By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice i...By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice is verified through phononmode analysis and room temperature molecular dynamics simulations. The carbon star lattice is found to be metallic due to the large states across the Fermi-level contributed by Pz orbital. Furthermore, the nanoribbons are also found to be metallic and no spin polarization occurs, except for the narrowest nanoribbon with one C12 ring, which has a ferromagnetic ground state. Our results show that carbon star lattice monolayer and nanoribbons have rich electronic properties with great potential in future electronic nanodevices.展开更多
In order to explain the lack of carbon stars in the Galactic bulge, we have made a detailed study of thermal pulseasymptotic giant branch （TP-AGB） stars by using a population synthesis code. The effects of the oxyge...In order to explain the lack of carbon stars in the Galactic bulge, we have made a detailed study of thermal pulseasymptotic giant branch （TP-AGB） stars by using a population synthesis code. The effects of the oxygen overabundance and the mass loss rate on the ratio of the number of carbon stars to that of oxygen stars in the Galactic bulge are discussed. We find that the oxygen overabundance which is about twice as large as that in the solar neighbourhood （close to the present observations） is insufficient to explain the rareness of carbon stars in the bulge. We suggest that the large mass loss rate may serve as a controlling factor in the ratio of the number of carbon stars to that of oxygen stars.展开更多
The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identif...The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identifications between the new IRAS Low-Resolution Spectrum （LRS） database and the new carbon star catalog, CGCS3. We have found nine new silicate carbon stars with silicate features around 10μm and/or 18 μm. These newly identified stars are located in the Regions Ilia and VII in the IRAS two-color diagram, which means they indeed have typical far infrared colors of silicate carbon stars. The infrared properties of each of these sources are discussed.展开更多
Carbon stars are excellent kinematic tracers of galaxies and can serve as a viable standard candle, so it is worthwhile to automatically search for them in a large amount of spectra. In this paper, we apply the effici...Carbon stars are excellent kinematic tracers of galaxies and can serve as a viable standard candle, so it is worthwhile to automatically search for them in a large amount of spectra. In this paper, we apply the efficient manifold ranking algorithm to search for carbon stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） pilot survey, whose performance and robustness are verified comprehensively with four test experiments. Using this algorithm, we find a total of 183 carbon stars, and 158 of them are new findings. According to different spectral features, our carbon stars are classified as 58 C-H stars, 11 C-H star candidates, 56 C-R stars, ten C-R star candidates, 30 C-N stars, three C-N star candidates, and four C-J stars. There are also ten objects which have no spectral type because of low spec- tral quality, and a composite spectrum consisting of a white dwarf and a carbon star. Applying the support vector machine algorithm, we obtain the linear optimum clas- sification plane in the J - H versus/-/- Ks color diagram which can be used to distinguish C-H from C-N stars with their J - H and H - Ks colors. In addition, we identify 18 dwarf carbon stars with their relatively high proper motions, and find three carbon stars with FUV detections likely have optical invisible companions by cross matching with data from the Galaxy Evolution Explorer. In the end, we detect four variable carbon stars with the Northern Sky Variability Survey, the Catalina Sky Survey and the LINEAR variability databases. According to their periods and ampli- tudes derived by fitting light curves with a sinusoidal function, three of them are likely semiregular variable stars and one is likely a Mira variable star.展开更多
We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10μm silicate features in absorption and the 1612 MHz OH...We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10μm silicate features in absorption and the 1612 MHz OH maser emission or/and the SiO molecular features. These objects were considered as carbon stars in the catalog based only on their locations in the infrared two-color diagram. Therefore to use the infrared two-color diagram to distinguish carbon-rich stars from oxygen- rich stars must be done with caution, because, in general, it has only a statistical meaning.展开更多
