We study the origin of the UV-excess in star clusters by performing N-body simulations of six clusters with N = 10 k and N = 100 k(single stars & binary systems) and metallicities of Z = 0.01, 0.001 and 0.0001, us...We study the origin of the UV-excess in star clusters by performing N-body simulations of six clusters with N = 10 k and N = 100 k(single stars & binary systems) and metallicities of Z = 0.01, 0.001 and 0.0001, using PETAR. All models initially have a 50% primordial binary fraction. Using Galev NB we convert the simulated data into synthetic spectra and photometry for the China Space Station Telescope(CSST) and Hubble Space Telescope(HST). From the spectral energy distributions we identify three stellar populations that contribute to the UVexcess:(1) second asymptotic giant branch stars, which contribute to the UV flux at early times;(2) naked helium stars and(3) white dwarfs, which are long-term contributors to the FUV spectra. Binary stars consisting of a white dwarf and a main sequence star are cataclysmic variable(CV) candidates. The magnitude distribution of CV candidates is bimodal up to 2 Gyr. The bright CV population is particularly bright in FUV-NUV. The FUV-NUV color of our model clusters is 1–2 mag redder than the UV-excess globular clusters in M87 and in the Milky Way. This discrepancy may be induced by helium enrichment in observed clusters. Our simulations are based on simple stellar evolution;we do not include the effects of variations in helium and light elements or multiple stellar populations. A positive radial color gradient is present in CSST NUV-y for main sequence stars in all models with a color difference of 0.2–0.5 mag, up to 4 half-mass radii. The CSST NUV-g color correlates strongly with HST FUV-NUV for NUV-g > 1 mag, with the linear relation FUV-NUV =(1.09 ± 0.12) ×(NUV-g) +(-1.01 ± 0.22). This allows for conversion of future CSST NUV-g colors into HST FUV-NUV colors, which are sensitive to UV-excess features. We find that CSST will be able to detect UVexcess in Galactic/extragalactic star clusters with ages >200 Myr.展开更多
Multiple stellar populations(MPs) in most star clusters older than 2 Gyr, as seen by lots of spectroscopic and photometric studies, have led to a significant challenge to the traditional view of star formation. In thi...Multiple stellar populations(MPs) in most star clusters older than 2 Gyr, as seen by lots of spectroscopic and photometric studies, have led to a significant challenge to the traditional view of star formation. In this field, spacebased instruments, in particular the Hubble Space Telescope(HST), have made a breakthrough as they significantly improved the efficiency of detecting MPs in crowded stellar fields by images. The China Space Station Telescope(CSST) and the HST are sensitive to a similar wavelength interval, but the CSST covers a field of view which is about 5–8 times wider than that of HST. One of its instruments, the Multi-Channel Imager(MCI),will have multiple filters covering a wide wavelength range from NUV to NIR, making the CSST a potentially powerful tool for studying MPs in clusters. In this work, we evaluate the efficiency of the designed filters for the MCI/CSST in revealing MPs in different color–magnitude diagrams(CMDs). We find that CMDs made with MCI/CSST photometry in appropriate UV filters are powerful tools to disentangle stellar populations with different abundances of He, C, N, O and Mg. On the contrary, the traditional CMDs are blind to multiple populations in globular clusters(GCs). We show that CSST has the potential of being the spearhead instrument for investigating MPs in GCs in the next decades.展开更多
We investigate the radial color gradients of galactic disks using a sample of - 20 000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies wi...We investigate the radial color gradients of galactic disks using a sample of - 20 000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar concentrations, sizes and luminosities to construct composite galaxies, and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies (R50 〈 3 kpc), almost all galaxies show negative disk color gradients with mean 9 - r gradient Ggr = -0.006 magkpc-1 and r - z gradient Grz = -0.018 mag kpc^-1. The disk color gradients are independent of the morphological types of galaxies and strongly dependent on the disk surface brightness μd, with lower surface brightness galactic disks having steeper color gradients. We quantify the intrinsic correlation between color gradients and surface brightness as Ggr = -0.011μd + 0.233 and Grz - -0.015μd + 0.324. These quantified correlations provide tight observational constraints on the formation and evolution models of spiral galaxies.展开更多
Motivated by recent developments in quantum fidelity and fidelity susceptibility, we study relations among Lie algebra, fidelity susceptibility and quantum phase transition for a two-state system and the Lipkin-Meshko...Motivated by recent developments in quantum fidelity and fidelity susceptibility, we study relations among Lie algebra, fidelity susceptibility and quantum phase transition for a two-state system and the Lipkin-Meshkov Glick model. We obtain the fidelity susceptibilities for SU(2) and SU(1, 1) algebraic structure models. From this relation, the validity of the fidelity susceptibility to signal for the quantum phase transition is also verified in these two systems. At the same time, we obtain the geometric phases in these two systems by calculating the fidelity susceptibility. In addition, the new method of calculating fidelity susceptibility is used to explore the two-dimensional XXZ model and the Bose-Einstein condensate (BEC).展开更多
