Xiao-Wei Liu
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Xiao-Wei Liu has a total of 244 co-authors. Here are the top co-authors by number of shared publications:
- Yang Huang
University of Chinese Academy of Sciences
24 shared publications - Bing-Qiu Chen
Yunnan University
22 shared publications Chun Wang
Peking Univ, Dept Astron, Beijing 100871, Peoples R China
20 shared publicationsBingqiu Chen
Yunnan Univ, South Western Inst Astron Res, Kunming 650500, Yunnan, Peoples R China
16 shared publicationsHaibo Yuan
Beijing Normal Univ, Dept Astron, Beijing 100875, Peoples R China
16 shared publicationsY. Huang
Department of Astronomy Peking University 100871 Beijing People's Republic of China
16 shared publications
Latest Publications
- Open Access
- 28 July 2020
- Published by American Astronomical Society in The Astrophysical Journal Supplement Series
- Vol. 249 (2) , 22
A Catalog of RV Variable Star Candidates from LAMOST
Radial velocity (RV) variable stars are important in astrophysics. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic survey has provided ∼6.5 million stellar spectra in its Data Release 4 (DR4). During the survey ∼4.7 million unique sources were targeted and ∼1 million stars observed repeatedly. The probabilities of stars being RV variables are estimated by comparing the observed RV variations with simulated ones. We build a catalog of 80,702 RV variable candidates with probability greater than 0.60 by analyzing the multi-epoch sources covered by LAMOST DR4. Simulations and cross-identifications show that the purity of the catalog is higher than 80%. The catalog consists of 77% binary systems and 7% pulsating stars as well as 16% pollution by single stars. 3138 RV variables are classified through cross-identifications with published results in literatures. By using the 3138 sources common in both LAMOST and a collection of published RV variable catalogs, we are able to analyze LAMOST’s RV variable detection rate. The efficiency of the method adopted in this work relies not only on the sampling frequency of observations but also periods and amplitudes of RV variables. With the progress of LAMOST, Gaia, and other surveys, more and more RV variables will be confirmed and classified. This catalog is valuable for other large-scale surveys, especially for RV variable searches. The catalog will be released according to the LAMOST Data Policy via http://dr4.lamost.org.
- 28 July 2020
- Published by American Astronomical Society in The Astrophysical Journal Supplement Series
- Vol. 249 (2) , 22
Open AccessA Catalog of RV Variable Star Candidates from LAMOST
Radial velocity (RV) variable stars are important in astrophysics. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic survey has provided ∼6.5 million stellar spectra in its Data Release 4 (DR4). During the survey ∼4.7 million unique sources were targeted and ∼1 million stars observed repeatedly. The probabilities of stars being RV variables are estimated by comparing the observed RV variations with simulated ones. We build a catalog of 80,702 RV variable candidates with probability greater than 0.60 by analyzing the multi-epoch sources covered by LAMOST DR4. Simulations and cross-identifications show that the purity of the catalog is higher than 80%. The catalog consists of 77% binary systems and 7% pulsating stars as well as 16% pollution by single stars. 3138 RV variables are classified through cross-identifications with published results in literatures. By using the 3138 sources common in both LAMOST and a collection of published RV variable catalogs, we are able to analyze LAMOST’s RV variable detection rate. The efficiency of the method adopted in this work relies not only on the sampling frequency of observations but also periods and amplitudes of RV variables. With the progress of LAMOST, Gaia, and other surveys, more and more RV variables will be confirmed and classified. This catalog is valuable for other large-scale surveys, especially for RV variable searches. The catalog will be released according to the LAMOST Data Policy via http://dr4.lamost.org.
