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The X-ray Background from the Warm Gas of the Galactic Halo

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Chinese Journal of Astronomy and Astrophysics 2001年第5期1卷 383-388页

作者： Yan-Jie Xue (national astronomical observatories, Chinese Academy of sciences,{2.) E-mail:jie@*** national astronomical observatories Chinese Academy of Sciences Beijing 100012

Within the framework of the hierarchical scenario of galaxy formation, spiral galaxies like our own Galaxy are still growing at present. This opens a possibility that one might be able to see X-ray galactic halos from gravitationally heated gas with temperatures of 106 K as a result of bremsstrahlung. An interesting issue is whether the X-ray background produced by the warm gas in the halo of our Galaxy is detectable. We present a simple estimate of the strength and spectrum of the X-ray background from the Galactic halo and compare with the recent findings of a spatially variable soft X-ray component seen towards the north Galactic polar cap by Kuntz et al. (2.01). It is shown that a good agreement, regardless of cosmological models, can be achieved if the gas fraction is as low as '~ 0.01. This requirement seems to be consistent with the extrapolated result from a number of independent observational and theoretical constraints established for groups and clusters of galaxies. In particular, the ex pected soft X-ray background from the warm gas of the Galactic halo is comparable to, or even exceeds that produced by the warm-hot gas in massive groups, and it may constitute the major source of contamination in the search for missing baryons through the detection of their soft X-ray emission, unless we can work out a way to properly remove the X-ray background (e.g., from anisotropy) from the halo of our Galaxy.

关键词： cosmology: diffuse radiation - Galaxy: formation - Galaxy: halo -X-rays: galaxies

Time Scales and Tidal Effects in Minor Mergers

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Chinese Journal of Astronomy and Astrophysics 2003年第5期3卷 395-409页

作者： Yu Lu and Jian-Yan Weinational astronomical observatories, Chinese Academy of sciences,{2. luyu national astronomical observatories Chinese Academy of Sciences Beijing 100012

We use controlled N-body simulation to investigate the dynamical processes(dynamical friction, tidal truncation, etc.) involved in the merging of small satellites into biggerhalos. We confirm the validity of some analytic formulae proposed earlier based on simplearguments. For rigid satellites represented by softened point masses, the merging time scale dependson both the orbital shape and concentration of the satellite. The dependence on orbital ellipticityis roughly a power law, as suggested by Lacey & Cole, and the dependence on satellite concentrationis similar to that proposed by White. When merging satellites are represented by non-rigid objects,Tidal effects must be considered. We found that material beyond the tidal radius are stripped *** decrease in the satellite mass might mean an increase in the merging time scale, but in fact,the merging time is decreased, because the stripped-off material carries away a proportionatelylarger amount of of orbital energy and angular momentum.

关键词： cosmology: dark matter galaxies: kinematics and dynamics galaxies:structure galaxies: interactions numerical methods

Inhomogeneity in Spectral Transmission of the Coated UB VRI Filters of BFOSC and its Influence on Photometry

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Chinese Journal of Astronomy and Astrophysics 2002年第6期2卷 563-575页

作者： Bao-An Yao and Liu Huang1 Shanghai astronomical Observatory, Chinese Academy of sciences, Shanghai 2.003.2.{2., Chinese Academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

In order to realize the Johnson UBV and Kron-Cousins RI photometric systems in BFOSC, glass filters were purchased according to the Bessell prescription. All the filters are anti-reflection coated,on both sides to increase the transmission. By comparing two dome flat-field exposures taken through any one of these filters set in two orientations 90degrees apart, inhomogeneities in the filter transmission is clearly demonstrated. Using a PDS microphotometer, we have confirmed that the form of their spectral transmission curve varied from point to point on the filters. This kind of inhomogeneity cannot be eliminated by dividing by flat-fielding exposure and must be ascribed to inhomogeneities in the coating. This is not some accidental defect in coating, it is in the existing coating technique because all the filters (including the narrow-band interference ones) for the BFOSC and a Hbeta filter made by another manufacturer showed a similar pattern. We found that for the studies of variable stars with amplitudes less than 0.05 mag. or studies aiming at establishing accurate C-M diagrams of star clusters, the usual uncoated Schott glass filters of Bessell's prescription are to be preferred.

