1. Karen Meech Institute for Astronomy TOPS 2003
TOPS Image Processing
Karen Meech
Institute for Astronomy
TOPS 2003
Image copyright, R. Wainscoat, IfA
Image courtesy K. Meech

2. Basic Image Processing
CCD is an array of detectors -- pixels
Each has a different sensitivity
We need to calibrate the instrumental effects

3. Today’s Goals Transfer your data files Learn how to analyze your data
Learn photometry software
Learn astrometry software
Learn how to measure positions
Weekend Assignment
Analyze your data
Think about science conclusions
Prepare something to share on Monday
Plots
List of problems/questions

4. Image Processing Steps
Bias Subtraction
Removes the low level e- put in so none left behind
Flat Field Correction
Exposures on a bright uniform source (sky, dome)
Cosmetic Corrections
Fixing bad columns
Fixing bad pixels
Cosmic Ray cleaning

5. Cosmetic Changes Random bright spots Only a problem if land on stars
High energy particles from space
“single” pixel hits
Only a problem if land on stars
Can affect photometry
Can Remove – but usually not necessary

6. Image Combining Increases S/N on object Decreases noise
Can remove background defects
Can simulate non-sidereal tracking

7. What the Teams will Do Jupiter Mars Extrasolar Planets Variable Stars
Photometry software
Measure pos, size
Mars
Extrasolar Planets
Differential photometry
Create light curve
Variable Stars
Photometry of stars
Differential photometry to get absolute calibration of variables
KBOs
Blinking to search frames for objects
Astrometry

8. Photometry Counting up how much light falls on the detector from star
Aperture
How big to use?
Sky Background
Where to measure?
How?
Background objects
Images, Courtesy J. Bauer

9. Photometry Types Absolute Differential True brightness
Photometric (Eggen-o-metric)
Requires standards
Differential
Tolerates some cloud
Corrects for extinction
Airmass
cloud
Measure many stars as reference
Noise & repeat measurements – S/N
Copyright R. Wainscoat
Images, Courtesy K. Meech

10. Differential Light curve
Images, Courtesy K. Meech

11. Astrometry Precise position meas Map 3-D sky to 2-D image Technique
Measure “centroids” of many stars
Fit for plate center
Fit for scale, rotation
Fit for warping, stretching
Requirements
Finding the objects
Blinking
Different color planes
memorization
6.6’ FOV (1/2 CCD) [above]
40” section [lower]
Images, Courtesy K. Meech

12. Astrometry Precise position meas Map 3-D sky to 2-D image Technique
Measure “centroids” of many stars
Fit for plate center
Fit for scale, rotation
Fit for warping, stretching
Requirements
Finding the objects
Blinking
Different color planes
memorization
6.6’ FOV (1/2 CCD) [above]
40” section [lower]
Images, Courtesy K. Meech