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 31 毫秒
1.
The proper motions and stellar magnitudes for more than 20 000 stars distributed in areas around eight open clusters in the directions of the Sagittarius-Carina and Perseus spiral arms were used to determine the cluster membership. Both spatial-kinematical and statistical criteria were used for member seletion. The luminosity functions of cluster members were constructed and used for the further data improvement. The safest portions of the luminosity function free both from evolved stars and faint field star contamination were used for mass function construction. The composite mass function was derived from the data on five young clusters with log t < 8.2. A dependence of the mass function slope on the adopted input parameters (mass-luminosity relation and distance scale) and on member selection procedure was tested. The slope was found to vary in a range from 1.36 to 1.80 for lg M/M⊙ between 0.3 and 1.2. A possible relation between the individual MF slopes and cluster ages was indicated. The results are in good agreement with published data.  相似文献   

2.
Using UBVRI CCD data taken from 104-cm Sampurnanand Telescope, ARIES, Nainital, we present the structure, initial mass function and mass segregation of three young age (∼10 Myr) open star clusters: NGC 2129, NGC 1502 and King 12. Based on photometric as well as astrometric criteria, the cluster member stars as well as field stars have been identified. We construct luminosity function which is further used to estimate the mass functions by employing theoretical stellar evolutionary isochrones. The entire cluster region mass function (MF) slopes for NGC 2129, NGC 1502 and King 12 are obtained as −2.55 ± 0.14, −2.73 ± 0.36 and −1.94 ± 0.12 respectively. It is found that changes in the MF slope of King 12 are significantly different compared to NGC 2129 and NGC 1502 from inner region to outer region. The MF slope for King 12 is steeper at larger radii. The dynamical relaxation times for all three clusters are found to be less than age of the clusters. This indicates that all these clusters are dynamically relaxed. We show that for NGC 1502 and King 12, passing off of low mass stars from the inner region of the clusters to the halo occurs during the course of evolution.  相似文献   

3.
We present the results from a CCD survey of the B -band luminosity function of nine clusters of galaxies, and compare them to published photographic luminosity functions of nearby poor clusters like Virgo and Fornax, and also to the field luminosity function. We derive a composite luminosity function by taking the weighted mean of all the individual cluster luminosity functions; this composite luminosity function is steep at bright and faint magnitudes and is shallow in-between.
All clusters have luminosity functions consistent with this single composite function. This is true both for rich clusters like Coma and for poor clusters like Virgo.
This same composite function is also individually consistent with the deep field luminosity functions found by Cowie et al. and Ellis et al., and also with the faint end of the Las Campanas Redshift Survey R -band luminosity function, shifted by 1.5 mag. A comparison with the Loveday et al. field luminosity function, which is well determined at the bright end, shows that the composite function, which fits the field data well fainter than M B=−19, drops too steeply between M B=−19 and −22 to fit the field data there.  相似文献   

4.
We analysis VI CCD data of two open clusters Haffner 11 and Czernik 31 in order to determine their luminosity function, mass function and mass-segregation for the first time. The observed luminosity function is corrected for both data incompleteness and field star contamination. Theoretical stellar evolutionary isochrones are used to convert luminosity function into mass function. The Mass function slopes are derived as 1.22 ± 0.42 and 1.55 ± 0.38 for Haffner 11 and Czernik 31 respectively. They agree with the Salpeter value (x=1.35) within the errors. The effect of mass segregation are observed in both the clusters. The estimated dynamical relaxation time is less than age of the clusters. This indicates that they are dynamically relaxed. The cause of relaxation may be due to the dynamical evolution or imprint of star formation or both.  相似文献   

