A New Association of Post-T Tauri Stars near the Sun
A New Association of Post-T Tauri Stars near the Sun
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太阳附近T后金牛座恒星的新协会
DOI：
10.1086/301539
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
E. Jilinski
中科院分区：
文献类型：
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作者：
C. Torres;L. da Silva;G. Quast;R. de la Reza;E. Jilinski
在以高纬度（B = -59°）活跃的星星ER Eri为中心的20° × 25°区域内观测ROSAT源，我们发现了附近一个星协的证据，我们称之为钟表星协（HorA），它由至少10颗非常年轻的恒星组成，其中一些是真正的后金牛座T星。我们建议其他六颗星作为这个拟议协会的可能成员。我们研究几个要求，一个年轻的恒星协会的特点。虽然没有一个单独的恒星能毫无争议地证明HorA的存在，但所有这些都为HorA的存在提供了强有力的证据。事实上，Li线的强度介于较老的经典金牛座T星和本协星之间。HorA相对于太阳的空间速度分量（U = -9.5 ± 1.0，V = -20.9 ± 1.1，W = -2.1 ± 1.9）与本星协的空间速度分量相差不远，因此它可能是本星协星星形成的最后阶段之一。在这个区域的天空中有一些更热和非X射线活跃的恒星，具有类似的空间速度，可能是HorA的大质量成员，其中包括附近的Be星星Achernar。其可能成员的质量分布函数的最大值约为0.7-0.9 M。我们估计它的距离为1060 pc，大小为1050 pc。如果是球形的，这个尺寸将大于测量的区域，并且许多其他成员可能被遗漏。ER Eri本身被发现不是成员，而是一个背景RS CVn样系统。我们还观察到三个控制区，两个在银河系的北方和南方纬度，第三个在已知的TW Hya协会（TWA），其年轻恒星的性质和分布加强了HorA的真实性。与TWA相反，HorA中唯一已知的双星是两个非常宽的系统。HorA比TWA更远离云层，也更古老（1.3亿年），可以提供一些关于金牛座T恒星周围圆盘寿命的线索。事实上，没有一个被提出的成员是IRAS源，表明其原始吸积盘演化的高级阶段。
Observing ROSAT sources in an area 20° × 25° centered at the high-latitude (b = -59°) active star ER Eri, we found evidences for a nearby association, that we call the Horologium association (HorA), formed by at least 10 very young stars, some of them being bona fide post–T Tauri stars. We suggest other six stars as possible members of this proposed association. We examine several requirements that characterize a young stellar association. Although no one of them, isolated, gives an undisputed prove of the existence of the HorA, all together practically create a strong evidence for it. In fact, the Li line intensities are between those of the older classical T Tauri stars and the ones of the Local Association stars. The space velocity components of the HorA relative to the Sun (U = -9.5 ± 1.0, V = -20.9 ± 1.1, W = -2.1 ± 1.9) are not far from those of the Local Association, so that it could be one of its last episodes of star formation. In this region of the sky there are some hotter and non–X-ray active stars, with similar space velocities, that could be the massive members of the HorA, among them, the nearby Be star Achernar. The maximum of the mass distribution function of its probable members is around 0.7–0.9 M☉. We estimate its distance as ∼60 pc and its size as ∼50 pc. If spherical, this size would be larger than the surveyed area, and many other members could have been missed. ER Eri itself was found to be not a member, but a background RS CVn–like system. We also observed three control regions, two at northern and southern Galactic latitudes and a third one in the known TW Hya association (TWA), and the properties and distribution of their young stars strengthen the reality of the HorA. Contrary to the TWA, the only known binaries in the HorA are two very wide systems. The HorA is much more isolated from clouds and older (∼30 Myr) than the TWA and could give some clues about the lifetime of the disks around T Tauri stars. Actually, none of the proposed members is an IRAS source indicating an advanced stage of the evolution of their primitive accreting disks.