Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular ...Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular clusters. These old clusters are all metal poor, the range of metallicity ([Fe/H]) is from-0.14 to-2.12. In general, our results are consistent with those derived by other methods, such as integrated spectra and photometry, and our study confirms the reliability of the method of Kong et al.展开更多
We present accurate positions and multi-color photometry for 41 starclusters detected by Melnick & D'odorico in the nearby spiral galaxy M33 as a partof the BATC Color Survey of the sky in 13 intermediate-band...We present accurate positions and multi-color photometry for 41 starclusters detected by Melnick & D'odorico in the nearby spiral galaxy M33 as a partof the BATC Color Survey of the sky in 13 intermediate-band filters from 3800to 10000A. The coordinates of the clusters are found from the HST Guide StarCatalog. By aperture photometry, we obtain the spectral energy distributions ofthe clusters. Using the relations between the BATC intermediate-band system andUBVRI broadband system, we derive their V magnitudes and B - V colors andfind that most of them are blue, which is consistent with previous findings.展开更多
In this second paper of our. series, we estimate the age of 41 star clusters,which were detected by Melnick & D'odorico in the nearby spiral galaxy M33, by comparing the integrated photometric measurements wit...In this second paper of our. series, we estimate the age of 41 star clusters,which were detected by Melnick & D'odorico in the nearby spiral galaxy M33, by comparing the integrated photometric measurements with theoretical stellar population synthesis models of Bruzual & Charlot. Also, we calculate the mass of these star clusters using the theoretical M/Lv ratio. The results show that, these star clusters formed continuously in M33 from ~ 7 × 106 - 1010 years and have masses between ~ 103 and 2 × 106 M . M33 frames were observed as a part of the BATC Multicolor Survey of the sky in 13 intermediate-band filters from 3800 to 10 000A.The relation between age and mass confirms that the sample star cluster masses systematically decrease from the oldest to the youngest.展开更多
We re-examine the properties of the star cluster population in the circumnuclear starburst ring in the face-on spiral galaxy NGC 7742, whose young cluster mass function has been reported to exhibit significant deviati...We re-examine the properties of the star cluster population in the circumnuclear starburst ring in the face-on spiral galaxy NGC 7742, whose young cluster mass function has been reported to exhibit significant deviations from the canonical power law. We base our reassessment on the clusters' luminosities(an observational quantity) rather than their masses(a derived quantity), and confirm conclusively that the galaxy's starburst-ring clusters—and particularly the youngest subsample, log(t yr^(-1)) ≤ 7.2—show evidence of a turnover in the cluster luminosity function well above the 90% completeness limit adopted to ensure the reliability of our results. This confirmation emphasizes the unique conundrum posed by this unusual cluster population.展开更多
We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at l...We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered proto- globular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.展开更多
In this work, we provide 2189 photometrically- and kinematically-selected candidate members of 24 star clusters from the LAMOST DR2 catalog. We perform two-step membership identification: selection along the stellar t...In this work, we provide 2189 photometrically- and kinematically-selected candidate members of 24 star clusters from the LAMOST DR2 catalog. We perform two-step membership identification: selection along the stellar track in the colormagnitude diagram, i.e., photometric identification, and selection from the distribution of radial velocities, i.e. the kinematic identification. We find that the radial velocities from the LAMOST data are very helpful in the membership identification. The mean probability of membership is 40% for the sample selected with radial velocity. With these 24 star clusters, we investigate the performance of the radial velocity and metallicity estimated with the LAMOST pipeline. We find that the systematic offsets in radial velocity and metallicity are 0.85 ± 1.26 km s-1and-0.08 ± 0.04 dex, with dispersions of 5.47+1.16-0.71 km s-1and 0.13+0.04-0.02 dex, respectively. Finally, we propose that the photometrically-selected candidate members of the clusters covered by the LAMOST footprint should be assigned higher priority so that more candidate stars can be observed.展开更多
We present the fundamental parameters of ten open star clusters,nominated from Kronberger et al.who presented some newly discovered stellar groups on the basis of the Two Micron All Sky Survey photometry and Digitized...We present the fundamental parameters of ten open star clusters,nominated from Kronberger et al.who presented some newly discovered stellar groups on the basis of the Two Micron All Sky Survey photometry and Digitized Sky Survey visual images.Star counts and photometric parameters(radius,membership,distance,color excess,age,luminosity function,mass function,total mass,and dynamical relaxation time) have been determined for these ten clusters for the first time.In order to calibrate our procedures,the main parameters(distance,age,and color excess) have been reestimated for another five clusters,which are also studied by Kronberger et al.展开更多
