Harold Corwin

IC 4088 is probably UGC 08140. That would also make it IC 843 and probably also NGC 4913. See those other objects for more.

Courtney Seligman has questioned the identity of this object. It was discovered by Bigourdan (it is number 309 in his list of "novae") who has only one estimate of its position on the same night, 13 May 1895, as the nearby but non-existent IC 4093 (which see). His reduced position puts Big 309 about one third of the way from his comparison star to the galaxy that we have all been taking as IC 4088. Bigourdan's brief description is "Objet dont l'existence est certaine et qui parait nebuleux; il est de grandeur 13,4-13,5 ou 13,5." (My translation: "Object whose existence is certain and which could be nebulous; its magnitude is 13.4-13.5 or 13.5.") His magnitude estimate puts it near the extreme limit of his 30-cm refractor.

Courtney originally suggested that Big 309 was a 16th magnitude star about 20 arcseconds north of the reduced position for the object. As we've seen in others of Bigourdan's observations, he has trouble with 16th magnitude stars. So, I'm not at all convinced that that star is his object. It could be, of course. But doubt remains, at least in my mind.

Here's why.

I call this observation of Bigourdan's an "estimate" because all of his "solid" measurements are given in his big tables with the precision of the position angle at 0.01 deg, (e.g. for NGC 4924, with two observations, PA = 140.94) and the distance at 0.1 arcseconds (NGC 4924 again: d = 6' 09.5"). For Big 309 = IC 4088, he has only one "observation" with PA = 90, and d = 1' 24" with respect to his comparison star, TYC 1995-2078-1. This estimate certainly does not carry his usual precision for a true measurement, and almost certainly not his usual accuracy of 2-3 arcseconds. I even suspect his distance to be expanded from an estimate of 1.'4 (but I note again that his big table has 1' 24", not 1.'4). His "measurement" bears the marks of a simple estimate. We don't know for sure that it is, but it certainly looks like it to me.

Here is a bit of a detour into some solid data that we will nevertheless make reference to below. The positions are for J2000.0 and are from Gaia EDR3. The magnitudes and colors are from SDSS photometry (transformed to UBVRI; note that the galaxy data are not on the RC3 photometric systems that I usually use). These are for three objects in the area that Bigourdan might have seen.

Star: RA = 13 01 50.44, Dec = +29 01 57.8
V = 16.16, B-V = 0.60, U-B = 0.07, V-R = 0.32, V-I = 0.72

North galaxy (UGC 8137 =: NGC 4912): RA = 13 01 33.59, Dec = +29 07 50.0
V = 13.64, B-V = 1.10, U-B = 0.64, V-R = 0.62, V-I = 1.32
V' = 12.98 with RC3 diameters
V' = 11.12 with SDSS PetroRad D and RC3 axis ratio

South galaxy (UGC 8140 = IC 843 =: NGC 4913 =: IC 4088): RA = 13 01 43.37, Dec = +29 02 40.9
V = 13.92, B-V = 1.02, U-B = 0.50, V-R = 0.57, V-I = 1.26
V' = 13.36 with RC3 diameters
V' = 11.91 with SDSS PetroRad D and RC3 axis ratio

V' is the surface brightness calculated with the transformed SDSS V magnitude, and with diameters as shown from either RC3 or from SDSS. The Petrosian diameters in SDSS are pretty good approximations of the effective (half light) diameters in RC3 (both, in fact, are supposed to be "metric" diameters, thus not affected by redshift), so the surface brightnesses are also decent approximations to what we'd have had in RC3 for the two galaxies.

The galaxies are seen to be 2-2.5 magnitudes brighter than the star. Given their more or less average surface brightnesses, both would have stood a good chance of being seen by an observer in "sweeping mode." In fact, I'm rather surprised that neither Safford nor Bigourdan picked up the northern galaxy. It is somewhat brighter and has a higher surface brightness, so I would have thought that one or the other of the observers would have seen it. Apparently, only Lord Rosse picked it up with his much larger telescope.

Given all this, I am going to list the southern galaxy as "NGC 4913: = IC 843 =: IC 4088" and the star as "IC 4088?" I obviously prefer the galaxy for carrying Big 309 and all the other numbers, but could of course be wrong.

I've found no previous observations in the area, aside from Lord Rosse's and Safford's. (The Heidelberg observers started taking photographic plates in the 1890's, roughly at the same time as Bigourdan's visual micrometric observations.) While Safford's are given in the Appendix to the NGC, Bigourdan makes no mention of them in either his main list, or in his "Complementary Measures" list. While it is just possible that Bigourdan saw the first IC before observing Big 309 on 13 May 1895, I doubt that that happened. The IC1 manuscript was received by the RAS from Dreyer on 10 Jan 1895, and "read" on the 11th. I don't know when it was printed and distributed, but it was certainly after those dates. So, Bigourdan would have had a couple of months at most to "digest" the new catalogue from Dreyer. And of course, he had no idea that LdR had been over the field before; as far as he was concerned, NGC 4912, NGC 4913, and NGC 4916 were 8+ degrees north with NGC 4914.

