Trending of comp stars

[ghawkins]

If I have two comp stars and I'm looking at their normalized relative flux plots, and one trends up and the other trends down with a similar but opposite slope, then am I correct in saying that some unknown systematic (likely airmass) is affecting the comp stars in different ways?  If the unknown systematic was affecting the comp stars in the same way, then the normalized relative flux plots for each comp star would be flat.

[karenacollins]

Based on your description, it sounds like one comp star is bluer and the average of all other comp stars, and the other comp star is redder than the average of the other comp stars. A comp star light curve will be flat if it has the same color as the average of all comparison stars you are using.

Karen

[ghawkins]

Data was only determined for two comp stars, and the target star, eclipsing binary V474 CAM.  The first comp star has B-V = 0.21 and the second comp star has B-V = 0.43.  There were significant airmass variations over the course of the measurement run as the astronomer was trying to collect the entire light curve in one evening and, to do this, had to allow the target well below 30 degrees elevation.