NGC/IC Project Restoration Effort

===== 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 Monsieur E. 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! I have had a copy for several years now courtesy of Jim Caplan, and it has come in handy several times.) 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. Finally, see the "notngc" files under UGC 3840 for more about Stephan's observations.

===== NGC 6610 See observing notes for NGC 6574. Identification uncertain.