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ASSA imaging group DSLR Photometry Talk 27 Nov 2015

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These are the slides for a talk I gave to the imaging group of the Astronomical Society of South Australia about DSLR photometry of variable stars on November 27 2015.

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ASSA imaging group DSLR Photometry Talk 27 Nov 2015

  1. 1. DSLR Photometry of Variable Stars David Benn, Nov 2015
  2. 2. Outline  Brief overview of variable stars  The varieties of variable star observing  What’s the goal?  Getting started with DSLR photometry  My setup  Procedure
  3. 3. Introduction to Variables Source: Society for popular astronomy
  4. 4. Introduction to Variables
  5. 5. Introduction to Variables https://en.wikipedia.org/wiki/File:Eclipsing_binary_star_animation_2.gif
  6. 6. Introduction to Variables http://www.citizensky.org
  7. 7. Introduction to Variables http://www.astrosurf.com/aras/novae/Nova2013Del.html
  8. 8. Variable Star Observing Varieties  Visual variable star estimation since 2009  Mostly binocular  Simple (technique, equipment) & quick  Great for long period variables, novae  ~0.1 magnitude precision  Wide-field DSLR photometry since late 2014  ~0.01 magnitude precision  Can quantify error  Not as precise as CCD or PEP but 10x lower cost  Repeatability; data re-use in future, e.g. for B, R
  9. 9. + CHOICE courses
  10. 10. What’s the goal?
  11. 11. What’s the goal?
  12. 12. What’s the goal?
  13. 13.  finder chart of W Sgr to describe technique Visual http://www.citizensky.org, Southern Gems tutorial
  14. 14. DSLR Photometry: My Setup  Overall motivation  low cost, time  suburban backyard  Canon 1100D with 200mm lens on LX-90 or tripod  Card table and light shield; light box for flats  Free or readily available software  IRIS (free; WINE on Mac), AstroImageJ, Muniwin, …  Spreadsheet (Excel, OpenOffice)  Sky Safari Pro (telescope control, with SkyFi)
  15. 15. DSLR Photometry: My Setup
  16. 16. DSLR Photometry: My Setup
  17. 17. DSLR Photometry: My Setup
  18. 18. My Setup
  19. 19. DSLR Bayer Array https://en.wikipedia.org/wiki/Bayer_filter
  20. 20. Some Considerations  B, V, R possible from a single image  May be more than one variable per image  ISO 100 or 200 or 400 for high dynamic range  Exposure: depends upon tripod vs tracked  Turn off auto features  noise reduction  lens cleaning
  21. 21. Procedure  Finder chart & photometry table  Locate field, take test frame to verify  Make notes, e.g. of conditions!  Deliberately under-focus for photometry  Convert RAW to software’s format, e.g. FITS  Calibration: lights, biases, flats, darks (maybe)  Stellar registration, for automatic photometry
  22. 22. Procedure  Extract green (or blue or red) channels  Determine photometry radii  Local coordinates of target, reference stars  Some software may automate via plate solve  Photometry on individual or stacked images  Look at error, residuals; change one or more reference (comparison, check) stars if too high  Ensemble-based transformation to V (or B or R)
  23. 23. Photometry Table from Finder Have to consider: • Magnitude • B-V when choosing reference stars.
  24. 24. Deliberately under-focus
  25. 25. DSLR: Bayer Array
  26. 26. Calibration
  27. 27. CFA Conversion
  28. 28. Stellar Registration
  29. 29. Extract R, G, B channels green channel: img-gN
  30. 30. Target Region
  31. 31. Target Region
  32. 32. Aperture Photometry
  33. 33. Aperture Photometry
  34. 34. Aperture Photometry
  35. 35. Aperture Photometry
  36. 36. Differential Photometry Source: AAVSO DSLR manual
  37. 37. Links  https://aavso.org  http://www.variablestarssouth.org  https://en.wikipedia.org/wiki/Binary_star  https://www.cfa.harvard.edu/news/2009-23  http://astro.unl.edu/naap/ebs/animations/ebs.html  http://www.popastro.com/news/newsdetail.php?id_nw=174  https://www.aavso.org/observed-minima-timings-eclipsing- binaries  https://en.wikipedia.org/wiki/Color_filter_array

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