probably powered by accretion onto central supermassive black holes while those with ratios smaller than 0.001 are probably powered by starbursts or other heating processes, or are Compton thick sources. Some ULIRGs have energy contributions from both. This ratio is low for most ULIRGs and hyperluminous infrared galaxies, which explains their low detection rate by ROSAT and ASCA. We also find that some ULIRGs have a similar soft X-ray luminosity vs. temperature relation to that for groups of galaxies and elliptical galaxies, suggesting a common origin of these systems. Our study also reveals a tight correlation between the hardness ratio and the soft X-ray luminosity for Seyfert 1s/QSOs. Key words: Infrared: galaxies --- X-rays: galaxies --- Galaxies: active --- Galaxies: Seyfert --- Galaxies: interactions PDF \| gzipped PS file \| zipped PS file \| Back to Contents
Periodic Variations of the Jet Flow Lorentz Factor in 3C 273 Shan-Jie Qian, Xi-Zhen Zhang, T. P. Krichbaum, J. A. Zensus, A. Witzel, A. Kraus, S. Britzen, H. Ungerechts and U. Lisenfeld E-mail: rqsj@class1.bao.ac.cn Abstract 3C 273 has been observed with VLBI for more than 30 years. The entire data have shown that the position angle of the superluminal knots ejected from the core varies periodically with a period of $\sim$ 15 years. Moreover, their apparent velocity observed during the period 1963 -- 1997 has systematically decreased by a factor of $\stackrel {$\gt}_{\sim}$ 2. These remarkable properties are explained in terms of a precessing jet model, in which the ejection Lorentz factor of the superluminal knots has been decreasing during the last thirty years and has superposed on it a short-term ( $\sim$ 5 year) oscillation. The periodic variations derived by the model-fitting are compared with the variations in the optical flux density. Binary black hole models are briefly discussed to show possible relations of the observed periods to the periods involved in a binary system (orbital motion, spin of black hole, accretion-disk rotation and Newtonian-driven precession etc.). Key words: Galaxies: jets --- quasars: individual: 3C 273 --- Galaxies: nuclei --- Radio continuum: galaxies --- Radiation mechanisms: nonthermal PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Optical Variability of 3C 273 Rui-Guang Lin E-mail: lin_rg@163.net Abstract B-band measurements of 3C 273 over some 110 years are compiled and used in a search for periodicities using the Jurkevich method. Periods of 2.0, 13.65 $\pm$ 0.20 and 22.5 $\pm$ 0.2 yr are found. If the long-term periodicity is from the instability of a slim disk, then the periodicity ( $\sim$ 13-yr or $\sim$ 22-yr) suggests masses of 10⁷ $M_{\odot}$ for the central black holes. Key words: Galaxies: active --- Galaxies: individual: 3C 273 PDF \| gzipped PS file \| zipped PS file \| Back to Contents
L183, a Quiescent Core? Jian-Jun Zhou, Xing-Wu Zheng and Yu-Xi Chen Abstract Some observed results of NH₃ (1,1) and (2,2) line emission in the starless dark cloud L183 are reported. Our observation suggests that the dense core of L183 has a size of $\sim$ 0.16 pc × 0.1 pc with a mass of $\sim$ 12 $M_{\odot}$ . A velocity gradient of 4 km s^-1 pc^-1 from the north to the south was detected. The velocity shift corresponds to a central mass of $\sim$ 5 $M_{\odot}$ . If it is caused by rotation, the mass would be much less than the value above. This suggests that there may be more mass in the envelope of L183 than in the central region. The analysis of our data and the evidence in the literature about L183 indicate that it may be undergoing a process of collapsing to form a low-mass binary dense core. Key words: ISM: clouds --- Stars: formation --- Stars: low-mass PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Peak Luminosity of Type Ia Supernovae and its Implications for the Cosmic Expansion Rate Xiao-Feng Wang, Zong-Wei Li and Li Chen E-mail: lizw@bnu.edu.cn Abstract Supernovae of type Ia (SNe Ia) are confirmed to be the best distance indicators to derive the cosmic expansion rate. The dispersion of their peak luminosity at optical bands (BVI) is approximate to 0.13 mag, after taking into account the effects of the second parameters (i.e., the initial decline rate $\Delta$ m₁₅(B) and (B-V) color at maximum light). The local calibrations from HST indicate an absolute magnitude of 19.48 $\pm$ 0.08 mag (in V band) for SNe Ia in spiral galaxies. The current expansion rate, H₀, is found to be 63.6 $\pm$ 1.8 (random) $\pm$ 5.7 km s^-1 Mpc^-1 (systematic). This value will decrease by 3% when the metallicity effect on the cepheid distances is considered. In addition, a marginal local outward flow of 4.0 $\pm$ 4.5% within the velocity-distance of 7000 km s^-1 can be inferred from SNe Ia for the Einstein-de Sitter universe; however, this outward flow is only 2.2 $\pm$ 4.4% for an accelerating expansion universe (which is supported by high-z SNe Ia). Key words: Cosmology: observations --- distance scale --- supernovae: general PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Third Peak of the 1998 Leonid Meteor Shower Yue-Hua Ma and You-Wen He E-mail: yhma@mail.pmo.ac.cn Abstract The Leonid meteor shower in November 1998 was observed widely by astronomers. The first peak, rich in bright meteors, appeared about 16 hours before the predicted maximum of the main shower. The main shower was also observed by both optical and radio methods during 19:00--21:00 UT on Nov.17, and the radio peak was over 2500 h^-1. About 18 hours after the main shower, an abnormal phenomenon in the ionosphere was detected by two separate ionosphere observing stations. And the very high abnormal phenomenon maintained over one hour. The phenomenon showed that the ionosphere was injected with a large amount of small dust particles that could not be observed in optical and radio. The observational results show that the Leonid meteor shower in 1998 had three peaks. Key words: Meteors: Leonid meteor shower PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Figure and Dynamical Parameters of Io Inferred from Internal Structure Models Hong Zhang and Cheng-Zhi Zhang E-mail: jupiter@nju.edu.cn Abstract The recent Galileo spacecraft explored Jupiter and its satellite system and provided us with new geodetic data. In order to discuss the dynamical parameters and secular tidal effect of Io, the theory of synchronous satellite is described in detail. Using the new geodetic data of Io, two sets of Io's internal structure models are constructed based on the asthenosphere assumption. The liberation parameters $\alpha$ , $\beta$ , $\gamma$ and dynamical flattening H are calculated for the models of Io. A comparison of Io with the Moon indicates that they are quite different in many characteristics in spite of the fact that they are approximately equal in mass and size and that they both orbit synchronously. Key words: Io --- synchronous orbit --- dynamical parameters PDF \| gzipped PS file \| zipped PS file \| Back to Contents
Orbit Determination Using Satellite-to-Satellite Tracking Data Ying-Chun Liu and Lin Liu E-mail: liuyc99@263.net Abstract Satellite-to-Satellite Tracking (SST) data can be used to determine the orbits of spacecraft in two ways. One is combined orbit determination, which combines SST data with ground-based tracking data and exploits the enhanced tracking geometry. The other is the autonomous orbit determination, which uses only SST. The latter only fits some particular circumstances since it suffers the rank defect problem in other circumstances. The proof of this statement is presented. The nature of the problem is also investigated in order to find an effective solution. Several methods of solution are discussed. The feasibility of the methods is demonstrated by their application to a simulation. Key words: Celestial mechanics: orbit determination --- Methods: miscellaneous PDF \| gzipped PS file \| zipped PS file \| Back to Contents

Chinese Journal of Astronomy and Astrophysics: Online Edition

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Copyright 2001--2007 All rights reserved. The National Astronomical Observatories of
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2001, Vol.1, No.3 (June 20, 2001) Contents

LETTER A Large Glitch in the Crab Pulsar Na Wang, Xin-Ji Wu, R. N. Manchester, Jin Zhang, A. G. Lyne and Aili Yusup ......................................................... p.195 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) RESEARCH PAPERS A DWT Power Spectrum Analysis of PSCz Galaxies Xiao-Hu Yang, Long-Long Feng and Yao-Quan Chu .......................... p.200 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Doppler Effect and Spectral Energy Distribution of Blazars Guang-Zhong Xie, Ben-Zhong Dai, Dong-Cheng Mei and Jun-Hui Fan ........ p.213 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) Soft X-ray Properties of Ultraluminous IRAS Galaxies Xiao-Yang Xia, Th. Boller, Zu-Gan Deng, G. Börner ...................... p.221 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) Periodic Variations of the Jet Flow Lorentz Factor in 3C 273 Shan-Jie Qian, Xi-Zhen Zhang, T. P. Krichbaum, J. A. Zensus, A. Witzel, A. Kraus, S. Britzen, H. Ungerechts and U. Lisenfeld ........ p.236 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Optical Variability of 3C 273 Rui-Guang Lin .......................................................... p.245 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) L183, a Quiescent Core? Jian-Jun Zhou, Xing-Wu Zheng and Yu-Xi Chen ............................ p.250 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Peak Luminosity of Type Ia Supernovae and its Implications for the Cosmic Expansion Rate Xiao-Feng Wang, Zong-Wei Li and Li Chen ................................ p.257 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Third Peak of the 1998 Leonid Meteor Shower Yue-Hua Ma and You-Wen He .............................................. p.271 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) The Figure and Dynamical Parameters of Io Inferred from Internal Structure Models Hong Zhang and Cheng-Zhi Zhang ......................................... p.275 Abstract \| \| PDF \| PS (.gz) \| PS (.zip) Orbit Determination Using Satellite-to-Satellite Tracking Data Ying-Chun Liu and Lin Liu .............................................. p.281 Abstract \| \| PDF \| PS (.gz) \| PS (.zip)
Abstract
A Large Glitch in the Crab Pulsar Na Wang, Xin-Ji Wu, R. N. Manchester, Jin Zhang, A. G. Lyne and Aili Yusup E-mail: wangna@bac.pku.edu.cn Abstract Using a new pulsar timing system at the 25-m radio telescope of Urumqi Astronomical Observatory, we have detected a large glitch in the Crab pulsar which occurred in 2000 July. The size of the glitch is $\Delta\nu/\nu \sim 2.4\times 10^{-8}$ , with a relative increment in frequency derivative $\Delta\dot{\nu}/\dot{\nu} \sim 5\times 10^{-3}$ . The observing system is introduced and the observed properties of the glitch are discussed. Key words: Stars:neutron --- pulsars:general PDF \| gzipped PS file \| zipped PS file \| Back to Contents
A DWT Power Spectrum Analysis of PSCz Galaxies Xiao-Hu Yang, Long-Long Feng and Yao-Quan Chu E-mail: xhyang@mail.ustc.edu.cn Abstract The power spectrum estimator based on the Discrete Wavelet Transformation (DWT) is applied to detect the clustering power in the IRAS Point Source Catalog Redshift Survey (PSCz). Comparison with mock samples extracted from N-body simulation shows that the DWT power spectrum estimator could provide a robust measurement of banded fluctuation power over a range of wavenumbers 0.1 $\sim$ 2.0 h Mpc^-1. We have fitted three typical CDM models (SCDM, $\tau$ CDM) using the Peacock-Dodds formula including non-linear evolution and redshift distortion. We find that, our results are in good agreement with other statistical measurements of the PSCz. Key words: large-scale structure of Universe --- Methods: N-body simulations PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Doppler Effect and Spectral Energy Distribution of Blazars Guang-Zhong Xie, Ben-Zhong Dai, Dong-Cheng Mei and Jun-Hui Fan E-mail: gzxie@public.km.yn.cn Abstract The relativistic beaming model is adopted to discuss quantitatively the observational differences between radio-selected BL Lac objects (RBLs) and X-ray-selected BL Lac objects (XBLs), and between BL Lac objects and flat spectrum radio quasars (FSRQs). The main results are the following: (1) In the Doppler corrected color-color ( $\alpha^{\rm in}_{\rm ro} - \alpha^{\rm in}_{\rm ox}$ ) diagram, XBLs and FSRQs occupy separated regions, while RBLs bridge the gap between them. These properties suggest that similar intrinsic physical processes operate in all the objects under a range of intrinsic physical conditions. (2) Our results are consistent with the results of Sambruna, Maraschi and Urry (1996) from other methods. We show the ( $\alpha_{xox}$ ) introduced by Sambruna to be a good index for describing the energy distribution because it represents the intrinsic energy distribution and includes the Doppler correction. (3) The Doppler effect of relativistic beaming is the main mechanism, and the physical differences (such as magnetic fields, electron energies) are also important complementary factors for understanding the relation between XBLs and RBLs; Key words: Blazars: general --- quasars: general --- radiation mechanism: nonthermal PDF \| gzipped PS file \| zipped PS file \| Back to Contents
