[论文解读] A Survey of Stellar Families: Multiplicity of Solar-Type Stars

Deepak Raghavan, Harold A. McAlister+7 more|Digital Archive @ GSU|Jul 2, 2010

Stellar, planetary, and galactic studies被引用 7

一句话总结

本研究利用多波段技术（包括长基线干涉测量、斑点成像和档案自行分析）对光谱型为F6–K3的太阳型恒星的多重性进行了全面调查。研究发现，56% ± 2% 的此类恒星为单星，该结果挑战了以往的估计，表明大多数太阳型恒星以孤立系统存在，其轨道周期峰值约为300年，质量比分布偏好近等质量双星。

ABSTRACT

I present the results of a comprehensive assessment of companions to 454 solar-type stars within 25 pc. New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the Center for High Angular Resolution Astronomy (CHARA) Array, (2) close companions with speckle interferometry, and (3) wide proper motion companions identified by blinking multi-epoch archival images. I have also obtained and included unpublished results from extensive radial velocity monitoring programs. The many sources utilized enable a thorough evaluation of stellar and brown dwarf companions. The results presented here include eight new companion discoveries, four of which are wide common proper motion pairs discovered by blinking archival images, and four more are from the spectroscopic data. The overall observed fractions of single, double, triple, and higher order systems are 57%ñ3%, 33%ñ2%, 8%ñ1%, and 3%ñ1%, respectively, counting all stellar and brown dwarf companions. The incompleteness analysis indicates that only a few undiscovered companions remain in this well-studied sample, showing that a majority of the solar-type stars are single. Bluer, more massive stars are more likely to have companions than redder, less massive ones. I confirm earlier expectations that more active stars are more likely to have companions. A preliminary, but important indication is that brown dwarfs, like planets, prefer stars with higher metallicity, tentatively suggesting that brown dwarfs may form like planets when they are companions to stars. The period distribution is unimodal and roughly Gaussian with peak and median values of about 300 years. The period-eccentricity relation shows a roughly flat distribution beyond the circularization limit of about 12 days. The mass-ratio distribution shows a clear discontinuity near a value of one, indicating a preference for twins, which are not confined to short orbital periods, suggesting that stars form by multiple formation mechanisms. The ratio of planet hosts among single, binary, and multiple systems are statistically indistinguishable, suggesting that planets are as likely to form around single stars as they are around components of binary or multiple systems at sufficiently wide separations.

研究动机与目标

• 精确测定太阳型恒星（F6–K3）的真实多重性频率。
• 通过结合多种观测技术，解决以往多重性研究中的矛盾。
• 评估在454颗恒星的明确定义样本中伴星检测的完整性。
• 通过比较单星、双星和多星系统的系外行星宿主频率，评估多重性对行星形成的影响。

提出的方法

• 从依巴谷星表中选取454颗太阳型恒星，要求精确视差（π > 40 mas）且视差不确定性较低（σπ/π < 0.05）。
• 利用CHARA阵列进行长基线干涉测量，探测分离角小于0.1弧秒的极近伴星。
• 应用斑点干涉测量技术，识别角分离度达约0.01弧秒的密近双星系统。
• 通过多历元档案图像的闪烁分析，识别宽距自行伴星。
• 整合径向速度监测数据，并与现有星表交叉匹配，构建完整的伴星清单。
• 进行统计完整性分析，估算样本中未被探测到的伴星比例。

实验结果

研究问题

• RQ1 在太阳型恒星中，单星、双星、三合星及更高阶系统的真正频率是多少？
• RQ2 在不同分离度范围内，当前对太阳型恒星伴星的普查完整性如何？
• RQ3 恒星伴星的轨道周期分布是怎样的？是否符合对数正态分布？
• RQ4 是否存在偏好质量比分布？该分布是否随轨道分离度变化？
• RQ5 拥有系外行星的恒星更可能是单星系统还是多星系统？

主要发现

• 观测到的单星频率为56% ± 2%，双星为33% ± 2%，三合星为8% ± 1%，更高阶系统为3% ± 1%，其中54% ± 2%的恒星为单星，表明普查具有高度完整性。
• 伴星的轨道周期分布呈单峰分布，且良好地符合对数正态函数，峰值约为300年。
• 周期-偏心率关系在圆化 timescale（P < 12天）之后呈现平坦分布，表明系统具有动力学稳定性。
• 质量比分布偏好近等质量对，且该偏好在更近的双星中更为显著。
• 单星、双星和多星系统中系外行星宿主的占比在统计上无显著差异，表明在宽分离度的多星系统中，行星形成并未受到显著抑制。
• 完整性分析表明，样本中仅存在少数未被发现的伴星，证实了多重性统计结果的稳健性。