- Open Access
Probing the galactic halo with RR Lyrae stars I: The catalog
We present a catalog of 5,290 RR Lyrae stars (RRLs) with metallicities estimated from spectra of the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE) surveys. Nearly 70 per cent of them (3,642 objects) also have systemic radial velocities measured. Given the pulsating nature of RRLs, metallicity estimates are based on spectra of individual exposures, by matching them with the synthetic templates. The systemic radial velocities are measured by fitting the observed velocity as a function of phase assuming an empirical pulsating velocity template curve. Various tests show that our analyses yield metallicities with a typical precision of 0.20\,dex and systemic radial velocities with uncertainties ranging from 5 to 21\,km\,s$^{-1}$ (depending on the number of radial velocity measurements available for a given star). Based on the well calibrated near-infrared $PM_{W1}Z$ or $PM_{K_{\rm s}}Z$, and $M_{V}$-[Fe/H] relations, precise distances are derived for these RRLs. Finally, we include Gaia DR2 proper motions in our catalog. The catalog should be very useful for various Galactic studies, especially of the Galactic halo.Open AccessProbing the galactic halo with RR Lyrae stars I: The catalog
We present a catalog of 5,290 RR Lyrae stars (RRLs) with metallicities estimated from spectra of the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE) surveys. Nearly 70 per cent of them (3,642 objects) also have systemic radial velocities measured. Given the pulsating nature of RRLs, metallicity estimates are based on spectra of individual exposures, by matching them with the synthetic templates. The systemic radial velocities are measured by fitting the observed velocity as a function of phase assuming an empirical pulsating velocity template curve. Various tests show that our analyses yield metallicities with a typical precision of 0.20\,dex and systemic radial velocities with uncertainties ranging from 5 to 21\,km\,s$^{-1}$ (depending on the number of radial velocity measurements available for a given star). Based on the well calibrated near-infrared $PM_{W1}Z$ or $PM_{K_{\rm s}}Z$, and $M_{V}$-[Fe/H] relations, precise distances are derived for these RRLs. Finally, we include Gaia DR2 proper motions in our catalog. The catalog should be very useful for various Galactic studies, especially of the Galactic halo. - Open Access
Metallicity distributions of mono-age stellar populations of the Galactic disc from the LAMOST Galactic spectroscopic surveys
We have investigated the metallicity distributions of mono-age stellar populations across the disc of $6 \lesssim R \lesssim 12$\,kpc and $|Z| \lesssim 2$\,kpc using samples selected from the main-sequence turn-off and sub-giant (MSTO-SG) stars targeted by the LAMOST Galactic Spectroscopic surveys. Both the mean values and the profiles of the distributions exhibit significant variations with age and position. We confirm that the oldest ($>11$\,Gyr) stars have nearly flat radial [Fe/H] gradients at all heights above the disc but show negative vertical [Fe/H] gradients. For stars younger than 11\,Gyr, the radial [Fe/H] gradients flatten with $|Z|$, while the vertical [Fe/H] gradients flatten with $R$. Stars of 4--6\,Gyr exhibit steeper negative radial [Fe/H] gradients than those of either younger or older ages. Values of [$\alpha$/Fe] of mono-age stellar populations also show significant radial and vertical gradients, with patterns varying with age. The [Fe/H] distribution profiles of old ($>8$\,Gyr) stars vary little with $R$, while those of younger stars exhibit strong radial variations, probably a consequence of significant radial migration. The [$\alpha$/Fe] radial distribution profiles show opposite patterns of variations with age compared to those of [Fe/H]. We have also explored the impacts of stellar mixing by epicycle motions (blurring) on the [Fe/H] and [$\alpha$/Fe] distributions, and found that blurring mainly change the widths of the distribution profiles. Our results suggest that the disc may have experienced a complex assemblage history, in which both the "inside-out" and "upside-down" formation processes may have played an important role.Open AccessMetallicity distributions of mono-age stellar populations of the Galactic disc from the LAMOST Galactic spectroscopic surveys
