Astronomical Data Collection and Processing of LLPVs in GGCs at the BGSU Observatory

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Astronomical Data Collection and Processing of
LLPVs in GGCs at the BGSU Observatory

• J Leon Wilde

TAA Seminar, UT, February 2nd, 2007
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Intro

• Before observing
• BGSUs telescope
• CCD Imaging
• Typical observing night
• Image processing
• My Thesis Work

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Before observing

• What to look at
• Where to look from
• What instruments?
• 0.5 m Reflecting telescope
• CCD imager

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The telescope
Incoming starlight
Secondary Mirror
Primary Mirror
Focus on optics
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The CCD Imager

• Charge Coupled Device
• Si diodes
• KAF-1000E
• Specs .pdf for
• KAF-1001E

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Why use CCDs?

• High QE
• High Linearity
• Large dynamic range
• Uniform response
• Low Noise
• Digital

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Our CCDs QE
Blue KAF-1001E Black KAF-1401E
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CCD Basic Design

• Our CCD
• 24x24 micron pixels
• 1024x1024 array

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Gate Structure/Function

• Voltage push
• Sends data to onboard amplifier and A/D converter
• Our CCD
• Two phase push
• Charge transfer efficiency 0.99997

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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

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CCD Drawbacks

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

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Dark Current

• Thermal activity on CCD chip

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CCD Linearity
SBIG ST8 Linearity Test
Pixel value (ADUs)
Integration time (seconds)
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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

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Blooming

• Our CCD
• No anti-blooming gates
• Were careful! ?

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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. Laydens computer
• Shut equipment down
• Go home!

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Image Processing

• Correct the images
• Optics arent perfect (dust donuts, vignetting)
• CCDs arent perfect
• Electronics arent perfect
• Observers arent 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

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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

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Processing

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

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Pretty pictures
Ring Galaxy AM 0644-741 from Hubble
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My Thesis WorkWhy Study LPVs?

• Variability provides distance calibrations
• LPVs are understudied
• For SIM (Space Interferometry Mission)

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Background

• What are they?

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Why look in GGCs?

• Stars are of the same age
• Stars are at the same distance
• Stars are similar in composition

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Detection

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

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GettingtheData
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NGC 6539

• 5 years of data
• Fe/H -0.66

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New GGCs

• New to us!
• Selected from Harris Catalogue
• min Dec
• max V_hb
• Small
• Core concentration
• E(B-V) - Foreground reddening
• Span of Fe/H

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PROMPT Images!
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PROMPT

• Back to Harris Catalogue
• Tracked down known LPVs
• Corrected coordinates

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PROMPT

• NGC 288

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PROMPT

• NGC 1261

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PROMPT

• NGC 1851

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Next steps

• Our data
• Finish processing / Photometery
• Learn DAOPHOT
• Perform DAOPHOT on recent data / NGC 6539
• PROMPT data
• Determine best collection method

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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/astr5
  11/lec11-f03.html
• http//www.wildealien.com/ccd/
• PowerPoint file available online
• http//physics.bgsu.edu/jlwilde/taatalk-feb07.ppt
  
• Contacting me
• jlwilde_at_bgsu.edu

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Thanks for your attention!