M67 Data Plotting in IDL

Finishing up a HW problem as an introduction to IDL, color-magnitude, color-color, reddening/extinction, distance modulus, etc:

Plotted color-color diagram of M67 data (white) with theoretical isochrone (yellow). Graph is (g-r) vs (r-i), corrected for reddening caused by dust in line of sight. This fit created by varying E(B-V), allowing set equations to then change A(g), A(r), A(i) appropriately.

Overplotting stars close to isochrone in red to see quality of fit:

NED gives an E(B-V) value of 0.035. The fit above is using E(B-V) = 0.05. 

Applying this reddening correction to a color-magnitude plot ((g-r) vs (r)) gives the following graph after vertically fitting the isochrone. Once again, stars close to the isochrone are overplotted in red, as those are the stars we actually want (in M67, same age and distance):

[note: obvious gap in red near bottom due to isochrone being non-continuous, fixable by extrapolating further points along the isochrone line]

The vertical fit needed to fit the isochrone to the data after adjusting for extinction reddening is the distance modulus µ. Here µ = 9.5, close to the literature value of 9.48. Using the formula µ = 5*log10(d) – 5, the distance d is found to be ≈749.328 parsecs, or about 0.794 kpc. One published paper gives the distance to M67 as 0.843 ± ~0.120 kpc, a range the distance here falls well within.