HST colour–magnitude diagrams of six old globular clusters in the LMC     

K. A. G. Olsen  P. W. Hodge  M. Mateo  E. W. Olszewski  R. A. Schommer  N. B. Suntzeff  & A. R. Walker 《Monthly notices of the Royal Astronomical Society》1998,300(3):665-685

We report on HST observations of six candidate old globular clusters in the Large Magellanic Cloud (LMC): NGC 1754, 1835, 1898, 1916, 2005 and 2019. Deep exposures with the F555W and F814W filters provide us with colour–magnitude diagrams that reach to an apparent magnitude in V of ∼25, well below the main-sequence turn-off. These particular clusters are associated with significantly high LMC field star densities and care was taken to subtract the field stars from the cluster colour–magnitude diagrams accurately. In two cases there is significant variable reddening across at least part of the image, but only for NGC 1916 does the differential reddening preclude accurate measurements of the CMD characteristics. The morphologies of the colour–magnitude diagrams match well those of Galactic globular clusters of similar metallicity. All six have well-developed horizontal branches, while four clearly have stars on both sides of the RR Lyrae gap. The abundances obtained from measurements of the height of the red giant branch above the level of the horizontal branch are 0.3 dex higher, on average, than previously measured spectroscopic abundances. Detailed comparisons with Galactic globular cluster fiducials show that all six clusters are old objects, very similar in age to classical Galactic globulars such as M5, with little age spread among the clusters. This result is consistent with ages derived by measuring the magnitude difference between the horizontal branch and main-sequence turn-off. We also find a similar chronology by comparing the horizontal branch morphologies and abundances with the horizontal branch evolutionary tracks of Lee, Demarque &38; Zinn. Our results imply that the LMC formed at the same time as the Milky Way Galaxy.  相似文献   

A search for high-velocity gas in massive star formation regions     

Yue-fang Wu  Yue-xing Li  Li-feng Zheng 《Chinese Astronomy and Astrophysics》1998,22(4):863-462

From the IRAS-PSC, 97 sources with steep FIR spectrum and another 8 were chosen for a search for high-velocity gas. Observations of the CO (J =1−0) line were made with the 13.3-m telescope at the Qinghai Station. The results show that 102 sources are associated with molecular gas. 9 of the sources have reference position problem and 21 have multiple spectrum. Of the remaining 72, 29 contain high-velocity gas, and of these 18 are new molecular outflow candidates. Their properties are discussed briefly in connection with massive young stellar objects.  相似文献   

北京天文台的WET三通道高速光度计     

姜晓军  胡景耀 《天文学报》1998,39(4):438-443

对北京天文台新近改造成的三通道高速光度计的结构和性能进行介绍,并给出了在兴隆站85公分望远镜的一些实测结果.  相似文献   

The globular cluster system of the Sagittarius dwarf spheroidal galaxy: the age of Terzan 8     

Montegriffo  Bellazzini  Ferraro  Martins  Sarajedini  & Fusi Pecci 《Monthly notices of the Royal Astronomical Society》1998,294(2):315-326

We present deep V - and I -band CCD photometry of the globular cluster Terzan 8, recently found to be a member of the globular cluster system of the Sagittarius dwarf spheroidal galaxy. We accurately estimate the metallicity of Terzan 8, and provide the first direct determination of the colour excess toward this cluster. Our robust age estimate confirms that this cluster is indeed coeval with typical Galactic globulars of comparable metal content, and thus it is probably significantly older than at least two other Sagittarius clusters, Terzan 7 and Arp 2. The implications of this result on the star formation history of the Sagittarius galaxy are briefly discussed.  相似文献   

Dynamical studies of cluster pairs in the Magellanic Clouds     

M. R. de Oliveira  H. Dottori  & E. Bica 《Monthly notices of the Royal Astronomical Society》1998,295(4):921-932

We performed N -body simulations of star cluster encounters with Hernquist's TREECODE in a CRAY YMP-2E computer under different initial conditions (relative positions and velocities, cluster sizes, masses and concentration degrees). The total number of particles per simulation ranged from 1024 to 20480. These models are compared with a series of isodensity maps of cluster pairs in the Magellanic Clouds. Evidence is found that during the interactions, transient morphological effects such as an expanded halo, isophotal deformation and isophotal twisting can occur as a result of tidal effects and dynamical friction. The simulations also show that different outcomes are possible depending on the initial parameters: (i) long-standing changes of concentration degree can occur after the collision; (ii) one member can disaggregate; or (iii) the pair can coalesce into a single cluster with a distinct structure compared with the original ones. These simulations can reproduce a wide range of morphological structures in observed cluster pairs.  相似文献   

