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1.
In this paper, using 2MASS photometry, we study the structural and dynamical properties of four young star clusters viz. King 16, NGC 1931, NGC 637 and NGC 189. For the clusters King 16, NGC 1931, NGC 637 and NGC 189, we obtain the limiting radii of 7′, 12′, 6′ and 5′ which correspond to linear radii of 3.6 pc, 8.85 pc, 3.96 pc and 2.8 pc respectively. The reddening values E(B?V) obtained for the clusters are 0.85, 0.65–0.85, 0.6 and 0.53 and their true distances are 1786 pc, 3062 pc, 2270 pc and 912 pc respectively. Ages of the clusters are 6 Myr, 4 Myr, 4 Myr and 10 Myr respectively. We compare their structures, luminosity functions and mass functions (φ(M)=dN/dM ∝ M ?(1+χ)) to the parameter τ=t age /t relax to study the star formation process and the dynamical evolution of these clusters. We find that, for our sample, mass seggregation is observed in clusters or their cores only when the ages of the clusters are comparable to their relaxation times (τ≥1). These results suggest mass seggregation due to dynamical effects. The values of χ, which characterize the overall mass functions for the clusters are 0.96±0.11, 1.16±0.18, 0.55±0.14 and 0.66±0.31 respectively. The change in χ as a function of radius is a good indicator of the dynamical state of clusters. 相似文献
2.
Michael A. Dopita Daniela Calzetti Jesús Maíz Apellániz William P. Blair Knox S. Long Max Mutchler Bradley C. Whitmore Howard E. Bond John MacKenty Bruce Balick Marcella Carollo Michael Disney Jay A. Frogel Robert O’Connell Donald Hall Jon A. Holtzman Randy A. Kimble Patrick McCarthy Francesco Paresce Abhijit Saha Alistair R. Walker Joe Silk Marco Sirianni John Trauger Rogier Windhorst Erick Young 《Astrophysics and Space Science》2010,330(1):123-131
We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc. 相似文献
3.
Robert W. Slawson Zoran Ninkov Elliott P. Horch 《Astrophysics and Space Science》2007,312(3-4):171-187
We have obtained and analyzed UBVRI
CCD frames of the young, 4–10 Myr, open cluster NGC 3293 and the surrounding field in order to study its stellar content and determine the cluster’s IMF. We found significantly fewer lower mass stars, M≤2.5M
⊙, than expected. This is particularly so if a single age for the cluster of 4.6 Myr is adopted as derived from fitting evolutionary
models to the upper main sequence. Some intermediate-mass stars near the main sequence in the HR diagram imply an age for the cluster of about 10 Myr. When compared with the Scalo (The stellar initial mass function. ASP
conference series, vol. 24, p. 201, 1998) IMF scaled to the cluster IMF in the intermediate mass range, 2.5≤M/M
⊙≤8.0 where there is good agreement, the high mass stars have a distinctly flatter IMF, indicating an over abundance of these stars, and there is a sharp turnover in the distribution at lower masses. The radial
density distribution of cluster stars in the massive and intermediate mass regimes indicate that these stars are more concentrated
to the cluster core whereas the lower-mass stars show little concentration. We suggest that this is evidence supporting the
formation of massive stars through accretion and/or coagulation processes in denser cluster cores at the expense of the lower
mass proto-stars.
R.W. Slawson and E.P. Horch are guest investigators at the University of Toronto Southern Observatory, Las Campanas, Chile. 相似文献
4.
Globular cluster systems (GCSs) of most early-type galaxies feature two peaks in their optical colour distributions. Blue-peak globular clusters (GCs) are believed to be old and metal-poor, whereas the ages, metallicities, and the origin of the red-peak GCs are still being debated. We obtained deep K-band photometry and combined it with Hubble Space Telescope observations in g and z to yield a full spectral energy distribution from the optical to the near-infrared. This now allows us to break the age–metallicity degeneracy. We used our evolutionary synthesis models galev for star clusters to compute a large grid of models with different metallicities and a wide range of ages. Comparing these models to our observations revealed a large population of intermediate-age (1–3 Gyr) and metal-rich (≈solar-metallicity) GCs, that will give us further insights into the formation history of this galaxy. 相似文献
5.
Per Carlqvist 《Astrophysics and Space Science》2010,327(2):267-278
NGC 1316 is a giant, elliptical galaxy containing a complex network of dark, dust features. The morphology of these features
has been examined in some detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is found that most of the features are constituted of long filaments. There also exist a great number of dark structures
protruding inwards from the filaments. Many of these structures are strikingly similar to elephant trunks in H ii regions in the Milky Way Galaxy, although much larger. The structures, termed mammoth trunks, generally are filamentary and often have shapes resembling the letters V or Y. In some of the mammoth trunks the stem of
the Y can be resolved into two or more filaments, many of which showing signs of being intertwined. A model of the mammoth
trunks, related to a recent theory of elephant trunks, is proposed. Based on magnetized filaments, the model is capable of
giving an account of the various shapes of the mammoth trunks observed, including the twined structures. 相似文献
6.
