Rigel Telescope Extinction Coefficients

The extinction coefficients for the Rigel telescope are determined by a least-squares linear fit to the apparent magnitude versus air mass for a list of standard stars obtained from Landolt's (1992, AJ, 104, 340) photometric determination of bright star magnitudes near the celestial equator. The abbreviated catalog used in the Rigel system is given here. The observed magnitude is given by

The color correction (k'') coefficients were fitted for in a global least-square parameter search, but were all consistent with zero, which we used for the subsequent analysis. For each (Johnson-Cousins) photometric filter the mean extinction coefficients, measured over eight nights of observation in May-June 2004, were

The Winer observatory is located about 100 miles SE of Kitt Peak National Observatory. Here's a plot of the mean extinction at KPNO from 4000 to 9000 Angstroms (red crosses, fitted cubic line) compared with the mean Winer values at the BVRI center wavelengths (squares). The mean extinction coefficients at Winer Observatory are consistently 0.02 - 0.03 higher than KPNO, probably a result of the lower elevation (5000' vs. 7000' at KPNO).