And that's it, all the information we have. Taken at face value, Bigourdan's reduced position falls about 20 arcseconds south of a star with V = 16.2 and B-V = 0.60. The V magnitude almost certainly puts the star out of Bigourdan's normal reach. The brightest object in the area that Bigourdan might consider as nebulous is the galaxy, so I am going to suggest that he actually did see it. In that case, I must stipulate that his estimated position is not as good as his "real" measurements. So, colons go on the identification.

Finally, as I've suggested above, this is probably one of the galaxies in the field of the object that Lord Rosse mistook for NGC 4914 (see NGC 4912 for that story). If so, this is NGC 4913, but even that is not quite certain. The only identification not carrying colons is IC 843. (Courtney and I have discussed all these objects at some length, and have hashed out these IDs as a result. This doesn't mean we're correct! It just means that of all the options, this is the one that seems to us to require the least "bending" of the original observations to match what we now see on the sky.)

I'll end with a curious note. If all three NGC/IC numbers actually do apply to the galaxy, this is only the second object to make an appearance in all three of Dreyer's catalogues (NGC 2947 = IC 547 = IC 2494 is the other).

― IC Notes by Harold Corwin

Harold Corwin

IC 843 = CGCG 160-102 = UGC 08140. This is probably also identical with NGC 4913 and IC 4088. Courtney Seligman has pointed out that the postions for IC 842 and IC 843 are within an arcminute or so of galaxies that Truman Henry Safford could have easily seen with the 18.5-inch Clark refractor at Dearborn Observatory, but that the identification of IC 843 with another galaxy five arcminutes north is almost certainly wrong.

The modern catalogues, starting with CGCG, got IC 842 right, but not IC 843. As Courtney noted, the latter number was put on an equally bright galaxy five arcminutes north of Safford's apparently intended object. The reason for this may be that the southern galaxy already had an IC number, IC 4088 (ironically, this number on this galaxy is not quite certain; see IC 4088 for the story) -- or it may simply be a mistake.

Here are some details. Safford found both galaxies on 3 May 1866. His position for IC 842 is given to 0.1 seconds of time and 0.1 arcminutes, so he thought that this position at least was fairly reliable (the RA is off by 0.8 seconds, and the Dec by one arcminute, 28 arcseconds). His position for IC 843 is less precise -- given to only a full second of time and a full arcminute -- but is virtually as accurate: it is 5 1/3 seconds off in RA, and 40 arcseconds in Dec. Safford's scanty descriptions, "pF" for IC 842 and "FbN" for IC 843, match these two galaxies well enough.

This galaxy is probably also be NGC 4913 and IC 4088. See the discussions under NGC 4912 and IC 4088 for those stories, also inspired by recent email discussions with Courtney.

― IC Notes by Harold Corwin

Courtney Seligman

Per Dreyer, IC 843 (Safford #3, 1860 RA 12 54 54, NPD 60 12.7) is "faint, brighter middle and nucleus." The position precesses to RA 13 01 37.8, Dec +29 02 02, only about 1.4 arcmin west-southwest of the galaxy listed above, the description is reasonable and there is nothing comparable within 5 arcmin, so the identification is essentially certain. Unfortunately, for unknown reasons, the galaxy nearly 6 arcmin to the north of Safford's position has been called IC 843 for donkey's years, hence the warning in the title for this entry that that galaxy, PGC 44908, is not IC 843, despite the fact that all catalogs and atlases list it as such.

On May 3, 1866, Safford discovered two objects in this region. For reasons involving an extremely belated publication of his observations, his discovery of those objects was not noticed in time to be properly included in the NGC, but Dreyer listed both of them (as IC 842 and 843) in the First Index Catalog. Both galaxies lie along the same parallel of declination, and given the way that observers of the 19th century scanned the sky, their nearly identical declinations (both in the sky and in Safford's list of 'novae') make it virtually certain that they are the two objects he observed. But as noted above, for unknown reasons, the galaxy nearly 6 arcmin to the north (PGC 44908) is the one that is universally listed as IC 843, and when Safford's #3 was rediscovered, it became IC 4088. Still, just because something has been called by the wrong name for many years does not make that right; it just makes it confusing. So this entry serves as a notice of the historical and continuing error, the entry for PGC 44908 describes the nature of the galaxy "formerly" known as IC 843, and as noted below, the entry for IC 4088 discusses the galaxy that is really Safford's #3.

― Courtney Seligman, Celestial Atlas

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