Soft X-ray Properties of Ultraluminous IRAS Galaxies Xiao-Yang Xia, Th. Boller, Zu-Gan Deng, G. Börner E-mail: xyxia@bac.pku.edu.cn Abstract We report on the results of cross-correlation of a sample of 903 Ultraluminous IRAS galaxies (ULIRGs) with the ROSAT-All Sky Survey Bright Source Catalogue and the ROSAT archived pointing observations. The sample of ULIRGs has been compiled from the recently released PSCz redshift survey. In total, 35 ULIRGs are securely detected by the ROSAT All-Sky Survey and pointing observations, five of which are blazars. The statistical properties of these sources in the soft X-ray band are determined and compared with their properties in other wavebands. We find that the ratio of the soft X-ray to the far-infrared flux spans about five orders of magnitude and reaches values of about unity. This ratio is a good indicator of the main energy source of ULIRGs. Those with soft X-ray to far-infrared flux exceeding 0.01 are probably powered by accretion onto central supermassive black holes while those with ratios smaller than 0.001 are probably powered by starbursts or other heating processes, or are Compton thick sources. Some ULIRGs have energy contributions from both. This ratio is low for most ULIRGs and hyperluminous infrared galaxies, which explains their low detection rate by ROSAT and ASCA. We also find that some ULIRGs have a similar soft X-ray luminosity vs. temperature relation to that for groups of galaxies and elliptical galaxies, suggesting a common origin of these systems. Our study also reveals a tight correlation between the hardness ratio and the soft X-ray luminosity for Seyfert 1s/QSOs. Key words: Infrared: galaxies --- X-rays: galaxies --- Galaxies: active --- Galaxies: Seyfert --- Galaxies: interactions PDF \| gzipped PS file \| zipped PS file \| Back to Contents
Periodic Variations of the Jet Flow Lorentz Factor in 3C 273 Shan-Jie Qian, Xi-Zhen Zhang, T. P. Krichbaum, J. A. Zensus, A. Witzel, A. Kraus, S. Britzen, H. Ungerechts and U. Lisenfeld E-mail: rqsj@class1.bao.ac.cn Abstract 3C 273 has been observed with VLBI for more than 30 years. The entire data have shown that the position angle of the superluminal knots ejected from the core varies periodically with a period of $\sim$ 15 years. Moreover, their apparent velocity observed during the period 1963 -- 1997 has systematically decreased by a factor of $\stackrel {$\gt}_{\sim}$ 2. These remarkable properties are explained in terms of a precessing jet model, in which the ejection Lorentz factor of the superluminal knots has been decreasing during the last thirty years and has superposed on it a short-term ( $\sim$ 5 year) oscillation. The periodic variations derived by the model-fitting are compared with the variations in the optical flux density. Binary black hole models are briefly discussed to show possible relations of the observed periods to the periods involved in a binary system (orbital motion, spin of black hole, accretion-disk rotation and Newtonian-driven precession etc.). Key words: Galaxies: jets --- quasars: individual: 3C 273 --- Galaxies: nuclei --- Radio continuum: galaxies --- Radiation mechanisms: nonthermal PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Optical Variability of 3C 273 Rui-Guang Lin E-mail: lin_rg@163.net Abstract B-band measurements of 3C 273 over some 110 years are compiled and used in a search for periodicities using the Jurkevich method. Periods of 2.0, 13.65 $\pm$ 0.20 and 22.5 $\pm$ 0.2 yr are found. If the long-term periodicity is from the instability of a slim disk, then the periodicity ( $\sim$ 13-yr or $\sim$ 22-yr) suggests masses of 10⁷ $M_{\odot}$ for the central black holes. Key words: Galaxies: active --- Galaxies: individual: 3C 273 PDF \| gzipped PS file \| zipped PS file \| Back to Contents
