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Albany, CA 94706
After I return home with my notes from an evening of deep sky observing, I like to compare my
observations with as many different sources as possible and verify that I did indeed observe the
object in question. I'll use various deep sky catalogues to check brightness, size, orientation, etc.
and also visual reports from astronomy magazines and personal correspondences. For bright
well-known objects there is no problem of identification, but for the vast number of extremely
faint NGC galaxies that is not always the case. While trying over the past several years to survey
the entire NGC with my 17.5", I've run across many NGC entries which appear erroneous in some
manner as listed in the 1973 RNGC update. In previous articles, a total of 69 cases involving 92
objects listed in the RNGC were discussed and a wide range of catalogue errors were noted
including misidentified objects, non-existent objects, incorrect coordinates and even object type.
I've been slowly accumulating a list of further errata uncovered while researching and verifying
my most recent observing notes. Although there has not yet been an update to Sulentic and Tifft's
RNGC, Roger Sinnott has recently edited an update to the NGC and IC, entitled NGC 2000.0
(Sky Publishing Corporation, 1988), which has incorporated many of my corrections and others
submitted by Dr. Harold Corwin of the University of Texas at Austin and Dr. Malcolm Thomson
to provide a much more accurate modern NGC and IC for epoch 2000.0.
In this article, 18 further cases are discussed and I've tried to arrive at the most reasonable conclusion for each. In some cases, an ambiguity still remains which may be difficult at this point to resolve. Most of the situations discussed involve very faint galaxies not usually found on amateur observing lists and for the vast majority of cases, the RNGC can be considered a reliable modern catalogue for NGC entries. Nevertheless, as more observers using 16" or larger scopes routinely reach the faintest NGC objects still more of these problem cases will come to light and cause confusion. If you encounter an ambiguous or erroneous entry in your deep sky observing, please send me a note and it may be included in future versions of the NGC.
NGC 930, 932: N932 was discovered by William Herschel and is the brightest member of a small group of galaxies. On 26 October 1872, Ralph Copeland using Lord Rosse's telescope noted a second object which is placed at 60" separation in PA 314.3 (NW). This object was not mentioned in the subsequent three observations of N930 but Dreyer included it as N930 when he compiled the NGC. I carefully examined the POSS print containing this field and did not find any object at Rosse's position although there is a small red condensation with dimensions 0.15'x 0.15' at the northeast edge of the galaxy. The RNGC mixes up the identifications and lists the main galaxy as N930 and calls N932 non-existent. Since Herschel was definitely the first to observe this galaxy, his number N932 should apply and the data listed in the RNGC under N930 should be transferred to N932. It is possible that Rosse's nova N930 refers to the red condensation mentioned above, although it is extremely faint and the position angle is incorrect.
NGC 2957: This galaxy was discovered by John Herschel as h617. His RA is exactly 1 minute too far west but his description of a "*13m near" matches a similar star off the SW edge. This galaxy is located 3' WNW of brighter N2963 which was discovered by his father William and reobserved by John on the same night he discovered N2957. John's offset from N2963 of 32s in RA pins down the identification N2957 = M+12-10-001+2 = Z332-064. Looking over the RNGC data, it is clear that the entry for N2957 is simply a duplicate of N2963. N2957 is a double system with dimensions 0.8'x0.3' and 0.4'x0.2' and a combined photographic mag of 15.3z. So, all columns referring to N2957 need updating to reflect this change in identification and the position changed to 09h 45.0m +73 06' (1975).
NGC 3704, 3707: These two entries are attributed to both Ainslie Common and Wilhelm Tempel in the NGC. Common's description in Copernicus, Vol 1 reads "2, F, R, on the parallel, star symmetrically placed between." At 13' due south of Common's single position (obtained from the setting circles) is a very faint pair of galaxies observed in my 17.5". The first of these galaxies is N3704 = M-02-29-037 at 11 30 04.6 -11 32 48 (2000) which has a mag 15 star 42" following. N3704 also has an extremely faint and compact companion 1.7' east with the mag 15 star between the galaxies as in Common's description, so it is a reasonable match for N3707 at 11 30 11.6 -11 32 37. For some reason, the RNGC ignores the second fainter galaxy of the pair and lists N3707 as nonexistent.