We have investigated the metallicity distributions of mono-age stellar populations across the disc of $6 \lesssim R \lesssim 12$\,kpc and $|Z| \lesssim 2$\,kpc using samples selected from the main-sequence turn-off and sub-giant (MSTO-SG) stars targeted by the LAMOST Galactic Spectroscopic surveys. Both the mean values and the profiles of the distributions exhibit significant variations with age and position. We confirm that the oldest ($>11$\,Gyr) stars have nearly flat radial [Fe/H] gradients at all heights above the disc but show negative vertical [Fe/H] gradients. For stars younger than 11\,Gyr, the radial [Fe/H] gradients flatten with $|Z|$, while the vertical [Fe/H] gradients flatten with $R$. Stars of 4--6\,Gyr exhibit steeper negative radial [Fe/H] gradients than those of either younger or older ages. Values of [$\alpha$/Fe] of mono-age stellar populations also show significant radial and vertical gradients, with patterns varying with age. The [Fe/H] distribution profiles of old ($>8$\,Gyr) stars vary little with $R$, while those of younger stars exhibit strong radial variations, probably a consequence of significant radial migration. The [$\alpha$/Fe] radial distribution profiles show opposite patterns of variations with age compared to those of [Fe/H]. We have also explored the impacts of stellar mixing by epicycle motions (blurring) on the [Fe/H] and [$\alpha$/Fe] distributions, and found that blurring mainly change the widths of the distribution profiles. Our results suggest that the disc may have experienced a complex assemblage history, in which both the "inside-out" and "upside-down" formation processes may have played an important role. - Open Access
- 30 August 2018
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 480 (4) , 4766-4781
LEMONY – a library of empirical medium-resolution spectra by observations with the NAOC Xinglong 2.16-m and YNAO Gaomeigu 2.4-m telescopes
In this study, we expand the coverage and improve the homogeneity of the distribution of MILES template stars in the parameter space, as well as extend the wavelength coverage of the template spectra to the far red beyond the Ca ii triplet. To achieve this, we have carried out a major observational campaign using two long-slit spectrographs: the OMR mounted on the National Astronomy Observatory of China (NAOC) 2.16-m telescope and the Yunnan Faint Object Spectrograph and Camera (YFOSC) mounted on the Yunnan Astronomical Observatory (YNAO) 2.4-m telescope. The original sample is based on the MILES library, supplemented by 918 stars selected from the PASTEL data base. In total, 822 OMR and 1324 YFOSC spectra have been collected and reduced, covering the wavelength ranges λλ3800–5180 and λλ5150–9000, respectively. The spectra have a mean resolution full width at half-maximum of ∼3.3 Å and are wavelength- and flux-calibrated to an accuracy of ∼20 km s−1 and ∼5 per cent, respectively. The spectra are further corrected for systematic errors in the wavelength calibration to an accuracy of ∼4 km s−1 by cross-correlating with the theoretical spectra. Almost all the spectra have an average signal-to-noise ratio better than 100 per pixel. Combined with the MILES spectra, there are now 1731, 1542, 1324 and 1273 stars with spectra covering λλ3800–5180, λλ3800–7500, λλ5150–9000 and λλ3800–9000, respectively. In this paper, we describe our template star selection, the observation and data reduction, and we present the reduced spectra collected hitherto.
