Astronomy 350 Au2002

CCD Differential Photometry of CY Aquarii

Part 5: Final Lab Report

Your final lab report should be written in your lab notebooks, and turned in on the day scheduled for the final exam:

5pm Thursday, December 12

Your final report, in effect, constitutes your final examination for this course, and should be entirely your own work. While you may assist each other during the previous 4 parts of this project, I want you to work through the questions and interpretive sections here on your own without collaboration with your fellow students. Read over this outline below in detail before you begin, and well in advance of the deadline. If you have questions, or need clarification, please consult with me in person or by email.

For your final write-up, try to organize all these various steps you have taken into a coherent narrative. Simply turning in your stack of notes will not be acceptable. You may type it up if you wish, or you may provide a hand-written report, in pen, if you write neatly. Please staple any supporting graphs to your report in the order they appear in the text, and given them clear (brief) figure captions with clean labels as appropriate. Neatness and overall organization and flow will count.

The outline I want you to use in organizing your results into your final report is as follows:


Briefly state the problem and what you intend to measure. Should be no more than 2 paragraphs.


Briefly describe the observations and the experimental data set that resulted from it. Again, no more than 2 paragraphs. This is where you present your POSS finder chart and your CCD image finder chart identifying the field and the stars you identified as the variable and comparison stars.

Data Reduction & Analysis:

Briefly describe how you measured the data and estimated uncertainties. This is where you should present your tables of flux (counts) measurements from Part 3. The discussion here should include any comparisons (e.g., the different ways of estimating the sky level and the seeing, and how they compared (e.g., as you did in Part 3), and your choice of photometry apertures.


Summarize how you converted the observed counts into instrumental magnitudes and computed the differential magnitudes.

Plot the raw instrumental magnitudes for Var, C1 and C2 against HJDmid with their uncertainties. These are the "raw" light curves. Look at the raw light curves for C1 and C2. Did they vary significantly during your observations? Specifically, do you see any systematic trends (e.g., steady increase or decrease in brightness over the data set) with time? If the night was reported by the on-site observer to be photometric, is the behavior of the raw light curves for the comparison stars consistent with this claim?

Now present your differential photometry, making two plots:

  1. Plot the difference light curves, V-0.5*(C1+C2) vs. HJDmid and C1-C2 vs. HJDmid. Using the plots from the web pages as a model.

  2. Plot the phased light curve of the variable, retrieving your light curve from the web database after submission.

In both cases remember to plot the error bars.

Compute the mean and the rms variation (standard deviation) of the comparison difference (C1-C2) in magnitudes (not the sigma of the mean). Since the data are all close to each other in value, you can do the mean and standard deviation computation in magnitudes without causing problems. Using the standard deviation of (C1-C2) as a reference value, answer the following:

  1. How much brighter was the variable star relative to your comparison stars (in magnitudes) during your observations? What was the range?

  2. What is the amplitude of variability in your CY Aquarii data set? Express it in units of magnitudes and in units of the standard deviation in C1-C2? Is your detection of variability in your particular data set statistically significant?

  3. What is the amplitude of variability in the full merged (phased) light curve of CY Aquarii in these same units? How "significant" is our detection of the variability in CY Aquarii in the full data set?

  4. How do the individual measurement errors on the raw instrumental magnitudes of CY Aquarii compare to the standard deviation of C1-C2?


Time to wrap it up. Start with a one paragraph summary of the results of this project (what did you set out to do and what you actually accomplished). Then address the question of what you might be done better if you had it to do over again, or what might be done next.

On the question of what might be done better, consider your answer to how the rms variations in the comparison stars (C1-C2) compared to the individual measurement errors of the brighter variable star. Look at your POSS finder chart. Would using comparison stars of comparable brightness to the variable let you exploit the full precision of the individual measurements? Think about it in terms of what dominates the uncertainty in the differential magnitude of the variable star: V-0.5*(C1+C2).

Compute the field of view of a 512x512 pixel CCD camera with 24-micron pixels mounted at the focus of the 12-inch f/10 Meade telescope. If we were to have used this telescope and CCD combination for the experiment instead of the YALO 1-meter and the ANDICAM CCD, are there any better candidates for comparison stars of comparable brightness to CY Aquarii that land within the CCD field in this case? [Hint: ask yourself if you really need to center CY Aqr on the exact center of the CCD field-of-view?] Do you think that the problem might be done with greater precision with a 12-inch telescope in Columbus rather than this particular 1-meter telescope in Chile? Comment on this possibility to wrap things up.

Your report should not be super detailed, but should give me enough information to form a judgment as to how well you got through each step of the lab, how well you understood what you were doing and drew connections between the different parts, and finally how well you can organize the results from all the separate parts into a coherent whole.

One of the goals of this class is to give you the conceptual and technical skills to understand how to treat astronomical data statistically. What I will be looking for is how well you demonstrate how to weave a critical consideration of measurement errors into your discussion of the lab results, and to recognize and assess their impact upon the experiment (as well as your ability to do the uncertainty estimates correctly).

This is not all that different than how one would organize observations, data analysis and interpretations into a scientific paper.

Return to the CY Aqr Lab Main Page

Go back to Part 4: Differential Photometry of CY Aqr

Updated: 2002 November 20 [rwp]

Copyright Richard W. Pogge, All Rights Reserved.