关键词： methods : data analysis techniques : photometric

Detectability of rotation-powered pulsars in future hard X-ray surveys

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Research in Astronomy and Astrophysics 2009年第11期9卷 1241-1258页

作者： Wei Wang national astronomical observatories Chinese Academy of Sciences Beijing 100012 China

Recent INTEGRAL/IBIS hard X-ray surveys have detected about 10 young pulsars. We show hard X-ray properties of these 10 young pulsars, which have a luminosity of 10^3. - 10^3. erg s^-1 and a photon index of 1.6-2.1 in the energy range of 2.-100 keV. The correlation between X-ray luminosity and spin-down power of Lx ∝ Lsd^1.3. suggests that the hard X-ray emission in rotation-powered pulsars is dominated by the pulsar wind nebula （PWN） component. Assuming spectral properties are similar in 2.-100keV and 2.10 keV for both the pulsar and PWN components, the hard X-ray luminosity and flux of 3. known young X-ray pulsars and 8 millisecond pulsars are obtained, and a correlation of Lx ∝ Lsd^1.5 is derived. About 2. known young X-ray pulsars and 1 millisecond pulsars could be detected with future INTEGRAL and HXMT surveys. We also carry out Monte Carlo simulations of hard X-ray pulsars in the Galaxy and the Gould Belt, assuming values for the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics and the Lx - Lsd reltions：Lx ∝Lsd^1.3. and Lx∝Lsd^1.5 More than 40 young pulsars （mostly in the Galactic plane） could be detected after ten years of INTEGRAL surveys and the launch of HXMT. So, the young pulsars would be a significant part of the hard X-ray source population in the sky, and will contribute to unidentified hard X-ray sources in present and future hard X-ray surveys by INTEGRAL and HXMT.

关键词： pulsars general -- stars neutron -- X-rays stars -- radiation mechanisms nontherrnal

Simulations for terrestrial planets formation

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Science China(Physics,Mechanics & Astronomy) 2009年第5期52卷 794-803页

作者： ZHANG Niu 1,2.&JI JiangHui 2.3.1Graduate University of Chinese Academy of sciences,{3. 100049,China 2.urple Mountain Observatory,Chinese Academy of sciences,Nanjing 2.0008,China 3.national astronomical observatories,Chinese Academy of sciences,{3. 100012,China Graduate University of Chinese Academy of sciences Beijing 100049 China Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China national astronomical observatories Chinese Academy of Sciences Beijing 100012 China

In this paper,the formation of terrestrial planets in the late stage of planetary formation is investigated using the two-planet *** that time,the protostar formed for about 3.Ma and the gas disk *** the model,the perturbations from Jupiter and Saturn are *** of the mass of outer planet,and the initial eccentricities and inclinations of embryos and planetesimals are also *** results show that,terrestrial planets are formed in 50 Ma,and the accretion rate is about 60%-80%.In each simulation,3.4 terrestrial planets are formed inside"Jupiter"with masses of 0.15 -3.6M⊕.In the 0.5-4 AU,when the eccentricities of planetesimals are excited,planetesimals are able to accrete material from wide radial *** plenty of water material of the terrestrial planet in the Habitable Zone may be transferred from the farther places by this *** could also happen a few times between two major planets only if the outer planet has a moderate mass and the small terrestrial planet could survive at some resonances over time scale of 10 8 *** one of our simulations,commensurability of the orbital periods of planets is very ***,a librating-circulating 3.2.configuration of mean motion resonance is found.

