天体的光度测量是测定接收到的天体的电磁辐射流量,天体物理学中也称之为测光.测光是天体物理研究中最基本的研究方法之一,由恒星的测光值可以得出其他重要的天体物理参量,如恒星的视星等(亮度)、色指数(颜色)、温度以及变星的光变曲线;结合恒星距离的测定,也可以得到其光度等物理特性.电荷耦合器件(CCD)作为新一代探测器得到广泛使用,针对探测器的数字化方式出现了各种不同的测光方法.首先简单介绍CCD探测器;然后重点介绍孔径测光以及它的适用范围;接着介绍点扩散函数测光和它的适用对象,包括在点扩散函数测光中用的两种比较新的点扩散函数模型——数字点扩散函数(digital PSF)和有效点扩散函数(ePSF);进一步介绍孔径测光和点扩散函数测光的对比,并引出一种把这两种方法结合起来的测光方法;作为测光方法近期的一项重要应用,介绍在密集场中变星光变的精确测定方法;最后总结这几种测光方法并对未来的方法改进提几点看法.%In astrophysics, the most fundamental measurable quantities of celestial objects are their radiative fluxes. The photometry is thus essential to stellar astrophysics, as it can lead to many important parameters, e.g. stellar luminosities, color indices, temperatures, and light curves of variable stars. Many new photometric methods are proposed to serve observations with Charge-Coupled Devices (CCDs) which have become the new generation of detectors. For isolated and bright stars in a CCD image aperture photometry works very well. The PSF-fitting photometry works better for apparently faint or crowded stars. Particularly, by using ePSF, a convolution of the PSF of the optical system with the spatial sensitivity functions of individual CCD pixels, the PSF fitting can yield accurate photometry under cases of undersampled PSF. The combined method of PSF fitting and aperture photometry can largely avoid the problems of the two previous methods and yield accurate photometry for both bright and faint stars. This method is suitable for the time-resolved photometry of pulsating variable stars. In a dense crowded field of stars, such as the central region of a globular cluster, the Image Subtraction Method (ISM) can be used to identify variable stars and obtain their accurate light curves which are difficult to be measured with the conventional softwares (e.g. DAOPHOT or DoPHOT).rnThis paper first gives a brief review of a CCD detector, the importance of photometry in astrophysics, and some astrophysical parameters relevant to stellar photometry. The paper then describes the aperture photometry and the PSF-fitting photometry in detail, including the new digital-PSF and ePSF modeling methods. By pointing out limits of these methods, this paper describes some more recent important approaches, i.e. the combined method of PSF fitting and aperture photometry and the ISM. Some directions of future development are finally discussed.
展开▼
