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2MASS photometry and age estimation of the globular clusters in the outer halo of M31

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Research in Astronomy and Astrophysics 2012年第2期12卷 115-126页

作者： Jun Ma 1,21 national astronomical observatories,chinese academy of sciences,beijing 100012,China 2 Key Laboratory of Optical Astronomy,national astronomical observatories,chinese academy of sciences,beijing 100012,China national astronomical observatories Chinese Academy of Sciences Beijing 100012 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

We present the first photometric results in J, H and Ks from 2MASS （Two Micron All Sky Survey） imaging of 10 classical globular clusters （GCs） in the far outer regions of M31. Combined with the V and I photometric data from previous literature, we constructed a color-color diagram between J - Ks and V - Ⅰ. By comparing the integrated photometric measurements with evolutionary models, we estimate the ages of these clusters. The results showed that all of these clusters are older than 3 × 109 yr, and among them four are older than 10 Gyr and the other six have intermediate ages between 3 - 8 Gyr. The masses for these outer-halo GCs are from 7.0 × 104 M to 1.02 × 10^6 M. We argued that GC2 and GC3, whose ages, metallicities and distance moduli are almost the same, were accreted from the same satellite galaxy, if they did not form in situ. The statistical results show that the ages and metallicities of these 10 M31 outer-halo GCs do not vary with projected radial position, and a relationship between age and metallicity does not exist.

关键词： galaxies: halos - galaxies: individual (M31) - star clusters: general

Discovery of an Optical Jet in the Rosette Nebula: Rosette HH2

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chinese Journal of Astronomy and Astrophysics 2003年第6期3卷 495-498页

作者： Jin-Zeng Linational astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

We report on the discovery of an optical jet - Rosette HH2 - in the RosetteNebula. The jet system bears unique features for residing at the center of a giant HII region, andits energy source is visible with apparently very low extinction along the line of sight. Unlikemost other Herbig-Haro jets, this jet indicates a high-excitation origin, and its extended portionshows a seemingly intact structure, instead of normally a shocked working surface, which isattributed to photoablation.

关键词： stars: formation stars: pre-main sequence herbig-haro objects ISM: jetsand outflows

A method to predict amplitude and date of maximum sunspot number

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chinese Science Bulletin 2000年第14期45卷 1287-1290页

作者： HAN Yanbenbeijing astronomical Observatory, chinese academy of sciences, national astronomical observatories, chinese academy of sciences, beijing 100012, China beijing astronomical Observatory Chinese Academy of Sciences National Astronomical Observatories Chinese Academy of Sciences Beijing China

A method to predict the amplitude and date of the maximum sunspot number is introduced. The regression analysis of the relationship between the variation rate of monthly sunspot numbers in the initial stage of solar cycles and both of the maximum and the time-length of ascending period of the cycle showed that they are closely correlative. In general, the maximum will be larger and the ascending period will be shorter when the rate is larger. The rate of sunspot numbers in the initial 2 years of the 23rd cycle is thus analyzed based on these grounds and the maximum of the cycle is predicted. For the smoothed monthly sunspot numbers, the maximum will be about 139.2 ±18.8 and the time-length of ascending period will be about 3.31 ±0.42 years, that is to say, the maximum will appear around the spring of the year 2000. For the mean monthly ones, the maximum will be near 170.1±22.9 and the time-length of ascending period will be about 3.42 ±0.46 years, that is to say, the appearing date of the maximum

关键词： solar activity prediction sunspot number 23rd solar cycle.

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, beijing 100012 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

The Two Mini-lobes of the CSO OQ208——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 200030 national astronomical observatories, 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) OQ208. 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 0.032±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 OQ208) - galaxies: active

IRAS 01005+7910:a High Galactic Latitude Post-AGB Star

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chinese Journal of Astronomy and Astrophysics 2002年第3期2卷 193-196页

作者： Jing-Yao Hunational astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

IRAS 01005+7910 is a cold IRAS source. We present its optical identification, photometric and spectroscopic observation results. Its optical counterpart is classified as a B2Ie star with V magnitude 10.85. Its Hα line shows the P Cygni profile. According to its location in the Galaxy (b = 16.6), we consider it to be a post-AGB star or a proto-planetary nebula.

关键词： stars: post-AGB - infrared: stars - stars: evolution

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, beijing 100012 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 39 variable stars are newly discovered, including 22 W ... 详细信息

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

A Method of Obtaining the Pitch Angle of Spiral Arms and the Inclination of Galactic Discs

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chinese Journal of Astronomy and Astrophysics 2001年第5期1卷 395-405页

作者： Jun Ma (national astronomical observatories, chinese academy of sciences, beijing 100012) E-mail:majun@*** national astronomical observatories Chinese Academy of Sciences Beijing 100012

We investigate the mathematical form, the symmetry of spiral structure and the projected images of galactic discs. The measured pitch angles of spiral arms and inclination angles of galactic discs for 60 spiral galaxies are presented. The global spiral structure is emphasized in the study. It is found that, except for small-scale distortions, the spiral arms of those galaxies that were classified as AC 12 in the arm classification system of Elmegreen & Elmegreen, can be represented by the logarithmic spiral form.

关键词： galaxies: spiral galaxies - galaxies: spiral arm disc: inclination

Pulsars in FIRST Observations

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chinese Journal of Astronomy and Astrophysics 2002年第2期2卷 146-150页

作者： Xiang-Hua Li and Jin-Lin Han national astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

We identify 16 pulsars from the Survey of Faint Images of the Radio Sky at Twenty-cm (FIRST) at 1.4 GHz. Their positions and total flux densities are extracted from the FIRST catalog. By comparing the source positions with those in the PSR catalog, we obtain better determined positions of PSR J1022+1001, J1518+4904, J1652+2651, and proper motion upper limits of PSR J0751+1807, J1012+5307, and J1640+2224. The proper motions of the other ten pulsars are consistent with the catalog values.

关键词： pulsar: general -stars: neutron