关键词： astrophysics exoplanet planetary formation n-body simulation

Infall and Outflow Activities in the Be star FY CMa

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Chinese Journal of Astronomy and Astrophysics 2001年第6期1卷 514-524页

作者： Hui-Lai Cao national astronomical observatories, Chinese Academy of sciences,{2. CAS-PKU Joint {3. Astrophysics Center, Peking University, {3. 100871 national astronomical observatories Chinese Academy of Sciences Beijing 100012 []CAS-PKU Joint Beijing Astrophysics Center Peking University Beijing 100871

Unusual activity of outflow mass motion connected with infall events was recorded for the B0.5 IVe star FY CMa in February 1987 from both archival IUE spectrograms of circumstellar N v resonance lines and optical spectra of Ha and HeI γ5876 A emission lines which showed inverse P Cygni-type profiles. We estimate the mass loss rate using ultraviolet Si IVresonance lines with expanding atmosphere modeling calculations, and describe how the radial pressure performs the dominant role in accelerating the stellar wind. We attempt to give a qualitative explanation for the activity observed for FY CMa in terms of circumstellar matter raining down to the star.

关键词： line: proffles - stars: activity - stars: emission-line Be -circumstellar matter - stars: mass-loss - ultraviolet: stars

The Two Mini-lobes of the CSO OQ2.8——VLBI Observations at 5 GHz and 8.4 GHz

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Chinese Journal of Astronomy and Astrophysics 2003年第6期3卷 505-512页

作者： Wei-Hua Wang, Xiao-Yu Hong and Tao AnShanghai astronomical Observatory, Chinese Academy of sciences, Shanghai 2.003. {2., Chinese Academy of sciences, beijing 100012 Shanghai astronomical Observatory Chinese Academy of Sciences Shanghai 200030 []National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

We present the results of VLBI observations at 5 GHz and 8.4 GHz of the compact symmetric object (CSO) OQ2.8. Images taken on four epochs at 5GHz and one at 8.4GHz show that the parsec radio structure of the source consists of two mini-lobes, both of them are resolved into two hot-spots. We note that the component D is stronger than the component C in the south-west region at 5 GHz, indicating that component D is less free-free absorbed than C at low frequency. On the basis of the separation of components A and D, a proper motion of 0.03.0}0.02.mas yrbetween the two mini-lobes is estimated. This value is about half the previous estimates based on the separation of components A and C with 8.4 GHz VLBI data. The reason for the decrease in the expansion velocity is discussed.

关键词： galaxies: individual (Mkn 668 OQ2.8) - galaxies: active

Learning Vector Quantization for Classifying astronomical Objects

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Chinese Journal of Astronomy and Astrophysics 2003年第2期3卷 183-190页

作者： Yan-Xia Zhang and Yong-Heng Zhaonational astronomical observatories, Chinese Academy of sciences,{2. national astronomical observatories CAS NAOC Beijing 100012 China

The sizes of astronomical surveys in different wavebands are increasing rapidly. Therefore, automatic classification of objects is becoming ever more important. We explore the performance of learning vector quantization (LVQ) in classifying multi-wavelength data. Our analysis concentrates on separating active sources from non-active ones. Different classes of X-ray emitters populate distinct regions of a multidimensional parameter space. In order to explore the distribution of various objects in a multidimensional parameter space, we positionally cross-correlate the data of quasars, BL Lacs, active galaxies, stars and normal galaxies in the optical, X-ray and infrared bands. We then apply LVQ to classify them with the obtained data. Our results show that LVQ is an effective method for separating AGNs from stars and normal galaxies with multi-wavelength data.

关键词： method: data analysis - method: statistical - catalogs

Searching for Variable Stars in and around Open Clusters

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Chinese Journal of Astronomy and Astrophysics 2002年第6期2卷 481-486页

作者： Yu Xin, Xiao-Bin Zhang and Li-Cai Dengnational astronomical observatories, Chinese Academy of sciences,{2. national astronomical observatories Chinese Academy of Sciences Beijing 100012 China

We present a snapshot-of our recent results of a variable star survey in 1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A total number of 3. variable stars are newly discovered, including 2. W ... 详细信息

关键词： open clusters : individual : NGC 188, NGC 7789 and M67 stars : variables