In the last 30 days

• Open/close Photometric study of W UMa type binaries in the intermediate open cluster NGC 7789

  Kandulapati Sriram and Pasagada Vivekananda Rao  2010 Res. Astron. Astrophys. 10 159 Tag this article

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  The light curve solutions of two W UMa binary systems in the intermediate open cluster NGC 7789 are presented in this paper. These variables were observed using the 2 m telescope of the IUCAA-Girawali Observatory. The V passband photometric solutions of the two W UMa binaries were obtained using the latest version of the W–D program. The result shows that both systems are H-subtype W UMa binaries with high mass ratios.

• Open/close A convergent mean shift algorithm to select targets for LAMOST

  Guang-Wei Li and Gang Zhao  2009 Res. Astron. Astrophys. 9 803 Tag this article

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  This paper firstly finds that the Mean Shift Algorithm used by the Observation Control System (OCS) Research Group of the University of Science and Technology of China in Survey Strategy System 2.10 (SSS2.10) to select targets for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is not convergent in theory. By carefully studying the mathematical formulation of the Mean Shift Algorithm, we find that it tries to find a point where some objective function achieves its maximum value; the Mean Shift Vector can be regarded as the ascension direction for the objective function. If we regard the objective function as the numerical description for the imaging quality of all targets covered by the focal panel, then the Mean Shift Algorithm can find the place where the imaging quality is the best. So, the problem of selecting targets is equal to the problem of finding the place where the imaging quality is the best. In addition, we also give some effective heuristics to improve computational speed and propose an effective method to assign point sources to the respective fibers. As a result, our program runs fast, and it costs only several seconds to generate an observation.

• Open/close Extending the Eigenvector 1 space to the optical variability of quasars

  Yu-Feng Mao et al  2009 Res. Astron. Astrophys. 9 529 Tag this article

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  We introduce a new physical parameter, the optical variability amplitude, to the well-established Eigenvector 1 space of quasars and test a sample of long-term B-band light curves of 42 Palomar–Green quasars monitored by Giveon et al. We find that the optical variability amplitude strongly correlates with the intensity ratio of FeII to Hβ, Hβ width and peak luminosity at 5007 Å. We briefly discuss the physical meaning of our findings and suggest that the Eddington ratio may be a key factor in determining a quasar's variability.

• Open/close Evolution of optical spectral index and variability properties of S5 0716+714

  Jian-Ming Hao et al  2010 Res. Astron. Astrophys. 10 125 Tag this article

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  We analyze the spectral variability and spectral evolution in the optical energy region by using multiband (BVRI) optical observations of S5 0716+714 spanning 1994 to 2005. The spectrum hardens when the source becomes brighter, which is consistent with general BL Lac objects. The spectral evolution parameter implies that the spectral variability is small in optical bands over 10 years. A simple model representing the variability of a synchrotron component can explain the spectral changes. In addition, we employ the z-transformed discrete correlation function (ZDCF) to analyze the optical multiband flux correlation. The long-term light curve behavior reveals that the variability time scales are 3.5 yr in the B-band, 3.3 yr in the V-band, 3.4 yr in the R-band and 3.5 yr in the I-band. The time lags between any two optical bands were not found when considering statistical errors.

• Open/close A study of active galactic nuclei in low surface brightness galaxies with Sloan Digital Sky Survey spectroscopy

  Lin Mei et al  2009 Res. Astron. Astrophys. 9 269 Tag this article

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  Active galactic nuclei (AGNs) in low surface brightness galaxies (LSBGs) have received little attention in previous studies. We present a detailed spectral analysis of 194 LSBGs from the Impey et al. (1996) APM LSBG sample which has been observed spectroscopically by the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). Our elaborate spectral analysis enables us to carry out, for the first time, reliable spectral classification of nuclear processes in LSBGs based on the standard emission line diagnostic diagrams in a rigorous way. Star-forming galaxies are common, as found in about 52% of LSBGs. We find that, contrary to some previous claims, the fraction of galaxies that contain AGNs is significantly lower than that found in nearby normal galaxies of high surface brightness. This is qualitatively in line with the finding of Impey et al. This result holds true even within each morphological type from Sa to Sc. LSBGs that have larger central stellar velocity dispersions or larger physical sizes tend to have a higher chance of harboring an AGN. For three AGNs with broad emission lines, the black hole masses estimated from the emission lines are broadly consistent with the well known M-σ _* relation established for normal galaxies and AGNs.