CCD Imaging and its Applications in Astronomy

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CCD Imaging and its Applications in Astronomy

• David A. Gribble, Jr.

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Organization

• CCD Technology
• Benefits in Astronomy
• Image Processing Primer
• Research in Variable Stars

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CCD Technology

• What is a CCD anyway?
• What about all these problems?
• Does size matter... Is bigger really better?

Kodak KAF-1600 CCD
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What is a CCD anyway?

• Charge-Coupled Device

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Quantum Efficiency

• How much of the light is captured?

SBIG Specifications for ST-8 CCD Camera
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CCD Technology

• What is a CCD anyway?
• What about all these problems?
• Does size matter... Is bigger really better?

Kodak KAF-4200 CCD
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CCDs arent perfect?

• The thermal signal grows with time
• The zero point is biased above true zero
• The on-chip amplifier adds random noise
• Thermal noise is non-constant from photosite to
  photosite
• Quantization (digitization) may act as a source
  of noise
• Some photosites are abnormal

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There are over 1500 previously
undetected galaxies in this 100 hour exposure.
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CCD Technology

• What is a CCD anyway?
• What about all these problems?
• Does size matter... Is bigger really better?

Kodak KAI-2091 M CCD
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Selecting the proper CCD

• What size should the pixels be?
• How many pixels do we need?
• Telescope meets chip

• Nyquist Sampling
• Oversampling
• Undersampling

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Nyquist Sampling Criterion

• Harry Nyquist and ATT
• Two Pixels / Star
• Point Spread Functions

P pixel width in microns F focal length in mm
S ( 205 P ) / F
F(Lundin) 3810 mm P(ST-8) 9 microns
S(arc seconds) ? .484
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Undersampling

• Less than two pixels / star
• may be acceptable for amateur astrophotos
• disadvantages
• Loss of resolution
• Square star images
• Correctable through image processing?
• NO! Lost information cannot be restored
• Re-sampling can help to smooth stars for a more
  pleasing picture

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Oversampling

• Why cant we just increase magnification?
• Spread the data over greater area
• Lowers the signal to noise ratio
• Resolving Power of the Telescope
• Remember the Nyquist Criterion
• Size and Cost Limitations

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Organization

• CCD Technology
• Benefits in Astronomy
• Image Processing Primer
• Research in Variable Stars

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Benefits in Astronomy

• Photometry
• Spectrometry
• Convenience and Speed
• Super Nova, Asteroid, and, extra-solar-system
  Planet Searches
• Adaptive Optics

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Adaptive Optics Systems

• Three different techniques
• Mirror shape adjustment
• Fast position correction
• Laser Guide Star
• The SBIG AO-7 and others
• What can they fix?
• Tracking errors
• Atmospheric effects
• Boost signal to noise ratio

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Lick Observatory Laser Guide Star Adaptive Optics
System
Sodium-Layer Laser
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Organization

• CCD Technology
• Benefits in Astronomy
• Image Processing Primer
• Research in Variable Stars

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NGC 6946 in Cepheus
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Organization

• CCD Technology
• Benefits in Astronomy
• Image Processing Primer
• Research in Variable Stars

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Research in Variable Stars

• What am I looking at?
• What Equipment can be used?
• We have images what now?

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Wednesday, September 23, 500 AM
M42 - Orion Nebula Red - 10 Seconds Green - 15
seconds Blue - 30 seconds
10 Lundin Refractor Wittenberg University Elgar
Weaver Observatory
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Research in Variable Stars

• What am I looking at?
• What Equipment can be used?
• We have images what now?

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Research in Variable Stars

• What am I looking at?
• What Equipment do I need?
• Ive got the images, but what now?

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To the board!
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The Next Step

• Process theta-c Orionis data according to
  algorithm.
• Collect data from the remaining Trapizium stars.
• Collect spectra from non-variable stars of the
  same spectral type
• Collect spectra from the Orion Nebula
• Match absorption lines from the non-variable
  star and the Orion Nebula to the absorption lines
  in the appropriate Trapizium star.

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Credits

• CCD Astronomy, Winter 1997, Sky
  PublishingCorporation
• Choosing and Using a CCD Camera, Richard Berry
• Astronomy Magazine, November 1998, Kalmbach
  Publishing, Co.
• The Lick Observatory -http//ep.llnl.gov/urp/scien
  ce/lgs_www
• SBIG - http//www.sbig.com/
• Dr. Daniel Fleisch
• Dr. Paul Voytas
• Julia Kregenow

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