Unfortunately, the NGC summary descriptions (from Tempel?) have some errors. The listing for N3704 mentions a mag 9-10 2' SSE of N3704, although the bright star is actually 2.6' WNW. Additionally, the description for N3707 mentions a "*15 (neb?) 2s following", which actually describes the mag 15 star 2.8s following N3704. Nevertheless, Common's description is sufficient to identify this pair of galaxies.
NGC 3950: In the observations of N3949, the observers at Birr Castle picked up a faint companion described on 31 Mar 1872 as "comp neb n about 2.5'." A later micrometric observation on 27 Apr 1875, placed this nova in position angle 356.5 , distance 154.6". At Lord Rosse's position there is a very faint galaxy (also catalogued as Ho 301b) which was observable in my 17.5" and verified on the POSS. Reinmuth also identifies this galaxy as N3950 in his 1926 photographic survey Die Herschel-Nebel. Instead, RNGC identifies N3950 with another very compact companion located almost 5' north of N3949. The RNGC 1975 coordinates of N3950 should be changed to identify the galaxy at 11h 52.4m +48 02' and the other columns updated to reflect this change.
NGC 4399, 4400, 4401: These 3 entries refer to bright "knots" or huge H11 regions within the low surface brightness galaxy N4395 discovered by William Herschel as V 29. His description reads "eF, vL, vlbM, r, 10'l, 8' or 9' b." John Herschel was the next to observe this low surface brightness galaxy and recorded "two nebulae running into one another; both eF, vL, the f rather the brighter. The positions of these two components are given individually and Dreyer used these as N4395 (V29.1) and N4401 (V29.2) in the NGC. The following component is actually the brightest of the large "knots" in N4395.
This galaxy was viewed on three occasions at Birr Castle and with the larger aperture recorded "a cluster of nebulae found" on 13 Apr 1850 and "there are 4 nebulae. The 3 f ones seem to be inv in a mass of F neby." Based on these observation, Dreyer included two additional entries: N4399 and N4401.
The sketch of these condensations made by Rosse match up well with my own observations with a 17.5" and can be identified on the POSS. Since these regions are visually observable, the appropriate RNGC type should be changed to "35" which designates a diffuse nebula within a galaxy instead of being listed as nonexistent.
NGC 6164, 6165: These entries refer to the two lobes (oriented NW-SE) of an unusual nebulosity discovered by John Herschel (h3633 and h3634). Although listed as a planetary in the RNGC, it is currently classified as an H11 region. So, the type of these two NGC entries should be change to 3 (Diffuse Nebula).
NGC 6270: This galaxy was recorded by first by Marth in 1864 and then by Stephan in 1870 in a group of 7 faint NGC galaxies. Dreyer included both observations as a single NGC entry as he did with their dual observations of N6263, 6264, 6265, 6269. Both observers placed N6270 46s of RA following N6269 = U10629 = M+05-40-012 which is located at 16 57 58.5 +27 51 19 (2000). Inspection of the POSS reveals a galaxy at this precise separation from NGC 6269 in the position stated by Marth and Stephan at 16 58 44.0 +27 51 32 (2000). The RNGC incorrectly selects as its candidate for N6269 an anonymous galaxy catalogued as MCG+05-40-015 which is located 9' east of N6269 but also 14' south! So, the RNGC has clearly misidentified N6270 and the position should be changed to 16 57.7 +27 54 (1975) and data changed to describe this galaxy.
NGC 6276, 6277: Although this pair of galaxies are attributed in the NGC to both Marth (m327, m328) and Stephan (List 2), Dreyer followed Stephan's micrometric positions close north- preceding N6278 in compiling the NGC. But while going to press, Dreyer comments in the notes and corrections section of the NGC that in receiving Marth's original observations it is clear that Marth's following object m328 = N6276 and m327 is a different preceding object (relisted as IC 1238).
Stephan's positions clearly give the following identifications:
N6276 17 00 45.1 +23 02 39 = M+04-40-010 = Z139-028 N6277 17 00 48.8 +23 02 22 =star N6278 17 00 50.3 +23 00 40 =U10656 = M+04-40-011 = Z139-029
The RNGC incorrectly identifies N6276 as the faint anonymous galaxy UGC 10650, located about 10' NW of N6278. Additionally, the data listed in the RNGC under N6277 actually applies to N6276.