5.
We present V and I photometry of two open clusters in the LMC down to V ∼26. The clusters were imaged with the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope ( HST ), as part of the Medium Deep Survey Key Project. Both are low-luminosity ( MV ∼−3.5), low-mass ( M ∼103 M⊙) systems. The chance discovery of these two clusters in two parallel WFPC2 fields suggests a significant incompleteness in the LMC cluster census near the bar. One of the clusters is roughly elliptical and compact, with a steep light profile, a central surface brightness μ V (0)∼20.2 mag arcsec−2, a half-light radius r hl∼0.9 pc (total visual major diameter D ∼3 pc) and an estimated mass M ∼1500 M⊙. From the colour–magnitude diagram and isochrone fits we estimate its age as τ∼(2–5)×108 yr. Its mass function has a fitted slope of Γ=Δlogφ( M )/Δlog M =−1.8±0.7 in the range probed (0.9≲ M /M⊙≲4.5). The other cluster is more irregular and sparse, having shallower density and surface brightness profiles. We obtain Γ=−1.2±0.4, and estimate its mass as M ∼400 M⊙. A derived upper limit for its age is τ≲5×108 yr. Both clusters have mass functions with slopes similar to that of R136, a massive LMC cluster, for which HST results indicate Γ∼−1.2. They also seem to be relaxed in their cores and well contained in their tidal radii.  相似文献   

6.
We report the present day mass functions (PDMFs) of 4 young open clusters over a mass range from 30 Jupiter masses to 3M_ . Three of these clusters have been chosen to have a similar age of ∼100 Myr. Their PDMFs are remarkably similar and are comparable to the field mass function. This suggests little impact of initial conditions (stellar density, metallicity) on the mass distribution and raises some issues concerning the currently debated star and brown dwarf formation theories. The fourth cluster is older (600 Myr) which allow us to investigate the effect of the cluster dynamical evolution on the shape of the mass function. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
为了缓解标准冷暗物质模型在解释一些观测现象时所遇到的困难，本文考察了倾斜冷暗物质谱模型。在ＢＢＫＳ原初扰动场统计理论的基础上，本文根据天体质量函数的计算公式和背景－天体相互作用的估计方法，计算了星系群和星系团的质量函数，并与最新观测质量函数作了对比，又分析和计算了在各种空洞尺度上天体密度的变化。计算结果表明，倾斜冷暗物质谱模型在与ＣＯＢＥ卫星观测结果相容的前提下，能在上述两个方面缓解标准冷暗物质模型所遇到的困难。  相似文献   

8.
A morphological analysis has been presented as a completed work for estimating the most physical properties of open star cluster NGC 7296. For this purpose, near‐IR database of the digital Two Micron All Sky Survey (2MASS) has been used. Center, radius, membership, distances, reddening, age, metallicity, luminosity and mass functions, total mass, mass segregation and the dynamical relaxation time of the cluster have been estimated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
We analyse a   z < 0.1  galaxy sample from the Sloan Digital Sky Survey focusing on the variation in the galaxy colour bimodality with stellar mass     and projected neighbour density Σ, and on measurements of the galaxy stellar mass functions. The characteristic mass increases with environmental density from about  1010.6  to     (Kroupa initial mass function,   H 0= 70  ) for Σ in the range  0.1–10 Mpc−2  . The galaxy population naturally divides into a red and blue sequence with the locus of the sequences in colour–mass and colour–concentration indices not varying strongly with environment. The fraction of galaxies on the red sequence is determined in bins of 0.2 in  log Σ  and     bins). The red fraction   f r   generally increases continuously in both Σ and     such that there is a unified relation:     . Two simple functions are proposed which provide good fits to the data. These data are compared with analogous quantities in semi-analytical models based on the Millennium N -body simulation: the Bower et al. and Croton et al. models that incorporate active galactic nucleus feedback. Both models predict a strong dependence of the red fraction on stellar mass and environment that is qualitatively similar to the observations. However, a quantitative comparison shows that the Bower et al. model is a significantly better match; this appears to be due to the different treatment of feedback in central galaxies.  相似文献   

