Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite
Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite
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DOI：
10.1051/0004-6361/201730781
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发表时间：
2017-04
影响因子：
6.5
通讯作者：
A. Butkevich;S. Klioner;L. Lindegren;D. Hobbs;F. V. Leeuwen
中科院分区：
文献类型：
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作者：
A. Butkevich;S. Klioner;L. Lindegren;D. Hobbs;F. V. Leeuwen
上下文通过依巴谷或盖亚等扫描天体测量卫星确定绝对视差依赖于两个观察方向之间所谓的基本角的短期稳定性。基本角的未校准变化可能在计算的松弛中产生系统误差。目标。我们研究的耦合之间的全球视差偏移和特定的变化的基本角度，即那些有关的卫星相对于太阳的姿态。方法.分析计算了由基本角、姿态和松弛度的小扰动所产生的观测量的变化。然后，我们寻找对观测量没有净影响的扰动组合。结果在无限小的视野的近似，它表明，某些扰动的基本角度是观测上无法区分的全球性的位移的视差。如果存在这类扰动，它们就不能从天体测量观测中校准，而是会产生全局视差偏差。天体测量的解决方案，使用直接和迭代方法的数值模拟，证实了这一理论结果。对于给定的基本角扰动幅度，基本角和太阳方位角越大，视差偏差越小。在这两个方面，盖亚的几何形状都比依巴谷更好。在盖亚的情况下，内部计量用于监测基本角度变化。此外，盖亚还具有探测众多类星体的优势，可以用来验证视差零点。
Context. Determination of absolute parallaxes by means of a scanning astrometric satellite such as Hipparcos or Gaia relies on the short-term stability of the so-called basic angle between the two viewing directions. Uncalibrated variations of the basic angle may produce systematic errors in the computed parallaxes. Aims. We examine the coupling between a global parallax shift and specific variations of the basic angle, namely those related to the satellite attitude with respect to the Sun. Methods. The changes in observables produced by small perturbations of the basic angle, attitude, and parallaxes were calculated analytically. We then looked for a combination of perturbations that had no net effect on the observables. Results. In the approximation of infinitely small fields of view, it is shown that certain perturbations of the basic angle are observationally indistinguishable from a global shift of the parallaxes. If these kinds of perturbations exist, they cannot be calibrated from the astrometric observations but will produce a global parallax bias. Numerical simulations of the astrometric solution, using both direct and iterative methods, confirm this theoretical result. For a given amplitude of the basic angle perturbation, the parallax bias is smaller for a larger basic angle and a larger solar aspect angle. In both these respects Gaia has a more favourable geometry than Hipparcos. In the case of Gaia, internal metrology is used to monitor basic angle variations. Additionally, Gaia has the advantage of detecting numerous quasars, which can be used to verify the parallax zero point.