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Chang R.X.,Chinese Academy of Sciences | Shen S.Y.,Chinese Academy of Sciences | Shen S.Y.,Key Laboratory for Astrophysics | Hou J.L.,Chinese Academy of Sciences
Astrophysical Journal Letters | Year: 2012

The disk galaxy UGC8802 has high neutral gas content and a flat profile of star formation rate compared to other disk galaxies with similar stellar mass. It also shows a steep metallicity gradient. We construct a chemical evolution model to explore its growth history by assuming its disk grows gradually from continuous gas infall, which is shaped by a free parameter - the infall-peak time. By adopting the recently observed molecular surface density related star formation law, we show that a late infall-peak time can naturally explain the observed high neutral gas content, while an inside-out disk formation scenario can fairly reproduce the steep oxygen abundance gradient. Our results show that most of the observed features of UGC8802 can be well reproduced by simply "turning the knob" on gas inflow with one single parameter, which implies that the observed properties of gas-rich galaxies could also be modeled in a similar way. © 2012. The American Astronomical Society. All rights reserved.. Source

Lin Z.,Shanghai University | Zhang J.,Shanghai University | Jiang Y.,Shanghai University | Jiang Y.,Key Laboratory for Astrophysics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

In this paper, by treating the hopping parameter in the Bose-Hubbard model as a perturbation, with the help of the resummed Green's function method and cumulant expansion, the momentum distribution function of an ultracold Bose system in a triangular optical lattice is calculated analytically. By its use, the time-of-flight absorption picture is plotted and the corresponding visibility is determined. A comparison between our analytical results and the experimental data of Becker exhibits a qualitative agreement. © 2012 American Physical Society. Source

Lin Z.,Shanghai University | Zhang J.,Shanghai University | Jiang Y.,Shanghai University | Jiang Y.,Key Laboratory for Astrophysics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

In this paper, we investigate systematically the Mott-insulator-superfluid quantum phase transitions for ultracold scalar bosons in triangular, hexagonal, and Kagomé optical lattices. With the help of the field-theoretical effective potential, by treating the hopping term in the Bose-Hubbard model as perturbation, we calculate the phase boundaries analytically for different integer filling factors. Our analytical results are in good agreement with recent numerical results. © 2012 American Physical Society. Source

Shen S.,Chinese Academy of Sciences | Shen S.,Key Laboratory for Astrophysics | Yang X.,Chinese Academy of Sciences | Yang X.,Shanghai JiaoTong University | And 3 more authors.
Astrophysical Journal | Year: 2014

We examine the statistical properties of the brightest group galaxies (BGGs) by using a complete spectroscopic sample of groups/clusters of galaxies selected from the Data Release 7 of the Sloan Digital Sky Survey. We test whether BGGs and other bright members of groups are consistent with an ordered population among the total population of group galaxies. We find that the luminosity distributions of BGGs do not follow the predictions from the order statistics (OS). The average luminosities of BGGs are systematically brighter than OS predictions. On the other hand, by properly taking into account the brightening effect of the BGGs, the luminosity distributions of the second brightest galaxies are in excellent agreement with the expectations of OS. The brightening of BGGs relative to the OS expectation is consistent with a scenario that the BGGs on average have overgrown about 20% masses relative to the other member galaxies. The growth (ΔM) is not stochastic but correlated with the magnitude gap (G 1, 2) between the brightest and the second brightest galaxy. The growth (ΔM) is larger for the groups having more prominent BGGs (larger G 1, 2) and averagely contributes about 30% of the final G 1, 2 of the groups of galaxies. © 2014. The American Astronomical Society. All rights reserved.. Source

Yang Y.-G.,Huaibei Normal University | Shao Z.-Y.,Chinese Academy of Sciences | Shao Z.-Y.,Key Laboratory for Astrophysics | Pan H.-J.,Chinese Academy of Sciences | Yin X.-G.,Huaibei Normal University
Publications of the Astronomical Society of the Pacific | Year: 2011

New CCD photometry for the eclipsing binary EH Cnc was made from 2009 to 2011, and five new eclipsing times are presented. Through using the updated Wilson-Devinney code, we first deduced the photometric solution at Χ2 = 0.9906. The results show that EH Cnc is aW-type contact binary, whose mass ratio and overcontact degree are q = 2.51 (±0.02) and f = 27.7% (±3.4%), respectively. By analyzing the O - C curve of EH Cnc, it is found that there exists a secular-period decrease with a cyclic variation. The period and semiamplitude are P3 = 16.6 (±0.4) yr and A = 0.0032 days (±0.0003 days), respectively. This kind of cyclic variation may probably be attributed to the light-time effect via the presence of an unseen third body, because the values of ΔQ1,2 are much smaller than the typical one for close binaries. The orbital period of EH Cnc continuously decreases at a rate of dP/dt = -1:01 (±0.05) × 10-7 days yr-1. This kind of secular period decrease may result from mass transfer from the primary to the secondary, accompanied by mass and angular momentum loss from the system. With the orbital period decreasing, the inner and outer Roche lobes will shrink, causing the contact degree to increase. Finally, binaries with decreasing periods, such as EH Cnc, will evolve into deep-contact configurations. © 2011. Source

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