5.2 The NICMOS History Tool
When reducing and analyzing NICMOS data, it is sometimes important to know certain aspects about the instrument or telescope history at the time the observations were made. This information is not always available in the image headers or *_spt.fits files. The STScI NICMOS group has implemented a WWW-based NICMOS History Tool. This tool accepts the exposure start time or the dataset name as input, and provides options for retrieving information about the plate scale, focus, coronagraphic hole position, prior SAA passages, or the spacecraft attitude history. The spacecraft attitude history, for example, can be important for understanding the behavior of coronagraphic data (Section 5.6), as is the coronagraphic hole position. The hole position is also helpful when reducing non-coronagraphic NIC2 data, as you may wish to mask out the hole when combining dithered data, or to know whether it has affected a target in your field (e.g., Section 4.6.3). The SAA information can help you to pre-screen your data for frames which may be impacted by SAA-induced cosmic ray persistence (see Section 4.7.2). The plate scale history is important for accurate astrometry and position measurements, since the scale of NICMOS varied somewhat with time as the dewar distortion changed (see Section 5.4).