We present metallicities and radial velocities for five old open clusters (NGC 6791, NGC 2420, NGC 2682, NGC 2158, and NGC 7789) using data from the seventh public data release of the Sloan Digital Sky Survey (SDSS...We present metallicities and radial velocities for five old open clusters (NGC 6791, NGC 2420, NGC 2682, NGC 2158, and NGC 7789) using data from the seventh public data release of the Sloan Digital Sky Survey (SDSS), which includes the directed stellar program SEGUE: Sloan Extension For Galactic Understanding and Exploration. The radial velocities are used to calculate cluster membership probabilities for stars in each cluster region. NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are found to have mean metallicities [Fe/H]= +0.08 ± 0.09, -0.38± 0.11, -0.08±0.05, -0.41 ±0.13 and -0.19 ± 0.13 dex (s.d.), respectively. The mean radial velocities for NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are Vr = -45.9 ± 0.2, +76.1 ± 0.2, +35.0 ± 0.2, +26.9 ± 0.2 and -48.2± 0.2 km s^-1(s.e.m.), respectively. We have compared our results with the values from literatures, and found that our metallicity of NGC 6791 is significantly underestimated (by about 0.3 dex) and our radial velocities of the open clusters agree well with the values derived using high-resolution spectroscopy.展开更多
The LIGO detection of gravitational waves(GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical ...The LIGO detection of gravitational waves(GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved. The Antarctic Survey Telescopes(AST3),located at Dome A, Antarctica, is uniquely situated for rapid response time-domain astronomy with its continuous night-time coverage during the austral winter. We report optical observations of the GW source(GW 170817) in the nearby galaxy NGC 4993 using AST3. The data show a rapidly fading transient at around 1 day after the GW trigger, with the i-band magnitude declining from 17:23 ± 0:13 magnitude to 17:72 ± 0:09 magnitude in ~1:8 h. The brightness and time evolution of the optical transient associated with GW 170817 are broadly consistent with the predictions of models involving merging binary neutron stars. We infer from our data that the merging process ejected about ~10^(-2) solar mass of radioactive material at a speed of up to 30% the speed of light.展开更多
Graphene as a two-dimensional material is prone to hydrocarbon contaminations,which can significantly alter its intrinsic electrical properties.Herein,we implement a facile hydrogenation-dehydrogenation strategy to re...Graphene as a two-dimensional material is prone to hydrocarbon contaminations,which can significantly alter its intrinsic electrical properties.Herein,we implement a facile hydrogenation-dehydrogenation strategy to remove hydrocarbon contaminations and preserve the excellent transport properties of monolayer graphene.Using electron microscopy we quantitatively characterized the improved cleanness of hydrogenated graphene compared to untreated samples.In situ spectroscopic investigations revealed that the hydrogenation treatment promoted the adsorption of water at the graphene surface,resulting in a protective layer against the re-deposition of hydrocarbon molecules.Additionally,the further dehydrogenation of hydrogenated graphene rendered a more pristine-like basal plane with improved carrier mobility compared to untreated pristine graphene.Our findings provide a practical post-growth cleaning protocol for graphene with maintained surface cleanness and lattice integrity to systematically carry a range of surface chemistry in the form of a well-performing and reproducible transistor.展开更多
基金Supported by the research grants from the China Manned Space Project with No. CMS-CSST-2021-A08。
文摘We study the origin of the UV-excess in star clusters by performing N-body simulations of six clusters with N = 10 k and N = 100 k(single stars & binary systems) and metallicities of Z = 0.01, 0.001 and 0.0001, using PETAR. All models initially have a 50% primordial binary fraction. Using Galev NB we convert the simulated data into synthetic spectra and photometry for the China Space Station Telescope(CSST) and Hubble Space Telescope(HST). From the spectral energy distributions we identify three stellar populations that contribute to the UVexcess:(1) second asymptotic giant branch stars, which contribute to the UV flux at early times;(2) naked helium stars and(3) white dwarfs, which are long-term contributors to the FUV spectra. Binary stars consisting of a white dwarf and a main sequence star are cataclysmic variable(CV) candidates. The magnitude distribution of CV candidates is bimodal up to 2 Gyr. The bright CV population is particularly bright in FUV-NUV. The FUV-NUV color of our model clusters is 1–2 mag redder than the UV-excess globular clusters in M87 and in the Milky Way. This discrepancy may be induced by helium enrichment in observed clusters. Our simulations are based on simple stellar evolution;we do not include the effects of variations in helium and light elements or multiple stellar populations. A positive radial color gradient is present in CSST NUV-y for main sequence stars in all models with a color difference of 0.2–0.5 mag, up to 4 half-mass radii. The CSST NUV-g color correlates strongly with HST FUV-NUV for NUV-g > 1 mag, with the linear relation FUV-NUV =(1.09 ± 0.12) ×(NUV-g) +(-1.01 ± 0.22). This allows for conversion of future CSST NUV-g colors into HST FUV-NUV colors, which are sensitive to UV-excess features. We find that CSST will be able to detect UVexcess in Galactic/extragalactic star clusters with ages >200 Myr.
