Four Oke-Gunn (OG) standards, HD 19445, HD 84937, BD+26 2606 and BD+17 4708 are used as standard stars for flux calibration in the BATC project. They are also widely used in the visual wavelength region in many other ...Four Oke-Gunn (OG) standards, HD 19445, HD 84937, BD+26 2606 and BD+17 4708 are used as standard stars for flux calibration in the BATC project. They are also widely used in the visual wavelength region in many other photometric projects. Over the years we have observed on 58 good photometric nights, and the data obtained are used for flux calibration. Normally two or three OG standards are observed in every photometric night. The data are used for getting the atmospheric extinction coefficients and instrumental magnitude zero point. We also use these data to make inter-comparisons among the magnitudes of these standard stars. As a result, we found the magnitudes of HD 19445, HD 84937 and BD+17 4708 to agree well with those estimated in previous work to within 0.03 magnitude. However, BD+26 2606 shows a larger deviation especially at short wavebands. Possible reasons are analyzed and the revised magnitudes are obtained for these standards. It is shown that the quality of flux calibration of the BATC fields is significantly approved by applying the new magnitudes.展开更多
We present the results of a variable star search in a field next to the edge-on galaxies NGC 4565 from the archive data of Beijing-Arizona-Taibei-Connecticut Multicolor Sky Survey. Three new variable stars were discov...We present the results of a variable star search in a field next to the edge-on galaxies NGC 4565 from the archive data of Beijing-Arizona-Taibei-Connecticut Multicolor Sky Survey. Three new variable stars were discovered. Based on spectra obtained from the 2.16m NAOC telescope, we identify two of these as RR Lyr stars and one as a special T Tauri star.展开更多
With a recently constructed composite quasar spectrum and the χ<SUP>2</SUP> minimization technique, we describe a general method for estimating the photometric redshifts of a large sample of quasars by de...With a recently constructed composite quasar spectrum and the χ<SUP>2</SUP> minimization technique, we describe a general method for estimating the photometric redshifts of a large sample of quasars by deriving theoretical color-redshift relations and comparing the theoretical colors with the observed ones. We estimated the photometric redshifts from the 5-band SDSS photometric data of 18678 quasars in the first major data release of SDSS and compared them with their spectroscopic redshifts. The difference is less than 0.1 for 47 % of the quasars and less than 0.2 for 68 %. Based on the calculation of the theoretical color-color diagrams of stars, galaxies and quasars both on the SDSS system and on the BATC system, we expect that we would be able to select candidates of high redshift quasars more efficaciously with the latter than with the former, provided the BATC survey can detect objects with magnitudes fainter than 21.展开更多
Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mix...Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm was applied to obtain a robust partition into two clusters, which allowed us to discuss the virial mass and velocity distribution of each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of 5.4h-1 Mpc are currently expanding at 583 km s-1 along a direction with a projection angle of 67.5°, and they will reach a maximum extent of 5.65 h-1 Mpc in about 1.0 h-1 Gyr.展开更多
文摘Four Oke-Gunn (OG) standards, HD 19445, HD 84937, BD+26 2606 and BD+17 4708 are used as standard stars for flux calibration in the BATC project. They are also widely used in the visual wavelength region in many other photometric projects. Over the years we have observed on 58 good photometric nights, and the data obtained are used for flux calibration. Normally two or three OG standards are observed in every photometric night. The data are used for getting the atmospheric extinction coefficients and instrumental magnitude zero point. We also use these data to make inter-comparisons among the magnitudes of these standard stars. As a result, we found the magnitudes of HD 19445, HD 84937 and BD+17 4708 to agree well with those estimated in previous work to within 0.03 magnitude. However, BD+26 2606 shows a larger deviation especially at short wavebands. Possible reasons are analyzed and the revised magnitudes are obtained for these standards. It is shown that the quality of flux calibration of the BATC fields is significantly approved by applying the new magnitudes.
基金Supported by the National Natural Science Foundation of China.
文摘We present the results of a variable star search in a field next to the edge-on galaxies NGC 4565 from the archive data of Beijing-Arizona-Taibei-Connecticut Multicolor Sky Survey. Three new variable stars were discovered. Based on spectra obtained from the 2.16m NAOC telescope, we identify two of these as RR Lyr stars and one as a special T Tauri star.
基金Supported by the National Natural Science Foundation of China.
文摘With a recently constructed composite quasar spectrum and the χ<SUP>2</SUP> minimization technique, we describe a general method for estimating the photometric redshifts of a large sample of quasars by deriving theoretical color-redshift relations and comparing the theoretical colors with the observed ones. We estimated the photometric redshifts from the 5-band SDSS photometric data of 18678 quasars in the first major data release of SDSS and compared them with their spectroscopic redshifts. The difference is less than 0.1 for 47 % of the quasars and less than 0.2 for 68 %. Based on the calculation of the theoretical color-color diagrams of stars, galaxies and quasars both on the SDSS system and on the BATC system, we expect that we would be able to select candidates of high redshift quasars more efficaciously with the latter than with the former, provided the BATC survey can detect objects with magnitudes fainter than 21.
基金the National Natural Science Foundation of China.
文摘Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm was applied to obtain a robust partition into two clusters, which allowed us to discuss the virial mass and velocity distribution of each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of 5.4h-1 Mpc are currently expanding at 583 km s-1 along a direction with a projection angle of 67.5°, and they will reach a maximum extent of 5.65 h-1 Mpc in about 1.0 h-1 Gyr.
