Andrew Cooper
Nov 12, 2023    Waikoloa, HI (map)
20cm f/6 Newtonian, Cave Astrola @ 136x
Seeing: 6 Transparency: 6 Moon: 0%

The star 19 Pup was reported to be nebulous by John Hershel and thus cataloged as NGC 2542, yet nothing can be discerned visually around the star, nothing appears in any of the survey imagery, use of higher magnification or a UHC filter does reveal anything than the usual glare of a 4.7 magnitude star

Harold Corwin

NGC 2542 = 19 Puppis = SAO 153942 = ADS 6647. John Herschel may have been misled by the faint companion to the brighter star. With a separation of only 2 arcsec, and a magnitude difference of 6.5, it would be very difficult to make out the fainter star except under extraordinarily fine conditions.

Reading what I wrote "several" years ago in March 2014, I'm struck by its irrelavance with what John Herschel had to say about the star: "A fine nebulous star 6' m, in the following part of the cluster [NGC 2539], and almost unconnected with it. The nebula is faint, but I feel confident that it is not the nebulous haze. (Notandum. -- Nothing more difficult than to prove a nebulous star of the 6th m and above.)" While this might be a description of a very close double star, it just doesn't read like it.

Yet, the conclusion is still the same -- there is no obvious nebulosity around the star on any of the optical sky surveys. So what did John Herschel see? We can only take him at his word, and accept the suggestion of faint nebulosity here that is overwhelmed by the light of the star on photographs. But we still need to prove that the nebulosity is indeed there.

― NGC Notes by Harold Corwin

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