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Yu Xin Xiao-Bin Zhang Li-Cai DengNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(6)
We present a snapshot of our recent results of a variable star survey in 1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A total number of 39 variable stars are newly discovered, including 22 W UMa stars, 10 EA (Algol) type binaries, one RR-lyr and one RRd pulsator, and five unclassified variables. 相似文献
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The new target of the Rosetta mission is comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G). In order to support the planning of the mission, in particular the strategy during the mapping and landing phases, we have performed numerical simulations of the rotational evolution of a comet in the orbit of 67P/C-G. In these simulations, the currently known observational constraints have been taken into account and a large set of initial conditions were considered. For most of the simulations, we observe that the sublimation-induced torques produce significant changes in the rotational parameters of a 67P/C-G-like comet. Typical rates of change for the spin period from the rendezvous up to the end of the nominal mission range from 0.001 to depending on different circumstances as described in the text. At perihelion, rates of change of the orientation of the angular momentum vector amount to about 0.01-. These simulations suggest that a specific strategy should be defined in order to monitor likely variations of the rotational parameters. As an example we show a possible optimized schedule for observations with the OSIRIS instrument to determine the rotational parameters of comet 67P/C-G and their possible evolution. 相似文献
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通过瞬变电磁法在平顶山西南部矿区探测主采煤层顶、底板富水异常区的成功实例,探讨PROTEM67D系统在探测埋深大于1000m地质体时的应用效果。认为在外业数据采集前,通过试验选择合适的工作参数,是完成深部异常体勘探的前提条件和重要保证。 相似文献
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O. Groussin G. Hahn P. L. Lamy R. Gonczi G. B. Valsecchi 《Monthly notices of the Royal Astronomical Society》2007,376(3):1399-1406
We present a new method to study the long-term evolution of cometary nuclei in order to estimate their original size, and we consider the case of comets 46P/Wirtanen (hereafter 46P) and 67P/Churyumov–Gerasimenko (hereafter 67P). We calculate the past evolution of the orbital elements of both comets over 100 000 yr using a Bulirsch–Stoer integrator and over 450 000 yr using a Radau integrator, and we incorporate a realistic model of the erosion of their nucleus. Their long-term orbital evolution is prominently chaotic, resulting from several close encounters with planets, and this result is independent of the choice of the integrator and of the presence or not of non-gravitational forces. The dynamical lifetime of comet 46P is estimated at ∼133 000 yr and that of comet 67P at ∼105 000 yr. Our erosion model assumes a spherical nucleus composed of a macroscopic mixture of two thermally decoupled components, dust and pure water ice. Erosion strongly depends upon the active fraction and the density of the nucleus. It mainly takes place at heliocentric distances <4 au and lasts for only ∼7 per cent of the lifetime. Assuming a density of 300 kg m−3 and an average active fraction over time of 10 per cent, we find an initial radius of ∼1.3 km for 46P and ∼2.8 km for 67P. Upper limit are obtained assuming a density of 100 kg m−3 and an active fraction of 100 per cent, and amounts to 21 km for 46P and 25 km for 67P. Erosion acts as a rejuvenating process of the surface so that exposed materials on the surface may only contain very little quantities of primordial materials. However, materials located just under it (a few centimetres to metres) may still be much less evolved. We will apply this method to several other comets in the future. 相似文献
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H. Bruntt D. Stello J. C. Suárez T. Arentoft T. R. Bedding M. Y. Bouzid Z. Csubry T. H. Dall Z. E. Dind S. Frandsen R. L. Gilliland A. P. Jacob H. R. Jensen Y. B. Kang S.-L. Kim L. L. Kiss H. Kjeldsen J.-R. Koo J.-A. Lee C.-U. Lee J. Nuspl C. Sterken R. Szabó 《Monthly notices of the Royal Astronomical Society》2007,378(4):1371-1384
