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NGC 6610 (18,772 of 18,816)

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NGC 6610

NGC 6610, GC 5908

History and Accurate Positions for the NGC/IC Objects (Corwin 2004)

NGC 6610 is probably NGC 6574. There is nothing at the catalogued position of N6610, and there are no reasonable changes to the calculated offsets (+1m 0.11s, -4' 31.3") from Stephan's nominal comparison star ("208 W. (A.C.) H.XVIII") that point to anything aside from very faint stars.

However, about 1.3 deg north, and 1.75 minutes following Stephan's nominal position is a star-galaxy pair that matches the offsets to within Stephan's normal observing errors (the actual offsets are +59.77s and -4' 32.5"). The galaxy, UGC 11198, also matches his description pretty well. So, I had taken this to be a very good candidate for NGC 6610, with some sort of confusion in Stephan's observing records.

But the question about the identity had originally come from Leos Ondra who posted it to one of the astronomy forums on the Internet in 1999. There, it attracted the attention of Steve Gottlieb who did the same kind of digging back into the literature that I did, but did not come up with a candidate. Brian Skiff suggested that NGC 6574, about 5 minutes west, might be N6610, but noted that there is no comparison star at the correct offsets.

Leos also noted a paper by Seares in PASP 28, 122, 1916 titled "Identification of NGC 6610." Brian checked a copy of that paper and found that the object Seares suggests is actually a plate defect on an early plate of the area. The object is not on either POSS1 or POSS2.

Finally, Leos sent me a copy of a note that he had had "off-list" from Jim Caplan, a research astronomer at the Observatoire de Marseille where Stephan observed and was director between 1866 and 1907. Jim called attention to a monograph containing a complete re-reduction of Stephan's observations by a Monsieur Esmiol, presumeably one of the younger astronomers at Marseille. This was published in 1916 after Stephan's retirement, and carries not only the reduced positions, but mean values of Stephan's micrometric measurements, too. (I had seen a copy of this at the library at ROE in the late 1970s, but failed to make a photocopy for myself -- bad move!).

The observation previously leading to the NGC number 6610 is listed in the monograph under the designation "anonyme" with completely different offsets (-1m 42.63s, -0' 14.0" from six settings in RA and 3 in Dec) from a completely different star (BD +14 3453). A footnote reads "Class\'e \`a tort 6610" ("Called 6610 by mistake"); this is apparently the only published "explanation" of this particular case. Reducing these observations with the GSC position for the comparison star puts the position directly on NGC 6574.

So, it looks like Brian is correct, though for a different reason than he probably envisioned. I am still curious, however, about the extraordinary coincidence of the earlier calculated offsets with the UGC 11198/BD +16 3447 pair. Where did Stephan's originally published positions come from? Jim tells me that many of Stephan's original observing records and reductions are still in existence; we may be able to eventually find an answer to this question.

Published comments

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a nonexistent object. Their coded description reads NF S.

Modern observations

[amastro] Identity of NGC 6610?

Browsing through my planetary nebulae folders last night, I came across one lose end: NGC 6610, classified as 'nonexistent' in NGC 2000.0 (and the NGC databases on the NGC/IC website). NGC 2000.0's position is 18h17.2m, +15d00' (2000.0). The original NGC described it as 'F,S,E,mbM,r' (this should mean 'faint, small, extended, much brighter in the middle, resolvable [mottled]', though I don't know how one and the same object can be small and extended). The discoverer was Stephan (of the Stephan Quintet): Comptes Rendus 83:328.

Strangely, I found among my notes on this object also the following reference, given by Vorontsov-Velyaminov in his book 'Gasnebel und Neue Sterne, p. 673): Seares, F., 'Identification of NGC 6610', PASP 28:122, 1916. This may be some misprint or so, but if someone interested has the volume at hand, I would be much interested in the results.

Clear skies, Leos

******************************************************

Leos Ondra, Skretova 6, 621 00 Brno, Czech Republic

ondra@bm.cesnet.cz

http://www.bm.cesnet.cz/~ondra

------------------------------------------------------------------------

Leos,

Only the 1st 1000 NGC designations are up-to-date in the public database on the Project's web site, so I went sleuthing in Dr. Corwin's notes to see if he at least had a precise position for it, or a paper chase/sleuthing trail documented, but alas, no such luck. It's very rare that he doesn't have a position for an NGC designated object, as if it's non-existent then he'll usually have the original 1860 position precessed to 1950. In this case, he doesn't, and he doesn't have a position for NGC 6611 either! Harold is still working on these precise position files, so suspect some additions/corrections to this entry in the not too distant future.

In any event, I've forwarded your e-mail on to Dr. Corwin as I'm not sure if he's a member of this list or not.

Thanks much!