A comprehensive nbody study of mass segregation in star clusters: energy equipartition and escape     

E. Khalisi &#;  P. Amaro-Seoane &#;  R. Spurzem &#; 《Monthly notices of the Royal Astronomical Society》2007,374(2):703-720

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Five young star clusters in the outer region of the Small Magellanic Cloud     

Andrés E. Piatti  Ata Sarajedini  Doug Geisler  Carme Gallart  Marina Wischnjewsky† 《Monthly notices of the Royal Astronomical Society》2007,382(3):1203-1212

Colour–magnitude diagrams in the Washington system are presented for the first time for five star clusters projected on to the outer region of the Small Magellanic Cloud (SMC). The clusters are found to have ages in the range 0.1–1.0 Gyr, as derived from the fit of isochrones with   Z = 0.004  . This sample increases substantially the number of young clusters in the outer SMC – particularly in the south-east quadrant – with well-derived parameters. We combine our results with those for other clusters in the literature to derive as large and homogeneous a data base as possible (totalling 49 clusters) in order to study global effects. We find no conclusive evidence for a dispersion in the cluster ages and metallicities as a function of their distance from the galaxy centre, in the SMC outer region. L 114 and 115, although very distant, are very young clusters, lying in the bridge of the SMC and therefore most likely formed during the interaction which formed this feature. We also find very good agreement between the cluster age–metallicity relation (AMR) and the prediction from a bursting model from Pagel & Tautvaišienė with a burst that occurred 3 Gyr ago. Comparing the present cluster AMR with that derived by Harris & Zaritsky for field stars in the main body of the SMC, we find that field stars and clusters underwent similar chemical enrichment histories during approximately the last couple of Gyr, but their chemical evolution was clearly different between 4 and 10 Gyr ago.  相似文献   

基于Atmega16的多点温湿度测控系统设计     

权伟  蔡淮  于小娟 《成都信息工程学院学报》2007,22(4):503-508

介绍了基于Atmega16单片机为检测和控制核心,并同多个数字温度传感器DS18B20及模拟湿度传感器HS1101构成温度与湿度的测控系统.给出了系统的总体设计方案、硬件设计及软件框图.所设计的粮情测控系统具有优良的性价比,通过系统软硬件的联合调试说明,该系统可以满足对温湿度及烟雾进行实时监控的需要,具有稳定性好、精度高等特点,有一定的应用价值.  相似文献   

The young star cluster system in the Antennae: evidence for a turnover in the luminosity function     

P. Anders  N. Bissantz  L. Boysen  R. de Grijs  U. Fritze-v.Alvensleben 《Monthly notices of the Royal Astronomical Society》2007,377(1):91-106

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Historical Evidence for the Birth of the Newly Discovered Pulsar PSR J1833-1034     

Zhen-Ru Wang  Min Li  Yi Zhao Astronomy Department  Nanjing University  Nanjing  Institute of Chinese Classics  Nanjing University  Nanjing 《中国天文和天体物理学报》2006,6(5)

Stimulated by the recent discovery of PSR J1833-1034 in SNR G21.5-0.9 and its age parameters presented by two groups of discovery, we demonstrate that the PSR J1833-1034 was born 2053 years ago from a supernova explosion, the BC 48 guest star observed in the Western Han (Early Han) Dynasty by ancient Chinese. Based on a detailed analysis of the Chinese ancient record of the BC 48 guest star and the new detected physical parameters of PSR J1833-1034, agreements on the visual position, age and distance between PSR J1833-1034 and the BC 48 guest star are obtained. The initial period P0 of PSR J1833-1034 is now derived from its historical and current observed data without any other extra assumption on P0 itself, except that the factor PP is a constant in its evolution until now.  相似文献