M40 is simply the double star Winnecke 4. The separation has
been steadily increasing since Winnecke first measured it at
49.2" in 1863 at a position angle of 88 degrees. Hipparcos in
1991 said 52.8" at 77 degrees. Intermediate measurements show
the pair to be separating on a straight line so they are a line
of sight pair. There seems to be some discrepancy about their
spectral color. Lick Observatory's catalog shows them as G0 and
F8 while Brian Skiff says K0III and G0V. Unfortunately my color
data is severely distorted by clouds, especially during the red
frames. I tried on a second night for new red data only to have
clouds again create a problem. Thus I'm not sure about my
colors. I did push them too but I seem to see a late G and early
F. Looking at other photos on line I see the few color ones
showing white and slightly blue though the Sloan Survey image
would appear to agree to Brian Skiff's K and G classification.
I'm likely too blue with the hotter star. The main reason for
imaging it was I'm trying