首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 25 毫秒
1.
In this study, we employ machine learning to build a catalog of DB white dwarfs(DBWDs) from the LAMOST Data Release(DR) 5. Using known DBs from SDSS DR14, we selected samples of highquality DB spectra from the LAMOST database and applied them to train the machine learning process.Following the recognition procedure, we chose 351 DB spectra of 287 objects, 53 of which were new identifications. We then utilized all the DBWD spectra from both SDSS DR14 and LAMOST DR5 to construct DB templates for LAMOST 1 D pipeline reductions. Finally, by applying DB parameter models provided by D. Koester and the distance from Gaia DR2, we calculated the effective temperatures, surface gravities and distributions of the 3 D locations and velocities of all DBWDs.  相似文献   

2.
A catalog of 995 C and late M type stars is compiled from the First Byurakan Survey of the sky (FBS). The question of effectively separating giants and dwarfs among the stars of spectral class M is examined using data from this catalog, the 2MASS survey, and a number of other catalogs. This has made it possible to determine the luminosity class of 846 class M stars from the FBS survey. In the sample of FBS late M stars, 187 are dwarfs and 659 are giants. The sample of FBS late M stars is compared statistically with the set of known samples of type M stars. The subsample of FBS M-giants is proved to be similar to Stephenson’s standard sample of M-giants. A detailed statistical analysis of these two samples is carried out. __________ Translated from Astrofizika, Vol. 50, No. 4, pp. 589–602 (November 2007).  相似文献   

3.
Kepler卫星提供的长时序、高精度的光度观测和郭守敬望远镜(LAMOST)提供的大规模光谱观测为研究恒星表面转动周期与富锂巨星锂丰度关系提供了良好的数据.将LAMOST搜寻到的富锂巨星与Kepler观测交叉,获得了619颗共同源,研究了其中295颗有良好观测数据的富锂巨星的表面转动.在205颗有星震学参数的恒星中提取出14颗恒星的转动周期,其中氦核燃烧星(HeB) 11颗,红巨星支(RGB) 2颗, 1颗演化阶段未确定.本样本中的极富锂巨星(A(Li) 3.3 dex)皆为HeB;对于90颗没有星震学参数的样本因而没有依靠星震学手段确定演化阶段的恒星中,有22颗提取出了自转周期.前者的自转探测率为6.8%,显著高于之前工作中大样本巨星2.08%的探测率.同时,此研究首次从自转周期的角度确认了恒星转动与巨星锂增丰存在相关性,在增丰程度较弱时,自转周期分布比较弥散;强锂增丰的星倾向于快速转动.富锂巨星与极富锂巨星在转动速度随锂丰度的演化上展现了两个序列,在转动-锂丰度图上的A(Li)≈3.3 dex处产生第2个下降序列,或许暗示了两者在形成机制上的不同.极富锂巨星的样本中,随巨星锂增丰程度增强,恒星转速加快.这种相关性为由转动引起的额外混合作为富锂巨星形成的机制提供了支持.  相似文献   

4.
在8000至8670的波长范围内,利用一个由144颗恒星光谱组成的光谱厍,我们对57个巨椭圆和S0星系(M_B<-21)的光谱和它们的平均光谱进行了光谱合成.这个光谐库包括了光谱型为G,K和M的巨星和矮星,它具有的金属丰度[Fe/H]覆盖了-0.1到-0.5的范围,表面重力log g为1.0至5.0.光谱合成的结果表明:巨椭圆和S0星系的金属丰度约为太阳的一倍半;有效表面重力分布在3.2—4.1的范围内;矮星在8400附近光的贡献可与巨星相比较.  相似文献   

5.
We have made near infrared spectroscopic observations of 10 symbiotic and 27 K-M comparison stars. For stars later than M3, we found the band depth of the triple-headed TiO absorption band to be sensitive to temperature and insensitive to gravity. We fitted the spectral type to the band depth with a standard error of 0.22 of a subtype and derived the spectral types for 6 symbiotic stars. We measured the EW of a large number of lines including the CaII lines (very sensitive to luminosity), the FeI and TiO lines (moderately sensitive) and the NaI lines (not sensitive). The EW of these lines vary with the spectral type, particularly for stars later than M3, both spectral type and luminosity effects must be considered. We give the luminosity classes for 10 of the brighter symbiotic stars, they are all giant stars, showing no features of bright giants or supergiants.  相似文献   

