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This is the third in a series of articles detailing a variety of errors in the Revised New General Catalogue
(RNGC) prepared by Jack Sulentic and William Tifft and published by the University of Arizona Press in
1973. The first two articles discussed a total of 47 cases involving 65 corrections. In this article we will
examine an additional 22 cases involving misidentifications and incorrect classifications in the RNGC.
As the modern update of J.L.E. Dreyer's century-old NGC, published by the Royal Astronomical Society in 1888, the RNGC is probably the single most important catalogue for the serious visual observer. The NGC itself was the culmination of the visual observations of the several 18th and 19th century observers. Although modern catalogues contain more precise physical data and positions, the NGC contains the lasting legacy of William and John Herschel, Lord Rosse, Bigourdan and others – great visual observers who were enthralled with the beauty of the universe and who attempted to record their sightings as accurately as possible at the time.
Although these observers used scopes as large as the 48" equatorial of William Lassell and the 72" Leviathan of Lord Rosse, it is entirely possible for the modern observer with a 16" or larger scope, dark skies and an accurate star atlas or photographic charts to track down virtually every legitimate entry in the NGC. The new Uranometria 2000.0 contains the entire NGC and makes this a feasible project! I suspect that many amateurs, equipped with large scopes that are now becoming commonplace will be delving into the several thousand faint galaxies catalogues in the NGC.
In revising the NGC, the authors of the RNGC face the formidable task of identifying most of the NGC entries on plates from the Palomar Sky Survey, published in 1954. In rich fields containing several faint galaxies, choosing the correct NGC object can be quite difficult! But in many cases it is clear that the RNGC identifications does not match the original NGC entry in position or description. Despite these errors, the RNGC is generally an excellent reference source in the vast majority of cases, since it includes both the original NGC visual description and a photographic descriptions based on the its appearance on the POSS plates. In this spirit, I hope these RNGC errata lists will help lead to an accurate modern version of the NGC.
Most of the errors discussed in this article were uncovered while trying to reconcile my own visual observations with various modern catalogues. I wish to thank Malcolm Thomson who researched and confirmed many of these RNGC errors.
NGC 77: Discovered by Frank Muller using the 26" refractor at Leander-McCormick observatory in Charlottesville, Virginia. Although their discovery positions were generally very imprecise due to poorly calibrated circles, Howe corrected the position to 00h 17.5m -22d 48m (1950). Examination of the POSS reveals a small, faint galaxy located precisely at this corrected position and this galaxy is identified in the ESO and Southern Galaxy Catalogue (SGC) as NGC 77 = E473-G15. Furthermore, Muller stated a mag 9 star is 2.8' west (in PA 280 ) and on the POSS a mag 10 star is exactly 3' west-northwest in PA 282 . The RNGC incorrectly identifies NGC 77 as M-04-02-003 which is located 16' southwest of Howe's corrected position.
Using the Guide Star Catalogue position, the 1975 coordinates for NGC 77 should be changed to 00 18 45.9 -22 40 15 and the data updated to describe E473-G15 (0.4'x0.4', 15.7B).
NGC 308: On 31 Dec 1866, Ball (one of Lord Rosse's assistants) recorded a faint nova 52" SE of NGC 307 in PA 150 (mean of two measures). In this exact position is a 15th magnitude star measured by Harold Corwin which Ball apparently mistook for a very small nebulous object. The RNGC mistakenly identifies N308 with an extremely faint anonymous companion to N307 situated 3.0' SW (mentioned in the UGC notes to N307). So, the type of N308 should be changed to 7 and the new description "=*".
NGC 447, 449: This field of galaxies involves several identification problems based on the NGC/IC entries for N443, 447, 449, 451, 453 and IC 1653, 1656, 1661. The IC listing are likely duplicate entries as follows: N443 = I1653 (poor declination given by d'Arrest for N443), N447 = I1656 and N451 = I1661.
Based on the NGC positions, the RNGC has reversed the identifications of N447 and N449 whose correct orientations should be sp-nf. UGC and CGCG misidentify N447 as N449 = IC 1656 and the N449 is identified as IC 1661 in CGCG. MCG identifies these galaxies correctly. The correct positions and identifications are summarized below:
RA (2000) Dec Identification 01 15 37.6 +33 04 00 N447 = I1656 = U00804 = M+05-04-006 = Z502-013 01 16 07.2 +33 05 23 N449 = I1658 = M+05-04-009 = Z502-018
NGC 1264: This member of the Perseus galaxy cluster (Abell 426) was discovered by Bigourdan at 03 18 00 +41 31.6 (2000). The RNGC misidentifies N1264 as Z540-085 = Chincarini-Rood 15 located at 03 17 51.1 +41 27 03 (2000). Bigourdan placed N1264 21.6' south of N1265 which he also discovered and precisely at this offset is U02651 at 03 17 59.5 +41 31 14 (2000). This galaxy is correctly identified in UGC and MCG (M+07-07-050).
