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A Primer on Image Acquisition and Data Reduction Using TheSky6, CCDSoft V5 and Microsoft Excel

A Primer on Image Acquisition and Data Reduction Using TheSky6, CCDSoft V5 and Microsoft Excel. Thomas C. Smith Dark Ridge Observatory ( DRO ) http://www.darkridgeobservatory.org. DRO. Topics of Conversation. Overview Tools for the job Taking images Reducing the image data

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A Primer on Image Acquisition and Data Reduction Using TheSky6, CCDSoft V5 and Microsoft Excel

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  1. A Primer on Image Acquisition and Data Reduction Using TheSky6, CCDSoft V5 and Microsoft Excel Thomas C. Smith Dark Ridge Observatory (DRO) http://www.darkridgeobservatory.org

  2. DRO Topics of Conversation • Overview • Tools for the job • Taking images • Reducing the image data • Processing and analyzing image data • Producing a light curve • Summary • Q&A

  3. DRO Overview Image acquisition and data processing have a completely different meaning when one is attempting to collect and analyze scientific data as opposed to creating wonderfully colorful and enjoyable “pretty pictures”.

  4. DRO Tools for the job • In this brief tutorial I will be using software created by Software Bisque as well as numerous algorithms that I have created in macro form in Microsoft Excel. • TheSky6 Pro and CCDSoft V5 are the tools that I commonly use for both image acquisition and data reduction. • Lets look at each commercial software program.

  5. DRO Tools for the jobTheSky6 planetarium software

  6. DRO Tools for the jobCCDSoft V5

  7. DRO Tools for the jobMS Excel • Microsoft Excel and the “smiley face” light curve generation algorithms From data to curve

  8. DRO Taking Images • Camera startup and cooling • Composing the field of view • Starting auto guiding • Setting the integration time • Choosing the filter(s) • Selecting the series count • Setting image storage location • Imaging and monitoring

  9. DRO Taking imagesCamera startup and cooling • Choose the correct CCD camera • Select the filter wheel (if applicable) • Select the focuser (if applicable) • Verify parameters • Connect to the camera • Initiate temperature regulation

  10. DRO Taking imagesComposing the field of view

  11. DRO Taking ImagesStarting auto guiding Linking TheSky6 to the telescope

  12. DRO Taking ImagesStarting auto guiding (Cont)

  13. DRO Taking ImagesStarting auto guiding (Cont)

  14. DRO Taking ImagesSetting the integration time • Some things to consider • Target ADU value • Sky background (Moon or dark) • Set this using the filter of choice • Image type • Make tests

  15. DRO Taking ImagesChoosing the filters • If you are going to image in several filters it is important to set the integration times for each filter appropriately • CCDSoft V5 shows only 4 filters but there is good control over the individual filters and camera binning (all facets of the filters and imaging can be scripted however to overcome this shortfall) • Single filter setup is simple

  16. DRO Taking ImagesSelecting the series count • Series counts are set in either the “Take Image” tab or in the “Color” tab.

  17. DRO Taking ImagesSetting image storage location

  18. DRO Taking ImagesImaging and monitoring

  19. DRO Reducing the image data • Once the image series has been collected it is time to “reduce” the image files through a series of pixel math • Bias frames • Dark frames • Flat field frames w/flat dark frames • What are these frames?

  20. DRO Reducing the image dataFrames explained • Bias frame • This is effectively a zero second light exposure at the same temperature as the science frames • Dark frame • This is an exposure that is the same time and temperature as the science frames but with the shutter closed (or light path covered) • Flat field frame • These are frames that eliminate the pixel-to-pixel variations and any optical path aberrations such as dust and vignetting

  21. DRO Processing and analyzing image data • Once the images have been reduced it is then a matter of finding objects of interest in them • For this an implementation of Sextractor is used within the CCDSoft application • Sextractor is written by Emmanuel Bertin, visit http://terapix.iap.fr/ for details • There are many things to learn about Sextractor but I will only be discussing a few things of interest

  22. DRO Processing and analyzing image dataSource extraction with CCDSoft

  23. DRO Processing and analyzing image dataSource extraction with CCDSoft (Cont)

  24. DRO Processing and analyzing image dataAstrometry with CCDSoft

  25. DRO Producing a light curveSource extraction rollup with CCDSoft (Cont)

  26. DRO Producing a light curveStar identification

  27. DRO Producing a light curveCCDSoft light curve tool

  28. DRO Producing a light curveExcel light curve plotting • Microsoft Excel is a powerful tool for performing various numerical and data function including • Statistical analysis • Standard spreadsheet data entry • Chart generation • Producing what-if scenarios • And much, much more

  29. DRO Producing a light curveExcel light curve plotting (cont) • I use the Visual Basic for Applications function and macro tools to process the raw text data files that are obtained from CCDSoft and to plot the resulting light curve as I feel appropriate • Full control of the charting environment through VBA makes reproducing chart characteristics simple and fast • I use the power of Excel to identify outlying data through a 3-sigma routine • I can optionally bin the data and create an additional curve for contrast with the raw data curve. • The entire plotting routine can go from raw data to light curves with significant statistical information available in just a few moments • Always being modified and added to for enhanced performance

  30. DRO Producing a light curveExcel light curve plotting (cont) • I have created many utility functions that perform things such as • Julian Date to Heliocentric Julian date conversion • Filtered image file move routines “triage” to aid in placing the files in the correct folder locations for analysis • 6 degree to 30 degree air mass calculations as well as the common >= 30 degree air mass routine • Routines to bulk update FIT header data from a specified folder of image (used when the RA/DEC data is incorrect to assist in the astrometric solution) • Many other support utilities that are used both internal to the light curve plotting routines and callable externally from most any COM-compliant application

  31. DRO Producing a light curveExcel light curve plotting (cont)

  32. DRO Producing a light curveExcel light curve plotting (cont) Seeing my “Smiley Face” in action!

  33. DRO Summary • Image reduction for science images is very different from that used to create “pretty pictures” • Many tools can be used and it is normally a matter of familiarity and preference • If things don’t look right then think about what might be causing the issues and reanalyze the data • Common desktop tools like Microsoft Excel make powerful partners in the world of astronomical photometry

  34. DRO Q & A Any questions about this process or anything in general that you would like to ask?

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