William C. Millar Graeme L. White Miroslav D. Filipović Jeffrey L. Payne Evan J. Crawford Thomas G. Pannuti Wayne D. Staggs 《Astrophysics and Space Science》2011,332(2):221-239
We present moderate-resolution (<5 Å) long-slit optical spectra of 51 nebular objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting the criterion of [S?ii]Total:Hα≥0.4 to confirm supernova remnants (SNRs) from optical spectra, we find that of 28 objects previously proposed as SNRs from optical observations, 22 meet this criterion with six showing [S?ii]Total:Hα of less than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated with the 28 previously proposed SNRs. Of these four, three (included in the 22 above) meet the criterion. In all, 22 of the 51 nebular objects meet the [S ii]Total:Hα criterion as SNRs while the nature of the remaining 29 objects remains undetermined by these observations. 相似文献
7.
S. Bilir T. Güver I. Khamitov T. Ak S. Ak K. B. Coşkunoğlu E. Paunzen E. Yaz 《Astrophysics and Space Science》2010,326(1):139-150
We present CCD BV and JHK
s
2MASS photometric data for the open cluster NGC 1513. We observed 609 stars in the direction of the cluster up to a limiting
magnitude of V∼19 mag. The star-count method showed that the centre of the cluster lies at α
2000=04
h
09
m
36
s
, δ
2000=49°28′43″ and its angular size is r=10 arcmin. The optical and near-infrared two-colour diagrams revealed the colour excesses in the direction of the cluster
as E(B−V)=0.68±0.06, E(J−H)=0.21±0.02 and E(J−K
s
)=0.33±0.04 mag. These results are consistent with normal interstellar extinction values. Optical and near-infrared Zero Age
Main-Sequences (ZAMS) provided an average distance modulus of (m−M)0=10.80±0.13 mag, which can be translated into a distance of 1440±80 pc. Finally, using Padova isochrones we determined the
metallicity and age of the cluster as Z=0.015±0.004 ([M/H]=−0.10±0.10 dex) and log (t/yr)=8.40±0.04, respectively. 相似文献
8.
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10.
F.P. Israel 《Astronomy and Astrophysics Review》1998,8(4):237-278
Summary. At a distance of 3.4 Mpc, NGC 5128 (Centaurus A) is by far the nearest active radio galaxy. It is often considered to be
the prototype Fanaroff-Riley Class I ‘low-luminosity’ radio galaxy, and as such it plays an important role in our understanding
of a major class of active galaxies. Its proximity has spawned numerous detailed investigations of its properties, yielding
unrivalled but still incomplete knowledge of its structure and dynamics.
The massive elliptical host galaxy is moderately triaxial and contains a thin, strongly warped disk rich in dust, atomic and
molecular gas and luminous young stars. Its globular cluster ensemble has a bimodal distribution of metallicities. Deep optical
images reveal faint major axis extensions as well as a system of filaments and shells. These and other characteristics are
generally regarded as strong evidence that NGC 5128 has experienced a major merging events at least once in its past.
The galaxy has a very compact, subparsec nucleus exhibiting noticeable intensity variations at radio and X-ray wavelengths,
probably powered by accretion events. The central object may be a black hole of moderate mass. Towards the nucleus, rich absorption
spectra of atomic hydrogen and various molecular species suggest the presence of significant amounts of material falling into
the nucleus, presumably ‘feeding the monster’. Emanating from the nucleus are linear radio/X-ray jets, becoming subrelativistic
at a few parsec from the nucleus. At about 5 kpc from the nucleus, the jets expand into plumes. Huge radio lobes extend beyond
the plumes out to to 250 kpc. A compact circumnuclear disk with a central cavity surrounds the nucleus. Its plane, although
at an angle to the minor axis of the galaxy, is perpendicular to the inner jets. The jet-collimating mechanism, probably connected
to the circumnuclear disk, appears to precess on timescales of order a few times 10 years.
This review summarizes the present state of knowledge of NGC 5128 and its associated radio source Centaurus A. Underlying
physical processes are outside its scope: they are briefly referred to, but not discussed.
Received 30 December 1997 相似文献
11.
12.