NGC 2721: This galaxy was discovered by William Herschel as II 529 and reobserved on two occasions by John Herschel. The NGC position exactly matches a moderately bright galaxy listed as M-01-23-015 and located at 08 58 56.5 -04 54 07 (2000). The declination given in the RNGC is 18' too far north. This mistake was noticed while using the U2000 atlas to star hop to this galaxy and verified on the POSS. Coincidentally, the MCG declination (copied into DSFG) is also 9' too far north (all the M-01-23-XX galaxies must be shifted 9' south).
NGC 2912: Discovered by Herman Schultz in his observation of N2911 and described as "follows h608 [N2911] some seconds about 2' north; but not observable". I'm not sure of his last comment but 1.3' ENE of N2911 is an extremely faint, extremely small, low surface brightness galaxy at 09 33 51.2 +10 09 30 (2000). A mag 14-15 star is 35" following. This galaxy is not listed in any of the modern catalogue except RNGC and based on its appearance on the POSS, I feel the identification is uncertain although this object does match Schultz's location. I missed detecting his galaxy in my 17.5" while viewing N2911.
NGC 3917: This nearly edge-on galaxy was found by William Herschel (II 824) although his polar distance was in error by 1 degree. The equivalence with John Herschel's h994 was noted by Dreyer, so the identification N3917 = U06815 is certain. The RA in the RNGC is 0.7 minutes following the correct place 11 49 26.8 +51 57 53 (2000).
NGC 3921: Once again, the RNGC has a poor RA and the listed position is 0.5 minutes of RA too far east. The position is correctly given in all other modern catalogues. RC3 gives a 2000 position of 11 51 06.1 +55 04 39.
NGC 3999: This entry is one of several galaxies discovered at Birr Castle in the N4005 cluster. According to the 25 April 1878 discovery notes, the position with respect to a mag 8 star (SAO 82077) is 277" in PA 201.3 (SSW). In this exact offset is the faint galaxy Z127-117 at 11 57 56.5 +25 04 05 (2000) and the CGCG identifies this galaxy as N3999. The RNGC position (and identification?) is clearly in error being 0.4 minutes of RA too far east and 4' north. The 1975 coordinates should read 11 56.7 +25 13.
NGC 5469: This object was discovered by Tempel in the N5416 group and described in his list VIII (AN 2527). This is a confusing situation because Tempel's observation appears to place this object 24s of RA following N5482 although Dreyer misinterpreted his description as following N5463. So the NGC position is incorrect. The RNGC has misidentified N5469 as Z074-062 = M+02-36-018. This galaxy is a close companion of N5423 and is roughly 90' from Tempel's position.
Harold Corwin has suggested that N5469 may be either Z074-121 or Z074-122 which both follow N5482 , although neither of these galaxies is a perfect fit.
NGC 6237, 6245, 6248: These three entries are from Swift from a group he discovered which also includes N6232 and N6236 and involve several errors in the RNGC and other catalogues. His positions for N6232, N6236 and N6248 match up reasonably well with the following galaxies at 2000 positions:
N6232 16 43 20.2 +70 37 57 =U10537 = M+12-16-007 = Z339-016 N6236 16 44 35.8 +70 46 50 =U10546 = M+12-16-008 = Z339-019 N6248 16 46 22.5 +70 21 21 =U10564 = M+12-16-009 = Z339-020 Now compare the following RNGC identifications and positions
It is clear that the galaxy identified as N6237 in the RNGC is actually N6248. Furthermore, the identification of N6248 is clearly in error in the RNGC (also in CGCG) and refers to the anonymous galaxy M+12-016-027 = Z339-036
There is no object at or near Swift's original position for N6237, so this object should be listed as nonexistent in the RNGC although Harold Corwin notes it is possible that N6237 is a duplicate entry for N6232 with a 1 minute error in RA (similar declinations).
Finally, The galaxy identified as N6245 in the RNGC is a good match with Swift's position (16 45 22 +70 48.3) although this galaxy is not "pL" as in the description and is too faint or small for inclusion in any other modern catalogues. On the POSS this galaxy appears >16pg and was not seen with my 17.5" on three attempts in dark skies. Based on negative sightings, this galaxy is probably too faint to be seen by Swift and N6245 should be listed as nonexistent in RNGC. Once again it is possible that this entry is a duplicate for N6236 with a 1 minute error in RA..
