Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment

Weihai, China

Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment

Weihai, China
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Gai N.,Dezhou University | Tang Y.,Dezhou University | Tang Y.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment | Yu P.,Chongqing Normal University | Dou X.,Dezhou University
Astrophysical Journal | Year: 2017

Asteroseismology is a powerful tool for constraining stellar parameters. NASA's Kepler mission is providing individual eigenfrequencies for a huge number of stars, including thousands of red giants. Besides the frequencies of acoustic modes, an important breakthrough of the Kepler mission is the detection of nonradial gravity-dominated mixed-mode oscillations in red giants. Unlike pure acoustic modes, mixed modes probe deeply into the interior of stars, allowing the stellar core properties and evolution of stars to be derived. In this work, using the gravity-mode period spacing and the large frequency separation, we construct the ΔΠ1-Δν asteroseismic diagram from models of subgiants and red giants with various masses and metallicities. The relationship ΔΠ1-Δν is able to constrain the ages and masses of the subgiants. Meanwhile, for red giants with masses above 1.5 M o, the ΔΠ1-Δν asteroseismic diagram can also work well to constrain the stellar age and mass. Additionally, we calculate the relative "isochrones" τ, which indicate similar evolution states especially for similar mass stars, on the ΔΠ1-Δν diagram. © 2017. The American Astronomical Society. All rights reserved..


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.


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.


Gai N.,Dezhou University | Gai N.,Chinese Academy of Sciences | Tang Y.,Dezhou University | Tang Y.,Chinese Academy of Sciences | Tang Y.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment
Astrophysical Journal | Year: 2015

The "bump" is a prominent feature of the red giant branch (RGB) luminosity function of stellar clusters. Through constructing a grid of models with different masses and metallicities to study the feature of the RGB bump luminosity we find that the luminosity increases almost monotonically with increasing mass for a given metallicity and decreases monotonically with increasing metallicity. Moreover, different stars have different shapes of the RGB bump. It is correlated with the sharpness of the H discontinuity, which is left over by the convection envelope during the first dredge-up. Using the periodicity in the small separations d01, d10 to probe the internal structure, we find that, at about half the acoustic radius, the sound speed has a sharp variation that is caused by a local depression of the first adiabatic exponent in the second helium ionization zone. It induces an oscillation modulation in d01, d10 with a period of 6.4 μ Hz. Meanwhile, in the same model, the base of the convective envelope is located at a relatively small acoustic radius , which is about 10-1. It is too deep to detect the exact location of the bottom of the outer convective envelope. In order to discriminate the evolutionary status of different stars, we calculate the asymptotic g-mode period spacing . We find that decreases monotonically with evolution. It is a reliable parameter for distinguishing stars in different positions of the RGB bump. © 2015. The American Astronomical Society. All rights reserved..


Tang Y.K.,Dezhou University | Tang Y.K.,Chinese Academy of Sciences | Tang Y.K.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment | Gai N.,Dezhou University | Gai N.,Chinese Academy of Sciences
Astrophysical Journal | Year: 2013

Stellar age is an important quantity in astrophysics, which is useful for many fields both in the universe and galaxies. It cannot be determined by direct measurements, but can only be estimated or inferred. We attempt to find a useful indicator of stellar age, which is accurate from the zero-age main sequence to the tip of red giant branch for low-mass stars. Using the Yale Rotation and Evolution Code (YREC), a grid of stellar models has been constructed. Meanwhile, the frequency of maximum oscillations' power νmax and the large frequency separation Δν are calculated using the scaling relations. For the stars, the masses of which are from 0.8 Ṁ to 2.8 Modot;, we can obtain the νmax and stellar age by combing the scaling relations with the four sets of grid models (YREC, Dotter et al., Marigo et al., and YY isochrones). We find that νmax is tightly correlated and decreases monotonically with the age of the star from the main sequence to the red giant evolutionary stages. Moreover, we find that the line shapes of the curves in the Age versus νmax diagram, which is plotted by the four sets of grid models, are consistent for red giants with masses from 1.1 Modot; to 2.8 Modot;. For red giants, the differences of correlation coefficients between Age and νmax for different grid models are minor and can be ignored. Interestingly, we find two peaks that correspond to the subgiants and bump of red giants in the Age versus νmax diagram. By general linear least-squares, we make the polynomial fitting and deduce the relationship between log(Age) and log(νmax) in red giants' evolutionary state. © 2013. The American Astronomical Society. All rights reserved.


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.


Chang Z.,CAS Institute of High Energy Physics | Chang Z.,Chinese Academy of Sciences | Lin H.-N.,CAS Institute of High Energy Physics | Jiang Y.,Shandong University | Jiang Y.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment
Astrophysical Journal | Year: 2014

Synchrotron radiation and Compton scattering are widely accepted as the most likely emission mechanisms of some astrophysical phenomena, such as gamma-ray bursts (GRBs) and active galactic nuclei. The measurement of the polarization of photons provides a useful tool to distinguish different emission mechanisms and structures of the emission region. Based on the differential cross section of a polarized photon scattered by an unpolarized electron of any initial momentum, we derive an analytical formula of polarization for beamed photons scattered by isotropic electrons with a power-law distribution. Numerical calculations are carried out in four special cases: electrons at rest, Thomson limit, head-on collision, and monochromatic electrons. It is found that the maximum polarization can be as high as 100% for low energy photons, if the electrons are at rest. Although polarization is highly suppressed due to the isotropic electrons, a maximum value of ∼10%-20% can still be achieved. The Compton scattering process can be used to explain the polarization of GRB 041219A and GRB 100826A. © 2014. The American Astronomical Society. All rights reserved.


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.


Peng Z.,CAS Center for Space Science and Applied Research | Peng Z.,Shandong Provincial Key Laboratory of Optical Astronomy and Solar Terrestrial Environment | Wang C.,CAS Center for Space Science and Applied Research | Hu Y.Q.,University of Chinese Academy of Sciences | And 3 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

Solar wind dynamic pressure (Pdyn) enhancements have been observed to cause large-scale auroral brightening. The mechanism for this kind of auroral brightening is still a topic of current space research. Using the global piecewise parabolic method Lagrangian remap (PPMLR)-MHD simulation model, we investigate three auroral brightening events caused by dynamic pressure enhancement under different interplanetary magnetic field (IMF) conditions: (1) Bz < 0 and By > 0 on 11 August 2000, (2) B z < 0 and By < 0 on 8 May 2001, and (3) B z ≥ 0 on 21 January 2005. We show that the auroral location depends on the IMF conditions. Under southward IMF conditions, when B y is negative, the duskside aurora is located more equatorward at around 70° magnetic latitude (MLAT) for all magnetic local times; when By is positive, the duskside aurora can even reach beyond 80° MLAT. A smaller and more localized response is seen when the IMF Bz is nearly zero or northward, as shown in previous studies. Our simulation results are consistent with these observations, indicating that the observed aurora activities could be caused by solar wind dynamic pressure enhancements. The simulation results suggest that the enhancement of Pdyn can increase the ionospheric transpolar potential and the corresponding field-aligned currents, leading to the observed auroral brightening. Copyright 2011 by the American Geophysical Union.


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.

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