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The coronal magnetic field reversal observed by the SOLARC instrument

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Science China(Physics,Mechanics & Astronomy) 2009年第11期52卷 1696-1701页

作者： LIU Yu SHEN YuanDeng Yunnan astronomical Observatory/national astronomical Observatories Kunming 650011China

High-sensitivity measurements for mapping coronal magnetic field have become possible since the recent development of infrared detection techniques. One urgent task that arises from the routine infrared observations is to interpret what the Stokes signals could indicate for coronal magnetic fields. It is the first time for us to successfully reveal the coronal field structure above a simple and stable sunspot on the photosphere using profiles of full Stokes parameters. In this paper, the author further points out the deficiency in any conclusions/judgements just based on incomplete polarization data. A magnetic flux reversal feature, observed from circular polarization data, may correspond to one or more coronal tubes with their front or farside arching apex there, more complicated than people imagined before. To exactly locate the infrared radiation sources, we need both circular and linear polarization data for an integrated analysis of them.

关键词： solar corona magnetic field infrared wavelength extrapolation

Gamma-Ray Bursts Subset and Supernova Remnants Low Radio-Frequency Turnover

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Chinese Physics Letters 2000年第8期17卷 623-624页

作者： LIU Xiang Urumqi astronomical Observatory National Astronomical ObservatoriesChinese Academy of SciencesUrumqi 830011

Durations of gamma-ray bursts(GRB's)are featured by>2s subset and<2s one,with initial corresponding energy ratio being 20:*** is found that supernova remants(SNR's)turnover frequencies peak at 100 and 500 *** assuming that GRB's originate from hypernova and making an analysis on the evolution of GRB's,we find that the initial energy of two GRB subsets leads to a different radio-frequency turnover of their remnant spectra,which accords positively with the turnover-frequency ratio of SNR's.

关键词： evolution supernova initial

On Hawking Radiation from a Charged Black Hole of Heterotic String Theory

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Communications in Theoretical Physics 2014年第4期61卷 491-494页

作者： Alexis Larraaga national astronomical Observatory National University of Colombia

We investigate the Hawking radiation of a GMGHS charged black hole from the heterotic string scenario by the massive particles turmeling method. We consider the spacetime background to be dynamical, incorporate the self-gravitation effect of the emitted particles and show that the tunneling rate is related to the change of Bekenstein- Hawking entropy and the derived emission spectrum does not deviate from the pure thermal spectrum of Schwrzschild＇s black hole.

关键词： quantum aspects of black holes thermodynamics strings and branes

Entropy Corrections for a Charged Black Hole of String Theory

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Communications in Theoretical Physics 2011年第1期55卷 72-74页

作者： Alexis Larraaga national University of Colombia National Astronomical Observatory

We study the entropy of the Gibbons-Maeda-Garfinkle-Horowitz-Strominger （GMGHS） charged black hole, originated from the effective action that emerges in the low-energy of string theory, beyond semiclassical approxi- mations. Applying the properties of exact differentials for three variables to the first law thermodynamics we derive the quantum corrections to the entropy of the black hole. The leading （logarithmic） and non leading corrections to the area law are obtained.

关键词： quantum aspects of black holes thermodynamics strings and branes

Testing the Universality of the TIS Model on Cluster Scales from the X-ray Surface Brightness Profiles

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Chinese Journal of Astronomy and Astrophysics 2001年第1期1卷 29-38页

作者： Yu-Ying Zhang (Beijing astronomical Observatory and national astronomical Observatories, Chinese Academy of Sciences, Beijing 100012) Beijing astronomical Observatory and national astronomical Observatories Chinese Academy of Sciences Beijing 100012

The truncated isothermal sphere (TIS) model has been recently suggested as an alternative for virialized dark halos (Shapiro et al. 1999). Both its profound theoretical motivation and its successful explanations for the galactic rotation curves and the gravitational scaling laws of clusters indicate that the TIS model is a promising candidate among other prevailing models such as the NFW profile and the Burkert profile. This promotes us to re-examine the universality of the TIS model on cluster scales from a different angle. Using an ensemble of X-ray surface brightness profiles of 45 clusters, we test the goodness of fit of the TIS predicted gas distributions to the X-ray data under the assumption of isothermal, hydrostatic equilibrium. Unlike the conventional B model or the NFW/Burkert profile, for which about half of the clusters have the reduced X2 values smaller than 2, the TIS model fails in the fitting of the X-ray surface brightness profiles of clusters in the sense that 38 out of the 45 clusters show X2 > 2. This may constitute a challenge for the universality of the TIS model unless the present analysis is seriously contaminated by other uncertainties including the negligence of non-gravitational heating processes and the unconventional sampling of the X-ray data.

