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Astronomical Data Collection and Processing of LLPV’s in GGC’s at the BGSU Observatory

Astronomical Data Collection and Processing of LLPV’s in GGC’s at the BGSU Observatory. J Leon Wilde. TAA Seminar, UT, February 2nd, 2007. Intro. Before observing… BGSU’s telescope CCD Imaging Typical observing night Image processing My Thesis Work. Before observing…. What to look at

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Astronomical Data Collection and Processing of LLPV’s in GGC’s at the BGSU Observatory

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  1. Astronomical Data Collection and Processing of LLPV’s in GGC’s at the BGSU Observatory J Leon Wilde TAA Seminar, UT, February 2nd, 2007

  2. Intro • Before observing… • BGSU’s telescope • CCD Imaging • Typical observing night • Image processing • My Thesis Work

  3. Before observing… • What to look at • Where to look from • What instruments? • 0.5 m Reflecting telescope • CCD imager

  4. The telescope Incoming starlight Secondary Mirror Primary Mirror Focus on optics

  5. The CCD Imager • “Charge Coupled Device” • Si diodes • KAF-1000E • Specs .pdf for KAF-1001E

  6. Why use CCDs? • High QE • High Linearity • Large dynamic range • Uniform response • Low Noise • Digital

  7. Our CCD’s QE Blue – KAF-1001E Black – KAF-1401E

  8. Our CCD 24x24 micron pixels 1024x1024 array CCD Basic Design

  9. Gate Structure/Function • Voltage push • Sends data to onboard amplifier and A/D converter • Our CCD • Two phase push • Charge transfer efficiency = 0.99997

  10. CCD illumination • Frontside • Photons pass through phasing gates • QE lower than Bs • Backside • Etched back • High QE • Hard to make, thus... • More expensive • Our CCD • Frontside

  11. CCD Drawbacks • Noise! • Dark current • A/D conversion • CCD flaws • Worked out during processing • Expensive! • Delicate manufacturing process • Better science means higher standards

  12. Dark Current • Thermal activity on CCD chip

  13. CCD Linearity SBIG ST8 Linearity Test Pixel value (ADU’s) Integration time (seconds)

  14. CCD Coatings • CCDs naturally insensitive to blue • Coatings used • Coronene & Lumogen phosphors • Lumogen better of the two • Lumogen commercially used in highlighters • Our CCD • “Blue Plus Transparent Gate”

  15. Our CCD No anti-blooming gates We’re careful!  Blooming

  16. Typical Night • Arrive an hour before sunset • Get equipment ready • Take bias frames / flat field frames • Observe! • Take more bias / flat fields • Send images to Dr. Layden’s computer • Shut equipment down • Go home!

  17. Image Processing • Correct the images • Optics aren’t perfect (dust donuts, vignetting) • CCDs aren’t perfect • Electronics aren’t perfect • Observers aren’t perfect • “The problem exists between the chair and the computer.” • “Garbage in, garbage out.” • Get science from the data • Convert ‘relative’ values into ‘real’ values • Programs: • IDL and IRAF

  18. Processing… • Zero (Bias) frame • Remove floor value • Subtract combined image from data • Dark frame • Remove dark current • Subtract combined image from data • Flat field • Remove non-uniformities arising from: • CCD flaws • Optics flaws • Divide combined image from data

  19. Processing… • Photometry • RR Lyrae Program, getting star magnitudes versus time • Pretty pictures • Combine images from different color filters

  20. Pretty pictures Ring Galaxy AM 0644-741 from Hubble

  21. My Thesis Work:Why Study LPV’s? • Variability provides distance calibrations • LPV’s are understudied • For SIM (Space Interferometry Mission)

  22. Background • What are they?

  23. Why look in GGC’s? • Stars are of the same age • Stars are at the same distance • Stars are similar in composition

  24. Detection • Acquire data over long enough time • Process images • Image subtraction • DAOPHOT, ISIS

  25. GettingtheData

  26. NGC 6539 • 5 years of data • [Fe/H] = -0.66

  27. New GGC’s • “New” to us! • Selected from Harris Catalogue • min Dec • max V_hb • Small: • Core concentration • E(B-V) - Foreground reddening • Span of [Fe/H]

  28. PROMPT Images!

  29. PROMPT • Back to Harris Catalogue • Tracked down known LPV’s • Corrected coordinates

  30. PROMPT • NGC 288

  31. PROMPT • NGC 1261

  32. PROMPT • NGC 1851

  33. Next steps… • Our data: • Finish processing / Photometery • Learn DAOPHOT • Perform DAOPHOT on recent data / NGC 6539 • PROMPT data: • Determine best collection method

  34. References • People • Dr Andy Layden for his time, Dr John Laird for his books • Mike Smitka • Brian Pohl & Dr. Bruce Carney, UNC Chapel Hill • Book • Steve B. Howell, 2000, Handbook of CCD Astronomy, Cambridge University Press • Websites • http://physics.bgsu.edu/~layden/observatory.htm • http://zebu.uoregon.edu/ccd.html • http://www.ccd.com/ccdu.html • http://www.astro.virginia.edu/class/oconnell/astr511/lec11-f03.html • http://www.wildealien.com/ccd/ • PowerPoint file available online • http://physics.bgsu.edu/~jlwilde/taatalk-feb07.ppt • Contacting me: • jlwilde@bgsu.edu

  35. Thanks for your attention!

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