6.
We present candidate members of the Pal 5,GD-1,Cetus Polar and Orphan tidal stellar streams found in LAMOST DR3,SDSS DR9 and APOGEE catalogs.In LAMOST DR3,we find 20,4 and 24 high confidence candidates of tidal streams GD-1,Cetus Polar and Orphan respectively.We also list 59,118 and 10 high confidence candidates of tidal streams Cetus Polar,Orphan and Pal 5,respectively from the SDSS DR9 spectroscopic catalog.Furthermore,we find seven high confidence candidates of the Pal 5 tidal stream in the APOGEE data.Compared with SDSS,the new candidates from LAMOST DR3 are brighter,so that together,more of the color-magnitude diagram,including the giant branch,can be explored.Analysis of the SDSS data shows that there are three metallicity peaks associated with the Orphan stream which also exhibit some spatial separation.The LAMOST data confirm multiple metallicities in this stream.The metallicity,given by the higher resolution APOGEE instrument,of the Pal 5 tidal stream is [Fe/H] ~-1.2,higher than that given earlier by SDSS spectra.Many previously unidentified stream members are tabulated here for the first time,along with existing members,allowing future researchers to further constrain the orbits of these objects as they move within the Galaxy's dark matter potential.  相似文献   

7.
Big data obtained from a stellar spectroscopic survey carried out using the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST, also known as Guo Shou Jing telescope) provide important information for studying chromospheric activity, variability of chromospheric activity, and chromospheric statistical properties, and for searching subdwarfs and extreme subdwarfs. Using as chromospheric activity indicator the Hα line, we detected 6391 active M stars among the 99741 stars in the M-star catalogue of the LAMOST survey. We also obtained the relationship between the fraction of active stars and the spectral types, which is consistent to previous results. We also studied the effects of activity on broadband photometric colors, and we did not see significant differences between active and inactive M stars. Using as spectroscopic molecular indicators the CaH123 and TiO5 lines, we found 1288 subdwarfs (including 120 active subdwarfs). We also found 15 extreme subdwarf (2 active extreme subdwarf) candidates. Our subdwarf candidates are slightly redder by about 0.05 mag in g-r compared with dwarfs using the g-r and r-i, and g-r and i-z color diagrams. Using our active M-star catalogue, we found that 898 stars exhibited Hα emission in at least two exposures (170 of them in at least three exposures). Among these 170 stars, 163 of them show variability in Hα emission on long timescales (more than 2.5 h). Furthermore, 34 stars show variability over short timescales (less than 2.5 h), and 29 actives show variability over both short and long time scales.  相似文献   

8.
The results of a spectral classification of 257 M stars observed in the Cepheus region are given. Their equatorial coordinates, photographic stellar magnitudes, and spectral subtypes were determined. These stars are giants and supergiants, in all probability. None of them appear in a catalog of variable stars. It is assumed that variability might be detected in many of them upon further study. Fifty-two of the stars have been identified with infrared sources.  相似文献   

9.
Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope. Most of them are main-sequence stars, but some of them are post main-sequence systems. They are good astrophysical laboratories for studying several problems such as the merging of binary stars, evolution of the common envelope, the origin of luminous red nova outbursts and the formation of rapidly rotating single stars with possible planetary systems. A large number of contact binary candidates were detected by several photometric surveys around the world and many of them were observed by the LAMOST spectroscopic survey. Based on follow-up observations,the evolutionary states and geometrical structures of some systems were understood well. In this review,we will introduce and catalog new stellar atmospheric parameters(i.e., the effective temperature(Teff), the gravitational acceleration(log(g)), metallicity([Fe/H]) and radial velocity(Vr)) for 9149 EW-type contact binaries that were obtained based on low-and medium-resolution spectroscopic surveys of LAMOST. Then we will focus on several groups of contact binary stars, i.e., marginal contact binary systems, deep and low-mass ratio contact binary stars, binary systems below the short-period limit of contact binaries and evolved contact binaries. Marginal contact binaries are at the beginning of the contact stage, while deep and low-mass ratio contact binary stars are at the final evolutionary stage of tidally locked binaries. Several statistical relations including the period-temperature relation are determined well by applying LAMOST data and their formation and evolutionary states are reviewed. The period-color relation of M-type binaries reveals that there are contact binaries below the short-period limit. Searching for and investigating contact binaries near and below this limit will help us to understand the formation of contact binary systems and a new prediction for the short-period limit is about 0.15 d. Some evolved contact binaries were detected by the LAMOST survey where both components are sub-giants or giants. They provide a good opportunity to investigate evolution of the common envelope and are the progenitors of luminous red novae like V1309 Sco.  相似文献   