基金supported by the National Natural Science Foundation of China (NSFC, Grant No. 12073090)the China Manned Space Project with NO.CMS-CSST-2021-A08,CMS-CSST-2021-B03。
文摘Multiple stellar populations(MPs) in most star clusters older than 2 Gyr, as seen by lots of spectroscopic and photometric studies, have led to a significant challenge to the traditional view of star formation. In this field, spacebased instruments, in particular the Hubble Space Telescope(HST), have made a breakthrough as they significantly improved the efficiency of detecting MPs in crowded stellar fields by images. The China Space Station Telescope(CSST) and the HST are sensitive to a similar wavelength interval, but the CSST covers a field of view which is about 5–8 times wider than that of HST. One of its instruments, the Multi-Channel Imager(MCI),will have multiple filters covering a wide wavelength range from NUV to NIR, making the CSST a potentially powerful tool for studying MPs in clusters. In this work, we evaluate the efficiency of the designed filters for the MCI/CSST in revealing MPs in different color–magnitude diagrams(CMDs). We find that CMDs made with MCI/CSST photometry in appropriate UV filters are powerful tools to disentangle stellar populations with different abundances of He, C, N, O and Mg. On the contrary, the traditional CMDs are blind to multiple populations in globular clusters(GCs). We show that CSST has the potential of being the spearhead instrument for investigating MPs in GCs in the next decades.
基金supported by the National Science Foundation of China(Grant Nos.10573028 and 10803016)the Key Project(Nos.10833005 and 10878003)+1 种基金the Group Innovation Project(No.10821302)the 973 program(Nos.2007CB815402 and 2007CB815403)
文摘We investigate the radial color gradients of galactic disks using a sample of - 20 000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar concentrations, sizes and luminosities to construct composite galaxies, and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies (R50 〈 3 kpc), almost all galaxies show negative disk color gradients with mean 9 - r gradient Ggr = -0.006 magkpc-1 and r - z gradient Grz = -0.018 mag kpc^-1. The disk color gradients are independent of the morphological types of galaxies and strongly dependent on the disk surface brightness μd, with lower surface brightness galactic disks having steeper color gradients. We quantify the intrinsic correlation between color gradients and surface brightness as Ggr = -0.011μd + 0.233 and Grz - -0.015μd + 0.324. These quantified correlations provide tight observational constraints on the formation and evolution models of spiral galaxies.
基金supported by the National Natural Science Foundation of China (Grant No. 11075101)the Shanghai Leading Academic Discipline Project,China (Grant No. S30105)the Shanghai Research Foundation,China (Grant No. 07d222020)
文摘Motivated by recent developments in quantum fidelity and fidelity susceptibility, we study relations among Lie algebra, fidelity susceptibility and quantum phase transition for a two-state system and the Lipkin-Meshkov Glick model. We obtain the fidelity susceptibilities for SU(2) and SU(1, 1) algebraic structure models. From this relation, the validity of the fidelity susceptibility to signal for the quantum phase transition is also verified in these two systems. At the same time, we obtain the geometric phases in these two systems by calculating the fidelity susceptibility. In addition, the new method of calculating fidelity susceptibility is used to explore the two-dimensional XXZ model and the Bose-Einstein condensate (BEC).
基金funded by the National Natural Science Foundation of China(Grant No.10773021)the Key Project No.10833005+1 种基金the Group Innovation Project No.10821302the 973 program with NKBRSFG 2007CB815403
文摘We present metallicities and radial velocities for five old open clusters (NGC 6791, NGC 2420, NGC 2682, NGC 2158, and NGC 7789) using data from the seventh public data release of the Sloan Digital Sky Survey (SDSS), which includes the directed stellar program SEGUE: Sloan Extension For Galactic Understanding and Exploration. The radial velocities are used to calculate cluster membership probabilities for stars in each cluster region. NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are found to have mean metallicities [Fe/H]= +0.08 ± 0.09, -0.38± 0.11, -0.08±0.05, -0.41 ±0.13 and -0.19 ± 0.13 dex (s.d.), respectively. The mean radial velocities for NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are Vr = -45.9 ± 0.2, +76.1 ± 0.2, +35.0 ± 0.2, +26.9 ± 0.2 and -48.2± 0.2 km s^-1(s.e.m.), respectively. We have compared our results with the values from literatures, and found that our metallicity of NGC 6791 is significantly underestimated (by about 0.3 dex) and our radial velocities of the open clusters agree well with the values derived using high-resolution spectroscopy.
