Harold Corwin

IC 2997 is not NGC 4090, though is often taken to be. The confusion is understandable, as there is nothing at Bigourdan's (and the IC's) position. It's worth noting here that Bigourdan recorded the two objects on the same night (his observations of N4090 are in his Appendix 8, "Complementary Observations").

Bigourdan's two observations of I2997, referred to the same star on the same night, are as discordant as any of his that I've seen: 43 arcseconds apart. He's clearly made an error, and I suspect that his error was to record a position angle of 150.80 degrees as 158.80 degrees. With that corrected, the two observations agree to within 4 arcsec. That is the position I've given in the table.

In any event, there is nothing exactly at this position, but 17.5 arcsec away is a 17th magnitude star that has another much brighter star at about PA = 155 degrees, distance 1.8 arcmin, an offset mentioned in his description for a star of "11.8-12". The actual magnitude is 13.5 (in B, 13.6 in R; both from USNO A2.0). This suggests that he glimpsed the 17th magnitude star -- with a 12-inch telescope, from the middle of Paris, in the late 1800's when street- lighting was becoming popular (stop laughing; it MIGHT be possible ...)

My own guess is that IC 2997 is actually another of Bigourdan's "fausse images" such as NGC 2529 and NGC 2531, or IC 2610 (all of which see). It's interesting that another of Bigourdan's lost nebulae, IC 2998 (which see), is also in the NGC 4092 group -- and was also glimpsed on the same night as this one.

― IC Notes by Harold Corwin

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