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Jarrod R. Hurley † Christopher A. Tout Sverre J. Aarseth Onno R. Pols 《Monthly notices of the Royal Astronomical Society》2001,323(3):630-650
We present a state-of-the-art N -body code which includes a detailed treatment of stellar and binary evolution as well as the cluster dynamics. This code is ideal for investigating all aspects relating to the evolution of star clusters and their stellar populations. It is applicable to open and globular clusters of any age. We use the N -body code to model the blue straggler population of the old open cluster M67. Preliminary calculations with our binary population synthesis code show that binary evolution alone cannot explain the observed numbers or properties of the blue stragglers. On the other hand, our N -body model of M67 generates the required number of blue stragglers and provides formation paths for all the various types found in M67. This demonstrates the effectiveness of the cluster environment in modifying the nature of the stars it contains, and highlights the importance of combining dynamics with stellar evolution. We also perform a series of N =10 000 simulations in order to quantify the rate of escape of stars from a cluster subject to the Galactic tidal field. 相似文献
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Membership determination is the key-important step to study open clusters, which can directly in?uence on the estimation of open clusters’ physical parameters. DBSCAN (Density Based Spatial Clustering of Applications with Noise) is a density-based clustering algorithm in data mining techniques. In this paper the DBSCAN algorithm has been used for the ?rst time to make the membership determination of the open clusters NGC 6791 and M 67 (NGC 2682). Our results indicate that the DBSCAN algorithm can effectively eliminate the contamination of ?eld stars. The obtained member stars of NGC 6791 exhibit clearly a doubled main-sequence structure in the color-magnitude diagram, implying that NGC 6791 may have a more complicated history of star formation and evolution. The clustering analysis of M67 indicates the presence of mass segregation, and the distinct relative motion between the central part and the outer part of the cluster. These results demonstrate that the DBSCAN algorithm is an effective method of membership determination, and that it has some advantages superior to the conventional kinematic method. 相似文献
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D. Stello T. Arentoft T. R. Bedding M. Y. Bouzid H. Bruntt Z. Csubry T. H. Dall Z. E. Dind S. Frandsen R. L. Gilliland A. P. Jacob H. R. Jensen Y. B. Kang S.-L. Kim L. L. Kiss H. Kjeldsen J.-R. Koo J.-A. Lee C.-U. Lee J. Nuspl C. Sterken R. Szabó 《Monthly notices of the Royal Astronomical Society》2006,373(3):1141-1150
We report on an ambitious multisite campaign aimed at detecting stellar variability, particularly solar-like oscillations, in the red giant stars in the open cluster M67 (NGC 2682). During the six-week observing run, which comprised 164 telescope nights, we used nine 0.6-m to 2.1-m class telescopes located around the world to obtain uninterrupted time series photometry. We outline here the data acquisition and reduction, with emphasis on the optimization of the signal-to-noise ratio of the low-amplitude (50–500 μmag) solar-like oscillations. This includes a new and efficient method for obtaining the linearity profile of the CCD response at ultrahigh precision (∼10 parts per million). The noise in the final time series is 0.50 mmag per minute integration for the best site, while the noise in the Fourier spectrum of all sites combined is 20 μmag. In addition to the red giant stars, this data set proves to be very valuable for studying high-amplitude variable stars such as eclipsing binaries, W UMa systems and δ Scuti stars. 相似文献
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赣江断裂带是江西省境内醒目的北北东向平移断裂构造带,由一系列北北东向、北东向和北西向断裂束组成,表现为一个大规模的左行走滑脆性剪切带并兼具伸展断陷和右旋走滑的成份。赣江断裂带在重力、航磁异常呈现为显著的梯度带,是一条晚中生代的岩浆岩带,控制了以鄱阳盆地为代表的一系列白垩纪-古近纪沉积盆地的形成与发育。该带在中生代的演化可分为早-中侏罗世压扭、晚侏罗早-白垩世左行平移和晚白垩世上盘斜落的右行平移3个阶段。在侏罗纪以来太平洋板块对欧亚大陆斜向俯冲的大背景下,赣江断裂带的形成和演化与华南广为发育的燕山期陆内造山作用密切相关,北北东向断裂的发育则直接受郯庐断裂早白垩世左行走滑活动控制,因而表现出“北强南弱”和“北早南晚”的特点。白垩纪时赣江断裂的活动方式与郯庐断裂一致,可认为是后者的南延。 相似文献