关键词： cosmology: theory -dark matter - galaxies: clusters: general- X-rays: galaxies

A comparison of stellar atmospheric parameters from the LAMOST and APOGEE datasets

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Research in Astronomy and Astrophysics 2015年第8期15卷 1125-1136页

作者： Yu-Qin Chen Gang Zhao Chao Liu Jing Ren Yun-Peng Jia Jing-Kun Zhao A-Li Luo Yue Wu Yong Zhang Yong-Hui Hou Yue-Fei Wang Ming Yang Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences Nanjing Institute of astronomical Optics & Technology National Astronomical ObservatoriesChinese Academy of Sciences

We have compared stellar parameters, including temperature, gravity and metallicity, for common stars in the LAMOST DR2 and SDSS DR12/APOGEE datasets. It is found that the LAMOST dataset provides a more well-defined red clump feature than the APOGEE dataset in the Teff versus log g diagram. With this advantage, we have separated red clump stars from red giant stars, and attempt to establish calibrations between the two datasets for the two groups of stars. The results show that there is a good consistency in temperature with a calibration close to the one-to-one line, and we can establish a satisfactory metallicity calibration of[Fe/H]APOGEE= 1.18[Fe/H]LAMOST ＋ 0.11 with a scatter of ～ 0.08 dex for both the red clump and red giant branch samples. For gravity, there is no correlation for red clump stars between the two datasets, and scatters around the calibrations of red giant stars are substantial. We found two main sources of scatter in log g for red giant stars. One is a group of stars with 0.00253 × Teff- 8.67 〈 log g 〈 2.6 located in the forbidden region, and the other is the contaminated red clump stars, which could be picked out from the unmatched region where stellar metallicity is not consistent with position in the Teff versus log g diagram. After excluding stars in these two regions,we have established two calibrations for red giant stars, log g APOGEE = 0.000615 ×Teff,LAMOST＋ 0.697 × log g LAMOST- 2.208（σ = 0.150） for [Fe/H] 〉-1 and log gAPOGEE= 0.000874×Teff,LAMOST＋0.588×log g LAMOST-3.117（σ = 0.167）for [Fe/H] 〈-1. The calibrations are valid for stars with Teff = 3800- 5400 K and log g = 0- 3.8 dex, and are useful in work aiming to combine the LAMOST and APOGEE datasets in a future study. In addition, we find that an SVM method based on asteroseismic log g is a good way to greatly improve the accuracy of gravity for these two regions, at least in the LAMOST dataset.

关键词： stars: late type—stars: fundamental parameters—stars: atmospheres—stars: abundances

Annual Modulation in Intraday Variability Timescales of Extragalactic Radio Sources

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Chinese Journal of Astronomy and Astrophysics 2001年第2期1卷 133-143页

作者： Shan-Jie Qian and Xi-Zhen Zhang (Beijing astronomical Observatory, national astronomical Observatories, Chinese Academy of Sciences, Beijing 100012) Beijing astronomical Observatory National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

Annual modulations in timescales of intraday variability (IDV hereafter) are discussed for six extragalactic sources: 0716+714, 0917+624, 0954+65, 1749+70, 1803+78 and 2007+77. The timescales calculated from scintillation theory are compared with the observational data . It is emphasized that systematic observations are required to identify the phenomenon and to determine the motion of the interstellar medium with respect to the Local Standard of Rest. In addition, significant deviations from the annual modulation could be due to intrinsic variations.

关键词： scattering - ISM: kinematics - BL Lacertae objects: individual: 0716+71 - quasars: individual: 0917+62 - radiation mechanisms: non-thermal

Terrain reconstruction from Chang'e-3 PCAM images

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Research in Astronomy and Astrophysics 2015年第7期15卷 1057-1067页

作者： Wen-Rui Wang Xin Ren Fen-Fei Wang Jian-Jun Liu Chun-Lai Li national astronomical Observatories Chinese Academy of Sciences

The existing terrain models that describe the local lunar surface have limited resolution and accuracy, which can hardly meet the needs of rover navigation,positioning and geological analysis. China launched the lunar probe Chang＇e-3 in December, 2013. Chang＇e-3 encompassed a lander and a lunar rover called ＂Yutu＂（Jade Rabbit）. A set of panoramic cameras were installed on the rover mast. After acquiring panoramic images of four sites that were explored, the terrain models of the local lunar surface with resolution of 0.02 m were reconstructed. Compared with other data sources, the models derived from Chang＇e-3 data were clear and accurate enough that they could be used to plan the route of Yutu.

关键词： space vehicles: rover -- space vehicles: instruments: panoramic camera-- methods: terrain reconstruction -- techniques: image processing: orthoimage

Distribution of magnetic shear angle at the ascending phase of CYCLE 23

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Science China Mathematics 2002年第Z1期45卷 12-18页

作者：敦金平张洪起张柏荣李如风 national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China National Astronomical Observatories Chinese Academy of Sciences Kunming 650011 China national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China national astronomical Observatories Chinese Academy of Sciences Kunming 650011 China

Using the vector magnetograms observed at Huairou Solar Observing Station of Na- tional astronomical Observatories, the magnetic shear angles of solar active regions at the as- cending phase of cycle 23 (1996-2000) were calculated. It is found that the statistical distribution of the magnetic shear angles can be fitted well by Gaussian curves. And the dominant sign of the magnetic shear angles is negative (positive) in the northern (southern) hemisphere. It is consistent with the N-S sign asymmetry of force-free field constant a and current helicity.

关键词： solar activity, magnetic shear angles.