Gang Zhao

Peking University, Peping, Beijing, China

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Publications (218)547.19 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: For the laboratory astrophysics community, those spectroscopic modeling codes extensively used in astronomy, e.g. Chianti, AtomDB, Cloudy and Xstar, cannot be directly applied to analyzing laboratory measurements due to their discrepancies from astrophysical cases. For example, plasma from an electron beam ion trap has an electron energy distribution that follows a Gaussian profile, instead of a Maxwellian one. The laboratory miniature for a compact object produced by a laser-driven implosion shows a departure from equilibrium, that often occurs in celestial objects, so we setup a spectral analysis system for astrophysical and laboratory (SASAL) plasmas to act as a bridge between them, which benefits the laboratory astrophysical community.
    Research in Astronomy and Astrophysics 10/2014; 14(10):1351. · 1.35 Impact Factor
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    ABSTRACT: We present distance determinations for a large and clean sample of red giant branch stars selected from the ninth data release of the Sloan Digital Sky Survey. The distances are calculated based on both observational cluster fiducials and theoretical isochrones. Distributions of distances from the two methods are very similar with peaks at about 10 kpc and tails extending to more than 70 kpc. We find that distances from the two methods agree well for the majority of the sample stars; though, on average, distances based on isochrones are 10% higher than those based on fiducials. We test the accuracy of our distance determinations using 332 stars from 10 Galactic globular and open clusters. The average relative deviation from the literature cluster distances is 4% for the fiducial-based distances and 8% for the isochrone-based distances, both of which are within the uncertainties. We find that the effective temperature and surface gravity derived from low-resolution spectra are not accurate enough to essentially improve the performance of distance determinations. However, for stars with significant extinction, effective temperature may help to better constrain their distances to some extent. We make our sample stars and their distances available from an online catalog. The catalog comprises 17,941 stars with reasonable distance estimations reaching to more than 70 kpc, which is suitable for the investigation of the formation and evolution of the Galaxy, especially the Galactic halo.
    The Astrophysical Journal 09/2014; 794(1):60. · 6.73 Impact Factor
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    ABSTRACT: We report the detection of a substellar companion orbiting an evolved intermediate-mass ($M_\star=2.4\,M_\odot$) star HD 14067 (G9 III) using precise Doppler technique. Radial velocities of this star can be well fitted either by a periodic Keplerian variation with a decreasing linear velocity trend (P=1455 days, $K_1=92.2$ m s$^{-1}$, $e=0.533$, and $\dot{\gamma}=-22.4$ m s$^{-1}$ yr$^{-1}$) or a single Keplerian orbit without linear trend (P=2850 days, $K_1=100.1$ m s$^{-1}$, and $e=0.697$). The minimum mass ($m_2\sin{i}=7.8\,M_{\rm J}$ for the model with a linear trend, or $m_2\sin{i}=9.0\,M_{\rm J}$ for the model without a linear trend) suggests a long-period giant planet around an evolved intermediate-mass star. The eccentricity of the orbit is among the highest known for planets ever detected around evolved stars.
    09/2014;
  • Kai Zhang, Gang Zhao, Weiguo Cao
    Tetrahedron 09/2014; 70(35):5659–5665. · 2.80 Impact Factor
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    ABSTRACT: Context. White dwarf-main sequence (WDMS) binaries are used to study several different important open problems in modern astrophysics. Aims. The Sloan Digital Sky Survey (SDSS) identified the largest catalogue of WDMS binaries currently known. However, this sample is seriously affected by selection effects and the population of systems containing cool white dwarfs and early-type companions is under-represented.Here we search for WDMS binaries within the spectroscopic data release 1 of the LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) survey. LAMOST and SDSS follow different target selection algorithms. Hence, LAMOST WDMS binaries may be drawn from a different parent population and thus help in overcoming the selection effects incorporated by SDSS on the current observed population. Methods. We develop a fast and efficient routine based on the wavelet transform to identify LAMOST WDMS binaries containing a DA white dwarf and a M dwarf companion, and apply a decomposition/fitting routine to their LAMOST spectra to estimate their distances and measure their stellar parameters, namely the white dwarf effective temperatures, surface gravities and masses, and the secondary star spectral types. Results. We identify 121 LAMOST WDMS binaries, 80 of which are new discoveries, and estimate the sample to be \sim90 per cent complete. The LAMOST and SDSS WDMS binaries are found to be statistically different. However, this result is not due to the different target selection criteria of both surveys, but likely a simple consequence of the different observing conditions. Thus, the LAMOST population is found at considerably shorter distances (\sim50-450 pc) and is dominated by systems containing early-type companions and hot white dwarfs. (abridged)
    Astronomy and Astrophysics 08/2014; · 5.08 Impact Factor
  • Tetrahedron 07/2014; 70(29):4373–4378. · 2.80 Impact Factor
  • Shan Qian, Gang Zhao
    ChemInform 06/2014; 45(24).