The properties and classification of IRAS 19111+2555 have so far not been well determined. We collect all the available information and data of this star, and take the data obtained by IRAS LRS and ISO SWS to discuss ...The properties and classification of IRAS 19111+2555 have so far not been well determined. We collect all the available information and data of this star, and take the data obtained by IRAS LRS and ISO SWS to discuss its properties and classification. The star is found to have a 3.1μm feature in absorption and a 10μm feature in emission, so it is possibly a new silicate carbon star.展开更多
We collected almost all Highly Processed Data Products （HPDP） of ISO SWS01 spectra for the Galactic visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich proto-planetary nebulae （PPNs）.Tho...We collected almost all Highly Processed Data Products （HPDP） of ISO SWS01 spectra for the Galactic visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich proto-planetary nebulae （PPNs）.Those infrared spectra are primarily analyzed and discussed.It is shown that either spectral shapes/peaks,or main molecular/dust features are evidenced to change in the sequence of visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich PPNs.Statistically,in this sequence,continua are gradually changed from blue to red and locations of spectral peaks of continua are also gradually changed from short wavelengths to long wavelengths.In addition,in this sequence,intensities of main molecular/dust features are also gradually changed from prominent in the short wavelengths to prominent in the long wavelengths.Furthermore,from 2MASS and IRAS photometric data,the sequence is also proved.Results in this paper strongly support the previous suggestion for the evolution sequence of carbon-rich objects in our Galaxy,that is the sequence of visual carbon stars → infrared carbon stars → extreme carbon stars → carbon-rich PPNs.展开更多
The availability of astrometfic data and radial velocities of carbon stars near the Galactic plane enables us to investigate the kinematics of the Milky Way, especially the rotation curve. The recently published Third...The availability of astrometfic data and radial velocities of carbon stars near the Galactic plane enables us to investigate the kinematics of the Milky Way, especially the rotation curve. The recently published Third U. S. Naval Observatory CCD Astrograph Catalog （UCAC3） provides the opportunity to test this problem using three-dimensional velocity in order to obtain more reliable rotation curves. We intend to study the Galactic rotation curve up to 15 kpc using the radial velocities and proper motions of carbon stars. The motivation for using UCAC3 is to provide high precision proper motions which have hardly been used in determining the rotation velocity of tracers. Seventy-four carbon stars and carbon-rich Mira variables toward the anti-center direction （90° 〈 l 〈 270°, ｜b｜ 〈 6°） are picked up from the literature then matched with UCAC3 carbon star candidates to obtain their proper motions. A rigorous geometrical method is employed to compute the rotation velocity of each object. Taking carbon stars as tracers, we find a flat rotation curve of 210 ± 12 kms^-1 assuming R0 = 8.0kpc for the galactocentric distance and V0 = 220kms^-1 for the rotation velocity of the Sun. Due to the uncertainties of distances, the rotation velocities are more dispersed if tangential velocities enter the calculation, compared to those derived from radial velocities only. However, the whole rotation curve shows coherence with previous results. Increasing observation and study of carbon stars would be desirable in order to provide more homogeneous data for the kinematical study of the Galactic disk.展开更多
Carbon stars and DZ white dwarfs are two types of rare objects in the Galaxy. In this paper, we have applied the label propagation algorithm to search for these two types of stars from Data Release Eight （DR8） of th...Carbon stars and DZ white dwarfs are two types of rare objects in the Galaxy. In this paper, we have applied the label propagation algorithm to search for these two types of stars from Data Release Eight （DR8） of the Sloan Digital Sky Survey （SDSS）, which is verified to be efficient by calculating precision and recall. From nearly two million spectra including stars, galaxies and QSOs, we have found 260 new carbon stars in which 96 stars have been identified as dwarfs and 7 identified as giants, and 11 composition spectrum systems （each of them consists of a white dwarf and a carbon star）. Similarly, using the label propagation method, we have obtained 29 new DZ white dwarfs from SDSS DR8. Compared with PCA reconstructed spectra, the 29 findings are typical DZ white dwarfs. We have also investigated their proper motions by comparing them with proper motion distribution of 9,374 white dwarfs, and fotmd that they satisfy the current observed white dwarfs by SDSS generally have large proper motions. In addition, we have estimated their effective temperatures by fitting the polynomial relationship between effective temperature and g-r color of known DZ white dwarfs, and found 12 of the 29 new DZ white dwarfs are cool, in which nine are between 6,000 K and 6,600 K, and three are below 6,000 K.展开更多
