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Zhou Z.-M.,CAS National Astronomical Observatories | Zhou Z.-M.,University of Chinese Academy of Sciences | Cao C.,Shandong University | Cao C.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment | Wu H.,CAS National Astronomical Observatories
Research in Astronomy and Astrophysics | Year: 2012

Stellar bars are important for the secular evolution of disk galaxies because they can drive gas into the galactic central regions. To investigate the star formation properties in barred galaxies, we presented a multi-wavelength study of two barred galaxies: NGC 2903 and NGC 7080. We performed the three-component bulge-disk-bar decomposition using the 3.6 μm images, and identified the bulges in the two galaxies as pseudobulges. Based on the narrowband Hα images, the star formation clumps were identified and analyzed. The clumps in the bulge regions have the highest surface densities of star formation rates in both galaxies, while the star formation activities in the bar of NGC 2903 are more intense than those in the bar of NGC 7080. Finally, we compared our results with the scenario of bar-driven secular evolution in previous studies, and discussed the possible evolutionary stages of the two galaxies. © 2012 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd. Source


Guo J.,Qingdao University of Science and Technology | Guo J.,University of Chinese Academy of Sciences | Li B.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment
Astrophysics and Space Science | Year: 2013

We examine the electron-ion streaming instabilities driven by drift velocities of the order of the electron thermal velocity in a nonmagnetized plasma by using one-dimensional electrostatic particle-in-cell code which adopts an ion-to-electron mass ratio of 1600. An initial state is set up where the ion bulk speed is zero while the electrons drift relative to ions, and where electrons are much hotter. We examine in detail four runs where the drift velocity is systematically varied from lower than to larger than the electron thermal velocity. In all runs the Langmuir waves with Doppler-shifted frequencies dominate early on when streaming instabilities are too weak to discern. And then intense ion-acoustic waves or Buneman instabilities appear, which tend to be accompanied by localized electron and ion beams. Ion-acoustic modes and Buneman modes co-exist in the system when the initial drift velocity is just over the electron thermal speed. Beam modes are excited when localized beams with large enough velocities appear. In the developed stage of instabilities, the direction in which density depressions propagate is always opposite to that of the localized ion beams. When the initial drift velocity is close to the electron thermal speed, categorizing the relevant instabilities is not easy, and one needs to examine in detail the wave dispersion diagrams at various stages of the evolution of the system. © 2013 Springer Science+Business Media Dordrecht. Source


Wu H.,CAS National Astronomical Observatories | Wu C.-J.,Beijing Normal University | Cao C.,Shandong University | Cao C.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment | And 2 more authors.
Research in Astronomy and Astrophysics | Year: 2012

We present the optical to mid-infrared SEDs of 11 debris disk candidates from Spitzer SWIRE fields. All the candidates are selected from SWIRE 24 μm sources matched with both the SDSS star catalog and the 2MASS point source catalog. They show an excess in the mid-infrared at 24 μm (K S - [24] Vega ≥ 0.44), indicating the presence of a circumstellar dust disk. The observed optical spectra show that they are all late-type main-sequence stars covering the spectral types of FGKM. Their fractional luminosities are well above 5 × 10 -5, even up to the high fractional luminosity of 1 × 10 -3. The high galactic latitudes of SWIRE fields indicate that most of these candidates could belong to the oldest stars in the thick disk. Our results indicate that high fractional luminosity debris disks could exist in old solar-like star systems, though they are still quite rare. Their discovery at high galactic latitudes also provides an excellent opportunity for further study of the properties and evolution of debris disks in regions of the Galaxy with low densities of ISM, called ISM poor environments. © 2012 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd. Source


Jiang Y.,Shandong University | Jiang Y.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment
Journal of High Energy Physics | Year: 2014

The mass deformed effective world-sheet theory of semi local vortices was constructed via the field theoretical method. By Euler-Lagrangian equations, the Ansatze for both the gauge field and the adjoint scalar were solved, this ensures that zero modes of vortices are minimal excitations of the system. Up to the 1/g2 order, all profiles are solved. The mass deformed effective action was obtained by integrating out the transverse plane of the vortex string. The effective theory interpolates between the local vortex and the lump. Respecting certain normalization conditions, the effective theory shows a Seiberg-like duality, which agrees with the result of the Kähler quotient construction. Source


Zhou Z.-M.,CAS National Astronomical Observatories | Cao C.,Shandong University | Cao C.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment | Cao C.,California Institute of Technology | Wu H.,CAS National Astronomical Observatories
Astronomical Journal | Year: 2015

Stellar bars are important internal drivers of secular evolution in disk galaxies. Using a sample of nearby spiral galaxies with weak and strong bars, we explore the relationships between the star formation feature and stellar bars in galaxies. We find that galaxies with weak bars tend coincide with low concentrical star formation activity, while those with strong bars show a large scatter in the distribution of star formation activity. We find enhanced star formation activity in bulges toward stronger bars, although not predominantly, consistent with previous studies. Our results suggest that different stages of the secular process and many other factors may contribute to the complexity of the secular evolution. In addition, barred galaxies with intense star formation in bars tend to have active star formation in their bulges and disks, and bulges have higher star formation densities than bars and disks, indicating the evolutionary effects of bars. We then derived a possible criterion to quantify the different stages of the bar-driven physical process, while future work is needed because of the uncertainties. © 2015. The American Astronomical Society. All rights reserved. Source

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