Stellar populations contain the most important information about star cluster formation and evolution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar popu...Stellar populations contain the most important information about star cluster formation and evolution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations(SSPs). However, discoveries of multiple stellar populations in Galactic globular clusters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar populations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ages. We present the history and progress of research in this active field, as well as some of the most recent improvements, including observational results and scenarios that have been proposed to explain the observations. Although our current ability to determine the origin of multiple stellar populations in star clusters is unsatisfactory, we propose a number of promising projects that may contribute to a significantly improved understanding of this subject.展开更多
As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data ...As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data Release 3(Gaia EDR3)and modern machine-learning methods offer unprecedented opportunities to identify OCs.In this study,we extended conventional HDBSCAN(e-HDBSCAN)for searching for new OCs in Gaia EDR3.A pipeline was developed based on the parallel computing technique to blindly search for OCs from Gaia EDR3within Galactic latitudes∣b∣<25°.As a result,we obtained 3787 star clusters,of which 83 new OCs were reported after cross-match and visual inspection.At the same time,the main star cluster parameters are estimated by color-magnitude diagram fitting.The study significantly increases the sample size and physical parameters of OCs in the catalog of OCs.It shows the incompleteness of the census of OCs across our Galaxy.展开更多
This paper presents Charge-Coupled Device time-series photometric observations of the open cluster NGC 1582 and its surrounding field with Johnson B,V and R filters by using the Nanshan 1 m telescope administered by X...This paper presents Charge-Coupled Device time-series photometric observations of the open cluster NGC 1582 and its surrounding field with Johnson B,V and R filters by using the Nanshan 1 m telescope administered by Xinjiang Astronomical Observatory.19 variable stars and three variable candidates were detected in a 45′×48.75′ field around the cluster.12 of the variable stars are newly-discovered variable objects.The physical properties,classifications and memberships of these 22 objects are studied through their light curves,their positions on the color-magnitude diagram and with archival data from the Naval Observatory Merged Astrometric Dataset.Among these objects,five are eclipsing binary systems,six are pulsating variable stars including one known S Scuti star and one newly-discovered RR Lyrae star.The distance to the RR Lyrae star is estimated to be 7.9 ± 0.3 kpc,indicating that the star is located far behind the cluster.Four variable stars are probable members of the cluster,and 13 of the 22 objects are confirmed to be field stars.展开更多
We present a study of the star 2MASS J22472238+5801214 with the aim of identifying its true nature which has hitherto been uncertain.This object,which is a member of the young cluster NGC 7380,has been variously propo...We present a study of the star 2MASS J22472238+5801214 with the aim of identifying its true nature which has hitherto been uncertain.This object,which is a member of the young cluster NGC 7380,has been variously proposed to be a Be star,a D-type symbiotic and a Herbig Ae/Be star in separate studies.Here we present optical spectroscopy,near-IR photometry and narrow band Hα imaging of the nebulosity in its environment.Analysis of all these results,including the spectral energy distribution constructed from available data,strongly indicate the source to be a Herbig Ae/Be star.The star is found to be accompanied by a nebulosity with an interesting structure.A bow-shock shaped structure,similar to a cometary nebula,is seen very close to the star with its apex oriented towards the photoionizing source of this region (i.e.the star DH Cep).An interesting spectroscopic finding,from the forbidden [SII] 6716,6731 and [OI] 6300 lines,is the detection of a blue-shifted high velocity outflow (200 ±50 km s-1) from the star.展开更多