/Bob

------------------------------------------------------------------------

The note by Seares says that there is nothing in the nominal NGC location of NGC 6610, and suggests there is small nebula at a place 10s further east. This appers on only a single plate, and there is nothing on the DSS here; almost certainly a plate defect. Seares' position is: 18 11 26 +14 57.2 (1875), which precesses to 18 17 06 +14 59.8 (2000). Looking at the DSS using SkyView (i.e. at the POSS-I red plates) gives a good example of what happens in the overlap region where one plate has good seeing (the +12 zone plate) and the other has poor seeing (+18 zone).

\Brian

------------------------------------------------------------------------

]Browsing through my planetary nebulae folders last night, I came

:

]Comptes Rendus 83:328.

Here is what I've found on N6610:

Stephan's original description (without accents) in Comptes Rendus reads: "Petite; faible; ovoide; belle condensation; parait resoluble." So, there is nothing much here to add to the NGC translation.

Stephan's original micrometric position:

Position for 1876: 18 11 39.45 +75 02 34.2 (North Polar Distance)

Again, Dreyer precessed this correctly in the NGC:

Position for 1860: 18 09 55.9 +75 02 50 (NPD) and

Position for 2000: 18 17 16.4 +15 00 03

Stephan also gave the position of this reference star (but not his offsets):

Position for 1876: 18 10 39.34 +74 58 02.9 (NPD)

Position for 2000: 18 16 16.0 +15 04 23 (2000)

This star is now known as BD+15 3419 = PPM 134481 = SAO 103545 with an

accurate position of 18 16 16.2 +15 04 17 (J2000)

There are no nonstellar objects near Stephan's position. Very close, though, is a star (GSC 1568-1439) at 18 17 17.2 +15 00 05 (J2000). Bigourdan was unsuccessful in recovering N6610 but Karl Reinmuth (Die Herschel-Nebel, 1926) in his photographic survey describes N6610 as "vF, S, lbM, v diffic; *10.7 sp 1.3'." This description appears to describe a clump of faint stars located at 18 17 21.4 +15 01 40 (J2000) with the nonstellar GSC designation 1568-1351.

So, that leaves us with a single star at 18 17 17.2 +15 00 05 or the clump of stars at 18 17 21.4 +15 01 40.

There are a couple of other possibilities -- Stephan may have confused the identification of his reference star with another 9th magnitude star or he may confused the direction of offset (such as north-south). If anything else shows up I'll let you know.

Steve Gottlieb

------------------------------------------------------------------------

Just a shot in the proverbial dark: I notice that NGC 6574 is closely 5m RA west of the nominal location. Apparently no decently bright offset star nearby, though.

For those new to NGC/IC sleuthing, Steve G.'s post was a model of how it's supposed to be done: going to primary sources and working forward.

\Brian

------------------------------------------------------------------------

Harold Corwin Jr

Hi, folks,

Leos Ondra led off some chat lately about NGC 6610. It turns out that the published evidence is conflicting. The original NGC source published by Stephan in Comptes Rendus 83, 328, 1876 (copied correctly into NGC by Dreyer) leads to differences of +1m 00.11m and -4' 31.3" in RA and Dec between the nebula and Stephan's nominal comparison star. About a degree north is the galaxy/star pair UGC 11198/BD +16 3447 with differences of +59.77s and -4' 32.5" (all at equinox 1876.0), within Stephan's usual observing errors of the differences from his first published numbers. So, I suggested that NGC 6610 = UGC 11198.

However, Jim Caplan at l'Obs. de Marseille has pointed out that one of Stephan's younger colleagues, E. Esmiol, at Marseille re-reduced all of Stephan's observations. These, including the mean values of Stephan's micrometric measurements, were all published in a monograph in 1916. There, the micrometric measurements for NGC 6610 (called "Anon" throughout the monograph) are given as -1m 42.63s, and -14.0s from the star BD +14 3453. Going through the math leads exactly to NGC 6574, already suggested by Brian Skiff as a possible candidate. Brian has also looked into a 1916 PASP note on the object published by Seares -- Seares's object was probably a plate defect.

I'm still curious as to how Stephan came up with the numbers he published in his 1876 CR paper. In particular, if the differences published by Esmiol in 1916 are correct, how do Stephan's original numbers happen to lead to position differences so closely resembling a star-galaxy pair in the same area of the sky? Jim tells me that much of Stephan's original material (observing logs, reduction papers, etc) survives at Marseille. He will check into this if he can find some spare time this summer.

In the meantime, I'm quite happy with NGC 6610 = NGC 6574. Not only do the revised micrometric data fit, but so does the description (unchanged in Esmiol's 1916 monograph). UGC 11198 is quite a bit fainter than is usual Stephan's notation "F", but is still bright enough that he could have seen it. But NGC 6574 clearly fits better.

So, the case not quite closed -- but is getting there. Best to all, Harold

------------------------------------------------------------------------

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