| 2002,
Vol.2, No.5 (October 20, 2002)
|
Letters
|
Cosmology
|
Extragalactic astronomy
|
The Galaxy
|
Stars
|
|
|
|
Instruments, observational techniques and data processing
|
|
|
| An Ancient Solar Eclipse Record
``Tian-da-yi'' in the 10th Century BC
Ci-Yuan Liu Affiliation: Shaanxi Observatory, Chinese Academy of Sciences, Lintong 710600 E-mail: liucy@ms.sxso.ac.cn
Abstract |
Verification of a Similar Cycle Prediction for the Ascending and Peak Phases of Solar Cycle 23 Jia-Long Wang (1), Jian-Cun Gong (2), Si-Qing Liu (2),Gui-Ming Le (2), Yan-Ben Han (1) and Jing-Lan Sun (1) Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing, China (2) Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100080 E-mail: Jialongw@btamail.net.cn (corresponding author) Abstract |
A Remark on Using Gravitational Lensing Probability as a Probe of the Central Regions of CDM Halos Yun Li Affiliation: National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 E-mail: liy@bao.ac.cn
Abstract |
| Comparisons of Infrared Colors and Emission-line Intensities between
Two types of Seyfert~2 Galaxies Lin-Peng Cheng, Yong-Heng Zhao and Jian-Yan Wei Affiliation: National Astronomical Observatories, CAS (NAOC), Beijing, China E-mail: linpeng@astro.as.utexas.edu (corresponding author) Abstract We study the relation between the infrared colors, [OIII] emission lines, gaseous absorbing column density (NH),and the detectability of the polarized (hidden) broad-line region (HBLR) in a large sample of 75 Seyfert 2 galaxies (Sy2s). From the indicators of star-formation activity, f60/f100 and LFIR/LB, we find some evidence that the Sy2s without HBLR show higher star-formation activities than those with HBLR, in agreement with previous prediction. Also, we confirm that the HBLR Sy2s tend to have a larger luminosity ratio of the core to the host galaxy, suggesting that the HBLR Sy2s display more powerful AGN activity. However, the level of obscuration found in previous papers is nearly indistinguishable between the two types of Sy2s. The results support the statement that the non-HBLR Sy2s, with a weaker core component and a stronger star-formation activity component, are intrinsically different from the HBLR Sy2s, which are Sy1 systems with a hidden powerful AGN core and a low star-formation activity. The indications are that the non-HBLR Sy2s might be at an earlier evolutionary phase than the HBLR Sy2s. Key words: galaxies: active --- galaxies: Seyfert --- polarization --- star formation PDF file (203 KB) | gzipped PS file (270 KB) | Back to Contents |
Information from the Kinematics of F and G Stars in the Solar Neighborhood Yu-Qin Chen, Gang Zhao and Jian-Rong Shi Affiliation: National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 E-mail: cyq@yac.bao.ac.cn (corresponding author) Abstract We have calculated the orbital parameters for 90 stars in Chen et al. and updated the kinematic data for stars in Edvardsson et al. by using the accurate Hipparcos parallaxes and proper motions, and recalculated the  -element abundances in Edvardsson et al. in a way consistent with Chen et al. The two sets of data are combined
in a study of stellar populations and characteristics of F & G stars in the solar neighborhood. We confirm the result of Chen et
al. that a distinguishable group of stars may belong to the thick disk rather than the thin disk. The ages for the stars are
determined using the theoretical isochrones of VandenBerg et al.
The age-metallicity relation is investigated for different subgroups according to distance from the sun and galactic orbital parameters.
It is found that a mixing of stars with different orbital parameters significantly affect the age-metallicity relation for the disk. Stars
with orbits confined to the solar circle all have metallicities
[Fe/H]>  0.3 irrespective of their distances from the sun or from the Galactic plane.Key words: stars: kinematics --- Galaxy: evolution --- Galaxy: solar neighborhood PDF file (322 KB) | gzipped PS file (582 KB) | Back to Contents |
A Statistical Model for Predicting the Average Abundance Patterns of Heavier Elements in Metal-Poor Stars Bo Zhang (1,2), Yan-Xia Zhang (3), Ji Li (1,3) and Qiu-He Peng (4) Affiliation: (1) Department of Physics, Hebei Normal University, Shijiazhuang 050016 (2) Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000 (3) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (4) Department of Astronomy, Nanjing University, Nanjing 210093 E-mail: zhangbo@hebtu.edu.cn (corresponding author) Abstract We have collected nearly all the available observed data of the elements from Ba to Dy in halo and disk stars in the metallicity range 4.0 < [Fe/H] < 0.5. Based on the observed data of Ba and Eu,
we evaluated the least-squares regressions of [Ba/Fe] on [Fe/H], and [Eu/H] on [Ba/H]. Assuming that the heavy elements (heavier than Ba)
are produced by a combination of the main components of s- and r-processes in metal-poor stars, and choosing Ba and Eu as
respective representative elements of the main s- and the main r-processes, a statistical model for predicting the Galactic
chemical evolution of the heavy elements is presented. With this model, we calculate the mean abundance trends of the heavy elements
La, Ce, Pr, Nd, Sm, and Dy with the metallicity. We compare our results with the observed data at various metallicities, showing that
the predicted trends are in good agreement with the observed trends, at least for the metallicity range
[Fe/H]  2.5. Finally, we
discuss our results and deduce some important information about the Galactic chemical evolution.Key words: stars: abundances --- stars: Population II --- Galaxy: evolution --- method: statistical PDF file (294 KB) | gzipped PS file (417 KB)| Back to Contents |