基金supported by the Strategic Priority Program of the Chinese Academy of Sciences(XDB41000000)the Pre-research Project on Civil Aerospace Technologies(D020101,D020202)of China National Space Administration+2 种基金the National Natural Science Foundation of China(41773063)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(QYZDY-SSWDQC028)the Fundamental Research Funds for the Central Universities。
基金supported by the National Basic Research Program(973 Program)of China(2013CB834900)the Chinese Polar Environment Comprehensive Investigation&Assessment Program(CHINARE2016-02-03)+21 种基金the National Natural Science Foundation of China(11573014,11673068,11325313,11633002,11433009,11725314)the Key Research Program of Frontier Sciences(QYZDY-SSW-SLH010,QYZDB-SSW-SYS005)the Strategic Priority Research Program"multi-waveband gravitational wave Universe”(XDB23040000)the Youth Innovation Promotion Association(2011231)of Chinese Academy of Sciencesfunds from Tsinghua UniversityNanjing UniversityBeijing Normal UniversityUniversity of New South WalesTexas A&M Universitythe Australian Antarctic Divisionthe National Collaborative Research Infrastructure Strategy(NCRIS)of Australiafunding from the Chinese Academy of Sciences through the Center for Astronomical Mega-Science and National Astronomical Observatory of China(NAOC)made possible through the use of the AAVSO Photometric All-Sky Survey(APASS)funded by the Robert Martin Ayers Sciences Fundfunded by the Australian Research Council(ARC)Centre of Excellence for Gravitational Wave Discovery(OzGrav),CE170100004the ARC Centre of Excellence for All-sky Astrophysics(CAASTRO),CE110001020the Centre of Excellence for All-sky Astrophysics in 3-Dimensions(ASTRO-3D),CE170100013provided by the Australian Astronomical Observatory(AAO)the ARC Future Fellowship grant,FT130101219supported by the National Basic Research Program(Project 973)of China(2014CB845800)the National Natural Science Foundation of China(11633001 and 11373014)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB23000000)
文摘The LIGO detection of gravitational waves(GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved. The Antarctic Survey Telescopes(AST3),located at Dome A, Antarctica, is uniquely situated for rapid response time-domain astronomy with its continuous night-time coverage during the austral winter. We report optical observations of the GW source(GW 170817) in the nearby galaxy NGC 4993 using AST3. The data show a rapidly fading transient at around 1 day after the GW trigger, with the i-band magnitude declining from 17:23 ± 0:13 magnitude to 17:72 ± 0:09 magnitude in ~1:8 h. The brightness and time evolution of the optical transient associated with GW 170817 are broadly consistent with the predictions of models involving merging binary neutron stars. We infer from our data that the merging process ejected about ~10^(-2) solar mass of radioactive material at a speed of up to 30% the speed of light.
基金This work was supported by the Chinese Scholarship Council(201406890016)NWA route‘meten&detecteren’+6 种基金the European Research Council under the European Union’s Seventh Framework Program(FP/2007-2013)/ERC Grant Agreement No.335879 project acronym‘Biographene’the Netherlands Organization for Scientific Research(Vidi 723.013.007)L.Wu and J.P.Hofmann acknowledge funding from The Netherlands Organization for Scientific Research(NWO)cofinancing by Shell Global Solutions International B.V.for the project 13CO2-6E.J.M.H.and V.M.acknowledge support by the Netherlands Center for Multiscale Catalytic Energy Conversion(MCEC)an NWO Gravitation program funded by the Ministry of Education,Culture and Science of the government of the Netherlandsa Vici grant of the NWO.
文摘Graphene as a two-dimensional material is prone to hydrocarbon contaminations,which can significantly alter its intrinsic electrical properties.Herein,we implement a facile hydrogenation-dehydrogenation strategy to remove hydrocarbon contaminations and preserve the excellent transport properties of monolayer graphene.Using electron microscopy we quantitatively characterized the improved cleanness of hydrogenated graphene compared to untreated samples.In situ spectroscopic investigations revealed that the hydrogenation treatment promoted the adsorption of water at the graphene surface,resulting in a protective layer against the re-deposition of hydrocarbon molecules.Additionally,the further dehydrogenation of hydrogenated graphene rendered a more pristine-like basal plane with improved carrier mobility compared to untreated pristine graphene.Our findings provide a practical post-growth cleaning protocol for graphene with maintained surface cleanness and lattice integrity to systematically carry a range of surface chemistry in the form of a well-performing and reproducible transistor.