ASTR 3510
Astronomical Observations and Instrumentation I: Imaging
Fall 2009
Lab #4:
Data Due: 1 December 2009 (Tuesday, in lab)
Write-up Due: 10 Decemebr 2009 (Last-day of classes)
Purpose:
Use the CCD to obtain deep, long-time exposure images of a star cluster, a galaxy, or a nebula.
Calibrate the image scales, and do the photometry on your object. The objects you observe may
also serve as a basis for your semester project. However, you will need to do a lab write-up that is
distinct from your final paper and presentation. In the lab write-up we want you to submit your
observing logs, your IRAF reduction scripts, and your final images in fits format. The lab write-up
will consist of the technical parts of your project. The Class Project will present the scientific
aspects.
Observations:
Select a target:
Select a target. It can be a star cluster, nebula, galaxy, supernova remnant, stellar wind bubble,
planetary nebula, or any other object you deem interesting. Some suggestions: NGC 6888, M33,
M42, NGC 281, The Veil Nebula, W3, NGC 7331, M1 (the crab nebula), The Bubble Nebula
(NGC7635). See Travis Rector’s or Russell Croman’s image galleries on the Web for inspiration.
Observe the object in at least three filters so you can plot color-color and color-magnitude diagrams
(for stars) and make a pretty RGB image.
You need to observe standard stars to calibrate both the atmospheric opacity for each filter and
to determine the magnitudes.
You will need to design the experiment and obtain the observations and calibration data. You will
need dark frames, flat fields, and Landolt standard stars (or other photometric calibrators).
Keep accurate and complete observing logs (electronically in a txt or doc file by handwritten is
OK) too). Turn these in when observations are complete.
2) Reductions
Reduce each nights images using IRAF. This includes dark subtraction, flat-field correction, and
magnitude calibration.
1) Combine the images to get rid of cosmic rays. Use USNO stars to determine coordinates and if
possible, generate a world coordinate system for the FITS header. We will talk about how to do
this in lab. (Summary, edit in relevant key words using HEDIT in IRAF).
2) Register the images taken through each filter and make a color-composite image of your target.
3) Estimate the photometric zero-point for the 24” for each filter using your calibration data.
4) Estimate the 3-sigma magnitude limit of your images in each filter.
5) Estimate the magnitude of the brightest unsaturated star in your field. Report the dynamic range
(magnitude difference of flux ratio) using the brightest unsaturated star’s magnitude and the 3sigma detection limit.
6) Estimate the brightness of the sky background in magnitudes per square arc-second.
7) Provide an estimate of your errors. What is the error of in the magnitude and flux of the
brightest star? What is the magnitude and flux error of the faintest star? What RMS is contributed
by the sky in each of the above objects? How does this compare to the read-noise?
Write-up:
Hand-in (electronically) your images and IRAF cl scripts. Write-up a short description of your
calibration results (photometric zero point, 3-sigma magnitude limits, and sky surface-brightness
estimates.