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    ABSTRACT: Strongly Mg-enhanced stars with [Mg/Fe] $>$ 1.0 show peculiar abundance patterns and hence are of great interest for our understanding of stellar formation and chemical evolution of the Galaxy. A systematical search for strongly Mg-enhanced stars based on the low-resolution $(R\simeq2000)$ spectra of the Sloan Digital Sky Survey (SDSS) is carried out by finding the best matched synthetic spectrum to the observed one in the region of Mg I b lines around $\lambda$5170\AA$~$via a profile matching method. The advantage of our method is that fitting parameters are refined by reproducing the [Mg/Fe] ratios of 47 stars from very precise high-resolution spectroscopic (HRS) analysis by Nissen and Schuster (2010); and these parameters are crucial to the precision and validity of the derived Mg abundances. As a further check of our method, Mg abundances are estimated with our method for member stars in four Galactic globular clusters (M92, M13, M3, M71) which cover the same metallicity range as our sample, and the results are in good agreement with those of HRS analysis in the literature. The validation of our method is also proved by the agreement of [Mg/Fe] between our values and those of HRS analysis by Aoki et al.(2013). Finally, 33 candidates of strongly Mg-enhanced stars with [Mg/Fe]$>$1.0 are selected from 14850 F and G stars. Follow-up observations will be carried out on these candidates with high-resolution spectroscopy by large telescopes in the near future, so as to check our selection procedure and to perform a precise and detailed abundance analysis and to explore the origins of these stars.
    Research in Astronomy and Astrophysics 05/2014; 14(11). · 1.35 Impact Factor
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    ABSTRACT: With the rapid developments in the exoplanet field, more and more terrestrial exoplanets are being detected. Characterising their atmospheres using transit observations will become a key datum in the quest for detecting an Earth-like exoplanet. The atmospheric transmission spectrum of our Earth will be an ideal template for comparison with future exo-Earth candidates. By observing a lunar eclipse, which offers a similar configuration to that of an exoplanet transit, we have obtained a high resolution and high signal-to-noise ratio transmission spectrum of the Earth's atmosphere. This observation was performed with the High Resolution Spectrograph at Xinglong Station, China during the total lunar eclipse in December 2011. We compare the observed transmission spectrum with our atmospheric model, and determine the characteristics of the various atmospheric species in detail. In the transmission spectrum, O2, O3, O2-O2, NO2 and H2O are detected, and their column densities are measured and compared with the satellites data. The visible Chappuis band of ozone produces the most prominent absorption feature, which suggests that ozone is a promising molecule for the future exo-Earth characterization. The individual O2 lines are resolved and O2 isotopes are clearly detected. Our new observations do not confirm the absorption features of Ca II or Na I which have been reported in previous lunar eclipse observations. However, features in these and some other strong Fraunhofer line positions do occur in the observed spectrum. We propose that these are due to a Raman-scattered component in the forward-scattered sunlight appearing in the lunar umbral spectrum. Water vapour absorption is found to be rather weak in our spectrum because the atmosphere we probed is relatively dry, which prompts us to discuss the detectability of water vapour in Earth-like exoplanet atmospheres.
    05/2014;
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    ABSTRACT: Enantioselective total syntheses of (+)-fawcettidine (I) and (+)-lycoposerramine Q (II) as well as the first total synthesis of (-)-lycopladine D (III) from a common intermediate is accomplished by a divergent path (not shown).
