用基于模型的方法估计和校正Vainu Bappu望远镜中阶梯摄谱仪的仪器扰动
Estimation and correction of the instrumental perturbations of Vainu Bappu Telescope Echelle spectrograph using a model-based approach
摘要：
在印度瓦伊努巴普望远镜（VBT）上运行的中阶梯摄谱仪是一种用于许多高分辨率光谱观测的通用仪器。目前正在作出协调一致的努力，以扩大该仪器在观测天文学新兴领域的科学能力。本研究旨在评估光谱仪进行精确径向速度（RV）测量的可行性。在目前的设计中，限制光谱仪RV精度的主要因素来自可移动光栅和狭缝;光学像差;与光学机械支架相关的位置不确定性以及光谱仪室中的环境和热不稳定性。由于环境中的温度和压力变化，RV不稳定性估计分别在120 $ \textrm{ms}^{-1} $和400 $ \textrm{ms}^{-1} $左右变化。光栅在光谱仪中的位置不确定性可引起跨越中阶梯阶的光谱移位$\sim1.4\,\textrm{kms}^{-1} $。Zemax模型用于克服零点定位的不确定性和运动部件重复性的缺乏。我们建议获得的ThAr灯的观察和使用Zemax模型作为参考，预测的光学元件的位置漂移。在观测运行开始时，校正了光学元件从标称位置的扰动。在模型和观测值之间获得良好的匹配后，我们建议使用Zemax模型来改进波长校准解决方案。在光谱仪的实时设置中，在模型参数被扰动后，我们可以在$\pm$ ~1像素的精度内匹配观测和模型。在本文中，我们提出的光学元件的扰动的估计和RV获得的影响。
英文摘要：
The Echelle spectrograph operating at Vainu Bappu Telescope (VBT), India, is a general purpose instrument used for many high-resolution spectroscopic observations. A concerted effort is being made to expand the scientific capability of the instrument in emerging areas of observational astronomy. The present study is aimed at evaluating the feasibility of the spectrograph to carry out precision Radial Velocity (RV) measurements. In the current design, major factors limiting the RV precision of the spectrograph arise from the movable grating and slit; optical aberrations; positional uncertainty associated with optomechanical mounts and environmental and thermal instabilities in the spectrograph room. RV instabilities due to temperature and pressure variations in the environment are estimated to vary around 120 $ \textrm{ms}^{-1} $ and 400 $ \textrm{ms}^{-1} $ respectively. The positional uncertainty of the grating in the spectrograph could induce a spectral shift $\sim1.4\,\textrm{kms}^{-1} $ across the Echelle orders. A Zemax model is used to overcome the uncertainty in the zero-positioning and lack of repeatability of the moving components. We propose to obtain the ThAr lamp observations and using the Zemax model as the reference, predict the drifts in the positions of the optical components. The perturbations of the optical components from the nominal position are corrected at the beginning of the observational run. After a good match is obtained between the model and the observations, we propose to use a Zemax model to improve the wavelength calibration solution. We could match the observations and model within $\pm$~1 pixels accuracy after the model parameters were perturbed in a real-time setup of the spectrograph. In this paper, we present the estimation of the perturbations of optical components and the effect on the RV obtained.
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