We report the results of a search for variable stars in the open cluster NGC 2141. Ten variable stars are detected, among which nine are new variable stars and they are classified as three short-period W UMa-type ecli...We report the results of a search for variable stars in the open cluster NGC 2141. Ten variable stars are detected, among which nine are new variable stars and they are classified as three short-period W UMa-type eclipsing binaries, two EAtype eclipsing binaries, one EB-type eclipsing binary, one very short-period RS CVntype eclipsing binary, one d-type RR Lyrae variable star, and one unknown type of variable star. The membership and physical properties are discussed, based on their light curves, positions in the color magnitude diagrams, spatial locations and periods.A known EB-type eclipsing binary is also identified as a blue straggler candidate in the cluster. Furthermore, we find that all eclipsing contact binaries have prominent asymmetric eclipses and display the O'Connell effect, which increases with a decrease in orbital periods. This suggests that the O'Connell effect is probably related to the evolution of the orbital period in short period eclipsing binary systems.展开更多
A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W ...A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems,one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δ Scuti stars.展开更多
We report the results of a time-series CCD photometric survey of variable stars in the field of open cluster NGC 2126. In about a one square degree field covering the cluster,a total of 21 variable candidates are dete...We report the results of a time-series CCD photometric survey of variable stars in the field of open cluster NGC 2126. In about a one square degree field covering the cluster,a total of 21 variable candidates are detected during this survey,of which 16 are newly found. The periods,classifications and spectral types of 14 newly discovered variables are discussed,which consist of six eclipsing binary systems,three pulsating variable stars,three long period variables,one RS CVn star,and one W UMa or δ Scuti star. In addition,there are two variable candidates,the properties of which cannot be determined. By a method based on fitting observed spectral energy distributions of stars with theoretical ones,the membership probabilities and the fundamental parameters of this cluster are determined. As a result,five variables are probably members of NGC 2126. The fundamental parameters of this cluster are determined as: metallicity to be 0.008Z , age log(t) = 8.95,distance modulus (m M)0 = 10.34 and reddening value E(B V ) = 0.55 mag.展开更多
A rarely studied open cluster,King 1 is observed using the 1.3-m telescope equipped with a 2 k×4 k CCD at Vainu Bappu Observatory,India.We analyze the photometric data obtained from CCD observations in both B and...A rarely studied open cluster,King 1 is observed using the 1.3-m telescope equipped with a 2 k×4 k CCD at Vainu Bappu Observatory,India.We analyze the photometric data obtained from CCD observations in both B and V bands.Out of 132 detected stars in the open cluster King 1 field,we have identified four stellar variables,and two among them are reported as newly detected binary systems.The parallax values from Gaia DR2 suggest that the open cluster King 1 is in the background of these two detected binary systems,falling along the same line of sight,giving rise to different parallax values.Periodogram analysis was carried out using Phase Dispersion Minimization(PDM)and the Lomb-Scargle(LS)method for all the detected variables.PHysics Of Eclipsing Binari Es(PHOEBE)is extensively employed to model various stellar parameters of both the detected binary systems.Based on the modeling results obtained from this work,one of the binary systems is reported for the first time as an Eclipsing Detached(ED)and the other as an Eclipsing Contact(EC)binary of W-type W UMa.展开更多
We present a snapshot of our recent results of a variable star survey in1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A totalnumber of 39 variable stars are newly discovered, including 22 W UM...We present a snapshot of our recent results of a variable star survey in1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A totalnumber of 39 variable stars are newly discovered, including 22 W UMa stars, 10EA (Algol) type binaries, one RR-lyr and one RRd pulsator, and five unclassifiedvariables.展开更多
Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution.The origin of the abundance patterns,however,still remains poorly und...Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution.The origin of the abundance patterns,however,still remains poorly understood.We have studied the impact of p-capture reaction cycles on the abundances of oxygen,sodium and aluminium considering nuclear reaction cycles of carbon-nitrogenoxygen-fluorine,neon-sodium and magnesium-aluminium in massive stars in stellar conditions of temperature range 2×10~7 to 10×10~7K and typical density of 10~2gm cc^(-1).We have estimated abundances of oxygen,sodium and aluminium with respect to Fe,which are then assumed to be ejected from those stars because of rotation reaching a critical limit.These ejected abundances of elements are then compared with their counterparts that have been observed in some metal-poor evolved stars,mainly giants and red giants,of globular clusters M3,M4,M13 and NGC 6752.We observe an excellent agreement with[O/Fe]between the estimated and observed abundance values for globular clusters M3 and M4 with a correlation coefficient above 0.9 and a strong linear correlation for the remaining two clusters with a correlation coefficient above 0.7.The estimated[Na/Fe]is found to have a correlation coefficient above 0.7,thus implying a strong correlation for all four globular clusters.As far as[Al/Fe]is concerned,it also shows a strong correlation between the estimated abundance and the observed abundance for globular clusters M13 and NGC 6752,since here also the correlation coefficient is above 0.7 whereas for globular cluster M4 there is a moderate correlation found with a correlation coefficient above 0.6.Possible sources of these discrepancies are discussed.展开更多
