20 years of Hubble Space Telescope optical modeling using Tiny Tim
20 years of Hubble Space Telescope optical modeling using Tiny Tim
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DOI：
10.1117/12.892762
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发表时间：
2011-09
期刊：
影响因子：
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通讯作者：
J. Krist;R. Hook;F. Stoehr
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文献类型：
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作者：
J. Krist;R. Hook;F. Stoehr
摘要点扩散函数（PSF）模型对于哈勃太空望远镜（HST）数据分析至关重要。不熟悉光学模拟技术的天文学家需要访问与其观测条件相匹配的PSF模型，因此任何HST建模软件都需要易于使用，并具有关于望远镜和仪器的详细信息。Tiny Tim PSF模拟软件包自1992年初发布以来一直是标准的HST建模软件。我们讨论了小蒂姆多年来的发展，新的仪器和光学性能已被纳入。我们还演示了如何小蒂姆PSF模型已恩用于HST数据分析。Tiny Tim可从tinytim.stsci.edu免费获得。关键词：哈勃太空望远镜，点扩散函数1.引言点扩散函数（PSF）是光学系统（如望远镜）成像的基本单位。它包括由像差修改的来自遮蔽的衍射，以及来自中高空间频率光学误差的散射。成像性能通常根据PSF属性来描述，例如分辨率和环绕能量。光学工程软件，包括光线追迹和物理光学传播软件包，在系统的设计阶段被用来预测PSF，以确保成像要求得到满足。但是一旦系统完成并运行，软件通常被打包，点扩散函数被认为是静态的，将在文档中描述以供科学家参考。在这种情况下，光学工程师运行软件来计算PSF，而光学系统的用户只需要知道它的基本特性。对于哈勃太空望远镜（HST）来说，情况绝对不是这样。为了从观察中提取最大的信息，即使是PSF的最小细节也很重要。一些例子包括：从观测图像中解卷积点扩散函数，以消除衍射引起的模糊，揭示精细结构;用点扩散函数卷积模型图像，以与观测图像进行比较;减去未分辨源的点扩散函数（星星或致密星系核），以揭示扩展结构（一个星周盘或宿主星系），否则在衍射和散射光的光环中是看不见的;将点扩展函数拟合到星星图像上，以获得精确的测光和天体测量，特别是如果它是一个具有混合点扩展函数的双星星星。与地面望远镜相比，HST非常稳定，因此其点扩展函数中的结构在很大程度上是时不变的。这允许使用PSF模型进行数据分析。在地面上，由于大气层和热引力引起的光学扰动而导致的可变PSF结构使得更难以产生与数据准确匹配的模型。然而，有效的HST PSF取决于许多参数，包括遮蔽、像差、指向误差、系统波长响应、物体颜色和检测器像素效应。精确的PSF模型必须考虑所有这些因素，其中一些可能取决于时间（焦点，遮蔽位置）或相机内的场位置（像差，CCD检测器电荷扩散，遮蔽图案，几何失真）。1.1早期HST PSF建模：TIM在1990年HST推出之前，各种商业和专有软件包被用来计算PSF。这些提供了HST的成像性能的预测，并指导了设计，但它们没有被未来的HST观测者使用。这些程序对一般HS T用户来说太复杂，要么不公开，要么太贵。他们也没有以科学家认为有用的形式提供PSF模型，例如包括探测器像素化和宽带系统响应的影响。
ABSTRACT Point spread function (PSF) models are critical to Hubble Space Te lescope (HST) data analysis. Astronomers unfamiliar with optical simulation techniques need access to PSF models that properly match the conditions of their observations, so any HST modeling software needs to be both easy-to-use and have detailed information on the telescope and instruments. The Tiny Tim PSF simulation software package has been the standard HST modeling software since its release in early 1992. We discuss the evolution of Tiny Tim over the years as new instruments and optical properties have been incorporated. We also dem onstrate how Tiny Tim PSF models have be en used for HST data analysis. Tiny Tim is freely available from tinytim.stsci.edu. Keywords: Hubble Space Telescope, point spread function 1. INTRODUCTION The point spread function (PSF) is the fundamental unit of imag e formation for an optical syst em such as a telescope. It encompasses the diffraction from obscurations, which is modified by aberrations, and the scattering from mid-to-high spatial frequency optical errors . Imaging performance is often described in terms of PSF properties, such as resolution and encircled energy. Optical engineering software, includi ng ray tracing and physical optic s propagation packages, are employed during the design phase of the system to predict the PSF to ensure that the imag ing requirements are met. But once the system is complete and operational, the software is usually packed away and the point spread function considered static, to be described in documentation for reference by the scientist. In this context, an optical engineer runs software to compute PSFs while the user of the optical system simply needs to know its basic characteristics. For the Hubble Space Telescope (HST), that is definitely not the case. To extract the maximum information out of an observation, even the smallest details of the PSF are important. Some examples include: deconvolvin g the PSF from an observed image to remove the blurring caused by diffraction and reveal fine structure; convolving a model image by the PSF to compare to an observed one; subtracting the PSF of an unresolved source (star or compact galactic nucleus) to reveal extended structure (a circumstellar disk or host galaxy) that would otherwise be unseen within the halo of diffracted and scattered light; and fitting a PSF to a star imag e to obtain accurate photometry and astrometry, especially if it is a binary star with blended PSFs Compared to ground-based telescopes HST is extremely stable, so the structure in its PSF is largely time-invariant. This allows the use of PSF models for data analysis. On the ground, the variable PSF structure due to the atmosphere and thermal-and-gravitationally-induced optical perturbations make it more difficult to produce a model that accurately matches the data. The effective HST PSF, though, is dependent on many parameters, including obscurations, aberrations, pointing errors, system wavelength response, object color, and detector pixel effects. An accurate PSF model must account for all of these, some of which may depend on time (focus, obscuration positions) or on field position within the camera (aberrations, CCD detector charge diffusion, obscuration patterns, geometric distortion). 1.1 Early HST PSF modeling: TIM Before launch of HST in 1990, a variety of commercial and proprietary software packages were used to compute PSFs. These provided predictions of HSTs imaging performance and guided the design, but they were not used by future HST observers. These programs were too complicated for general HS T users, and either were not publicly available or were too expensive. They also did not provide PSF models in forms that scientists would find useful, such as including the effects of detector pixelization and broadband system responses.