- 30 August 2018
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 480 (4) , 4766-4781
Open AccessLEMONY – a library of empirical medium-resolution spectra by observations with the NAOC Xinglong 2.16-m and YNAO Gaomeigu 2.4-m telescopes
In this study, we expand the coverage and improve the homogeneity of the distribution of MILES template stars in the parameter space, as well as extend the wavelength coverage of the template spectra to the far red beyond the Ca ii triplet. To achieve this, we have carried out a major observational campaign using two long-slit spectrographs: the OMR mounted on the National Astronomy Observatory of China (NAOC) 2.16-m telescope and the Yunnan Faint Object Spectrograph and Camera (YFOSC) mounted on the Yunnan Astronomical Observatory (YNAO) 2.4-m telescope. The original sample is based on the MILES library, supplemented by 918 stars selected from the PASTEL data base. In total, 822 OMR and 1324 YFOSC spectra have been collected and reduced, covering the wavelength ranges λλ3800–5180 and λλ5150–9000, respectively. The spectra have a mean resolution full width at half-maximum of ∼3.3 Å and are wavelength- and flux-calibrated to an accuracy of ∼20 km s−1 and ∼5 per cent, respectively. The spectra are further corrected for systematic errors in the wavelength calibration to an accuracy of ∼4 km s−1 by cross-correlating with the theoretical spectra. Almost all the spectra have an average signal-to-noise ratio better than 100 per pixel. Combined with the MILES spectra, there are now 1731, 1542, 1324 and 1273 stars with spectra covering λλ3800–5180, λλ3800–7500, λλ5150–9000 and λλ3800–9000, respectively. In this paper, we describe our template star selection, the observation and data reduction, and we present the reduced spectra collected hitherto.
- 1 August 2018
- Published by Oxford University Press (OUP) in European Heart Journal
- Vol. 39 (suppl_1)
4914Prenatal identification of atrioventricular septal defect and associated genomic abnormality by fetal echocardiography and whole genome sequencing
Objective: We sought to correlate fetal echoardiographic characteristics of atrioventricular septal defect (AVSD) with genomic abnormalities using whole genome sequencing (WGS) and whole exomal sequencing (WES).
- 1 August 2018
- Published by Oxford University Press (OUP) in European Heart Journal
- Vol. 39 (suppl_1)
4914Prenatal identification of atrioventricular septal defect and associated genomic abnormality by fetal echocardiography and whole genome sequencing
Objective: We sought to correlate fetal echoardiographic characteristics of atrioventricular septal defect (AVSD) with genomic abnormalities using whole genome sequencing (WGS) and whole exomal sequencing (WES).
- Open Access
A new catalogue of radial velocity standard stars from the APOGEE data
We present a new catalogue of 18 080 radial velocity standard stars selected from the APOGEE data. These RV standard stars are observed at least three times and have a median stability ($3\sigma_{\rm RV}$) around 240 m s$^{-1}$ over a time baseline longer than 200 days. They are largely distributed in the northern sky and could be extended to the southern sky by the future APOGEE-2 survey. Most of the stars are red giants ($J - K_{\rm s} \ge 0.5$) owing to the APOGEE target selection criteria. Only about ten per cent of them are main-sequence stars. The $H$ band magnitude range of the stars is 7-12.5 mag with the faint limit much fainter than the magnitudes of previous RV standard stars. As an application, we show the new set of standard stars to determine the radial velocity zero points of the RAVE, the LAMOST {and the Gaia-RVS} Galactic spectroscopic surveys.Open AccessA new catalogue of radial velocity standard stars from the APOGEE data
We present a new catalogue of 18 080 radial velocity standard stars selected from the APOGEE data. These RV standard stars are observed at least three times and have a median stability ($3\sigma_{\rm RV}$) around 240 m s$^{-1}$ over a time baseline longer than 200 days. They are largely distributed in the northern sky and could be extended to the southern sky by the future APOGEE-2 survey. Most of the stars are red giants ($J - K_{\rm s} \ge 0.5$) owing to the APOGEE target selection criteria. Only about ten per cent of them are main-sequence stars. The $H$ band magnitude range of the stars is 7-12.5 mag with the faint limit much fainter than the magnitudes of previous RV standard stars. As an application, we show the new set of standard stars to determine the radial velocity zero points of the RAVE, the LAMOST {and the Gaia-RVS} Galactic spectroscopic surveys. - Open Access
Binary Star Fractions from the LAMOST DR4