10.
Chemical evolution of the Magellanic Clouds: analytical models   总被引：1，自引：0，他引：1  
We have extended our analytical chemical evolution modelling ideas for the Galaxy to the Magellanic Clouds. Unlike previous authors (Russell &38; Dopita, Tsujimoto et al. and Pilyugin), we assume neither a steepened initial mass function nor selective galactic winds, since among the α-particle elements only oxygen shows a large deficit relative to iron and a similar deficit is also found in Galactic supergiants. Thus we assume yields and time delays identical to those that we previously assumed for the solar neighbourhood. We include inflow and non-selective galactic winds and consider both smooth and bursting star formation rates, the latter giving a better fit to the age–metallicity relations. We predict essentially solar abundance ratios for primary elements and these seem to fit most of the data within their substantial scatter. Our model for the Large Magellanic Cloud also gives a remarkably good fit to the anomalous Galactic halo stars discovered by Nissen &38; Schuster.   Our models predict current ratios of Type Ia supernova to core-collapse supernova rates enhanced by 50 and 25 per cent respectively relative to the solar neighbourhood, in fair agreement with ratios found by Cappellaro et al. for Sdm–Im relative to Sbc galaxies, but these ratios are sensitive to detailed assumptions about the bursts and a still higher enhancement in the Large Magellanic Cloud has been deduced from X-ray studies of remnants by Hughes et al. The corresponding ratios integrated over time up to the present are slightly below 1, but they exceed 1 if one compares the Magellanic Clouds with the Galaxy at times when it had the corresponding metallicities.  相似文献   

11.
As part of a long‐term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high‐precision DDO photoelectric observations for a sample of 33 red giant candidates projected in the fields of nine Galactic open clusters. These data are supplemented with UBV photoelectric photometry of 24 of these stars as well as with CORAVEL radial‐velocity observations for 13 red giant candidates in four of the clusters. We also present Washington photoelectric photometry of a small sample of red giant candidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with UBV and DDO data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While E (B –V) colour excesses were determined from combined B – V and DDO colours, calibrations of the DDO system were used to derive MK spectral types, effective temperatures and metallicities. The derived DDO metallicities range between values typical of moderately metal‐poor clusters ([Fe/H] = –0.19) to moderately metal‐rich ([Fe/H] = 0.25) ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
We present the results of a survey of the open star cluster Melotte 111 in Coma Berenices, undertaken using the USNO‐B1.0 and 2MASS Point Source catalogues. On the basis of their astrometric and photometric properties, we have identified 60 new candidate members with masses in the range 1.007 < M < 0.269 M⊙. We estimate a membership probability for each by extracting control clusters from the proper motion vector diagram. All 60 are found to have greater than 60 per cent probability of being cluster members, which if they are confirmed as members, more than doubles the number of known cluster members. We also have I and Z photometry for 100 low mass candidate members of the cluster, 13 of which we suggest may be brown dwarfs. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
Recently, De Marchi, Paresce & Pulone studied a sample of 20 globular clusters and found that all clusters with high concentrations have steep stellar mass functions while clusters with low concentration have comparatively shallow mass functions. No globular clusters were found with a flat mass function and high concentration. This seems curious since more concentrated star clusters are believed to be dynamically more evolved and should have lost more low-mass stars via evaporation, which would result in a shallower mass function in the low-mass part.
We show that this effect can be explained by residual-gas expulsion from initially mass segregated star clusters, and is enhanced further through unresolved binaries. If gas expulsion is the correct mechanism to produce the observed trend in the   c –α  -plane, then observation of these parameters would allow to constrain cluster starting conditions such as star formation efficiency and the time-scale of gas expulsion.  相似文献   

14.
The Sun-to-Mercury mass ratio adopted by the International Astronomical Union (6023600 ± 250) was obtained in 1987 by analyzing Mariner 10 observations (Anderson et al. 1987) and since then has not been improved. The large number of asteroids in Mercury-approaching orbits and the ever-increasing accuracy of their observations allow the mass of Mercury to be estimated by a different method. We have improved the orbital parameters of 43 asteroids and obtained 6023440 ± 530 for the Sun-to-Mercury mass ratio through a simultaneous solution based on their optical and radar observations. A further improvement in this estimate is possible in the immediate future owing to the rapid increase in the number of known asteroids whose observations can be used to solve this problem.  相似文献   

15.
In the present work, we used the near-infrared JHKs photometric data from the 2-Micron All Sky Survey (2MASS) to determine the morphological and photometric parameters for two rarely studied open star clusters; King 13 and Berkeley 53. Luminosity function, mass function and dynamical relaxation time have been determined for the two clusters. We estimated the distances of 2.11±0.25 Kpc and 3.51±0.21 Kpc for King 13 and Berkeley 53 respectively, and both clusters have the same age 1.00±0.12 Gyr at solar metallicity; z=0.019.  相似文献   

