[论文解读] The ESPRI project: astrometric exoplanet search with PRIMA I. Instrument description and performance of first light observations

J. Sahlmann, Thomas Henning+43 more|Archive ouverte UNIGE (University of Geneva)|Dec 10, 2012

Adaptive optics and wavefront sensing参考文献 42被引用 26

一句话总结

本文展示了ESPRI项目在甚大望远镜干涉仪上利用PRIMA进行首次观测的性能，实现了高精度天体测量以探测系外行星。其结果表明，天体测量精度达到30 μas，但识别出未被监测的光路组件是系统误差的主要来源，限制了精度低于探测系外行星所需的10–100 μas阈值。

ABSTRACT

The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for the discovery and study of planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years and to detect their barycentric motions due to orbiting planets. We present the operation principle, the instrument's implementation, and the results of a first series of test observations. A comprehensive overview of the instrument infrastructure is given and the observation strategy for dual-field relative astrometry is presented. The differential delay lines, a key component of the PRIMA facility which was delivered by the ESPRI consortium, are described and their performance within the facility is discussed. Observations of bright visual binaries are used to test the observation procedures and to establish the instrument's astrometric precision and accuracy. The data reduction strategy for astrometry and the necessary corrections to the raw data are presented. Adaptive optics observations with NACO are used as an independent verification of PRIMA astrometric observations. The PRIMA facility was used to carry out tests of astrometric observations. The astrometric performance in terms of precision is limited by the atmospheric turbulence at a level close to the theoretical expectations and a precision of 30 micro-arcseconds was achieved. In contrast, the astrometric accuracy is insufficient for the goals of the ESPRI project and is currently limited by systematic errors that originate in the part of the interferometer beamtrain which is not monitored by the internal metrology system. Our observations led to the definition of corrective actions required to make the facility ready for carrying out the ESPRI search for extrasolar planets.

研究动机与目标

• 确立甚大望远镜干涉仪上PRIMA设施在通过恒星质心运动探测系外行星方面的天体测量性能。
• 验证该仪器在红外K波段利用明亮视觉双星作为测试目标时，实现双场相对天体测量的能力。
• 识别并校正影响天体测量精度的干涉光路系统中的系统性误差，这些误差使精度低于探测系外行星所需的10–100 μas阈值。
• 为未来ESPRI项目的研究论文及PRIMA设施用户提供参考框架。
• 通过指导对测距系统进行改进，以监测此前未被监测的光路段，从而为未来实现高精度天体测量铺平道路。

提出的方法

• 在明亮视觉双星（如HD 10360、HD 66598）上进行首次观测的天体测量实验，以测试观测流程与性能。
• 利用ESPRI联合体开发的关键组件——差分延迟线，实施双探测器相对天体测量。
• 采用数据处理策略以校正大气湍流和仪器漂移的影响，包括条纹跟踪和相位校准。
• 利用NACO自适应光学观测作为独立验证，确认PRIMA的天体测量视场比例和测量结果。
• 通过光路误差函数（公式20）建立系统误差模型，将未被监测的光程差（Δε(t)）识别为主要误差源。
• 提出将内部测距系统扩展至M9之后的光路段，以减少系统误差。

实验结果

研究问题

• RQ1 PRIMA设施在首次观测期间的天体测量精度和准确度如何？
• RQ2 PRIMA天体测量中占主导地位的系统性误差来源是什么，特别是在未被监测的光路中？
• RQ3 PRIMA天体测量视场比例与NACO自适应光学的独立测量相比如何？
• RQ4 当前光路配置在多大程度上能够支持探测木星质量行星所需的10–100 μas精度？
• RQ5 为实现ESPRI系外行星巡天所需的天体测量精度，测距系统需要进行哪些改进？

主要发现

• PRIMA设施实现了30 μas的天体测量精度，已接近由大气湍流决定的理论极限。
• 目前天体测量的准确度不足以满足ESPRI项目需求，主要受限于未被内部测距系统监测的光路组件。
• 系统性误差主要由非共光路项Δε(t)主导，其来源为M9至M1之间的光路段，该段未被监测。
• 对11″双星的独立NACO天体测量与PRIMA测量结果在13 mas以内一致，证实PRIMA视场比例的准确度约为0.1%。
• 在五天内对一颗明亮11″双星的重复测量中，其散布达到约3 mas，表明存在显著的残余系统性误差。
• 未来改进需将测距系统的端点扩展至M2或更远，以缓解最主要的系统性误差源，并实现亚10 μas精度。