Stellar systems composed of single, double, triple or high-order systems are rightfully regarded as the fundamental building blocks of the Milky Way. Binary stars play an important role in formation and evolution of the Galaxy. Through comparing the radial velocity variations from multi-epoch observations, we analyze the binary fraction of dwarf stars observed with the LAMOST. Effects of different model assumptions such as orbital period distributions on the estimate of binary fractions, are investigated. The results based on log-normal distribution of orbital periods reproduce the previous complete analyses better than the power-law distribution. We find that the binary fraction increases with $T_{\rm eff}$ and decreases with [Fe/H]. We first investigate the relation between $\alpha$-elements and binary fraction in such a large sample as the LAMOST. The old stars with high [$\alpha$/Fe] dominate higher binary fraction than young stars with low [$\alpha$/Fe]. At the same mass, former forming stars possess a higher binary fraction than newly forming ones, which may be related with the evolution of the Galaxy.Open AccessBinary Star Fractions from the LAMOST DR4
Stellar systems composed of single, double, triple or high-order systems are rightfully regarded as the fundamental building blocks of the Milky Way. Binary stars play an important role in formation and evolution of the Galaxy. Through comparing the radial velocity variations from multi-epoch observations, we analyze the binary fraction of dwarf stars observed with the LAMOST. Effects of different model assumptions such as orbital period distributions on the estimate of binary fractions, are investigated. The results based on log-normal distribution of orbital periods reproduce the previous complete analyses better than the power-law distribution. We find that the binary fraction increases with $T_{\rm eff}$ and decreases with [Fe/H]. We first investigate the relation between $\alpha$-elements and binary fraction in such a large sample as the LAMOST. The old stars with high [$\alpha$/Fe] dominate higher binary fraction than young stars with low [$\alpha$/Fe]. At the same mass, former forming stars possess a higher binary fraction than newly forming ones, which may be related with the evolution of the Galaxy. - 22 February 2018
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 476 (3) , 3278-3289
The selection function of the LAMOST Spectroscopic Survey of the Galactic Anti-centre
We present a detailed analysis of the selection function of the LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC). LSS-GAC was designed to obtain low-resolution optical spectra for a sample of more than 3 million stars in the Galactic anti-centre. The second release of value-added catalogues of the LSS-GAC (LSS-GAC DR2) contains stellar parameters, including radial velocity, atmospheric parameters, elemental abundances, and absolute magnitudes deduced from 1.8 million spectra of 1.4 million unique stars targeted by the LSS-GAC between 2011 and 2014. For many studies using this data base, such as those investigating the chemodynamical structure of the Milky Way, a detailed understanding of the selection function of the survey is indispensable. In this paper, we describe how the selection function of the LSS-GAC can be evaluated to sufficient detail and provide selection function corrections for all spectroscopic measurements with reliable parameters released in LSS-GAC DR2. The results, to be released as new entries in the LSS-GAC value-added catalogues, can be used to correct the selection effects of the catalogue for scientific studies of various purposes.
- 22 February 2018
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 476 (3) , 3278-3289
The selection function of the LAMOST Spectroscopic Survey of the Galactic Anti-centre
We present a detailed analysis of the selection function of the LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC). LSS-GAC was designed to obtain low-resolution optical spectra for a sample of more than 3 million stars in the Galactic anti-centre. The second release of value-added catalogues of the LSS-GAC (LSS-GAC DR2) contains stellar parameters, including radial velocity, atmospheric parameters, elemental abundances, and absolute magnitudes deduced from 1.8 million spectra of 1.4 million unique stars targeted by the LSS-GAC between 2011 and 2014. For many studies using this data base, such as those investigating the chemodynamical structure of the Milky Way, a detailed understanding of the selection function of the survey is indispensable. In this paper, we describe how the selection function of the LSS-GAC can be evaluated to sufficient detail and provide selection function corrections for all spectroscopic measurements with reliable parameters released in LSS-GAC DR2. The results, to be released as new entries in the LSS-GAC value-added catalogues, can be used to correct the selection effects of the catalogue for scientific studies of various purposes.