Binary stars are common in star clusters and galaxies, but the detailed effects of binary evolution are not taken into account in some color-magnitude diagram (CMD) studies. This paper studies the CMDs of twelve globu...Binary stars are common in star clusters and galaxies, but the detailed effects of binary evolution are not taken into account in some color-magnitude diagram (CMD) studies. This paper studies the CMDs of twelve globular clusters via binarystar stellar populations. The observational CMDs of the star clusters are compared to those of binary-star populations, and then the stellar metallicities, ages, distances and reddenings of these star clusters are obtained. The paper also tests the different effects of binary and single stars on CMD studies. It is shown that binaries can better fit the observational CMDs of the sample globular clusters compared to single stars. This suggests that the effects of binary evolution should be considered when modeling the CMDs and stellar populations of star clusters and galaxies.展开更多
基金the Chinese Acadeinv of Sciences,the Chinese National Naturnal Science Foundation and the Ministry of sciences and technology of ChinaThe project is also supported in part by the National Science Foundation(grant IXT 93-01805)by Arizona State University,the University of Arizona and Western Connecticut State University
文摘Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular clusters. These old clusters are all metal poor, the range of metallicity ([Fe/H]) is from-0.14 to-2.12. In general, our results are consistent with those derived by other methods, such as integrated spectra and photometry, and our study confirms the reliability of the method of Kong et al.
基金the Chinese Academy of Sciencesthe,the Chinese National Natural Science Foundation and the Ministry of Sciences and Technology of ChinaThe project is also supported partly by the National Science Foundation (grant INT 93-01805)+1 种基金 by Arizona State Universitythe University of Arizona and Western ConetiutState Universitv.
文摘We present accurate positions and multi-color photometry for 41 starclusters detected by Melnick & D'odorico in the nearby spiral galaxy M33 as a partof the BATC Color Survey of the sky in 13 intermediate-band filters from 3800to 10000A. The coordinates of the clusters are found from the HST Guide StarCatalog. By aperture photometry, we obtain the spectral energy distributions ofthe clusters. Using the relations between the BATC intermediate-band system andUBVRI broadband system, we derive their V magnitudes and B - V colors andfind that most of them are blue, which is consistent with previous findings.
基金Supported by the National Natural Science Foundation of China
文摘In this second paper of our. series, we estimate the age of 41 star clusters,which were detected by Melnick & D'odorico in the nearby spiral galaxy M33, by comparing the integrated photometric measurements with theoretical stellar population synthesis models of Bruzual & Charlot. Also, we calculate the mass of these star clusters using the theoretical M/Lv ratio. The results show that, these star clusters formed continuously in M33 from ~ 7 × 106 - 1010 years and have masses between ~ 103 and 2 × 106 M . M33 frames were observed as a part of the BATC Multicolor Survey of the sky in 13 intermediate-band filters from 3800 to 10 000A.The relation between age and mass confirms that the sample star cluster masses systematically decrease from the oldest to the youngest.
基金supported by the National Key Research and Development Program of China(Grant 2017YFA0402702)the National Natural Science Foundation of China(Grant Nos.U1631102,11373010and 11633005)
文摘We re-examine the properties of the star cluster population in the circumnuclear starburst ring in the face-on spiral galaxy NGC 7742, whose young cluster mass function has been reported to exhibit significant deviations from the canonical power law. We base our reassessment on the clusters' luminosities(an observational quantity) rather than their masses(a derived quantity), and confirm conclusively that the galaxy's starburst-ring clusters—and particularly the youngest subsample, log(t yr^(-1)) ≤ 7.2—show evidence of a turnover in the cluster luminosity function well above the 90% completeness limit adopted to ensure the reliability of our results. This confirmation emphasizes the unique conundrum posed by this unusual cluster population.
