[论文解读] Multiplicity among T Tauri stars in OB and T associations: Implications for binary star formation

W. Brandner, J. M. Alcalá+3 more|arXiv (Cornell University)|Jul 6, 1995

Stellar, planetary, and galactic studies参考文献 2被引用 6

一句话总结

本研究利用高分辨率成像和近红外测光，调查了OB星协和T星协中T Tauri双星的多重性，发现195颗观测恒星中有31颗具有物理伴星。在120–1800 AU分离距离下，T Tauri星的双星频率与太阳邻近区主序星的双星频率一致，表明恒星演化各阶段的双星系统可能具有相似的形成机制。

ABSTRACT

We present first results of a survey for companions among X-ray selected pre-main sequence stars, most of them being weak-line T Tauri stars (WTTS). These T Tauri stars have been identified in the course of optical follow-up observations of sources from the ROSAT All Sky Survey associated with star forming regions. The areas surveyed include the T associations of Chamaeleon and Lupus as well as Upper Scorpius, the latter being part of the Scorpius Centaurus OB association (Sco OB 2). Using SUSI at the NTT under subarcsec seeing conditions we observed 195 T Tauri stars through a 1$\\mu$m ("Z") filter and identified companions to 31 of them (among these 12 subarcsec binaries). Based on statistical arguments we conclude that almost all of them are indeed physical (i.e. gravitationally bound) binary or multiple systems. For 10 systems located in Upper Scorpius and Lupus, we additionally obtained spatially resolved near-infrared photometry in the J, H, and K bands with the MPIA 2.2m telescope at ESO, La Silla. The near-infrared colours of the secondaries are consistent with those of dwarfs and are clearly distinct from those of late type giant stars. Based on astrometric measurements of some binaries we show that the components of these binaries are common proper motion pairs, very likely in a gravitationally bound orbit around each other. We find that the overall binary frequency among T Tauri stars in a range of separations between 120 and 1800 AU is in agreement with the binary frequency observed among main sequence stars in the solar neighbourhood. However, we note that within individual regions the spatial distribution of binaries -- within a distinct range of separation -- is non-uniform. In particular, in Upper

研究动机与目标

• 确定在星体形成区中，T Tauri星前主序星双星和多星系统的频率与性质。
• 利用天体测量和测光数据评估所观测到的伴星是否为物理束缚系统或视线方向上的光学双星。
• 将T Tauri星的多重性特征与太阳邻近区主序星的特征进行比较。
• 研究单个星体形成区中双星的空间分布模式。
• 评估这些发现对双星形成理论的启示。

提出的方法

• 使用NTT望远镜上的SUSI仪器，配合1μm（'Z'）滤光片进行高分辨率成像，探测195颗T Tauri星的伴星。
• 利用位于拉西拉的MPIA 2.2米望远镜对10个系统进行J、H和K波段的空间分辨近红外测光。
• 分析次星成分的近红外颜色，以区分矮星与晚型巨星，确认其为低质量恒星。
• 利用天体测量数据识别具有共同自行的双星对，表明其存在引力束缚。
• 应用统计方法评估所探测到伴星的物理关联可能性。
• 将T Tauri星在120–1800 AU分离距离下的双星频率与太阳邻近区主序星的双星频率进行比较。

实验结果

研究问题

• RQ1 OB星协和T星协中T Tauri星的双星和多星系统的频率是多少？
• RQ2 所探测到的伴星是物理束缚系统还是视线方向上的光学双星？
• RQ3 T Tauri星的多重性频率与太阳邻近区主序星的多重性频率相比如何？
• RQ4 在单个星体形成区内，双星的空间分布是否非均匀？
• RQ5 这些多重性特征对双星形成机制有何启示？

主要发现

• 在195颗观测到的T Tauri星中，有31颗被发现拥有伴星，其中12颗为亚角秒级双星。
• 统计分析表明，几乎所有探测到的伴星均为物理束缚、引力束缚系统。
• 次星成分的近红外颜色与矮星一致，且与巨星明显不同，支持其为低质量、前主序星的性质。
• 天体测量数据确认了多个系统的共同自行，表明其具有长期轨道束缚。
• 在120–1800 AU分离距离下，T Tauri星的整体双星频率与太阳邻近区主序星的观测双星频率一致。
• 在上天蝎座和路西塔尼亚等单个区域中，双星在给定分离距离范围内的空间分布呈非均匀性，表明存在区域特异的形成或动力学演化效应。