    ChemInform 04/2014; 45(14).
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    ABSTRACT: Enantioselective synthesis of functionalized fluorinated dihydropyrano[2,3-c]pyrazoles has been achieved via a diaminocyclohexane-thiourea catalyzed cascade Michael addition and Thorpe-Ziegler type cyclization in high yields (up to 98%) with moderate to good enantioselectivity (up to 90% ee).
    Chinese Chemical Letters 04/2014; · 1.18 Impact Factor
  • The Astrophysical Journal Letters 03/2014; 784(2):L46. · 6.35 Impact Factor
  • Jinhao Chen, Yuepeng Cai, Gang Zhao
    Advanced Synthesis & Catalysis 01/2014; · 5.54 Impact Factor
  • Yinbi Li, Ali Luo, Gang Zhao, Youjun Lu
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    ABSTRACT: Hyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions of (binary) stars with the central massive black hole(s). In this paper, we firstly select F and G type main sequence stars from about 370,000 stellar spectra of DR7. Then, we select 369 high velocity stars from main sequence samples using the radial velocity distribution. Finally, we find 13 possible unbound hyper-velocity star candidates from the 369 high velocity stars.
    12/2013;
  • Kefeng Tan, Gang Zhao
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    ABSTRACT: It is now generally believed that the Galaxy was formed through hierarchical merging, which means that different components of the Galaxy may have experienced different chemical evolution histories. Since alpha elements are mainly produced by core collapse supernovae, they are closely associated with the star formation history of the Galaxy. In this regard, Galactic components with different alpha elemental abundance patterns may show different behaviors in beryllium abundances since the production of beryllium is correlated with the cosmic rays and thus the supernovae. A recent study by Nissen & Schuster (2010) has revealed the existence of two distinct halo populations in the solar neighborhood based on the alpha elemental abundances and kinematics of 94 dwarf stars. We determined beryllium abundances for some of these stars and find systematic differences in beryllium abundances between these two halo populations. Our results consolidate the conclusion of two distinct halo populations in the solar neighborhood. Our results also show that beryllium abundance is a very good indicator of star formation rate, and could be used to trace the substructures of the Galactic halo.
    12/2013;
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    ABSTRACT: The Strömgren-Crawford (SC) intermediate-band photometric system is a very powerful and efficient one for the detailed study of stars, and therefore the Milky Way and local universe. However, due to the narrow bandwidth, low efficiency of detectors and serious atmospheric extinction in u band, and high photometric accuracy required, there was only one all sky survey in this system finished a decade ago, which is restricted to stars brighter than 8.3 mag in y (equal to V) in the solar neighborhood. In this context, it is the right time to carry out an all sky survey to a completeness depth of ~19 mag, equivalent to a volume-completed distance 4 kpc for solar-type stars. For stars brighter than 15 mag in V, the expected photometric accuracies are ~0.01mag. With these stars, high precision 3D extinction map can be obtained thanks to the β index. Stellar atmospheric parameters can be determined with accuracies comparable to those from high-resolution spectroscopy. Fundamental parameters like stellar luminosities and distances can be reliably estimated as well. We propose to use the Nanshan 1m telescope to start the survey in early 2014 in the Northern sky. There are several 1-m class telescopes in Chile which can be used to perform the Southern sky survey. This entire survey, when finished, will greatly improve our knowledge on stars and the Galaxy, and will provide us the first 6D map of the Milky Way together with the LAMOST survey and the Gaia mission.
    12/2013;
  • Wen Liu, Gang Zhao
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    ABSTRACT: DABCO catalyzed the cross-Rauhut-Currier/transesterification reaction of α-cyano-α,β-unsaturated ketones and aryl acrylates was discovered. The reaction rate law was determined by an integral method under pseudo-first-order reaction conditions, which assisted in proposing the mechanism of cross-Rauhut-Currier reaction promoted by Brønsted acid and establishing the rate-determining step.