文摘We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered proto- globular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.
基金supported by the Strategic Priority Research Program "The Emergence of Cosmological Structures" of the Chinese Academy of Sciences (Grant No. XDB09000000)the National Key Basic Research Program of China (2014CB845700)+3 种基金CL acknowledges the National Natural Science Foundation of China (NSFC, Grant Nos. 11373032, 11333003 and U1231119)XYC acknowledges the NSFC (Grant No. 11403036)the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. Y429012001)two Young Researcher Grants from National Astronomical Observatories, Chinese Academy of Sciences
文摘In this work, we provide 2189 photometrically- and kinematically-selected candidate members of 24 star clusters from the LAMOST DR2 catalog. We perform two-step membership identification: selection along the stellar track in the colormagnitude diagram, i.e., photometric identification, and selection from the distribution of radial velocities, i.e. the kinematic identification. We find that the radial velocities from the LAMOST data are very helpful in the membership identification. The mean probability of membership is 40% for the sample selected with radial velocity. With these 24 star clusters, we investigate the performance of the radial velocity and metallicity estimated with the LAMOST pipeline. We find that the systematic offsets in radial velocity and metallicity are 0.85 ± 1.26 km s-1and-0.08 ± 0.04 dex, with dispersions of 5.47+1.16-0.71 km s-1and 0.13+0.04-0.02 dex, respectively. Finally, we propose that the photometrically-selected candidate members of the clusters covered by the LAMOST footprint should be assigned higher priority so that more candidate stars can be observed.
基金the National Aeronautics and Space Administration and the National Science Foundation (NASA)
文摘We present the fundamental parameters of ten open star clusters,nominated from Kronberger et al.who presented some newly discovered stellar groups on the basis of the Two Micron All Sky Survey photometry and Digitized Sky Survey visual images.Star counts and photometric parameters(radius,membership,distance,color excess,age,luminosity function,mass function,total mass,and dynamical relaxation time) have been determined for these ten clusters for the first time.In order to calibrate our procedures,the main parameters(distance,age,and color excess) have been reestimated for another five clusters,which are also studied by Kronberger et al.
基金supported by a Macquarie Research Fellowship and by Strategic Priority Program ‘The Emergence of Cosmological Structures’ of the Chinese Academy of Sciences(Grant XDB09000000)support from the National Natural Science Foundation of China(Grant Nos.11073001,11373010 and 11473037)
文摘Stellar populations contain the most important information about star cluster formation and evolution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations(SSPs). However, discoveries of multiple stellar populations in Galactic globular clusters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar populations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ages. We present the history and progress of research in this active field, as well as some of the most recent improvements, including observational results and scenarios that have been proposed to explain the observations. Although our current ability to determine the origin of multiple stellar populations in star clusters is unsatisfactory, we propose a number of promising projects that may contribute to a significantly improved understanding of this subject.
基金supported by the National SKA Program of China No.2020SKA0110300Joint Research Fund in Astronomy(U1831204)under cooperative agreement between the National Natural Science Foundation of China(NSFC)+5 种基金the Chinese Academy of Sciences(CAS)the National Key Research and Development Program of China(2018YFA0404603)the NSFC(Nos.11863002 and 11961141001)supported by the Yunnan Academician Workstation of Wang Jingxiu(No.202005AF150025)China Manned Space Project with NO.CMS-CSST-2021-A08Sino-German Cooperation Project(No.GZ 1284)。
文摘As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data Release 3(Gaia EDR3)and modern machine-learning methods offer unprecedented opportunities to identify OCs.In this study,we extended conventional HDBSCAN(e-HDBSCAN)for searching for new OCs in Gaia EDR3.A pipeline was developed based on the parallel computing technique to blindly search for OCs from Gaia EDR3within Galactic latitudes∣b∣<25°.As a result,we obtained 3787 star clusters,of which 83 new OCs were reported after cross-match and visual inspection.At the same time,the main star cluster parameters are estimated by color-magnitude diagram fitting.The study significantly increases the sample size and physical parameters of OCs in the catalog of OCs.It shows the incompleteness of the census of OCs across our Galaxy.
