Harold Corwin

NGC 2330 and NGC 2334. Malcolm has not been happy with my assignments of NGC 2330 and NGC 2334 to IC 457 and IC 465. After going over all of the extant historical evidence once again, I'm not happy, either. But I'm not sure what to do about it. Here's the story.

William Herschel swept over this field twice, finding -- so he thought -- two nebulae, II 736 (on 9 Feb 1788) and II 862 (on 28 Dec 1790). His positions reduce to 07 07 21, +50 14.2 and 07 07 03, +50 14.4 (both for B1950.0). Since NGC 2332 is well over a minute of time preceding either of these, I think that both observations refer to NGC 2340. That galaxy is, in any case, the brightest in the group. William Herschel's descriptions are consistent with his observations referring to the same galaxy.

When John Herschel swept up the field about 35 years later, he picked up NGC 2340 twice and NGC 2332 once. His positions and descriptions match the two galaxies well, so there is no reason to doubt that he actually did see both.

After another 25 year gap, Lord Rosse turned his 72-inch "Leviathan" on the field. Unfortunately, the three sketches he made during his first two observations in January of 1851 did not appear in his 1861 monograph. He had only a short note under his entry for h 430, "Several knots around; 430 is E np, sf" (the directions should read "sp, nf"). So, when John Herschel assembled the GC, he had only this scanty note on which to base the entry for GC 1492. Consequently, the position for GC 1492 is very rough (06 58+-, 39 36+-; RA and NPD for 1860), and the description reads only "Several near h 430 (?426, 433, & 1 nov[a])."

When Dreyer was preparing Lord Rosse's observations for publication, he transcribed the details missing from the 1861 monograph, giving us the first two night's notes and sketches. Unfortunately, the arrows in the sketches are pointing in the wrong directions, and (as I noted) north and south are reversed in the notes for the first night's observations of NGC 2332 = h 430. I think that the first two sketches must come from only the first night: one shows NGC 2332 and a new nebula, with the second showing NGC 2340 and another nova. I also think that these are the objects which Dreyer intended to include in the NGC. This is the reason that I earlier adopted the NGC numbers 2330 and 2334 for them, in spite of the large differences in position from the NGC positions (from Bigourdan's observations; more on these below).

The notes for Lord Rosse's second night refer to five novae, as well as the two known objects. A third sketch -- apparently from that night -- shows a total of nine nebulae. A third observation in 1863 refers to only six of these, with Dreyer adding the comment, "Zeta, iota, and theta not noticed this night." This is understandable as Lord Rosse says "A fog prevented these being well seen."

In any event, Dreyer clearly had evidence for nine nebulae in the field, yet chose to include NGC numbers for only four. Perhaps he did this because he thought he had good positions for only those four -- two from John Herschel via the GC, and two from Bigourdan (more on Bigourdan's observations just below) for two of the "novae."

However, given the confusion of the directions in the sketches and the observing notes, Dreyer was unable to sort out the field satisfactorily. So, he put question marks on Lord Rosse's initials under the numbers 2330 and 2334, adopting Bigourdan's positions published in his (Bigourdan's) first list. Dreyer could have inserted numbers for the remaining five nebulae, trusting to future observers to provide good positions, but unfortunately, did not.

It is here that Bigourdan's complete observations could have provided positions for most of Lord Rosse's novae, had he (Bigourdan) chosen to publish them before the NGC appeared. For, on two nights in November of 1885, Bigourdan measured eight novae of his own, including six real nebulae, in addition to the two known nebulae. Unfortunately, he chose to publish only two of his novae. By startlingly bad luck, the two he did publish are stars. The six real galaxies remain buried in his massive tables of observational details and did not appear until 1907 in the Observations of Paris Observatory.

Consequently, Dreyer put the two stars, with Bigourdan's positions and descriptions, into the NGC. While his clear intent was to include two of Lord Rosse's nebulae, he just as clearly -- with Bigourdan's unknowing assistance -- botched the job.

So, what do we do with the two errant NGC numbers? If we assign them to the stars which Bigourdan's positions and descriptions point at, we do Dreyer's intentions (and John Herschel's in the GC as well) a disservice. If, on the other hand, we assign them to the two novae that Lord Rosse found in 1851 (IC 457 and IC 465), then we incur Malcolm's wrath and my own furrowed brow. My solution is to adopt both options with lots of question marks, knowing full well that neither is satisfactory. Dreyer has simply not left us enough information to make any clear choice.

As a footnote, I should mention that Heinrich Kobold also stumbled across this problem in 1893. He published a short note in AN 3184 with good positions for NGC 2332, 2340, and nine other nebulae which he assumed included those found by Lord Rosse. However, he could not find Bigourdan's two published novae (the ones with NGC numbers), understandable since those are stars. Dreyer put all of Kobold's novae into the first IC, and included a note reporting Kobold's negative observations of the two NGC numbers.

Finally, a footnote to the footnote: Kobold published his complete observations in the Strassburg Annalen in 1909. There, he has two observations of IC 459, but has reversed the signs on the offsets for one of them. He apparently discovered this before he published his short announcement in AN, so he did not publish a non-existent object (one object, IC 462, is a star, however). Since his monograph was published long after the observations, and long after he found the error, it's puzzling that he should let the mistake stand. The fact that the wrong signs are not just typos is shown by his including the second observation as if it were for another object. Also, his summary list of reduced positions includes only the IC objects (with the correct number of observations for each), so the decision to publish the incorrect observations is doubly puzzling. I certainly wouldn't have done it that way!

― IC Notes by Harold Corwin

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