ChJAA -- 2005, Vol.5, No.4

An Analytic Model of Galactic Winds and Mass Outflows

Cheng-Gang Shu^{1, 2, 3}, Hou-Jun Mo^3,4, Shu-De Mao⁵

¹ Joint Center for Astrophysics, Shanghai Normal University, Shanghai 200234; cgshu@center.shao.ac.cn
² Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030
³ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, Postfach 1317 D-85741 Garching, Germany
⁴ Astronomy Department, University of Massachusetts, Amherst, MA 01003, USA ⁵ Jodrell Bank Observatory, Univ. of Manchester, Macclesfield, Cheshire SK11 9DL, UK

Abstract
Galactic winds and mass outflows are observed both in nearby starburst galaxies and in high-redshift star-forming galaxies. We develop a simple analytic model to understand the observed superwind phenomenon with a discussion of the model uncertainties. Our model is built upon the model of McKee & Ostriker for the interstellar medium. It allows one to predict how properties of a superwind, such as wind velocity and mass outflow rate, are related to properties of its star-forming host galaxy, such as size, gas density and star formation rate. The model predicts a threshold of star formation rate density for the generation of observable galactic winds. Galaxies with more concentrated star formation activities produce superwinds with higher velocities. The predicted mass outflow rates are comparable to (or slightly larger than) the corresponding star formation rates. We apply our model to both local starburst galaxies and high-redshift Lyman break galaxies, and find its predictions to be in good agreement with current observations. Our model is simple and so can be easily incorporated into numerical simulations and semi-analytical models of galaxy formation.

Key words: galaxies: starburst -- galaxies: ISM -- galaxies: kinematics and dynamics -- galaxies: formation and evolution

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Stellar Population Analysis of Galaxies based on Genetic Algorithms

Abdel-Fattah Attia¹, H. A. Ismail¹, I. M. Selim ¹, A. M. Osman ¹, I. A. Isaa ¹, M. A. Marie ², A. A. Shaker ¹

¹ National Research Institute of Astronomy and Geophysics (NRIAG), 11421 Helwan, Cairo, Egypt; attiaa1@yahoo.com
² Cairo University, Faculty of Science, Astronomy Department, Egypt

Abstract
We present a new method for determining the age and relative contribution of different stellar populations in galaxies based on the genetic algorithm. We apply this method to the barred spiral galaxy NGC 3384, using CCD images in U, B, V, R and I bands. This analysis indicates that the galaxy NGC 3384 is mainly inhabited by old stellar population (age > 10⁹yr). Some problems were encountered when numerical simulations are used for determining the contribution of different stellar populations in the integrated color of a galaxy. The results show that the proposed genetic algorithm can search efficiently through the very large space of the possible ages.

Key words: methods: numerical -- galaxies: stellar population -- galaxies: individual (NGC 3384).

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Discovery of 13 New Variable Stars in the Field of the Open Cluster NGC 2168 (M35)

Juei-Hwa Hu¹, Wing-Huen Ip ¹, Xiao-Bin Zhang², Zhao-Ji Jiang², Jun Ma², Xu Zhou²

¹ Institute of Astronomy, National Central University, Chung Li 32054, Taiwan; d939003@astro.ncu.edu.tw
² National Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012

Abstract
A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems, one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of $\delta$ Scuti stars.

Key words: open clusters: individual (NGC 2168) -- stars: variables (general) -- binaries: general

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Evidence of Evolution in the Dense Cores in Massive Star Forming Regions

Jian-Jun Zhou^{1, 2}, Jarken Esimbek¹, Ji-Xian Sun³, Bing-Gang Ju³, Jing-Jiang Sun³ ¹ National Astronomical Observatories/Urumqi observatory, Chinese Academy of Sciences, Urumqi 830011; zhoujj@ms.xjb.ac.cn
² Graduate School of the Chinese Academy of Science, Beijing 100080
³ Qinghai Station of Purple mountain Observatory, Chinese Academy of Science, Delingha, Qinghai 817000

Abstract
The excitation of H₂O masers usually needs very high density gas, hence it can serve as a marker of dense gas in HII region. We selected a sample of H₂O maser sources from Plume et al. (four with, and four without detected CS(J=7-6) emission), and observed them in ¹³CO(J=1-0) and C¹⁸O (J=1-0). C¹⁸O (J=1-0) emission was detected only in three of the sources with detected CS(J=7-6) emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.