NGC 6581: This galaxy was discovered by Stephan (I). The coordinates of his 8th magnitude offset star are off a bit and when this correction is applied (11s of RA and 30" of dec) his micrometric position is 18 12 20.3 +25 39 40 (2000). This corresponds almost exactly with M+04-43-010 = Z142-021 located at 18 12 18.4 +25 39 44 (2000). To further pin down this ID, Stephan's description mentions "between 2 faint stars" and there is a mag 14 star at the northeast end and a mag 15 star at the south end of this galaxy which were recorded in my 17.5" observation.
Bigourdan also recorded a "nebulous star" near N6581 although his position for IC 1280 is an excellent match with N6581. Because of this match, this galaxy is identified as IC 1280 in MCG, CGCG and UGC (notes to U11150). It seems logical to assume IC 1280 = N6581, although according to Malcolm Thomson, Bigourdan mentions both objects in the same observation (could he have mistaken N6581 because of the error in Stephan's position?)
The object identified as N6581 in the RNGC is U11155, which is part of a double system with IC 4697 in the UGC 11156 galaxy group and is located 13' south of Stephan's position.
NGC 7065, 7065A: The RNGC positions are offset 2' south from the following GSC 2000 positions:
N7065 21 26 42.4 -06 59 42 =M-01-54-017 N7065A 21 26 57.8 -07 01 18 =M-01-54-018
Coincidentally, this causes the RNGC declination to actually match that of N7065A although the RNGC orientation is correct.
Dreyer attributed N7065 to both Marth (m440) and d'Arrest. He noted a slight discrepancy in their position and decided to use d'Arrest's position for the NGC. Their individual positions precessed to 2000 are:
m440 21 26 58 -07 02 d'A 21 26 45 -07 00.1
Comparing these positions with the GSC strongly suggests that while d'Arrest observed the galaxy identified as N7065, Marth actually recorded the companion galaxy N7065A! Both of these faint galaxies were visible in my 17.5" and neither was significantly more prominent. So, it is possible that N7065A = M-01-54-018 should have been included by Dreyer as a separate entry from Marth.
NGC 7112, 7113: These objects were found by Swift in July 1886 and Marth in April 1863, respectively. Their discovery positions (precessed to 2000) and descriptions are as follows:
N7112 21 42 20 +12 34 47 eeF, S, R, pB* with dist companion close p; v diff. N7113 21 42 27 +12 37 vF, S, stell
The RNGC and CGCG identify these numbers with the following two galaxies:
(R)N7112 21 42 22.9 +12 29 54 =U11794 = M+02-55-010 = Z427-014 (R)N7113 21 42 26.7 +12 34 09 = M+02-55-009 = Z427-016
MCG does not assign a NGC number to the first galaxy but identifies the second galaxy as N7112.
Marth's position for N7113 is 3' too far south but is an exact match in RA. Swift's RA for N7112 matches M+02-55-010 although his declination would then be 5' off and actually matches N7113. Furthermore, his description "pB* with dist companion p" applies to N7113 as mag 8.7 SAO 107337 is located 1' preceding. This bright star also has a "distant companion", which is a mag 13 star 53" ENE. Finally, if Swift was not aware of Marth's discovery then he most likely recorded the brighter of the pair which is N7113. So, based on Swift's visual observation seems reasonable to assume N7112 = N7113.
NGC 7129, 7133: These two numbers refer to a bright reflection nebula some 5' x 4' in extent involving 3 stars of mag 9-10 (N7129, discovered by WH) and a very faint reflection nebula about 3' long involving 2 stars of mag 12 to the northeast (N7133, discovered by Bigourdan). The latter object may just be a fainter extension of N7129.
William Herschel described IV 75 as "3 stars about 9m involved in nebulosity." This nebula was reobserved by John Herschel and his description is similar: "a very coarse triple star involved in a nebulous atmosphere." His mean position for one of these stars is: 21 42 59.0 +66 06 12 (2000).
The RNGC places N7133 to the southeast of N7129 which disagrees with the orientation on the POSS and also their own rectangular coordinates. In addition, the 1975 position for N7129 in the RNGC, 21 40.7 +65 59 (2000), is off by 1.7 minutes of R.A. based on inspection of the POSS. So, the 1975 coordinates of N7129 should be changed to 21 42.4 +65 59 and the position of N7133 also requires a similar modification in RA.
