2008 Vol.8 No.6 Issue

A Positioning System based on Communication Satellites and the Chinese Area Positioning System (CAPS)

Guo-Xiang Ai¹, Hu-Li Shi¹, Hai-Tao Wu², Yi-Hua Yan¹,, Yu-Jing Bian², Yong-Hui Hu², Zhi-Gang Li², Ji Guo² and Xian-De Cai¹

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; aigx@bao.ac.cn
² National Time Service Center, Chinese Academy of Sciences, Lintong 710600, China

Abstract
The Chinese Area Positioning System (CAPS) is a positioning system based on satellite communication that is fundamentally different from the 3``G" (GPS, GLONASS and GALILEO) systems. The latter use special-purpose navigation satellites to broadcast navigation information generated on-board to users, while the CAPS transfers ground-generated navigation information to users via the communication satellite. In order to achieve accurate Positioning, Velocity and Time (PVT), the CAPS employs the following strategies to overcome the three main obstacles caused by using the communication satellite: (a) by real-time following-up frequency stabilization to achieve stable frequency; (b) by using a single carrier in the transponder with 36MHz band-width to gain sufficient power; (c) by incorporating Decommissioned Geostationary Orbit communication satellite (DGEO), barometric pressure and Inclined Geostationary Orbit communication satellite (IGSO) to achieve the 3-D positioning. Furthermore, the abundant transponders available on DGEO can be used to realize the large capacity of communication as well as the integrated navigation and communication. With the communication functions incorporated, five new functions appear in the CAPS: (1) combination of navigation and communication; (2) combination of navigation and high accuracy orbit measurement; (3) combination of navigation message and wide/local area differential processing; (4) combination of the switching of satellites, frequencies and codes; and (5) combination of the navigation message and the barometric altimetry. The CAPS is thereby labelled a PVT5C system of high accuracy. In order to validate the working principle and the performance of the CAPS, a trial system was established in the course of two years at a cost of about 20 million dollars. The trial constellation consists of two GEO satellites located at E87.5 and E110.5, two DGEOs located at E130 and E142, as well as barometric altimetry as a virtual satellite. Static and dynamic performance tests were completed for the Eastern, the Western, the Northern, the Southern and the Middle regions of China. The evaluation results are as follows: (1) land static test, plane accuracy range: C/A code, 15 $\sim$ 25m; P code, 5 $\sim$ 10 meters; altitude accuracy range, 1 $\sim$ 3m; (2) land dynamic test, plane accuracy range, C/A code, 15 $\sim$ 25m; P code, 8 $\sim$ 10m; (3) velocity accuracy, C/A code, 0.13 $\sim$ 0.3 $\rm m s^{-1}$ , P code, 0.15 $\sim$ 0.17 $\rm m s^{-1}$ ; (4) timing accuracy, C/A code, 160ns, P code, 13ns; (5) timing compared accuracy of Two Way Satellite Time and Frequency Transfer (TWSTFT), average accuracy, 0.068ns; (6) random error of the satellite ranging, 10.7mm; (7) orbit determination accuracy, better than 2m. The above stated random error is 1 ${\sigma}$ error. At present, this system is used as a preliminary operational system and a complete system with 3 GEO, 3 DGEO and 3 IGSO is being established.

Key Words: astronomy application -- satellite navigation -- satellite communication -- astrometry -- astronomic technique

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The Effect of AGN and SNe Feedback on Star Formation, Reionization and the Near Infrared Background

Lei Wang ¹, Ji-Rong Mao ², Shou-Ping Xiang ¹ and Ye-Fei Yuan ¹

¹ Center for Astrophysics, University of Science and Technology of China, Hefei 230026, China wsl2008@mail.ustc.edu.cn
² Yunnan Observatory, National Astronomical Observatories, Chinese Academy of Sciences, Kunming 650011, China

