The Science of Calibration
The Science of Calibration
复制标题
校准科学
DOI：
--
复制
发表时间：
2012
期刊：
影响因子：
--
通讯作者：
S. Kent
中科院分区：
文献类型：
--
作者：
S. Kent
本文对校准天文数据所涉及的许多问题进行了广泛的概述，涵盖了从无线电波到伽马射线的全部电磁频谱，并考虑了地面和太空任务。这些问题包括绝对校准和相对校准的科学驱动因素、校准背后的物理原理以及将校准从实验室转移到天文来源的机制、作为天文标准的校准网络的需求，以及大型调查和任务所面临的一些挑战。1. 人们可以认为电磁辐射具有四维特征（如果天空上的立体角是二维的，则为五维）。此外，每个维度都可以用绝对值和精度的范围来表示。人们寻求校准的正是这个空间。这些尺寸及其范围可描述如下：通量（测量单位，例如，erg cm−2 s−1 hz−1）通常在特定频率、波长或能量下指定。我们感兴趣的校准对象的总通量范围约为23年（太阳到最微弱的LSST对象）。像开普勒任务（Borucki et al. 2006）这样的高精度实验在其行星掩星搜索计划中达到了10微马格量级的精度，或50年的范围。测量波长有两个目的。一种是指定测量磁通的带通。另一种是测量红移等量。我们可能获得信号的范围是25年左右，尽管还没有探索极端情况。在低频端，极限最终由星际介质的等离子体频率决定，约为3khz。在高能的一端，大约100 TeV以上的光子从微波背景散射出去存在一个截止点。（星系源，如果存在的话，可能会被探测到更高的能量。）目前精度最高的测量可能是利用径向速度测量的p行星搜索，大约1米/秒，或10年的范围。1
This paper presents a broad overview of the many issues invol ved in calibrating astronomical data, covering the full electrom agnetic spectrum from radio waves to gamma rays, and considering both ground-based and s p ce-based missions. These issues include the science drivers for absolute and re lative calibration, the physics behind calibration and the mechanisms used to transfer it fr om the laboratory to an astronomical source, the need for networks of calibrated as tronomical standards, and some of the challenges faced by large surveys and missions. 1. The Hyperspace of all data One can think of electromagnetic radiation as being characterized by four d imensions (or five if one allows that a solid angle on the sky is two-dimensional.) Furthermo re, each dimension can be characterized by a range in both absolute value and in precision. It is this space that one seeks to calibrate. These dimensions and their rang s can be described as follows: Flux (measured, e.g., in erg cm −2 s−1 hz−1) is usually specified at a specific frequency, wavelength or energy. The objects that we are interested in calibrating span a range in total flux of approximately 23 decades (sun to faintest LSST objects). A high precision experiment such as the Kepler Mission (Borucki et al. 2006) attains a precision of order 10 micromags, or a range of 5 decades , in its planetary occultation search program. Wavelength is measured for two purposes. One is to specify the bandpass in which a flux is measured. The other is to measure quantities such as redshift. The range over which we might possibly obtain a signal is of order 25 decades, although the extremes are not yet explored. At the low freque ncy end, the limit is ultimately set by the plasma frequency of the interstellar medium, which is of order 3 khz. At the high energy end, a cuto ff exists for photons above about 100 TeV from scattering o ff the microwave background. (Galactic sources, if any exist, presumably could be detected to still higher energies.) The highest precision measurements at present are probably those of p lanet searches utilizing radial velocity measurements roughly 1 meter /sec, or a range of 10 decades. 1