标题： 环形区域内的相对天体测量学 显示英文标题

标题： Relative astrometry in an annular field

摘要： 背景。 以1米级空间望远镜在微角秒级别或以下进行相对天体测量已被多次提出作为系外行星探测和表征的工具，以及用于天体物理学和基础物理的多个前沿课题。 目标。 本文研究了基于环形视场的仪器概念相对于传统焦平面成像（成像连续区域靠近望远镜光轴）的潜在优势。 方法。 根据Gaia EDR3中比G=12星等更亮的参考恒星在天空中的分布情况，回顾了相对天体测量的基本方面。 通过分析和模拟评估了目标星等低至G=8星等的场星统计特性。 结果。 观测效率得益于对单个目标的先验知识，因为源模型可以通过少量测量得到改进。 专用观测（10-20小时）可以将系外行星的轨道倾角限制在几度以内。 观测策略可以定制以包含一个恒星样本，实现参考框架，该样本足够大以将剩余目录误差平均到所需的微角秒级别。 对于大多数目标，环形视场提供的参考恒星数量通常比传统视场多四到七倍。 每个目标的最亮参考恒星亮度高出多达2星等。 结论。 所提出的环形视场望远镜概念在观测灵活性和/或天体测量性能方面优于传统设计。 因此，它似乎是对未来相对天体测量任务优化的一个有吸引力的贡献。 显示英文摘要

摘要： Background. Relative astrometry at or below the micro-arcsec level with a 1m class space telescope has been repeatedly proposed as a tool for exo-planet detection and characterization, as well as for several topics at the forefront of Astrophysics and Fundamental Physics. Aim. This paper investigates the potential benefits of an instrument concept based on an annular field of view, as compared to a traditional focal plane imaging a contiguous area close to the telescope optical axis. Method. Basic aspects of relative astrometry are reviewed as a function of the distribution on the sky of reference stars brighter than G = 12 mag (from Gaia EDR3). Statistics of field stars for targets down to G = 8 mag is evaluated by analysis and simulation. Results. Observation efficiency benefits from prior knowledge on individual targets, since source model is improved with few measurements. Dedicated observations (10-20 hours) can constrain the orbital inclination of exoplanets to a few degrees. Observing strategy can be tailored to include a sample of stars, materialising the reference frame, sufficiently large to average down the residual catalogue errors to the desired microarcsec level. For most targets, the annular field provides typically more reference stars, by a factor four to seven in our case, than the conventional field. The brightest reference stars for each target are up to 2 mag brighter. Conclusions. The proposed annular field telescope concept improves on observation flexibility and/or astrometric performance with respect to conventional designs. It appears therefore as an appealing contribution to optimization of future relative astrometry missions.