基金supported by the National Natural Science Foundation of China under Grant No.11273051the program of Light in China Western Region(LCWR,Grant Nos.XBBS201221 and 2015-XBQN-A-02)
文摘This paper presents Charge-Coupled Device time-series photometric observations of the open cluster NGC 1582 and its surrounding field with Johnson B,V and R filters by using the Nanshan 1 m telescope administered by Xinjiang Astronomical Observatory.19 variable stars and three variable candidates were detected in a 45′×48.75′ field around the cluster.12 of the variable stars are newly-discovered variable objects.The physical properties,classifications and memberships of these 22 objects are studied through their light curves,their positions on the color-magnitude diagram and with archival data from the Naval Observatory Merged Astrometric Dataset.Among these objects,five are eclipsing binary systems,six are pulsating variable stars including one known S Scuti star and one newly-discovered RR Lyrae star.The distance to the RR Lyrae star is estimated to be 7.9 ± 0.3 kpc,indicating that the star is located far behind the cluster.Four variable stars are probable members of the cluster,and 13 of the 22 objects are confirmed to be field stars.
基金funded by the Department of Space, Government of India
文摘We present a study of the star 2MASS J22472238+5801214 with the aim of identifying its true nature which has hitherto been uncertain.This object,which is a member of the young cluster NGC 7380,has been variously proposed to be a Be star,a D-type symbiotic and a Herbig Ae/Be star in separate studies.Here we present optical spectroscopy,near-IR photometry and narrow band Hα imaging of the nebulosity in its environment.Analysis of all these results,including the spectral energy distribution constructed from available data,strongly indicate the source to be a Herbig Ae/Be star.The star is found to be accompanied by a nebulosity with an interesting structure.A bow-shock shaped structure,similar to a cometary nebula,is seen very close to the star with its apex oriented towards the photoionizing source of this region (i.e.the star DH Cep).An interesting spectroscopic finding,from the forbidden [SII] 6716,6731 and [OI] 6300 lines,is the detection of a blue-shifted high velocity outflow (200 ±50 km s-1) from the star.
基金Supported by the National Natural Science Foundation of China
文摘We report the results of a search for variable stars in the open cluster NGC 2141. Ten variable stars are detected, among which nine are new variable stars and they are classified as three short-period W UMa-type eclipsing binaries, two EAtype eclipsing binaries, one EB-type eclipsing binary, one very short-period RS CVntype eclipsing binary, one d-type RR Lyrae variable star, and one unknown type of variable star. The membership and physical properties are discussed, based on their light curves, positions in the color magnitude diagrams, spatial locations and periods.A known EB-type eclipsing binary is also identified as a blue straggler candidate in the cluster. Furthermore, we find that all eclipsing contact binaries have prominent asymmetric eclipses and display the O'Connell effect, which increases with a decrease in orbital periods. This suggests that the O'Connell effect is probably related to the evolution of the orbital period in short period eclipsing binary systems.
文摘A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems,one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δ Scuti stars.
基金supported by the National Natural Science Foundation of China through Grant Nos. 10873016, 10803007, 10473012, 10573020, 10633020, 10673012, 10603006, 10773015 and 10778720the National Basic Research Program of China (973 Program) No. 2007CB815403the Knowledge Innovation Program of Chinese Academy of Sciences
文摘We report the results of a time-series CCD photometric survey of variable stars in the field of open cluster NGC 2126. In about a one square degree field covering the cluster,a total of 21 variable candidates are detected during this survey,of which 16 are newly found. The periods,classifications and spectral types of 14 newly discovered variables are discussed,which consist of six eclipsing binary systems,three pulsating variable stars,three long period variables,one RS CVn star,and one W UMa or δ Scuti star. In addition,there are two variable candidates,the properties of which cannot be determined. By a method based on fitting observed spectral energy distributions of stars with theoretical ones,the membership probabilities and the fundamental parameters of this cluster are determined. As a result,five variables are probably members of NGC 2126. The fundamental parameters of this cluster are determined as: metallicity to be 0.008Z , age log(t) = 8.95,distance modulus (m M)0 = 10.34 and reddening value E(B V ) = 0.55 mag.