The composition and structure of interstellar dust are important and complex for the study of the evolution of stars and the interstellar medium(ISM).However,there is a lack of corresponding experimental data and mode...The composition and structure of interstellar dust are important and complex for the study of the evolution of stars and the interstellar medium(ISM).However,there is a lack of corresponding experimental data and model theories.By theoretical calculations based on ab-initio method,we have predicted and geometry optimized the structures of Carbon-rich(C-rich)dusts,carbon(^(12)C),iron carbide(Fe C),silicon carbide(Si C),even silicon(^(28)Si),iron(^(56)Fe),and investigated the optical absorption coefficients and emission coefficients of these materials in 0D(zero-dimensional),1D,and 2D nanostructures.Comparing the nebular spectra of the supernovae(SN)with the coefficient of dust,we find that the optical absorption coefficient of the 2D^(12)C,^(28)Si,^(56)Fe,Si C and Fe C structure corresponds to the absorption peak displayed in the infrared band(5–8)μm of the spectrum at 7554 days after the SN1987A explosion.It also corresponds to the spectrum of 535 days after the explosion of SN2018bsz,when the wavelength was in the range of(0.2–0.8)and(3–10)μm.Nevertheless,2D Si C and Fe C correspond to the spectrum of 844 days after the explosion of SN2010jl,when the wavelength is within(0.08–10)μm.Therefore,Fe C and Si C may be the second type of dust in SN1987A corresponding to infrared band(5–8)μm of dust and may be in the ejecta of SN2010jl and SN2018bsz.The nano-scale C-rich dust size is~0.1 nm in SN2018bsz,which is 3 orders of magnitude lower than the value of 0.1μm.In addition,due to the ionization reaction in the supernova remnant(SNR),we also calculated the Infrared Radiation(IR)spectrum of dust cations.We find that the cation of the 2D layered(Si C)^(2+)has a higher IR spectrum than those of the cation(Si C)^(1+)and neutral(Si C)^(0+).展开更多
In the Wide-field Infrared Survey Explorer （WISE） all-sky source catalog there are 76 million mid-infrared point sources that were detected in the first three WISE bands and have association with only one 2MASS near...In the Wide-field Infrared Survey Explorer （WISE） all-sky source catalog there are 76 million mid-infrared point sources that were detected in the first three WISE bands and have association with only one 2MASS near-IR source within 3. We search for their identifications in the SIMBAD database and find 3.2 million identified sources. Based on these known sources, we establish three criteria for selecting candidate asymptotic giant branch （AGB） stars in the Galaxy, which are three defined zones in a color-color diagram, Galactic latitude ｜b｜ 〈 20°, and ＂corrected＂ WISE third-band W3c≤ 11. Applying these criteria to the WISE＋2MASS sources, 1.37 million of them are selected. We analyze the WISE third-band W3 distribution of the selected sources, and further establish that W3〈8 is required in order to exclude a large fraction of normal stars from them. We therefore find 0.47 million candidate AGB stars in our Galaxy from the WISE source catalog. Using W3c, we estimate their distances and derive their Galactic distributions. The candidates are generally distributed around the Galactic center uniformly, with 68% （1-σ） of them within approximately 8 kpc. We discuss the idea that optical spectroscopy can be used to verify the C-rich AGB stars in our candidates, and thus a fraction of them （-10%） will be good targets for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） survey that is planned to start in fall of 2012.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.11274356)the Ministry of Environmental Protection of China(Grant Nos.200909086 and 201109037)
文摘By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice is verified through phononmode analysis and room temperature molecular dynamics simulations. The carbon star lattice is found to be metallic due to the large states across the Fermi-level contributed by Pz orbital. Furthermore, the nanoribbons are also found to be metallic and no spin polarization occurs, except for the narrowest nanoribbon with one C12 ring, which has a ferromagnetic ground state. Our results show that carbon star lattice monolayer and nanoribbons have rich electronic properties with great potential in future electronic nanodevices.
