FIRST, a fibered aperture masking instrument II. Spectroscopy of the Capella binary system at the diffraction limit
FIRST, a fibered aperture masking instrument II. Spectroscopy of the Capella binary system at the diffraction limit
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首先，光纤孔径掩蔽仪器 II。
DOI：
10.1051/0004-6361/201321894
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发表时间：
2013
影响因子：
6.5
通讯作者：
F. Allard
中科院分区：
文献类型：
--
作者：
E. Huby;G. Duchêne;G. Duchêne;F. Marchis;S. Lacour;Guy Perrin;T. Kotani;É. Choquet;É. Choquet;E. Gates;O. Lai;F. Allard
目标。 FIRST 是一款原型仪器，旨在展示瞳孔重映射技术的功能，使用单模光纤并在可见波长下工作。我们的近期目标是展示仪器的高角分辨率能力，并表明仪器的光谱分辨率能够表征恒星伴星。方法。 FIRST-18仪器是FIRST-9的改进版本，它同时重组两组九根光纤而不是一组，从而大大增强了(u, v)平面覆盖范围。我们报告了使用安装在利克天文台 3 米谢恩望远镜上的 FIRST-18 在 14 个月（≳4 个轨道周期）内对五车二双星系统的三个历元进行的观测。我们观测期间的双星分离范围为望远镜在光谱带中心波长的衍射极限的 0.8 至 1.2 倍。结果。我们成功解析了五车二双星系统的各个历元，在最佳观测条件下天体测量精度可达1mas。 FIRST 还可以在 600−850 nm 范围内以前所未有的 R ~ 300 光谱分辨率直接测量两个成分之间的光谱通量比。特别是，我们的数据可以检测众所周知的通量比光谱的整体斜率，从而估计“枢轴”波长为 0.64 ± 0.01 μ m，在该波长处冷却器组件变得最亮。两种成分（特别是 H α 线、TiO 和 CN 波段）的有效温度差异产生的光谱特征已被用来约束恒星参数。我们为这两个组件得出的有效温度略低于该系统的既定特性（5−7%）。这种差异主要来自于比最先进的恒星大气模型预测的分子特征更深的分子特征，这表明光球模型中使用的分子线列表不完整和/或振荡器强度被低估，最有可能与 CN 分子有关。结论。这些结果证明了 FIRST（一种基于光纤光瞳重映射的仪器）在高角分辨率方面的强大功能，并表明光谱通量比的直接测量为表征鲜为人知的同伴提供了有价值的信息。
Aims. FIRST is a prototype instrument built to demonstrate the capabilities of the pupil remapping technique, using single-mode fibers and working at visible wavelengths. Our immediate objective is to demonstrate the high angular resolution capability of the instrument and to show that the spectral resolution of the instrument enables characterization of stellar companions. Methods. The FIRST-18 instrument is an improved version of FIRST-9 that simultaneously recombines two sets of nine fibers instead of one, thus greatly enhancing the ( u , v ) plane coverage. We report on observations of the binary system Capella at three epochs over a period of 14 months (≳4 orbital periods) with FIRST-18 mounted on the 3 m Shane telescope at Lick Observatory. The binary separation during our observations ranges from 0.8 to 1.2 times the diffraction limit of the telescope at the central wavelength of the spectral band. Results. We successfully resolved the Capella binary system at all epochs, with an astrometric precision as good as 1 mas under the best observing conditions. FIRST also gives access to the spectral flux ratio between the two components directly measured with an unprecedented spectral resolution of R ~ 300 over the 600−850 nm range. In particular, our data allow detection of the well-known overall slope of the flux ratio spectrum, leading to an estimation of the “pivot” wavelength of 0.64 ± 0.01 μ m, at which the cooler component becomes the brightest. Spectral features arising from the difference in effective temperature of the two components (specifically the H α line, TiO, and CN bands) have been used to constrain the stellar parameters. The effective temperatures we derive for both components are slightly lower (5−7%) than the well-established properties for this system. This difference mainly comes from deeper molecular features than those predicted by state-of-the-art stellar atmospheric models, suggesting that molecular line lists used in the photospheric models are incomplete and/or oscillator strengths are underestimated, most likely concerning the CN molecule. Conclusions. These results demonstrate the power of FIRST, which is a fibered pupil remapping-based instrument, in terms of high angular resolution and show that the direct measurement of the spectral flux ratio provides valuable information to characterize little known companions.