On the Red Edge of the 
Scuti Instability StripYan Xu (1,2), Zhi-Ping Li (1), Li-Cai Deng (1) and Da-Run Xiong (3) Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing 100012, China (2) Department of Physics, Tianjin Normal University, Tianjin 300073 (3) Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 E-mail: xuyan@ns3.bao.ac.cn (corresponding author) Abstract The
Scuti star catalogue is used to derive the observational locations of such stars on the HR diagram. The
theoretical and observational instability strips are compared to check the theoretical red edge obtained by considering non-local
time-dependent convection theory. The observational instability strip almost overlaps with the theoretical one, but the observed blue
and red envelopes are hotter than the theoretical edges. The distribution of
Scuti stars in the pulsation strip is not uniform.Key words: stars: variables:
Sct --- stars: oscillations --- stars: HR diagramPDF file (228 KB) | gzipped PS file (363 KB) | Back to Contents |
| Optical Flash of GRB 990123: Constraints on the Physical
Parameters of the Reverse Shock Yi-Zhong Fan, Zi-Gao Dai, Yong-Feng Huang and Tan Lu Affiliation: Department of Astronomy, Nanjing University, Nanjing 210093 E-mail: daizigao@public1.ptt.js.cn (corresponding author) Abstract The optical flash accompanying GRB 990123 is believed to be powered by the reverse shock of a thin shell. With the best-fit physical parameters for GRB 990123 and the assumption that the parameters in the optical flash are the same as in the afterglow, we show that: 1) the shell is thick rather than thin, and we have provided the light curve for the thick shell case which coincides with the observation; 2) the theoretical peak flux of the optical flash accounts for only 3×10-4 of the observed. In order to remove this discrepancy, the physical parameters, the electron energy and magnetic ratios, 
and  , should
be 0.61 and 0.39, which are very different from their values for the late afterglow.Key words: gamma rays: bursts --- gamma rays: theory PDF file (133 KB) | gzipped PS file (59 KB) | Back to Contents |
| The Radial Structure of Pulsar Radio Emission Regions Xin-Ji Wu (1, 2, 3), Zhan-Kui Huang (1, 2) and Xuan-Bin Xu (1, 2) Affiliation: (1) Department of Astronomy, Peking University, Beijing 100871 (2) The Chinese Academy of Sciences-Peking University Joint Beijing Astrophysics Center, Beijing 100871 (3) Urumqi Astronomical Observatory, National Astronomical Observatories, Chinese Academic of Science, Urumqi 830011 E-mail: wuxj@bac.pku.edu.cn (corresponding author) Abstract An important parameter in the study of the radial structure of the pulsar radio emission region is the altitude of the emission, but this cannot be derived directly from the observations. The altitude can be expressed as a function of frequency,  , and the method of
K analysis can be used to calculate the power law index
for 18 pulsars observed at two frequencies,
610 MHz and 1408 MHz and for three pulsars observed at three or more frequencies. The average value of
is 0.27, which indicates that the emission altitude increases
with decreasing frequency and that the radial structure is compact.Key words: stars: pulsars PDF file (180 KB) | gzipped PS file (192 KB) | Back to Contents |
| New Variable Stars Discovered as By-product of the Beijing Astronomical Observatory Supernova Survey Min-Zhi Kong (1, 2), Yu-Lei Qiu (1), Chuan-Jian Shen (1), Jin-Song Deng (1, 3, 4), Bo Zhang (2) and Jing-Yao Hu (1) Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing 100012, China (2) Department of Physics, Heibei Normal University, Shijiazhuang 050016 (3) Research Center for the Early Universe, Univ. of Tokyo, Bunkyo-Ku, Tokyo, Japan (4) Department of Astronomy, Univ. of Tokyo, Bunkyo-Ku, Tokyo, Japan E-mail: qiuyl@nova.bao.ac.cn (corresponding author) Abstract The Beijing Astronomical Observatory (BAO) 0.6 m telescope has been used for nearby supernova survey in more than 3000 fields, covering a total area of 235 deg2. More than 260000 CCD images have been collected since April 1996, with 45 supernovae discovered. We searched for variables in about 90000 images taken during 1996--1998. For the fields in which long period variables (LPVs) were discovered, we reduced further images taken from 1999 to 2000, for the period estimation. Among the 280000 stars selected from the survey fields, i.e., brighter than 18 mag, we discovered seven new LPVs and reconfirmed three known LPVs. Additionally, we found 146 variable star candidates, and reconfirmed about 20 previously known or suspected objects. Key words: stars: variables --- supernovae --- surveys PDF file (325 KB) | gzipped PS file (594 KB) | Back to Contents |
| Ghost Images in Schmidt CCD Photometry Bin Yang (1, 2), Jin Zhu (1) and Yu-Ying Song (2, 3) Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing 100012, China (2) Department of Astronomy, Beijing Normal University, Beijing 100875 (3) Beijing Planetarium, Beijing 100044 E-mail: yangbin@bac.pku.edu.cn (corresponding author) Abstract The wide field of the Schmidt telescope implies a greater chance of the field containing bright objects, and the presence of a corrector lens produces a certain type of ghost images. We summarize and confirm the features of such ghost images in Schmidt CCD photometry. The ghost images could be star-like under special observational conditions. The zenith distance of the telescope, among other factors, is found to correlate with different patterns of the ghost images. Some relevant issues are discussed and possible applications of our results are suggested. Key words: instrumentation: detector --- techniques: photometric --- stars: imaging PDF file (929 KB) | gzipped PS file (2515 KB) | Back to Contents |