基金Project supported by the National Natural Science Foundation of China (Grant No 10647003)the Foundations of Xinjiang University,China (Grant Nos 070195 and BS060109)
文摘In order to explain the lack of carbon stars in the Galactic bulge, we have made a detailed study of thermal pulseasymptotic giant branch （TP-AGB） stars by using a population synthesis code. The effects of the oxygen overabundance and the mass loss rate on the ratio of the number of carbon stars to that of oxygen stars in the Galactic bulge are discussed. We find that the oxygen overabundance which is about twice as large as that in the solar neighbourhood （close to the present observations） is insufficient to explain the rareness of carbon stars in the bulge. We suggest that the large mass loss rate may serve as a controlling factor in the ratio of the number of carbon stars to that of oxygen stars.
基金Supported by the National Natural Science Foundation of China.
文摘The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identifications between the new IRAS Low-Resolution Spectrum （LRS） database and the new carbon star catalog, CGCS3. We have found nine new silicate carbon stars with silicate features around 10μm and/or 18 μm. These newly identified stars are located in the Regions Ilia and VII in the IRAS two-color diagram, which means they indeed have typical far infrared colors of silicate carbon stars. The infrared properties of each of these sources are discussed.
基金funded by the National Natural Science Foundation of China(Grant Nos.11390371,11303036,11390374,11233004 and 61202315)The Guo Shou Jing Telescope(the Large Sky Area Multi-Object Fiber Spectroscopic Telescope,LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences+6 种基金Funding for the project has been provided by the National Development and Reform CommissionFunding for SDSS-Ⅲ has been provided by the Alfred P.Sloan Foundationthe Participating Institutionsthe National Science Foundationthe U.S.Department of Energy Office of Sciencefunded by NASANSF
文摘Carbon stars are excellent kinematic tracers of galaxies and can serve as a viable standard candle, so it is worthwhile to automatically search for them in a large amount of spectra. In this paper, we apply the efficient manifold ranking algorithm to search for carbon stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） pilot survey, whose performance and robustness are verified comprehensively with four test experiments. Using this algorithm, we find a total of 183 carbon stars, and 158 of them are new findings. According to different spectral features, our carbon stars are classified as 58 C-H stars, 11 C-H star candidates, 56 C-R stars, ten C-R star candidates, 30 C-N stars, three C-N star candidates, and four C-J stars. There are also ten objects which have no spectral type because of low spec- tral quality, and a composite spectrum consisting of a white dwarf and a carbon star. Applying the support vector machine algorithm, we obtain the linear optimum clas- sification plane in the J - H versus/-/- Ks color diagram which can be used to distinguish C-H from C-N stars with their J - H and H - Ks colors. In addition, we identify 18 dwarf carbon stars with their relatively high proper motions, and find three carbon stars with FUV detections likely have optical invisible companions by cross matching with data from the Galaxy Evolution Explorer. In the end, we detect four variable carbon stars with the Northern Sky Variability Survey, the Catalina Sky Survey and the LINEAR variability databases. According to their periods and ampli- tudes derived by fitting light curves with a sinusoidal function, three of them are likely semiregular variable stars and one is likely a Mira variable star.
文摘We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10μm silicate features in absorption and the 1612 MHz OH maser emission or/and the SiO molecular features. These objects were considered as carbon stars in the catalog based only on their locations in the infrared two-color diagram. Therefore to use the infrared two-color diagram to distinguish carbon-rich stars from oxygen- rich stars must be done with caution, because, in general, it has only a statistical meaning.