Key words: ISM: molecules -- masers -- radio lines: ISM--stars: formation

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The Effect of Method of Constructing the Mass Distribution on Single Stellar Populations

Feng-Hui Zhang, Li-Fang Li, Zhan-Wen Han

National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; gssephd@public.km.yn.cn

Abstract
We use two methods of constructing the initial mass distribution, the traditional way and Monte Carlo simulation, to obtain integrated U-B, B-V, V-R and V-I colours and absorption-line indices defined by the Lick Observatory image dissector scanner (referred to as Lick/IDS), for instantaneous burst solar-metallicity single stellar populations with ages in the range 1-15Gyr. We find that the evolutionary curves of all colours obtained by the traditional method are smoother than those by Monte Carlo simulation, that the U-B and B-V colours obtained by the two methods agree with one another, while the V-R and V-I colours by the traditional method are bluer than those by Monte Carlo simulation. A comparison of the Lick/IDS absorption-line indices shows that the variations in all the indices by the traditional method are smoother than that for the Monte Carlo simulation, and that all the indices except for TiO₁ and TiO₂ are consistent with those for the Monte Carlo simulation.

Key words: star: evolution -- galaxies: star clusters -- galaxies: stellar content

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Precession of the Orbital Plane of Binary Pulsars and Significant Variabilities

Bi-Ping Gong

Department of Astronomy, Nanjing University, Nanjing 210093; bpgong@nju.edu.cn

Abstract
There are two ways of expressing the precession of orbital plane of a binary pulsar system, given by Barker & O'Connell, Apostolatos et al. and Kidder, respectively. We point out that these two ways actually come from the same Lagrangian under different degrees of freedom. Damour & Schäfer and Wex & Kopeikin applied Barker & O'Connell's orbital precession velocity in pulsar timing measurement. This paper applies Apostolatos et al.'s and Kidder's orbital precession velocity. We show that Damour & Schäfer's treatment corresponds to negligible Spin-Orbit induced precession of periastron, while Wex & Kopeikin and this paper both found significant (but not equivalent) effects. The observational data of two typical binary pulsars, PSR J2051-0827 and PSR J1713+0747, apparently support a significant Spin-Orbit coupling effect. Specific binary pulsars with orbital plane nearly edge on could discriminate between Wex & Kopeikin and this paper: if the orbital period derivative of the double-pulsar system PSRs J0737-3039 A and B, with orbital inclination angle i=87.7_-29⁺¹⁷deg, is much larger than that of the gravitational radiation induced one, then the expression in this paper is supported, otherwise Wex & Kopeikin's is supported.

Key words: pulsars: binary pulsars - geodetic precession: individual (PSR J2051-0827, PSR J1713+0747, PSRs J0737-3039 A and B)

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Quantum Instability of Magnetized Stellar Objects

R. González Felipe¹, H. J. Mosquera Cuesta^2,3, A. Pérez Martínez ⁴, H. Pérez Rojas ⁴

¹ Departamento de Física and Centro de Física Teórica de Partículas, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal; gonzalez@cftp.ist.utl.pt
² Instituto de Cosmologia, Relatividade e Astrofísica (ICRA-BR), Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, CEP 22290-180, Urca, Rio de Janeiro, RJ, Brazil
³ Centro Latino-Americano de Física, Avenida Wenceslau Braz 71, CEP 22290-140 fundos, Botafogo, Rio de Janeiro, Brazil
⁴ Instituto de Cibernética, Matemática y Física, Calle E No. 309, 10400 La Habana, Cuba

Abstract
The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields. After including quantum effects in the investigation of the structural properties of these systems, it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures. Highly magnetized white dwarfs should collapse producing a supernova type Ia, while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode, too. A comparison of our results with a set of the available observational data of some compact stars is also presented, and the agreement between this theory and observations is verified.

Key words: dense matter--equation of state--instabilities--stars: magnetic fields--stars: neutron, white dwarfs

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A Narrow Band Chandra X-ray Analysis of SNR 3C 391

Yang Su and Yang Chen

Department of Astronomy, Nanjing University, Nanjing 210093; ysu@nju.edu.cn

Abstract
We present narrow-band and equivalent width (EW) images of the thermal composite supernova remnant (SNR) 3C 391 in the X-ray emission lines of Mg, Si and S using the Chandra ACIS Observational data. The EW images reveal the spatial distribution of the emission of the metal species Mg, Si and S in the remnant. They have a clumpy structure similar to that seen in the broadband diffuse emission, suggesting that they are largely of interstellar origin. We find an interesting finger-like feature protruding outside the southwestern radio border of the remnant, somewhat similar to the jet-like Si structure found in the famous SNR Cas A. This feature may possibly be the debris of the jet of ejecta from an asymmetrical supernova explosion of a massive progenitor star.

