Accurate photometry with adaptive optics in the presence of anisoplanatic effects with a sparsely sampled PSF
Accurate photometry with adaptive optics in the presence of anisoplanatic effects with a sparsely sampled PSF
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在存在稀疏采样 PSF 的等晕效应的情况下，通过自适应光学器件进行精确光度测量
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发表时间：
2009
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通讯作者：
R. Schoedel
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作者：
R. Schoedel
在用自适应光学观测稠密恒星场的分析中，非等晕效应会引起显著的系统光度不确定性。程序包已经开发了一个空间可变的PSF，但他们需要有足够数量的明亮，孤立的恒星在图像中存在充分的采样PSF。对银河系中心进行成像尤其具有挑战性。我们提出了两种方法来处理空间可变的PSF时，只有一个或非常少的合适的PSF参考星存在于现场。局部PSF拟合与星算法应用于数据。可以通过两种方式找到令人满意的结果：（a）通过将局部提取的PSF核心与从场中最亮的星星估计的PSF翼合并来创建局部PSF;（B）用从场中最亮的星星估计的PSF对图像进行维纳去卷积，并随后对去卷积图像上的局部PSF进行估计。该方法进行了测试真实的，和人工图像。在局部PSF提取和拟合之前对图像进行维纳反卷积的方法给出了良好的结果。它将点源测光中的系统效应限制为~2-5%，在通过H波段滤光片观察的28”x 28”视场上的漫发射中的系统效应限制为~10%。特别注意的是如何反卷积改变图像的噪声特性。结果表明，解卷积能保持恒星的平均位置和平均通量。然而，如果像这里所做的那样在PSF拟合中忽略协方差的存在，则PSF拟合算法的估计不确定性太小。然而，可以从模拟图像或通过比较独立数据集上的测量来确定适当的比例因子。
Anisoplanatic effects can cause significant systematic photometric uncertainty in the analysis of dense stellar fields observed with adaptive optics. Program packages have been developed for a spatially variable PSF, but they require that a sufficient number of bright, isolated stars in the image are present to adequately sample the PSF. Imaging the Galactic center is particularly challenging. We present two ways of dealing with spatially variable PSFs when only one or very few suitable PSF reference stars are present in the field. Local PSF fitting with the StarFinder algorithm is applied to the data. Satisfying results can be found in two ways: (a) creating local PSFs by merging locally extracted PSF cores with the PSF wings estimated from the brightest star in the field; (b) Wiener deconvolution of the image with the PSF estimated from the brightest star in the field and subsequent estimation of local PSFs on the deconvolved image. The methodology is tested on real, and on artificial images. The method involving Wiener deconvolution of the image prior to local PSF extraction and fitting gives excellent results. It limits systematic effects to ~2-5% in point source photometry and ~10% in diffuse emission on fields-of-view as large as 28" x 28" and observed through the H-band filter. Particular attention is given to how deconvolution changes the noise properties of the image. It is shown that mean positions and fluxes of the stars are conserved by the deconvolution. However, the estimated uncertainties of the PSF fitting algorithm are too small if the presence of covariances is ignored in the PSF fitting as has been done here. An appropriate scaling factor can, however, be determined from simulated images or by comparing measurements on independent data sets.