ngVLTI：用于毫角秒尺度成像的四望远镜VLTI扩展的成本与可行性
ngVLTI: Cost and Feasibility of a Four-Telescope VLTI Expansion for Milliarcsecond-Scale Imaging
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中文总结 AI 辅助
研究评估通过增加四台8米级单元望远镜扩展VLTI（即ngVLTI）的成本与可行性，其能提供密集uv覆盖实现毫角秒成像及光谱成像立方体。介绍了紧凑望远镜概念、光学设计等，估算每台望远镜成本约8000万欧元，升级具成本竞争力且技术可行。
中文摘要 AI 辅助
我们评估了通过增加四台8米级单元望远镜（UT）来扩展甚大望远镜干涉仪（VLTI）的成本和技术可行性，此升级称为新一代VLTI（ngVLTI）。这种升级将提供密集且均匀的uv覆盖，基线长达220米，能在毫角秒角分辨率下对从太阳系天体到遥远活动星系核等各种科学目标进行真正成像。每个图像在单一波长重建，跨仪器光谱通道重复重建可得到光谱成像立方体，这是VLTI全新的能力，使其接近ALMA在近红外波长的成像能力。基于此科学目标，我们研究了一种紧凑望远镜概念，包括快速（f/0.64）、分段、抛物面主镜，其馈入与现有VLTI基础设施兼容的地下卡塞格伦焦点。我们总结了光学设计，其在1弧分视场和匹配良好的重成像光瞳上实现衍射极限性能，讨论了选择60段、1.2米主镜背后的机械权衡（镜质量约13.5吨，高度移动质量约50吨），并量化了望远镜结构的重力弯曲及其导致的光学灵敏度随指向仰角的变化。然后给出每台望远镜约8000万欧元（2026年价格）的粗略成本估算，细分为分段主镜、自适应副镜、卡塞格伦光路、支架、外壳和辅助仪器。提议的升级在成本上具有竞争力且技术上可行，为帕拉纳尔天文台在ELT时代提供了长期展望。
英文摘要
We assess the cost and technical feasibility of extending the Very Large Telescope Interferometer (VLTI) through the addition of four 8 m-class Unit Telescopes (UTs), an upgrade we refer to as the new generation VLTI (ngVLTI). Such an upgrade would provide a dense and homogeneous uv coverage with baselines up to 220 m, enabling true imaging at milliarcsecond angular resolution across science cases ranging from Solar System bodies to distant active galactic nuclei. Because each image is reconstructed at a single wavelength, repeating the reconstruction across the spectral channels of the instrument would deliver spectral-imaging cubes -- a qualitatively new capability for the VLTI, bringing it close to the imaging power of ALMA at near-infrared wavelengths. Motivated by this scientific case, we examine a compact telescope concept consisting of a fast ($f/0.64$), segmented, parabolic primary mirror feeding a subterranean coudé focus compatible with the existing VLTI infrastructure. We summarise the optical design, which achieves diffraction-limited performance over a 1 arcmin field of view and a well-matched reimaged pupil, discuss the mechanical trade-offs behind the choice of a 60-segment, 1.2 m primary -- a mirror mass of ~13.5 tons and an altitude moving mass of ~50 tons -- and quantify the gravitational flexure of the telescope structure and its resulting optical sensitivity as a function of pointing elevation. We then present a back-of-the-envelope cost estimate of order 80 MEuro per telescope (2026 prices), broken down into the segmented primary, adaptive secondary, coudé train, mount, enclosure, and ancillary instrumentation. The proposed upgrade appears both cost-competitive and technically achievable, offering a long-term perspective for Paranal Observatory in the ELT era.
