vdB 156 in Andromeda

The rarely shot vdB 156 may be Sidney van den Bergh's mistake. He thought it to be a reflection region more than three degrees in diameter lit up by Omicron Andromedae. But it actually comprises four parts, vdB 156a through d, and it’s the second-largest object in the vdB catalogue.

More recent studies suggest that the area has multiple sources of light that make it visible. A 1986 paper Dr. Adolph Witt pointed me to that was written by René Racine contains this short comment regarding vdB 156 and Omicron And:

“156 o And; association probable but not certain; other stars may contribute to illumination.”

Dr. Witt himself added, “I would agree with this assessment. A single illuminating star produces a nebula, whose surface brightness decreases with radial offset from the star. Your image appears to show mainly integrated flux nebulae (IFN) with several localized brightness enhancements, one produced by Omicron And.”

Many thanks to him for taking the time to help a neophyte like me understand a little more about what I see in an image like this one.