16.
We develop a new method to determine the linear mass power spectrum using the mass function of galaxy clusters. We obtain the rms mass fluctuation  σ( M )  using the expression for the mass function in the Press & Schechter, Sheth, Mo & Tormen and Jenkins et al. formalisms. We apply different techniques to recover the adimensional power spectrum  Δ2( k )  from  σ( M )  namely the   k eff  approximation, the singular value decomposition and the linear regularization method. The application of these techniques to the τCDM and ΛCDM GIF simulations shows a high efficiency in recovering the theoretical power spectrum over a wide range of scales. We compare our results with those derived from the power spectrum of the spatial distribution of the same sample of clusters in the simulations obtained by application of the classical Feldman, Kaiser & Peacock (FKP) method. We find that the mass function based method presented here can provide a very accurate estimate of the linear power spectrum, particularly for low values of k . This estimate is comparable to, or even better behaved than, the FKP solution.
The principal advantage of our method is that it allows the determination of the linear mass power spectrum using the joint information of objects of a wide range of masses without dealing with specific assumptions on the bias relative to the underlying mass distribution.  相似文献   

17.
From photographic plate data of Shanghai Astronomical Observatory with a time baseline of 87 years, proper motions and membership probabilities of 364 stars in the open cluster NGC 6530 region are reduced. On the basis of membership determination, luminosity function and segregation effect of the cluster are discussed with details. Spatial mass segregation is obviously present in NGC 6530 while there is no clear evidence for a velocity-mass (or velocity-luminosity) dependence. The observed spatial mass segregation for NGC 6530 might be due to a combination of initial conditions and relaxation process.  相似文献   

18.
We present dark energy models in an anisotropic Bianchi type-VI0 (B-VI0) space-time with a variable equation of state (EoS). The EoS for dark energy ω is found to be time dependent and its existing range for derived models is in good agreement with the recent observations of SNe Ia data (Knop et al. in Astrophys. J. 598:102 2003), SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004b) and latest a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift type Ia supernovae and galaxy clustering (Hinshaw et al. in Astrophys. J. Suppl. 180:225, 2009; Komatsu et al. in Astrophys. J. Suppl. 180:330, 2009). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical and geometric aspects of the models are also discussed in detail.  相似文献   

19.
We present the first CCD photometric UBVRI observations of the not-so-well-studied open cluster NGC 1624 (OCl 403, Cr 53; α2000 = 04 h 40 m 36 s; δ2000 = + 50˚ 27′ 42″ Trumpler class = I 2 p N). This cluster was observed on 01 February 2004 with the 2 m Himalayan Chandra Telescope at Hanle using a LN2 cooled 2k × 2k CCD. The cluster presents differential reddening with E(B-V) values ranging from 0.70 to 0.90 mag, which could be attributed to the presence of the HII region wherein the cluster is embedded. It is found to be at a distance of 6.025 ± 0.5 kpc and the age of this cluster is estimated to be ∼3.98 × 106 years. In view of these parameters, it can be considered as a young enough cluster located in the direction of the Perseus constellation with the galactic coordinates of l = 155˚.35 and b = + 02 ˚.58. Thus it could also be used as a suitable candidate for tracing the Outer Perseus spiral arm of our Galaxy. The initial mass function slope is derived as 1.65 ± 0.25 by applying the corrections for field star contamination and data incompleteness. This is in good agreement with the Salpeter value within the limits of errors.  相似文献   

20.
Automated search for star clusters in J, H, K s data from 2MASS catalog has been performed using the method developed by Koposov et al. (2008). We have found and verified 153 new clusters in the interval of the galactic latitude −24° < b < 24°. Color excesses E(B − V), distance moduli and ages were determined for 130 new and 14 yet-unstudied known clusters. In this paper, we publish a catalog of coordinates, diameters, and main parameters of all the clusters under study. A special web-site available at has been developed to facilitate dissemination and scientific usage of the results.  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