By systematically searching regions around planetary nebulae (PNe) for signs of interactions of their precursors’ wind with
ambient matter we found a number of huge IRAS dust structures. Some of them may be chance projections, but a few appear to
be real, like those around NGC 6826 and NGC 2899. In the case of NGC 6826 we noticed a giant (∼2°) bipolar dust emission,
whose axis is along the proper motion of the central star. The PN itself is offset in the direction of motion both as to the
center of this ∼30 pc large dust structure and to the center of a similarly large new Hα nebula. NGC 2899 was found in the center of a 14×11 pc quadrupolar cavity, whose directions of axes coincide with the directions
of the main axes of the optical PN. In both cases, the formation of these structures appears to have commenced in the asymptotic
giant branch (AGB) phase. 相似文献
13.
Hui Dong Sui-Jian Xue Cheng Li Fu-Zhen Cheng Center for Astrophysics University of Science Technology of China Hefei National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2004,4(5):427-439
Chandra observations of the Seyfert-2 galaxies NGC 2110 and NGC 7582 are presented. With the superb spatial resolution of Chandra we found that in NGC 7582 the soft (≤2 keV) and hard (2-10 keV) X-rays are emitted in different regions, consistent with the report by Xue et al. By comparing the present X-ray data with the previous infrared data, we determined that the soft X-ray region is the site of starburst activities. We found no significant temporal variations during our observations. We confirm the previous finding that NGC 2110 and NGC 7582 are flat-spectrum sources. We argue that the flat spectra may result from a cold absorbing material such as envisaged in the “dual absorbed” model. Strong Fe Kα emission feature is detected in 6-7keV. Its equivalent width is so large that it cannot be reproduced by using the Galactic column density of - 10^22 cm^-2. 相似文献
14.
本文利用疏散昨团NGC2286天区内250颗恒星的相对自行及成员概率判定资料，首次对该星团的半径、光度函数以及内部运动等做较深入的研究，分析表明对NGC2286这个中等年龄的星团，正处于动力学演化的初级阶段，在空间和速度上都没有表现出象年老疏散星团M67那样较为明显的分层效应。 相似文献
15.
NGC4151的长期光变行为 总被引：4，自引：0，他引：4
本文收集了NGC4151近90年的光学资料,并用Jurkevich分析方法对其进行了光变周期分析其光变存在一个14．04±0．8年的长周期,且该天体的谱型与源的亮度强烈相关。 相似文献
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17.
本文利用地面光学望远镜ＮＧＣ４１５１进行国际联测所得的结果,通过周期图方法的逐步回归方法得到了该目标目标的一些较为明显的光变周期。结果表明,ＮＧＣ４１５１存在两个主要光变周期。一个是所有光学波段存在约１４天的周期,另一个是连续谱存在３０天周期,而对于Ｈα和Ｈβ则分别为２４和３８天的周期。 相似文献
18.
介绍恒星形成区ＮＧＣ７５３８的Ｈ和Ｋｓ波段偏振成像的观测结果．近５′视场的偏振图像揭示了与亮红外源ＩＲＳ１１１成协的年轻星团和红外星云的复杂结构．ＩＲＳ１３星云的偏振图像表明星云的近红外辐射主要来自对深埋红外源ＩＲＳ１的反射;其形态可解释为颜色很红的高偏振的壳层包围着的低消光气泡．ＩＲＳ１周围的近红外的偏振强度在ＩＲＳ１双极分子外流方向上呈现出一较小的壳结构．ＩＲＳ４在近红外表现为双源,其中较红的源ＩＳＲ４ｂ周围观测到中心对称的偏振图像．ＩＲＳ５与亮星云成协,ＩＲＳ６则处于一组星的中心．在ＩＲＳ５和ＩＲＳ６周围的星云中没有观测到偏振．ＩＫＳ９照亮着两块星云,ＩＲＮ１和ＩＲＮ２．ＩＲＮ１星云有很好的锥形并包含一高偏振的喷流成分．云中较高偏振的部分对应较蓝的颜色,显示着其较大的视向张角的外流腔结构．与复杂的ＩＲＳ９区分子外流相比较,ＩＲＮ１星云与在ＮＥＳＷ方向的外流相符合．首次证认了ＩＲＳ１１近红外点源,并观测到其周围有一组星和很暗的星云物质 相似文献
19.
20.
田凯平 《中国科学院上海天文台年刊》2000,128(21):58-71
利用上海天台1.56m反射望远镜1992－1993年拍摄的测光底片的PDS测量结要,采用P.B.Stetson所提供的照相星等归算方法,得到了789颗生的B,V星等,并与GJTR的测光结果进行了比较,同时在已得出疏散星团NGC1750和NGC1758天区恒星的自行和测光结果的基础上,确定了两个星团包括面密度,并径,距离,年龄,光度函数和质量函数等在内在基本参数,并对运行学特征也进行了讨论。从而,进一步证实了这一天区确定存在的两个独立的动力学系统。 相似文献