Abstract
Feedback from supernovae (SNe) and from active galactic nuclei (AGN) accompanies the history of star formation and galaxy evolution. We present an analytic model to explain how and when the SNe and AGN exert their feedback effects on the star formation and galaxy evolution processes. By using SNe and AGN kinetic feedback mechanisms based on the Lambda Cold Dark Matter (LCDM) model, we explore how these feedback mechanisms affect the star formation history (SFH), the Near-Infrared Background (NIRB) flux and the cosmological reionization. We find the values of the feedback strengths, $\epsilon_{\rm AGN}=1.0^{+0.5}_{-0.3}$ and $\epsilon_{\rm SN}=0.04^{+0.02}_{-0.02}$ , can provide a reasonable explanation of most of the observational results, and that the AGN feedback effect on star formation history is quite different from the SNe feedback at high redshifts. Our conclusions manifest quantitatively that these feedback effects decrease star formation rate density (SFRD) and the NIRB flux (in 1.4 - 4.0 $\mu$ m), and postpone the time of completion of the cosmological reionization.

Key Words: cosmology: theory - galaxies: evolution - infrared: general - stars: formation

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Infrared Galaxies in the Nearby Universe

Jian-Ling Wang ^1,2

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; wjianl@bao.ac.cn

² Graduate School of Chinese Academy of Sciences, Beijing 100049, China

Abstract
We used the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) to study the morphological properties of 1137 nearby infrared (IR) galaxies, most of which are brighter than 15.9mag in r-band. This sample was drawn from a cross-correlation of the Infra-Red Astronomical Satellite (IRAS) point source catalog redshift survey with DR5 at z $z \lesssim 0.08$ 0.08 . Based on this IR galaxy sample, we constructed five volume-limited sub-samples with IR luminosity ranging from $10^{9.5} \Lsun$ to $10^{12} \Lsun$ . By deriving the IR luminosity functions (LF) for different morphological types, we found that normal spiral galaxies are the dominant population below L_IR $\LIR \sim 8\times 10^{10} L_\odot$ ; while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond L_IR $\LIR \simeq 5\times10^{10}\Lsun$ . As the IR luminosity decreases, the IR galaxies become more compact and have lower stellar masses. The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe, while, in contrast, the contribution from peculiar galaxies is only 39%.

Key Words: galaxies: evolution -- galaxies: interactions -- galaxies: starburst -- infrared: galaxies -- galaxies: luminosity function

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An X-Ray Study of Lobe-Dominated Radio-Loud Quasars with XMM-Newton

Li-Ming Dou ^1,2 and Wei-Min Yuan ¹

¹ National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011, China; dlm@ynao.ac.cn

² Graduate School of Chinese Academy of Sciences, Beijing 100049, China

Abstract:
We report on our results of X-ray spectral analysis for a sample of radio-loud quasars covering a wide range of the radio core-dominance parameter, R, from core-dominated to lobe-dominated objects, using data obtained mostly with the XMM-Newton Observatory. We find that the spectral shape of the underlying power-law continuum is flat even for the lobe-dominated objects (average photon index $\sim1.5$ ), indistinguishable from that of core-dominated quasars. For lobe-dominated objects, contribution of X-rays from the jets is expected to be very small based on previous unification schemes, more than one order of magnitude lower than the observed X-ray luminosities. Assuming that radio-loud quasars follow the same X-ray-UV/optical luminosity relation for the disk-corona emission as found for radio-quiet quasars, we estimate the X-ray flux contributed by the disk-corona component from the optical/UV continuum. We find that neither the luminosity, nor the spectral shape, of the disk-corona X-ray emission can account for the bulk of the observed X-ray properties. Thus in lobe-dominated quasars, either the disk-corona X-ray emission is much enhanced in strength and flatter in spectral shape (photon index $\sim1.5$ ) compared to normal radio-quiet quasars, or their jet X-ray emission is much enhanced compared to their weak radio core-jet emission. If the latter is the case, our result may imply that the jet emission in X-rays is less Doppler beamed than that in the radio. As a demonstrating example, we test this hypothesis by using a specific model in which the X-ray jet has a larger opening angle than the radio jet.