NGC 6297, 6298: These entries are from Swift (discovered 8 July 1885 and 1 Aug 1885) as a close pair located between two stars and the orientation of the pair is given as sp-nf.
Swift's position for N6297 was 20s of RA too far west, but Bigourdan observed and corrected the RA so the identification is clear. This galaxy (U10690) is situated between a mag 12 star 1.8' ESE and a mag 13 star 0.9' WNW and is located at 17 03 36.6 +62 01 33 (2000).
But Bigourdan failed to find N6298 and examination of the POSS reveals there is only a single galaxy between the two stars mentioned by Swift The RNGC incorrectly identifies N6298 as a member of an extremely faint triple group located 48s of RA following N6297 while Swift's position is just 5s following. Furthermore, the RNGC has a typo for the RA listing 11h instead of 17h. Most likely, N6298 is nonexistent although it is possible Swift was confused and recorded the same object on the two separate evenings.
NGC 6393, 6394: Swift recorded this pair of entries on 7 July 1885 (list I). His position for N6393 is an excellent match with U10889 = M+10-25-055 which is located 3.8' SE of mag 8 SAO 30431 at 17 30 21.4 +59 38 24 (2000). This galaxy was apparently also recorded by Swift in his list IX (object 81).
N6394 was placed 3.5' due north of N6393 but there is no object at this position on the POSS and Bigourdan was not able to locate a possible candidate. In an attempt to select an object for N6394, the RNGC identifies N6394 as M+10-25-054, although this faint galaxy is located about 7' SSW of N6393 and is not a viable candidate. Curiously, his descriptions for N6393 and N6394 are very similar, causing me to question is he somehow recorded the same object twice. In any case, the RNGC identification is in error and N6394 is nonexistent.
NGC 6470, 6471, 6472, 6477: N6477 was described by Swift as the last of 6 galaxies in a faint group including NGC 6456, 6463, 6470, 6471, 6472, and 6477. He recorded these objects on two nights: 1886, Jun 9 and 1886 Sep 25. There are several uncertain or invalid identifications in the RNGC (and other catalogues) including N6470, N6471 and N6472 and N6477 because of imprecise coordinates and similar descriptions ("eeeF, eS, R, eee dif") implying these were near Swift's visual threshold. In any case, the galaxy identified in the RNGC as N6477 is most likely Swift's N6472 at 17 44 03.0 +67 37 49 (2000). This galaxy is just 8s of RA following Swift's position of N6472.
Harold Corwin proposes that Swift's N6477 may be a faint galaxy at 17 44 30.6 +67 36 40 (2000), although this galaxy is 15s of RA preceding Swift's position and 1.5' south. It is also possible that Swift mistook a faint star for this object.
Returning to N6472, the listing in the RNGC (also UGC, CGCG, MCG) applies to N6470 = Z321-039 = M +11-21-025 located at 17 44 14.7 +67 37 10 (2000). In this case Swift's position is just 4s preceding this galaxy.
Continuing this reassignment, the listing under N6470 in the RNGC (again in UGC, CGCG, MCG) applies to N6471 = U10973a = Z321-038w = M+11-21-023 at 17 44 12.9 +67 35 35 (2000). Once again, Swift's position is a very good match, being only 2s of RA west of this galaxy.
Finally, the galaxy identified as N6471 in RNGC is U10973b = Z321-038b = M+11-21-024. This object is an extremely faint and compact companion off the SE edge of the real N6471 described above. I logged this galaxy as a mag 15 star 30" SE of N6471 and did not record a nebulous image.
NGC 6491, 6493: This pair of galaxies are from two Swift observations on 5 June 1885 and 13 June 1885 and recorded in AN 2683. He recorded a pair of galaxies described as NW-SE although the correct orientation is SW-NE. Assuming his error was confusing the orientations, then the RNGC has reversed the identifications of this pair and the UGC, MCG, CGCG and RC3 have the correct identifications. Here is a comparison of Swift's and Harold Corwin's measured 1950 positions for the pair:
N6491 HC 17 49 29.7 +61 32 38 #78 17 49 19.6 +61 32 37 N6493 HC 17 49 52.0 +61 34 14 #79 17 49 34.7 +61 31 19
I have some doubts regarding this solution. The single galaxy seen first on 13 June was #79 = N6493. Swift's position for this galaxy is actually just 5s of RA following and 1' S of the SW member of the pair. Also, it is reasonable to assume that Swift picked up the brighter galaxy on his first observation (the separation is only 3 arcmin) and the SW object is by far more obvious visually. In my 17.5", the NE galaxy was very difficult, appearing as a very low surface brightness spot which required averted vision (I probably would have missed it if I wasn't previously aware) while the SW galaxy was visible with direct vision and had a fairly prominent core.