NGC 7413, 7414: On 2 Sept 1886 Swift recorded the following two objects in his list 4:
N7413 22 54 48 +13 13 05 (2000) eeF, pS, R, e diff, 8 or 10 st. in an irregular line p, s of 2 N7414 22 54 48 +13 15 35 (2000) eeeF, S, R, eee dif, n of 2
According to these positions, Swift placed N7414 2.5' due north of N7413. Using the 20" refractor at Chamberlin Observatory, Herbert Howe made a number of micrometric measurements of NGC objects and corrected the position of N7413 14s further east. This would place N7413 at 22 55 02 +13 13 05 (2000). This position matches up precisely with the following galaxy at the following GSC position for 2000. Furthermore, there is a string of stars to the SW exactly matches Swift's description.
N7413 22 55 03.1 +13 13 14 =M+02-58-035 = Z430-029
No galaxy exists at either Swift's original position for N7414 or by applying Howe's offset although there are a couple of very faint stars about 2' N of N7413. Instead, the RNGC has identified N7414 with an extremely small and faint anonymous object located 5' ENE of N7413. So, N7414 should be listed as nonexistent in RNGC with a possible identification as a faint star.
NGC 7553: This object was by the Rosse observers in a group of galaxies with brightest member N7550. Neither Rosse nor Schultz, who also examined the field, gave specific positions for this object so I'm not sure how Dreyer arrived at the NGC position. A diagram of the field was made at Birr Castle on 6 Oct 1877 and confirmed on 10 Oct 1877 and the four galaxies, N7547, N7549, N7550 and N7553 are shown. Although the direction of drift shown is somewhat off, it is easy to match the objects sketched with the POSS with the exception of N7553. The brightest galaxy near Rosse's position is Z454-015 at 23 15 32.9 +19 03 01 (2000) and this is the galaxy identified as N7553 in RNGC (with imprecise coordinates).
Although it is very possible that this was the object seen at Birr Castle, the sketch does not match up well with this galaxy and actually falls closer an extremely faint star and galaxy at 23 15 38.7 +18 58 25 (2000) which may be too faint to have been picked up visually. Finally, there is a close double star near Z454-015 at 23 15 36.3 +19 01 54 (2000) but probably the galaxy would be more prominent.
Assuming the RNGC has identified the correct object, the 1975 position should be modified to 23 14.3 +18 55.
NGC 7740: Discovered by Bigourdan and placed at 23 43 30 +27 19 (2000). At this location is the mag 14.9z galaxy Z476-123, with a precise position 23 43 32.2 +27 18 42 (2000). The RNGC and CGCG both identify N7740 with a much fainter galaxy (Z476-122, 15.6z) located 4.3' NW of Z476-123.
Having viewed this field with my 17.5", I can state that Z476-123 is definitely much more conspicuous visually. In conjunction with the nearly perfect match in coordinates, it is clear that CGCG and RNGC have both misidentified N7740. So, the 1975 coordinates for N7740 should be changed to 23 42.3 +27 10, the magnitude changed to 15.0 and the new description updated to describe Z476-123.
1. Gottlieb, S.; W.S.Q.J. No. 76, April 1989. 2. Gottlieb, S.; W.S.Q.J. No. 72, April 1988. 3. Gottlieb, S.; W.S.Q.J. No. 64, April 1986. 4. Sulentic, J. & Tifft, W.; 'A Revised New General Catalogue', University of Arizona Press,1973. 5. Dreyer, J.L.E.; 'New General Catalogue...', R.A.S., London, 1888. 6. Rosse; 'Observations of Nebulae & Clusters of Stars...', Royal Dublin Society, Dublin, 1880. 7. Nilson, P.; 'Uppsala General Catalogue of Galaxies', Uppsala, 1973. 8. Zwicky, F.; 'Catalogue of Galaxies & Clusters of Galaxies', Calif Institute of Technology, 1961-68. 9. 'Palomar Observatory Sky Survey', National Geographic Society, Calif Institute of Technology, 1954. 10. Sinnott, R.; 'NGC 2000.0', Sky Publishing Corporation, 1988.