Key Words: galaxies: active -- quasars: general -- galaxies: X-ray -- galaxies: radio continuum

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Reconstruction of Gas Temperature and Density Profiles of the Galaxy Cluster RX J1347.5-1145

Qiang Yuan^1,2, Tong-Jie Zhang^1,3 and Bao-Quan Wang⁴

¹ Department of Astronomy, Beijing Normal University, Beijing 100875, China

² Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; tjzhang@bnu.edu.cn

³ Kavli Institute for Theoretical Physics China, Institute of Theoretical Physics, Chinese Academy of Sciences (KITPC/ITP-CAS), Beijing 100080, China

⁴ Department of Physics, Dezhou University, Dezhou 253023, China

Abstract
We use observations of Sunyaev-Zel'dovich effect and X-ray surface brightness to reconstruct the radial profiles of gas temperature and density under the assumption of a spherically symmetric distribution of the gas. The method of reconstruction, first raised by Silk & White, depends directly on the observations of the Sunyaev-Zel'dovich effect and the X-ray surface brightness, without involving additional assumptions such as the equation of state of the gas or the conditions of hydrostatic equilibrium. We applied this method to the cluster RX J1347.5-1145, which has both the Sunyaev-Zel'dovich effect and X-ray observations with relative high precision. It is shown that it will be an effective method to obtain the gas distribution in galaxy clusters. Statistical errors of the derived temperature and density profiles of gas were estimated according to the observational uncertainties.

Key Words: X-rays: galaxies: clusters -- cosmology: theory -- cosmic microwave background -- galaxies: clusters: individual (RX J1347.5-1145)
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Rotation Profiles of Solar-like Stars with Magnetic Fields

Wu-Ming Yang ¹ and Shao-Lan Bi^2,3

¹ Department of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000, China; wuming.yang@hotmail.com

² Department of Astronomy, Beijing Normal University, Beijing 100875, China

³ National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011, China

Abstract
We investigate the rotation profile of solar-like stars with magnetic fields. A diffusion coefficient of magnetic angular momentum transport is deduced. Rotating stellar models with different mass incorporating the coefficient are computed to give the rotation profiles. The total angular momentum of a solar model with only hydrodynamic instabilities is about 13 times larger than that of the Sun at the age of the Sun, and this model can not reproduce quasi-solid rotation in the radiative region. However, the solar model with magnetic fields not only can reproduce an almost uniform rotation in the radiative region, but also a total angular momentum that is consistent with the helioseismic result at the 3 $\sigma$ level at the age of the Sun. The rotation of solar-like stars with magnetic fields is almost uniform in the radiative region, but for models of 1.2-1.5 $M_{\odot}$ , there is an obvious transition region between the convective core and the radiative region, where angular velocity has a sharp radial gradient, which is different from the rotation profile of the Sun and of massive stars with magnetic fields. The change of angular velocity in the transition region increases with increasing age and mass.

Key Words: stars: evolution -- stars: rotation -- stars: magnetic fields

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The Gas-to-Dust Relation in the Dark Cloud L1523 - Observational Evidence for CO Gas Depletion

H. G. Kim, B. G. Kim and J. H. Jung

Korea Astronomy and Space Science Institute, 61-1, Hwaam, Yuseong, Daejeon 305-348, Korea; hgkim@kasi.re.kr

Abstract
Correlation between gas and dust column density has been studied for the dark globule L1523. The ¹³CO(J=1 $\rightarrow$ 0) emission is used for tracing the gas, and the IR emissions, for tracing the dust constituent. In order to match the beam resolution between the images, a beam de-convolution algorithm based on the Maximum Correlation Method (MCM) was applied on the Infrared Astronomical Satellite (IRAS) data. The morphology of ¹³CO column density map shows a close correlation to that of 100 $\mu$ m dust optical depth. The distribution of the optical depth at 100 $\mu$ m follows that of gas column density more closely than does the flux map at either 60 or 100 $\mu$ m. The ratio of the ¹³CO column density to the 100 $\mu$ m optical depth shows a decreasing trend with increasing dust optical depth in the central part, indicating possible molecular gas condensation onto dust particles. The excessive decrease in the CO column density in the envelope may most probably be due to the photo-dissociation of CO molecules.