Key words: ISM: supernova remnants -- X-rays: ISM -- X-rays: individual (3C 391) -- ISM: lines and bands

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Population Synthesis for Mira Variables

Chun-Hua Zhu and Chao-Zheng Zha

Department of Physics, Xinjiang University, Urumqi 830046; xdzch2002@yahoo.com.cn

Abstract
By means of a population synthesis code, we investigate the Mira variables. Their birth rate (over 0.65yr^-1) and their number ( $\sim$ 130000) in the Galaxy are estimated. For all possible Mira variables, ranges of their initial masses, pulsating periods, mass losses and lifetimes are given. We check our model with the observed Mira variables near the Sun and our results prove to be valid.

Key words: stars: late-type -- stars: variables -- stars: fundamental parameters

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Magneto-induced Line Broadening of Magneto-sensitive Lines in Solar Magnetized Atmospheres

Zhong-Quan Qu¹, Shuai Wang^{1, 2}, Cheng-Lin Xu^1,
2, Xiao-Yu Zhang¹, Ming-Guo Sun^{1, 2}, Chun-Lan Jin^{1, 2}

¹National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, Kunming 650011; zqqu@vip.km169.net
² Graduate School of the Chinese Academy of Sciences, Beijing 100039

Abstract

We analyze the spectral line broadening of those magneto-sensitive lines in solar magnetized atmospheres. The broadening at the line wings is due to the increase of the effective width of energy levels involved in Zeeman splitting, and the broadening at the line core also originated in Zeeman splitting under the condition that the Zeeman components are mixed. Therefore, the magneto-induced or Zeeman broadening take effects on the whole line. The observed Stokes parameter data in a sunspot and outside it acquired by Solar Stokes Spectrum Telescope (S³T) are analyzed for the demonstration of this mechanism, and the Zeeman broadening rates are calculated for FeI6302.5 under some assumptions. Our result shows that the broadening is increased as the magnetic field strength becomes stronger, but the rate of increase at the line core is decreased as the field strength increases, while the rate at the wing does not show such an obvious regularity. The broadening is more effective in the line core than in the wings.

Key words: sunspots -- line: profiles-magnetic fields -- radiative transfer-polarization

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A New Solar Radio Spectrometer at 1.10-2.06GHz and First Observational Results

Hui-Rong Ji¹, Qi-Jun Fu¹, Yi-Hua Yan¹, Yu-Ying Liu¹, Zhi-Jun Chen¹, Cheng-Ming Tan¹, Cong-Ling Cheng, De-Bang Lao¹, Shu-Ke Li², Zhi-Qiang Wang², Min-Hong Yu², Jian-Nong Liu², Li-Kang Zhang², Ji-Yong Gao²

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; jihr@bao.ac.cn
² Hebei Semiconductor Research Institute, Shijiazhuang 050051

Abstract

An improved Solar Radio Spectrometer working at 1.10-2.06GHz with much improved spectral and temporal resolution, has been accomplished by the National Astronomical Observatories and Hebei Semiconductor Research Institute, based on an old spectrometer at 1-2GHz. The new spectrometer has a spectral resolution of 4MHz and a temporal resolution of 5ms, with an instantaneous detectable range from 0.02 to 10 times of the quiet Sun flux. It can measure both left and right circular polarization with an accuracy of 10% in degree of polarization. Some results of preliminary observations that could not be recorded by the old spectrometer at 1-2GHz are presented.

Key words: instrumentation: spectrometer -- sun: radio radiation

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ERRATUM: ``Statistics of the Galactic Supernova Remnants'' (ChJAA, 5(2), 165 [2005])

Jian-Wen Xu, Xi-Zhen Zhang and Jin-Lin Han

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; xjw@ns.bao.ac.cn

Abstract
We thank Dr. Dave Green (MRAO, UK) for one comment and one identified problem in our paper. The comment is that we did not discuss selection effects of the current sample of supernova remnants, which can be found in Case & Bhattacharya (1998) and Green (2004). The problem is the mis-usage of some SNR distances in Gusienov et al. (2003) and other references which were obtained from the assumed $\Sigma$ -D relation. We mixed them to other data to derive the SNR diameters and SNR luminosity for statistics. This seriously affects the discussions in Section 3.3 and Figures 3 and 4. We cleaned out the flawed data and revise this part of the paper in the electronic version at http://www.chjaa.org.

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ChJAA, 2005, Vol.5, No.4

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org

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Created by Aiying Zhou 2005-08-07