文摘The properties and classification of IRAS 19111+2555 have so far not been well determined. We collect all the available information and data of this star, and take the data obtained by IRAS LRS and ISO SWS to discuss its properties and classification. The star is found to have a 3.1μm feature in absorption and a 10μm feature in emission, so it is possibly a new silicate carbon star.
基金supported by grants from the National Natural Science Foundation of China (Nos. 10503011,10533050 and 10803023)the Natural Science Foundation Project of CQ CSTC (2008BB0153)and the Chinese Academy of Sciences
文摘We collected almost all Highly Processed Data Products （HPDP） of ISO SWS01 spectra for the Galactic visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich proto-planetary nebulae （PPNs）.Those infrared spectra are primarily analyzed and discussed.It is shown that either spectral shapes/peaks,or main molecular/dust features are evidenced to change in the sequence of visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich PPNs.Statistically,in this sequence,continua are gradually changed from blue to red and locations of spectral peaks of continua are also gradually changed from short wavelengths to long wavelengths.In addition,in this sequence,intensities of main molecular/dust features are also gradually changed from prominent in the short wavelengths to prominent in the long wavelengths.Furthermore,from 2MASS and IRAS photometric data,the sequence is also proved.Results in this paper strongly support the previous suggestion for the evolution sequence of carbon-rich objects in our Galaxy,that is the sequence of visual carbon stars → infrared carbon stars → extreme carbon stars → carbon-rich PPNs.
基金funded by the National Natural Science Foundation of China(NSFC) (Grant Nos 10673005 and 10973009)
文摘The availability of astrometfic data and radial velocities of carbon stars near the Galactic plane enables us to investigate the kinematics of the Milky Way, especially the rotation curve. The recently published Third U. S. Naval Observatory CCD Astrograph Catalog （UCAC3） provides the opportunity to test this problem using three-dimensional velocity in order to obtain more reliable rotation curves. We intend to study the Galactic rotation curve up to 15 kpc using the radial velocities and proper motions of carbon stars. The motivation for using UCAC3 is to provide high precision proper motions which have hardly been used in determining the rotation velocity of tracers. Seventy-four carbon stars and carbon-rich Mira variables toward the anti-center direction （90° 〈 l 〈 270°, ｜b｜ 〈 6°） are picked up from the literature then matched with UCAC3 carbon star candidates to obtain their proper motions. A rigorous geometrical method is employed to compute the rotation velocity of each object. Taking carbon stars as tracers, we find a flat rotation curve of 210 ± 12 kms^-1 assuming R0 = 8.0kpc for the galactocentric distance and V0 = 220kms^-1 for the rotation velocity of the Sun. Due to the uncertainties of distances, the rotation velocities are more dispersed if tangential velocities enter the calculation, compared to those derived from radial velocities only. However, the whole rotation curve shows coherence with previous results. Increasing observation and study of carbon stars would be desirable in order to provide more homogeneous data for the kinematical study of the Galactic disk.
基金funded by the National Natural Science Foundation of China(Grant Nos.10973021 and 11303036)SDSS-III has been provided by the Alfred P.Sloan Foundation+2 种基金the Participating Institutionsthe National Science Foundationthe U.S.Department of Energy Ofce of Science
文摘Carbon stars and DZ white dwarfs are two types of rare objects in the Galaxy. In this paper, we have applied the label propagation algorithm to search for these two types of stars from Data Release Eight （DR8） of the Sloan Digital Sky Survey （SDSS）, which is verified to be efficient by calculating precision and recall. From nearly two million spectra including stars, galaxies and QSOs, we have found 260 new carbon stars in which 96 stars have been identified as dwarfs and 7 identified as giants, and 11 composition spectrum systems （each of them consists of a white dwarf and a carbon star）. Similarly, using the label propagation method, we have obtained 29 new DZ white dwarfs from SDSS DR8. Compared with PCA reconstructed spectra, the 29 findings are typical DZ white dwarfs. We have also investigated their proper motions by comparing them with proper motion distribution of 9,374 white dwarfs, and fotmd that they satisfy the current observed white dwarfs by SDSS generally have large proper motions. In addition, we have estimated their effective temperatures by fitting the polynomial relationship between effective temperature and g-r color of known DZ white dwarfs, and found 12 of the 29 new DZ white dwarfs are cool, in which nine are between 6,000 K and 6,600 K, and three are below 6,000 K.