    Organic & Biomolecular Chemistry 12/2013; · 3.57 Impact Factor
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    ABSTRACT: Enantioselective total syntheses of (+)-fawcettidine and (+)-lycoposerramine Q as well as the first total synthesis of (-)-lycopladine D from a common intermediate have been accomplished by a divergent path. The common intermediate was derived from a Hajos-Parrish-like diketone by a stereoselective Birch reduction and a Suzuki coupling. The synthesis of (-)-lycopladine D featured an allylic oxidation and a biomimetic aminoketalization while the route to (+)-fawcettidine and (+)-lycoposerramine Q highlighted an oxidative rearrangement.
    Organic Letters 11/2013; · 6.14 Impact Factor
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    ABSTRACT: We present stellar parameters and abundances of 15 elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Y and Ba) for 23 field RR Lyrae variables based on high-resolution (R ~ 60 000) and high signal-to-noise (S/N~ 200) spectra obtained using the High Dispersion Spectrograph on the Subaru Telescope. Six stars in the sample have more than one spectrum observed at different pulsation phases. The derived abundance ratios of [X/Fe] for 14 elements (except for Ba) do not vary during the pulsation cycle. An interesting curve of [Ba/Fe] versus phase is detected for the first time and it shows decreasing [Ba/Fe] with increasing temperature at a given metallicity. Combining with data in the literature, abundances of most RR Lyrae stars as a function of [Fe/H] follow the same trends as those of dwarf stars, but [Sc/Fe] and [Y/Fe] ratios of RR Lyrae stars at solar metallicity are lower than those of dwarf stars. The kinematics of RR Lyrae stars indicate that three comparatively metal-rich RR Lyrae stars might originate from the thick disk and they show higher [α/Fe] ratios than RR Lyrae stars with thin disk kinematics. Among 23 RR Lyrae stars, two special objects are found with abnormal abundances; TV Lib has high [α/Fe], [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios while TW Her has solar [α/Fe] but significantly lower [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios as compared with other RR Lyrae stars.
    Research in Astronomy and Astrophysics 11/2013; 13(11):1307-1329. · 1.35 Impact Factor
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    ABSTRACT: We find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the mid-plane as well as azimuthally. These findings are based on LAMOST spectroscopic velocities for a sample of ~400,000 F-type stars, combined with proper motions from the PPMXL catalog for which we have derived corrections to the zero points based in part on spectroscopically discovered galaxies and QSOs from LAMOST. In the region within 2 kpc outside the Sun's radius and +/-2 kpc from the Galactic midplane, we show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior. We discuss this in the context of other recent findings, and conclude that we are likely seeing the signature of vertical disturbances to the disk due to an external perturbation.
    The Astrophysical Journal 09/2013; 777(1). · 6.73 Impact Factor

Publication Stats

636 Citations
547.19 Total Impact Points

Institutions

  • 2014
    • Peking University
      • Department of Astronomy
      Peping, Beijing, China
  • 2001–2014
    • Chinese Academy of Sciences
      • • Key Laboratory of Synthetic Chemistry of Natural Substances
      • • Purple Mountain Observatory
      • • Shanghai Astronomical Observatory
      Peping, Beijing, China
    • Shanghai Research Institute of Chemical Industry
      Shanghai, Shanghai Shi, China
    • China Academy of Chinese Medical Sciences
      Peping, Beijing, China
  • 2007–2013
    • University of Science and Technology of China
      • Department of Chemistry
      Hefei, Anhui Sheng, China
  • 2012
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
    • Sun Yat-Sen University
      • Department of Chemical Engineering
      Shengcheng, Guangdong, China
  • 2008–2012
    • Shanghai University
      • Department of Chemistry
      Shanghai, Shanghai Shi, China
  • 2004–2012
    • Northeast Institute of Geography and Agroecology
      • • Key Laboratory of Synthetic Chemistry of Natural Substances
      • • Key Laboratory of Organofluorine Chemistry
      • • State Key Laboratory of Organometallic Chemistry
      Beijing, Beijing Shi, China
  • 2011
    • Tokyo Institute of Technology
      • Earth and Planetary Sciences Department
      Edo, Tōkyō, Japan
  • 2009
    • Xinjiang University
      Hsin-chien, Jiangxi Sheng, China
    • University of Milan
      Milano, Lombardy, Italy