10.
The stellar composition of the Tycho-2 Catalogue in the range B-V = 0· m 75–1· m 25 has been reproduced through Monte Carlo simulations. For young and old stars of the red giant clump (RGC), the red giant branch, subgiants, red dwarfs, and thick-disk giants, we have specified the distributions in coordinates, velocities, B-V, and M V as a function of B-V and calculated their reduced proper motions, photometric distances from the (B-V)-M V calibration, and photoastrometric distances from the reduced proper motion-M V calibration. Our simulations have shown the following: (1) a sample of thin-disk giants within 500 pc with an admixture of less than 10% of other stars can be produced; (2) a sample of dwarfs within 100 pc almost without any admixture of other stars can be produced; (3) the Local Spiral Arm affects the RGC composition of any magnitude-limited catalog in favor of giants younger than 2 Gyr; (4) the samples produced using reduced proper motions can be used for kinematic studies, provided that the biases of the quantities being determined are simulated and taken into account; (5) the photometric distances correlate with the photoastrometric ones because of the correlation between the proper motion and magnitude; (6) the photometric distances are closer to the true ones for the red giant branch and red dwarfs as the categories of stars with a clear (B-V)-M V relation, while the photoastrometric distances are closer to the true ones for the RGC, subgiants, and thick-disk giants; (7) the calculated distances differ systematically from the true ones, but they can be used to analyze the three-dimensional distribution of stars. Our simulations confirm the validity of our previous selection of RGC stars from Tycho-2.  相似文献   

11.
The Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) published its first data release(DRl)in 2013,which is currently the largest dataset of stellar spectra in the world.We combine the PASTEL catalog and SIMBAD radial velocities as a testing standard to validate stellar parameters(effective temperature T_(eff),surface gravity log g,metallicity[Fe/H]and radial velocity V_r)derived from DR1.Through cross-identification of the DR1 catalogs and the PASTEL catalog,we obtain a preliminary sample of 422 stars.After removal of stellar parameter measurements from problematic spectra and applying effective temperature constraints to the sample,we compare the stellar parameters from DR1 with those from PASTEL and SIMBAD to demonstrate that the DR1 results are reliable in restricted ranges of T_(eff).We derive standard deviations of 110 K,0.19 dex and 0.11 dex for T_(eff),log g and[Fe/H]respectively when T_(eff)8000 K,and 4.91 km S~(-1) for V_r when T_(eff)10 000 K.Systematic errors are negligible except for those of V_r.In addition,metallicities in DR1 are systematically higher than those in PASTEL,in the range of PASTEL[Fe/H]-1.5.  相似文献   

12.
The first part of this paper discusses how planet formation proceeds in the disks orbiting M dwarf stars. These environments are different from those associated with solar‐type stars in several ways: The planet forming clock (set by orbits) runs slower, the disks are more prone to evaporation, the supply of raw material is lower, the snowline is closer in, and planetary systems are more easily disrupted. Because of these considerations, red dwarfs are less likely to harbor giant planets, but can readily produce smaller planets. The second part of this paper describes stellar evolution calculations for M dwarfs, which live far longer than the current age of the universe. These diminutive stellar objects remain convective over most of their lives, continue to burn hydrogen for trillions of years, and do not experience red giant phases in their old age. Instead, red dwarfs turn into blue dwarfs and finally white dwarfs. This work also shows (in part) why larger stars become red giants. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
RR Lyrae stars,a well-known type of pulsating variable stars,have been known about for more than a century.A large amount of photometric data on RR Lyrae stars has been accumulated by space-and ground-based sky surveys,but the spectral data are relatively poor.Fortunately,the LAMOST sky survey project provides an opportunity to view them from the point of view of spectra.We collect the atmospheric parameters of 1685 RR Lyrae stars provided by the LAMOST catalog,and carry out research by using the reliable T_(eff).We find that there is a clear correlation between their Teff and pulsation periods,which is consistent with the pulsation and evolution theories of RR Lyrae stars.In addition,we focus on those RR Lyrae stars with abnormal temperatures.After analyzing the data from several photometric surveys,we find that some of these temperature anomalies are misclassified variable stars(e.g.,eclipsing binaries,pulsating stars on main sequence),and some are RR Lyrae binary candidates.For the latter,the temperatures of potential companions should be lower and their luminosities should not be neglected(e.g.,red giant stars).We obtain that the ratio of temperature anomaly stars to all the sample stars is 4%,which means that the impact on the further analysis(e.g.,kinematics analysis) is low.We also present the catalogs of spectral anomaly RR Lyrae stars.  相似文献   

14.
本文以亮星星表1982年版的资料为依据,统计了双星比例随光谱型的变化。发现巨星的双星比例由B、A型的50％左右逐渐下降到M型的24％,而矮星的双星比例不随光谱型下降,都在50％左右。还发现各主要类型脉动变星中的双星比例比上述相应光谱区内的双星比例高约10％。这可能说明成双性与恒星演化和脉动特性均有某种关系。造父变星中双星比例高达53％是很值得仔细研究的问题。  相似文献   

