[论文解读] A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun: I. Atmospheric parameters and color similarity to the Sun

G. F. Porto de Mello, R da Silva+2 more|arXiv (Cornell University)|Dec 29, 2013

Stellar, planetary, and galactic studies参考文献 88被引用 29

一句话总结

本研究对距离太阳50秒差距内的太阳类星进行了一项测光与光谱调查，利用颜色相似性指数和高分辨率光谱学方法，识别出大气参数和测光特性与太阳极为接近的恒星。研究共识别出五颗新的可能太阳孪生星，以及一颗主要候选星（HD 140690），其近紫外与可见光谱与太阳高度一致，凸显其在系外行星与SETI研究中的重要性。

ABSTRACT

Solar twins and analogs are fundamental in the characterization of the Sun's place in the context of stellar measurements, as they are in understanding how typical the solar properties are in its neighborhood. They are also important for representing sunlight observable in the night sky for diverse photometric and spectroscopic tasks, besides being natural candidates for harboring planetary systems similar to ours and possibly even life-bearing environments. We report a photometric and spectroscopic survey of solar twin stars within 50 pc of the Sun. Hipparcos absolute magnitudes and (B-V)_Tycho colors were used to define a 2 sigma box around the solar values, where 133 stars were considered. Additional stars resembling the solar UBV colors in a broad sense, plus stars present in the lists of Hardorp, were also selected. All objects were ranked by a color-similarity index with respect to the Sun, defined by uvby and BV photometry. Moderately high-resolution, high-S/N spectra were used for a subsample of equatorial-southern stars to derive Teff, log g, and [Fe/H] with average internal errors better than 50 K, 0.20 dex, and 0.08 dex, respectively. Ages and masses were estimated from theoretical HR diagrams. The color-similarity index proved very successful. We identify and rank new excellent solar analogs, which are fit to represent the Sun in the night sky. Some of them are faint enough to be of interest for moderately large telescopes. We also identify two stars with near-UV spectra indistinguishable from the Sun's. We present five new "probable" solar twin stars, besides five new "possible" twins. Masses and ages for the best solar twin candidates lie very close to the solar values, but chromospheric activity levels range somewhat. We propose that the solar twins be emphasized in the ongoing searches for extra-solar planets and SETI searches.

研究动机与目标

• 识别距离太阳50秒差距内、在大气参数和测光颜色上与太阳匹配的太阳孪生星。
• 评估恒星候选体在多种测光系统和光谱波段范围内作为太阳类比物的保真度。
• 基于uvby和BV测光，利用颜色相似性指数量化候选恒星与太阳的相似性。
• 通过光谱学和理论赫罗图，测定最佳候选体的大气参数（Teff, log g, [Fe/H]），并估算其年龄和质量。
• 识别出近紫外光谱与太阳无法区分的恒星，使其适用于紫外优化的天体物理研究。

提出的方法

• 以太阳的依巴谷绝对星等和(B-V)Tycho颜色为中心，定义一个2σ测光框，筛选出133颗初始候选体。
• 纳入Hardorp列表中的额外恒星，以及UBV颜色与太阳相似的恒星，以扩大样本范围。
• 应用基于uvby和BV测光的颜色相似性指数，按与太阳颜色的接近程度对候选体进行排序。
• 对南天部分恒星子样本获取中等高分辨率、高信噪比光谱，以分别获得Teff、log g和[Fe/H]，其内部误差分别小于50 K、0.20 dex和0.08 dex。
• 利用理论赫罗图（HR图）估算最佳候选体的年龄和质量。
• 将推导出的测光与光谱参数与太阳值进行比较，识别出在颜色和大气参数上均处于3σ范围内的恒星。

实验结果

研究问题

• RQ1 在距离太阳50秒差距内的恒星中，哪些在测光颜色和大气参数上最接近太阳？
• RQ2 颜色相似性指数在识别高保真度太阳类比星和孪生星方面有多高效？
• RQ3 哪些恒星的近紫外光谱与太阳无法区分，其在其他参数上又如何表现？
• RQ4 最佳太阳孪生候选体的估计年龄和质量是多少，与太阳相比有何差异？
• RQ5 由于其太阳样特性，哪些恒星是最优候选体，可用于系外行星搜寻和SETI研究？

主要发现

• 颜色相似性指数成功识别出测光特性在太阳3σ范围内的候选体，证实其可靠性。
• 识别出五颗新的可能太阳孪生星：HD 98649、HD 118598、HD 150248和HD 164595，其质量与等时线年龄在不确定度范围内与太阳一致。
• HD 140690被确定为最佳太阳类比星，其近紫外与可见光谱与太阳完全无法区分，且大气参数与太阳匹配。
• 还识别出五颗新的可能太阳孪生星，其大气参数和测光保真度接近太阳值。
• 最佳孪生星候选体的色球层活动水平存在差异，表明尽管具有太阳样参数，其磁活动仍有所不同。
• 本研究建议在正在进行的系外行星与SETI搜寻中优先考虑太阳孪生星，因其具有孕育类地系的高潜力。