L183, a Quiescent Core? Jian-Jun Zhou, Xing-Wu Zheng and Yu-Xi Chen Abstract Some observed results of NH₃ (1,1) and (2,2) line emission in the starless dark cloud L183 are reported. Our observation suggests that the dense core of L183 has a size of $\sim$ 0.16 pc × 0.1 pc with a mass of $\sim$ 12 $M_{\odot}$ . A velocity gradient of 4 km s^-1 pc^-1 from the north to the south was detected. The velocity shift corresponds to a central mass of $\sim$ 5 $M_{\odot}$ . If it is caused by rotation, the mass would be much less than the value above. This suggests that there may be more mass in the envelope of L183 than in the central region. The analysis of our data and the evidence in the literature about L183 indicate that it may be undergoing a process of collapsing to form a low-mass binary dense core. Key words: ISM: clouds --- Stars: formation --- Stars: low-mass PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Peak Luminosity of Type Ia Supernovae and its Implications for the Cosmic Expansion Rate Xiao-Feng Wang, Zong-Wei Li and Li Chen E-mail: lizw@bnu.edu.cn Abstract Supernovae of type Ia (SNe Ia) are confirmed to be the best distance indicators to derive the cosmic expansion rate. The dispersion of their peak luminosity at optical bands (BVI) is approximate to 0.13 mag, after taking into account the effects of the second parameters (i.e., the initial decline rate $\Delta$ m₁₅(B) and (B-V) color at maximum light). The local calibrations from HST indicate an absolute magnitude of 19.48 $\pm$ 0.08 mag (in V band) for SNe Ia in spiral galaxies. The current expansion rate, H₀, is found to be 63.6 $\pm$ 1.8 (random) $\pm$ 5.7 km s^-1 Mpc^-1 (systematic). This value will decrease by 3% when the metallicity effect on the cepheid distances is considered. In addition, a marginal local outward flow of 4.0 $\pm$ 4.5% within the velocity-distance of 7000 km s^-1 can be inferred from SNe Ia for the Einstein-de Sitter universe; however, this outward flow is only 2.2 $\pm$ 4.4% for an accelerating expansion universe (which is supported by high-z SNe Ia). Key words: Cosmology: observations --- distance scale --- supernovae: general PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Third Peak of the 1998 Leonid Meteor Shower Yue-Hua Ma and You-Wen He E-mail: yhma@mail.pmo.ac.cn Abstract The Leonid meteor shower in November 1998 was observed widely by astronomers. The first peak, rich in bright meteors, appeared about 16 hours before the predicted maximum of the main shower. The main shower was also observed by both optical and radio methods during 19:00--21:00 UT on Nov.17, and the radio peak was over 2500 h^-1. About 18 hours after the main shower, an abnormal phenomenon in the ionosphere was detected by two separate ionosphere observing stations. And the very high abnormal phenomenon maintained over one hour. The phenomenon showed that the ionosphere was injected with a large amount of small dust particles that could not be observed in optical and radio. The observational results show that the Leonid meteor shower in 1998 had three peaks. Key words: Meteors: Leonid meteor shower PDF \| gzipped PS file \| zipped PS file \| Back to Contents
The Figure and Dynamical Parameters of Io Inferred from Internal Structure Models Hong Zhang and Cheng-Zhi Zhang E-mail: jupiter@nju.edu.cn Abstract The recent Galileo spacecraft explored Jupiter and its satellite system and provided us with new geodetic data. In order to discuss the dynamical parameters and secular tidal effect of Io, the theory of synchronous satellite is described in detail. Using the new geodetic data of Io, two sets of Io's internal structure models are constructed based on the asthenosphere assumption. The liberation parameters $\alpha$ , $\beta$ , $\gamma$ and dynamical flattening H are calculated for the models of Io. A comparison of Io with the Moon indicates that they are quite different in many characteristics in spite of the fact that they are approximately equal in mass and size and that they both orbit synchronously. Key words: Io --- synchronous orbit --- dynamical parameters PDF \| gzipped PS file \| zipped PS file \| Back to Contents
Orbit Determination Using Satellite-to-Satellite Tracking Data Ying-Chun Liu and Lin Liu E-mail: liuyc99@263.net Abstract Satellite-to-Satellite Tracking (SST) data can be used to determine the orbits of spacecraft in two ways. One is combined orbit determination, which combines SST data with ground-based tracking data and exploits the enhanced tracking geometry. The other is the autonomous orbit determination, which uses only SST. The latter only fits some particular circumstances since it suffers the rank defect problem in other circumstances. The proof of this statement is presented. The nature of the problem is also investigated in order to find an effective solution. Several methods of solution are discussed. The feasibility of the methods is demonstrated by their application to a simulation. Key words: Celestial mechanics: orbit determination --- Methods: miscellaneous PDF \| gzipped PS file \| zipped PS file \| Back to Contents