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arXiv 1105.6093astro-ph.GA
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对毕宿星团进行了一次深入的全天普查

A deep all-sky census of the Hyades

S. Roeser, E. Schilbach, A. E. Piskunov, N. V. Kharchenko, R. -D. Scholz

摘要:

在PPMXL星表的基础上,我们在距离星团中心30 pc的区域内对质量约为0.2 m太阳的毕星团进行了全天普查。我们使用PPMXL的自行收敛点方法来确定可能的运动成员。从2 MASS测光和CMC 14 r '-波段测光,我们得出经验的颜色绝对星等图,最后,确定光度成员的所有运动学候选人。这是第一次对毕宿星团进行深度(r' < 17)全天空观测,可以对星团进行完整的三维分析。测量完成,至少达到M_{K_s} = 7.3或0.25 m_sun。我们发现724个恒星系统与毕宿星的空间速度共同运动,它们的总质量为435 m太阳。潮汐半径约为9秒差距,275米太阳(364个系统)受到引力束缚。这是集群本身。它的质量密度分布完全符合Plummer模型,中心密度为2.21 m_sun*pc^-3,核心半径r_co = 3.10 pc,半质量半径r_h = 4.1 pc。在一个和两个潮汐半径之间的体积中还有另一个100 m_太阳(晕),另一个60 m_太阳距离中心30 pc。强烈的质量分离是集群中固有的。现今的光度和质量函数在星团的不同部分(核心、日冕、晕和共同运动者)有明显的不同。它们是强烈的演变相比,目前青睐的初始质量函数。对星系团速度色散的分析表明,其中约20%的成员是双星。作为一个副产品,我们发现,目前可用的理论等时线是不能够充分描述的近红外颜色的绝对星等关系,这些集群恒星的质量小于约0.6 m太阳。

英文摘要:

On the basis of the PPMXL catalogue we perform an all-sky census of the Hyades down to masses of about 0.2 m_sun in a region up to 30 pc from the cluster centre. We use the proper motions from PPMXL in the convergent point method to determine probable kinematic members. From 2MASS photometry and CMC14 r'-band photometry, we derive empirical colour-absolute magnitude diagrams and, finally, determine photometric membership for all kinematic candidates. This is the first deep (r' < 17) all-sky survey of the Hyades allowing a full three-dimensional analysis of the cluster. The survey is complete down to at least M_{K_s} = 7.3 or 0.25 m_sun. We find 724 stellar systems co-moving with the bulk Hyades space velocity, which represent a total mass of 435 m_sun. The tidal radius is about 9 pc, and 275 m_sun (364 systems) are gravitationally bound. This is the cluster proper. Its mass density profile is perfectly fitted by a Plummer model with a central density of 2.21 m_sun*pc^-3 and a core radius of r_co = 3.10 pc, while the half-mass radius is r_h = 4.1 pc. There are another 100 m_sun in a volume between one and two tidal radii (halo), and another 60 m_sun up to a distance of 30 pc from the centre. Strong mass segregation is inherent in the cluster. The present-day luminosity and mass functions are noticeably different in various parts of the cluster (core, corona, halo, and co-movers). They are strongly evolved compared to presently favoured initial mass functions. The analysis of the velocity dispersion of the cluster shows that about 20% of its members must be binaries. As a by-product, we find that presently available theoretical isochrones are not able to adequately describe the near-infrared colour-absolute magnitude relation for those cluster stars that are less massive than about 0.6 m_sun.

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