In spectroscopy there is one additional calibration that is not done in normal CCD imaging. If you only plan to measure the Doppler shifts of features or changes in them relative to the continuum, then the flat-field calibration, while it might make the spectra more presentable, is not needed. It is also important to understand that unless you are doing spectral photometry (not a recommended project for most amateurs) that the Flat is a completely unnecessary step in reducing spectra. That polynomial of the extraction from the Flat is divided into the data. Instead it is extracted identically to the spectra and modeled with a low-order polynomial. The Flat is not directly divided into the CCD frame containing the spectra. The Flat plays a different roll in spectroscopy. The Dark will be subtracted from the spectrum to remove the background noise in each pixel. And we will apply the dark in very much the same way you would use a Dark frame for normal CCD imaging. The Flat frame is used to calibrate its relative response to other pixels.In spectroscopy the Dark is an important calibration. The Dark frame is used to tell how much noise there is in the pixel. In order to calibrate the pixel we need to know how much noise it would have gathered without the light falling on it and how it responds relative to the other pixels around it. Each pixel can be thought as a mini-detector of light with its own calibration properties. Many of the basic principles of CCD image reduction also apply to the reduction of spectra. The other goal is to dymystify the reduction of spectra and unchain the enthusiastic amateur from their black-box to let them understand and take more control of how their data is reduced. One goal of this tutorial is to de-mystify that process and make amateurs as confortable with reducing spectra as they are with reducing CCD images or photometry. But to do real science, it helps to understand exactly how the data are gathered.įor most amateurs, their spectrograph might come with some canned software that is for all intents and purposes a black box that you put the CCD images from the spectrograph in one end and get one-dimensional spectra out the other with no hint of what happens in-between. This opens up a whole new domain for citizen science. The name continues to be in use! Current funding is provided by the Chandra X-ray Science Center and the NASA High Energy Astrophysics Science Archive Center.Amateur astronomers have increasingly better access to affordable spectrographs they can use with their telescope to take spectra of objects in the night sky. The new project was referred to, jokingly, as DS9 (Deep Space 9), the logical extension of the Star Trek series. This project was funded by the NASA Applied Information Systems Research Program, under the title "Future Directions for Astronomical Image Display". In 1998, while working with Eric, William Joye began a complete rewrite of TNG, based on the experience developed while supporting TNG. In particular, it utilized XPA, (X11 Public Access, also written by Eric) which allowed TNG to be scripted via a shell, or from other application. It explored new GUI interfaces and supported a new external analysis interface. TNG was based on IRAF's XIMTOOL graphics libraries and Tcl. In the mid 1990's, with the administrative support of Steve Murray, Eric Mandel developed SAOtng, or (SAOImage, The Next Generation), named after the Star Trek series. Since Mike's departure from SAO, SAOImage has been maintained by Jessica Mink. SAOImage was a brilliant program, implementing techniques in scientific visualization 30 years ago that are still being used by today's applications. In fact, it was one of the first X11 based applications publicly made available. SAOImage was first implemented in X10, then reimplemented in X11. In 1990, Mike Van Hilst, at the Smithsonian Astrophysical Observatory, Center for Astrophysics, Harvard University, developed SAOImage under the direction of Eric Mandel.
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