Key Words: ISM: clouds --- ISM: dust --- ISM: molecules

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A GRB Follow-up System at the Xinglong Observatory and Detection of the High-Redshift GRB 060927

Wei-Kang Zheng ^1,2, Jin-Song Deng ¹, Meng Zhai ^1,2, Li-Ping Xin ^1,2, Yu-Lei Qiu ¹, Jing Wang ¹, Xiao-Meng Lu ^1,2, Jian-Yan Wei ¹ and Jing-Yao Hu ¹

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, Chi

² Graduate School of Chinese Academy of Sciences, Beijing 100049, China

Abstract
A gamma-ray burst (GRB) optical photometric follow-up system at the Xinglong Observatory of National Astronomical Observatories of China (NAOC) has been constructed. It uses the 0.8-m Tsinghua-NAOC Telescope (TNT) and the 1-m EST telescope, and can automatically respond to GRB Coordinates Network (GCN) alerts. Both telescopes slew relatively fast, being able to point to a new target field within $\sim 1$ min upon a request. Whenever available, the 2.16-m NAOC telescope is also used. In 2006 the system responded to 15 GRBs and detected seven early afterglows. In 2007 six GRBs have been detected among 18 follow-up observations. TNT observations of the second most distant GRB 060927 (z=5.5) are shown, which started as early as 91s after the GRB trigger. The afterglow was detected in the combined image of the first 19 x 20s unfiltered exposures. This GRB follow-up system has joined the East-Asia GRB Follow-up Observation Network (EAFON).

Key Words: gamma-rays: bursts -- gamma-rays: observations -- telescopes

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Sodium Enrichment in Yellow Supergiants: a Perspective from the Uncertainties of Reaction Rates

Lei Zhao, Qiu-He Peng and Xin-Lian Luo

Department of Astronomy, Nanjing University, Nanjing 210093, China; camford@163.com

Abstract
Sodium overabundance in yellow supergiants has stumped people for more than 20 years. The purpose of this paper is to explore this problem from the perspective of nuclear physics. We investigate carefully the CNO and NeNa cycles that are responsible for sodium production. We investigate some key reactions in the appropriate network. We show whether and how the sodium output can be affected by the rate uncertainties in these reactions. In this way, we evaluate if a reaction is important enough to deserve a better determination of its rate in terrestrial laboratories.

Key Words: nuclear reactions -- nucleosynthesis -- stars: abundances -- supergiants

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The Near-Contact Binary FU Ara: New Observations, a Photometric Study and Preliminary

A. Paschke ¹, F. Acerbi ² and C. Barani ³

¹ Weierstr 30, 8630 Rueti, Switzerland

² Via Zoncada 51, 26845 Codogno (LO), Italy; acerbifr@tin.it

³ Via Molinetto 35, 26845 Triulza di Codogno (LO), Italy

Abstract
A new CCD ( $\emph{V}$ ) light curve is presented for the semi-detached binary system FU Ara. The light curve, obtained in 2007, is the first one since the last 50 years. With our data we were able to determine six new times of minimum light and refined the period of the system to 0.8645049 days. A Wilson-Devinney analysis leads to a solution of a semi-detached configuration, composed of a main-sequence primary component of spectral type F5, fractionally smaller than its Roche lobe, and an evolved secondary component of spectral type K1 which fills its Roche lobe, and which is overluminous and oversized as compared with the main-sequence. The two components of FU Ara differ considerably in effective temperature. It is classified as an FO Virginis type of near-contact binary system. Assuming a reasonable value for the mass of the primary component, an estimate of the absolute elements of FU Ara has been made, on the assumption that the primary has a mass corresponding to its spectral type according to Svechnikov & Taidakova.