15.
The derivation of element abundances of stars is a key step in detailed spectroscopic analysis. A spectroscopic method may suffer from errors associated with model simplifications. We have developed a new method of deriving the various element abundances of stars based on the calibration established from a group of standard stars. We perform principal component analysis(PCA) on a homogeneous library of stellar spectra, and then use machine learning to calibrate the relationship between principal components and element abundances. By testing with spectral libraries S4 N and MILES, we find that our procedure provides good consistency when spectra from a homogeneous set of observations are used, and it could be expanded to stars with quite a wide range of stellar parameters, with both dwarfs and giants. Moreover, we discuss the four key factors that have a significant impact on the results of derived element abundances,including the resolution of the spectra, wavelength range, the signal-to-noise ratio(S/N) of spectra and the number of principal components adopted.  相似文献   

16.
新一代大规模光谱巡天项目产生了近千万条低分辨率恒星光谱,基于这些光谱数据,介绍一种名为The Cannon的机器学习方法。该方法完全基于已知恒星大气参数(有效温度、表面重力加速度和金属丰度等)的光谱数据,通过数据驱动来构建特征向量,建立光谱流量特征和恒星参数的函数对应关系,进而应用到观测光谱数据中,实现对恒星光谱的大气参数求解。The Cannon的主要优势为不直接基于任何恒星物理模型,适用性更广;由于使用了全谱信息,即便对于低信噪比光谱也能得到较高可信度的参数结果,该算法在大规模恒星光谱的数据处理和参数求解方面具有明显的优势。此外,还利用The Cannon得到LAMOST光谱数据中K巨星和M巨星的恒星参数。  相似文献   

17.
The JHKL' photometry and 2.3–4 μm spectrophotometry of some M giants, S type stars and carbon stars are presented in this paper. It is found that in combination with IRAS data, the energy spectra in 1–100 μm of S type stars are intermediate between those of M giants and carbon stars, which are obviously different. The spectrophotometry in the near infrared shows that, besides carbon stars, which have HCN and C2H2 strong absorptions at 3.1 μm, some S type stars have the similar but weaker absorption in the same spectral region. However, no trace of any absorption at 3.1 μm can be seen in M giants. These results probably provide more evidence for the M-S-C sequence in the late stage of stellar evolution.  相似文献   

18.
We present spectra of 59 nearby star candidates, M dwarfs and white dwarfs, previously identified using high proper motion catalogues and the DENIS database. We review the existing spectral classification schemes and spectroscopic parallax calibrations in the near-infrared J band and derive spectral types and distances of the nearby candidates. Forty-two stars have spectroscopic distances smaller than 25 pc, three of them being white dwarfs. Two targets lie within 10 pc, one M8 star at 10.0 pc (APMPM J0103−3738), and one M4 star at 8.3 pc (L 225−57). One star, LHS 73, is found to be among the few subdwarfs lying within 20 pc. Furthermore, together with LHS 72, it probably belongs to the closest pair of subdwarfs we know.  相似文献   

19.
The masses and temperatures of young low-mass stars and brown dwarfs in star-forming regions are not yet well established because of uncertainties in the age of individual objects and the spectral type–temperature scale appropriate for objects with ages of only a few Myr. Using multi-object optical spectroscopy, 45 low-mass stars and brown dwarfs in the Trapezium Cluster in Orion have been classified and 44 of these confirmed as bona fide cluster members. The spectral types obtained have been converted to effective temperatures using a temperature scale intermediate between those of dwarfs and giants, which is suitable for young pre-main-sequence objects. The objects have been placed on a Hertzsprung–Russell (HR) diagram overlaid with theoretical isochrones. The low-mass stars and the higher mass substellar objects are found to be clustered around the 1 Myr isochrone, while many of the lower mass substellar objects are located well above this isochrone. An average age of 1 Myr is found for the majority of the objects. Assuming coevality of the sources and an average age of 1 Myr, the masses of the objects have been estimated and range from  0.018 to 0.44 M⊙  . The spectra also allow an investigation of the surface gravity of the objects by measurement of the sodium doublet equivalent width. With one possible exception, all objects have low gravities, in line with young ages, and the Na indices for the Trapezium objects lie systematically below those of young stars and brown dwarfs in Chamaeleon, suggesting that the 820 nm Na index may provide a sensitive means of estimating ages in young clusters.  相似文献   

20.
In this work we present a stellar structure model from the f(R)-gravity point of view capable of describing some classes of stars(white dwarfs, brown dwarfs, neutron stars, red giants and the Sun). This model is based on f(R)-gravity field equations for f(R) = R + f_2R~2, hydrostatic equilibrium equation and a polytropic equation of state. We compare the results obtained with those found by Newtonian theory. It has been observed that in these systems, where high curvature regimes emerge,stellar structure equations undergo modifications. Despite the simplicity of this model, the results are satisfactory. The estimated values of pressure, density and temperature of the stars are within those determined by observations. This f(R)-gravity model has proved to be necessary to describe stars with strong fields such as white dwarfs, neutron stars and brown dwarfs, while stars with weaker fields, such as red giants and the Sun, are best described by Newtonian theory.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号