Swift's position for #78 = N6491 exactly matches the brighter SW member in declination but is 10s of RA too small. Finally, neither of Swift's positions are a good match for the NE member in RA or declination. So, I would suggest N6491 = N6493 = U11008 = M+10-25-103 while the fainter NE galaxy U11011 = M+10-25-105 was not seen by Swift.
NGC 6607, 6608, 6609: These three numbers come from a large group of 8 galaxies (N6592, 6594, 6597, 6601, 6607, 6608, 6609, 6617) discovered by Swift on 14 June and 4 Aug of 1885. His descriptions for N6608 and N6609 both mention a faint star near and the last galaxy in the group does have a mag 14 star close south. Swift's 2000 positions for this trio are:
N6607 18 11 58 +61 19 59 N6608 18 12 13 +61 20 12 N6609 18 12 18 +61 20 13
Near this position is a close pair of galaxies with very similar declinations and 2.2' arcmin separation and a third extremely faint edge-on about 2' south of the pair. In my observation of the two galaxies on a parallel, I missed seeing the edge-on galaxy south and it appears extremely faint on the POSS. Curiously, Swift recorded N6607 as "eF" and both N6608 and N6609 as "vF".
N6607 18 12 14.9 +61 19 59 GSC N6608? 18 12 29 +61 18.0 edge-on gx not in GSC N6609? 18 12 33.6 +61 19 54 GSC
Assuming the first of these galaxies is N6607, then Swift's RA is 17s too large. Applying this offset, then N6608 and N6609 are both reasonable matches for the second galaxy although N6609 is an exact match. Probably because Swift gave N6608 and N6609 nearly identical declinations, CGCG has identified the pair as N6608 and N6609. Finally, RNGC and MCG both reverse the identifications of N6608 and N6609 suggested above.
I'm not convinced, though, that Swift viewed the edge-on because of its faintness and discrepancy in the declination.
NGC 6941: This galaxy was discovered by Stephan and his micrometric position pins down the identification N6941 = M-01-52-010 at 20 36 23.4 -04 37 07 (2000). This galaxy is incorrectly classified as a globular cluster in the RNGC and the error is repeated in NGC 2000.0 and early versions of the U2000.0 star atlas.
NGC 7076: This object was first recorded by William Herschel as III 936. His position was 7 min 54 sec following Alpha Cephei and 16' north. This places it at the 2000 position 21 26.5 +62 51. Just 2' north of this position is the planetary Abell 75 which was rediscovered by Abell but not associated with the NGC number. The ESO-Strausberg planetary catalogue also uses the Abell designation.
RNGC lists N7076 as a diffuse nebula instead of a planetary and furthermore the declination is 6' too far south. The ESO-Strausberg catalogue gives a precise 2000 position 21 26 24.1 +62 53 27.
NGC 7485, 7486: John Herschel recorded a single galaxy h2207 = N7485 at 23 06 02.9 +34 06 14 (2000) with a mag 10 star 5' preceding in the same parallel. This position is an excellent match to U12360 = M+06-50-022 at 23 06 04.9 +34 06 28 (2000) and both of these catalogues identify this galaxy as N7485. Furthermore, there is a mag 9 star 7' WNW matching Herschel's description.
The RNGC identifies N7485 as U12358 which is an extremely faint edge-on galaxy in PA 97 located 4.8' NW of N7485 = U12360 at 23 05 46.2 +34 09 15 (2000). I was barely able to view this galaxy in my 17.5" and it is certainly not the object recorded by Herschel. The correct data for N7485 is listed in the RNGC under N7486.
This field was observed twice at Birr Castle and the 1871 observation mentions a "D neb f a little s [of N7485]". In 1876 Copeland again logged this galaxy (GC 6251) as "vF, vS, undoubtedly seen, position angle 109.5 ± and distance 114 arcsec." This object entered the NGC as N7486. At this precise offset from N7485 is compact group of 4 faint stars which I also mistook as a nebulous object in my 17.5"! The GSC shows two of these mag 15 stars at 6" separation with a mean position of 23 06 13.2 +34 06 11 (2000). So, the type of N7486 should be changed 7 and the new description to "= group of 4 stars".