基金Supported by the National Natural Science Foundation of China。
文摘The composition and structure of interstellar dust are important and complex for the study of the evolution of stars and the interstellar medium(ISM).However,there is a lack of corresponding experimental data and model theories.By theoretical calculations based on ab-initio method,we have predicted and geometry optimized the structures of Carbon-rich(C-rich)dusts,carbon(^(12)C),iron carbide(Fe C),silicon carbide(Si C),even silicon(^(28)Si),iron(^(56)Fe),and investigated the optical absorption coefficients and emission coefficients of these materials in 0D(zero-dimensional),1D,and 2D nanostructures.Comparing the nebular spectra of the supernovae(SN)with the coefficient of dust,we find that the optical absorption coefficient of the 2D^(12)C,^(28)Si,^(56)Fe,Si C and Fe C structure corresponds to the absorption peak displayed in the infrared band(5–8)μm of the spectrum at 7554 days after the SN1987A explosion.It also corresponds to the spectrum of 535 days after the explosion of SN2018bsz,when the wavelength was in the range of(0.2–0.8)and(3–10)μm.Nevertheless,2D Si C and Fe C correspond to the spectrum of 844 days after the explosion of SN2010jl,when the wavelength is within(0.08–10)μm.Therefore,Fe C and Si C may be the second type of dust in SN1987A corresponding to infrared band(5–8)μm of dust and may be in the ejecta of SN2010jl and SN2018bsz.The nano-scale C-rich dust size is~0.1 nm in SN2018bsz,which is 3 orders of magnitude lower than the value of 0.1μm.In addition,due to the ionization reaction in the supernova remnant(SNR),we also calculated the Infrared Radiation(IR)spectrum of dust cations.We find that the cation of the 2D layered(Si C)^(2+)has a higher IR spectrum than those of the cation(Si C)^(1+)and neutral(Si C)^(0+).
基金supported in part by the Pre-phase Studies of Space Science Projects of the Chinese Academy of Sciences,National Basic Research Program of China(973 Project, 2009CB824800)the National Natural Science Foundation of China (Grant No.11073042)funded by the National Aeronautics and Space Administration
文摘In the Wide-field Infrared Survey Explorer （WISE） all-sky source catalog there are 76 million mid-infrared point sources that were detected in the first three WISE bands and have association with only one 2MASS near-IR source within 3. We search for their identifications in the SIMBAD database and find 3.2 million identified sources. Based on these known sources, we establish three criteria for selecting candidate asymptotic giant branch （AGB） stars in the Galaxy, which are three defined zones in a color-color diagram, Galactic latitude ｜b｜ 〈 20°, and ＂corrected＂ WISE third-band W3c≤ 11. Applying these criteria to the WISE＋2MASS sources, 1.37 million of them are selected. We analyze the WISE third-band W3 distribution of the selected sources, and further establish that W3〈8 is required in order to exclude a large fraction of normal stars from them. We therefore find 0.47 million candidate AGB stars in our Galaxy from the WISE source catalog. Using W3c, we estimate their distances and derive their Galactic distributions. The candidates are generally distributed around the Galactic center uniformly, with 68% （1-σ） of them within approximately 8 kpc. We discuss the idea that optical spectroscopy can be used to verify the C-rich AGB stars in our candidates, and thus a fraction of them （-10%） will be good targets for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） survey that is planned to start in fall of 2012.
