Harold Corwin

The IC1 position falls on an empty patch of sky. There are stars and asterisms in the area, but nothing leaps out as a "vF (? S Cl)" as Dreyer characterizes this in the IC. The "* 9.5 close" is indeed near the nominal position, but this does not help in identifying Bigourdan's object. Could this be another case like NGC 2529 and 2531 (which see), imaginary nebulae which Bigourdan recognized as "fausse image"?

Checking his big table, we find that Bigourdan saw the object twice. He estimated its position on both nights with respect to a nearby star, which he called "An. b", to be PA = 120 degrees, distance = 1.3 arcmin. He tells us that "An. b" is +8.5 seconds and +2.5 arcmin from BD +19d 3021. There is a star there, so I've reduced his estimated position using a position for the star that I measured on DSS. This leads directly to an asterism of three stars that match Bigourdan's description perfectly.

So what went wrong? Checking the list of new nebulae in CR 112, 703, 1891 in which this object appears, we find that his position (copied faithfully into IC1 by Dreyer) does not agree with the correctly reduced position. Further, his description reads, "... [the new object] is situated near BD +19d 3021 at p = 120 degrees, d = 1.3 arcmin."

He must have confused his observing records and used the position of the BD star for his reduction. (He did, in fact, use the BD star, but only to estimate the position of "An. b".) As I found, when we use his correct comparison star, his estimated position falls almost exactly in the asterism.

When Bigourdan prepared his vast set of observations for publication in 1912, he must have re-reduced the positions of all of his new nebulae. IC 1140 has its correct position in the tables of new nebulae. I suspect that the reason Bigourdan did not notice the mistake is that the position was precessed to equinox 1860 for the 1891 CR list, while the 1912 list is for equinox 1900.

― IC Notes by Harold Corwin

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