基金MHRD TEQIP-Ⅲ for awarding fellowships for pursuing Ph.D.s at Gauhati UniversityFunding for the DPAC has been provided by national institutions,in particular the institutions participating in the Gaia Multilateral Agreement.
文摘A rarely studied open cluster,King 1 is observed using the 1.3-m telescope equipped with a 2 k×4 k CCD at Vainu Bappu Observatory,India.We analyze the photometric data obtained from CCD observations in both B and V bands.Out of 132 detected stars in the open cluster King 1 field,we have identified four stellar variables,and two among them are reported as newly detected binary systems.The parallax values from Gaia DR2 suggest that the open cluster King 1 is in the background of these two detected binary systems,falling along the same line of sight,giving rise to different parallax values.Periodogram analysis was carried out using Phase Dispersion Minimization(PDM)and the Lomb-Scargle(LS)method for all the detected variables.PHysics Of Eclipsing Binari Es(PHOEBE)is extensively employed to model various stellar parameters of both the detected binary systems.Based on the modeling results obtained from this work,one of the binary systems is reported for the first time as an Eclipsing Detached(ED)and the other as an Eclipsing Contact(EC)binary of W-type W UMa.
基金This paper is supported in part by Chinese National Natural ScienceFoundation through grant 10173013 and by The Ministry of Science and Technology of China through grant G19990754.
文摘We present a snapshot of our recent results of a variable star survey in1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A totalnumber of 39 variable stars are newly discovered, including 22 W UMa stars, 10EA (Algol) type binaries, one RR-lyr and one RRd pulsator, and five unclassifiedvariables.
文摘Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution.The origin of the abundance patterns,however,still remains poorly understood.We have studied the impact of p-capture reaction cycles on the abundances of oxygen,sodium and aluminium considering nuclear reaction cycles of carbon-nitrogenoxygen-fluorine,neon-sodium and magnesium-aluminium in massive stars in stellar conditions of temperature range 2×10~7 to 10×10~7K and typical density of 10~2gm cc^(-1).We have estimated abundances of oxygen,sodium and aluminium with respect to Fe,which are then assumed to be ejected from those stars because of rotation reaching a critical limit.These ejected abundances of elements are then compared with their counterparts that have been observed in some metal-poor evolved stars,mainly giants and red giants,of globular clusters M3,M4,M13 and NGC 6752.We observe an excellent agreement with[O/Fe]between the estimated and observed abundance values for globular clusters M3 and M4 with a correlation coefficient above 0.9 and a strong linear correlation for the remaining two clusters with a correlation coefficient above 0.7.The estimated[Na/Fe]is found to have a correlation coefficient above 0.7,thus implying a strong correlation for all four globular clusters.As far as[Al/Fe]is concerned,it also shows a strong correlation between the estimated abundance and the observed abundance for globular clusters M13 and NGC 6752,since here also the correlation coefficient is above 0.7 whereas for globular cluster M4 there is a moderate correlation found with a correlation coefficient above 0.6.Possible sources of these discrepancies are discussed.
基金supported by the National Natural Science Foundation of China (Grant No. 10963001)Yunnan Science Foundation(2009CD093)the Scientific Research Foundation of Dali University (DYKF2009 No. 1)
文摘Binary stars are common in star clusters and galaxies, but the detailed effects of binary evolution are not taken into account in some color-magnitude diagram (CMD) studies. This paper studies the CMDs of twelve globular clusters via binarystar stellar populations. The observational CMDs of the star clusters are compared to those of binary-star populations, and then the stellar metallicities, ages, distances and reddenings of these star clusters are obtained. The paper also tests the different effects of binary and single stars on CMD studies. It is shown that binaries can better fit the observational CMDs of the sample globular clusters compared to single stars. This suggests that the effects of binary evolution should be considered when modeling the CMDs and stellar populations of star clusters and galaxies.