Quasometry，它的使用和目的
Quasometry, Its Use and Purpose
摘要：
类星体测量是对天体位置和非常遥远的河外天体（如类星体、星系核和类星体）视运动的精确测量。我们使用这个术语来确定一个特定的研究领域，其方法不同于一般的天体测量学。准测量的主要目的是将亚毫角秒射电坐标系（ICRF）与天体测量卫星建立的现有和新出现的具有类似精度的光学参考系联系起来。讨论了实现这一目标的一些主要困难，例如，类星体宿主的扩展结构，天空中的视运动，光学变化，星系伴星，昏暗。除了战略目的之外，准测量无疑对全球天体测量测量是有用的，因为它有助于验证甚至校正由此产生的参考系。在全球天体测量解中使用遥远类星体的测量有两种选择：1）嵌入观测方程组的硬约束; 2）带向误差的{ \it后验}拟合。对这两种方案的优缺点进行了评述。一组相对较小的约200个精心挑选的参考类星体可以大大提高太空任务的天体测量价值，如果它们足够明亮，稳定，相当均匀地分布在天空中，并且是ICRF中的定义源。我们提出了一个正在进行的计划，在USNO构建一套质量的光学类星体所需的属性，并提高ICRF与新的来源，在已知的，良好的观测类星体是稀缺的。
英文摘要：
Quasometry is precision measurement of celestial positions and apparent motion of very distant extragalactic objects, such as quasars, galactic nuclei, and QSOs. We use this term to identify a specific area of research, the methodology of which differs from that of general astrometry. The main purpose of quasometry is to link the sub-milliarcsecond radio frame (ICRF) with the existing and emerging optical reference frames of similar accuracy, constructed by astrometric satellites. Some of the main difficulties in achieving this goal are discussed, e.g., the extended structures of quasar hosts, apparent motion on the sky, optical variability, galactic companions, faintness. Besides the strategic purpose, quasometry is undoubtedly useful for global astrometric surveys, as it helps to verify or even correct the resulting reference frames. There are two options of using measurements of distant quasars in a global astrometric solution: 1) hard constraints embedded in the fabric of observational equations; 2) {\it a posteriori} fitting of zonal errors. The relative benefits and shortcoming of the two options are reviewed. A relatively small set of about 200 carefully selected reference quasars can go a long way in improving the astrometric value of a space mission, if they are sufficiently bright, stable, fairly uniformly distributed on the sky, and are defining sources in the ICRF. We present an ongoing program at the USNO to construct a quality set of optical quasars with the required properties and to enhance the ICRF with new sources in the areas where known, well-observed quasars are scarce.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