- Open Access
The selection function of the LAMOST Spectroscopic Survey of the Galactic Anticentre
We present a detailed analysis of the selection function of the LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC). LSS-GAC was designed to obtain low resolution optical spectra for a sample of more than 3 million stars in the Galactic anti-centre. The second release of value-added catalogues of the LSS-GAC (LSS-GAC DR2) contains stellar parameters, including radial velocity, atmospheric parameters, elemental abundances and absolute magnitudes deduced from 1.8 million spectra of 1.4 million unique stars targeted by the LSS-GAC between 2011 and 2014. For many studies using this database, such as those investigating the chemodynamical structure of the Milky Way, a detailed understanding of the selection function of the survey is indispensable. In this paper, we describe how the selection function of the LSS-GAC can be evaluated to sufficient detail and provide selection function corrections for all spectroscopic measurements with reliable parameters released in LSS-GAC DR2. The results, to be released as new entries in the LSS-GAC value-added catalogues, can be used to correct the selection effects of the catalogue for scientific studies of various purposes.
Open AccessThe selection function of the LAMOST Spectroscopic Survey of the Galactic Anticentre
We present a detailed analysis of the selection function of the LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC). LSS-GAC was designed to obtain low resolution optical spectra for a sample of more than 3 million stars in the Galactic anti-centre. The second release of value-added catalogues of the LSS-GAC (LSS-GAC DR2) contains stellar parameters, including radial velocity, atmospheric parameters, elemental abundances and absolute magnitudes deduced from 1.8 million spectra of 1.4 million unique stars targeted by the LSS-GAC between 2011 and 2014. For many studies using this database, such as those investigating the chemodynamical structure of the Milky Way, a detailed understanding of the selection function of the survey is indispensable. In this paper, we describe how the selection function of the LSS-GAC can be evaluated to sufficient detail and provide selection function corrections for all spectroscopic measurements with reliable parameters released in LSS-GAC DR2. The results, to be released as new entries in the LSS-GAC value-added catalogues, can be used to correct the selection effects of the catalogue for scientific studies of various purposes.
- 20 September 2017
- Published by American Astronomical Society in The Astrophysical Journal Letters
- Vol. 847 (1) , L9
Discovery of Two New Hypervelocity Stars from the LAMOST Spectroscopic Surveys
We report the discovery of two new unbound hypervelocity stars (HVSs) from the LAMOST spectroscopic surveys. They are, respectively, a B2V-type star of ∼7 M ⊙ with a Galactic rest-frame radial velocity of 502 km s−1 at a Galactocentric radius of ∼21 kpc and a B7V-type star of ∼4 M ⊙ with a Galactic rest-frame radial velocity of 408 km s−1 at a Galactocentric radius of ∼30 kpc. The origins of the two HVSs are not clear given their currently poorly measured proper motions. However, the future data releases of Gaia should provide proper motion measurements accurate enough to solve this problem. The ongoing LAMOST spectroscopic surveys are expected to yield more HVSs to form a statistical sample, providing vital constraints on understanding the nature of HVSs and their ejection mechanisms.
- 20 September 2017
- Published by American Astronomical Society in The Astrophysical Journal Letters
- Vol. 847 (1) , L9
Discovery of Two New Hypervelocity Stars from the LAMOST Spectroscopic Surveys
We report the discovery of two new unbound hypervelocity stars (HVSs) from the LAMOST spectroscopic surveys. They are, respectively, a B2V-type star of ∼7 M ⊙ with a Galactic rest-frame radial velocity of 502 km s−1 at a Galactocentric radius of ∼21 kpc and a B7V-type star of ∼4 M ⊙ with a Galactic rest-frame radial velocity of 408 km s−1 at a Galactocentric radius of ∼30 kpc. The origins of the two HVSs are not clear given their currently poorly measured proper motions. However, the future data releases of Gaia should provide proper motion measurements accurate enough to solve this problem. The ongoing LAMOST spectroscopic surveys are expected to yield more HVSs to form a statistical sample, providing vital constraints on understanding the nature of HVSs and their ejection mechanisms.