Key Words: binaries: eclipsing -- stars: fundamental parameters -- stars: individual: FU Ara

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Revisiting the Local Kinematics of the Milky Way using the New Hipparcos Data

Fang-Ting Yuan Zi Zhu Da-Li Kong

Department of Astronomy, Nanjing University, Nanjing 210093, China; yuanfangting@gmail.com

Abstract
With the new Hipparcos data recently released, we reexamine the kinematics in the solar neighborhood. Two different populations of objects, namely the thin-disk O-B5 stars and the thick-disk K-M giants, are selected for tracing the kinematical parameters of the Galaxy. Using a 3-D kinematical model, the components of the solar motion and the Oort constants are derived. The solutions and the kinematics inferred from both types of stars are analyzed. The results obtained with the new data are compared with those from the old Hipparcos data. We conclude that the present solution provides a more reliable estimation of the Oort constants, thanks to the new reduction of the Hipparcos data that provides even more accurate astrometric measurements of stars.

Key Words: astrometry -- Galaxy: disk -- Galaxy: solar neighborhood -- Galaxy: kinematics and dynamics

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Properties of the He I 10830Å Line in Solar Flares

Qiu-Sheng Du and Hui Li

Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China; duqs@pmo.ac.cn

Abstract
We study the properties of the line in nine selected solar flares, using spectral data obtained with the at and photospheric images from the onboard the . Our results indicate that, over an area of 3- 8, the line shows emission exceeding the continuum in nearby quiet region when the X-ray class of the flare reaches a threshold value (C4.5). The line emission is detected only in the kernels of the brightenings, but is not associated with the size of the flare. It is found that, whenever the line shows excess emission over the nearby continuum both the and the lines display enhanced intensities exceeding their preflare intensities. The line emission can occasionally extend into the umbra of the involved sunspot, which is inconsistent with previous studies. The weak component of line changes from emission to absorption earlier than does the main component. Our results favor the photoionization-reconnection mechanism for the excitation of the line.

Key Words: Sun: flares -- Sun: infrared -- line: profiles

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The Emission Heights of Transition Region Lines in an Equatorial Coronal Hole and the Surrounding Quiet Sun

Hui Tian ^1,2, Li-Dong Xia ³, Jian-Sen He ¹, Bo Tan ¹ and Shuo Yao ¹

¹ Department of Geophysics, Peking University, Beijing 100871, China; tianhui924@163.com

² Max-Planck-Institut für Sonnensystemforschung, D-37191 Katlenburg-Lindau, Germany

³ School of Space Science and Physics, Shandong Univ. at Weihai, Weihai 264209, China

Abstract
Using the correlation between the radiance or Doppler velocity and the extrapolated magnetic field, we determined the emission heights of a set of solar transition region lines in an equatorial coronal hole and in the surrounding quiet Sun region. We found that for all of the six lower-transition-region lines, the emission height is about 4-5Mm in the equatorial coronal hole, and around 2Mm in the quiet Sun region. This result confirms the previous findings that plasma with different temperature can coexist at the same layer of transition region. In the quiet Sun region, the emission height of the upper-transition-region line Ne VIII is almost the same that of the lower-transition-region line, but in the coronal hole, it is twice as high. This difference reveals that the outflow of Ne VIII is a signature of solar wind in the coronal hole and is just a mass supply to the large loops in the quiet Sun.

Key Words: Sun: transition region -- Sun: magnetic fields -- Sun: solar wind -- Sun: UV radiation

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ChJAA, 2008, Vol.8, No.6

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org

Copyright 2001--2008 All rights reserved. The National Astronomical Observatories of
Chinese Academy of Sciences, P.R. China. This Journal or parts thereof, may not be
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