Coordinate Confusion with NGC 4437...and 4417 and 4517.

[Roelof Platenkamp]

Last night I acquired 2 hours on data of NGC 4437. After processing the galaxy looked rather different from what I expected. After a bit of research I found that the coordinates that ACP uses are actually the coordinates of NGC 4417!!
In addition, NGC 4437 and NGC 4517 are actually the same galaxy. The confusion stems from a handwriting error that dates back to 1940! See the two pictures of the Seligman Atlas:
Annotation 2020-01-30 091038.jpgAnnotation NGC 4437 2020-01-30 114902.jpg

So, I will now try again using NGC 5417 in ACP, these coordinates are correct and will yield the desired object.

Roelof

[Roelof Platenkamp]

Oops..of course I meant NGC 4517!!

[Dick Berg]

Hi Roelof,

Here are some interesting facts about this/these galaxies.

Here are the J2000 coordinates as they appear in the MiniSAC catalog. ACP uses it when you only specify the target name in a plan and not the coordinates as well.

NGC 4417 12.4474 9.583
NGC 4437 12.4467 9.583
NGC 4517 12.5460 0.100

From SIMBAD (http://simbad.u-strasbg.fr/simbad/) using "Query by identifier" these are the more precise J2000 coordinates:

NGC 4417 12.44740 09.58412 - galaxy in pair of galaxies
NGC 4437 12.54600 00.11504 - (SIMBAD reverts this ID correctly to NGC 4517
NGC 4517 12.54600 00.11504 - active galaxy nucleus

SIMBAD is an authoritative online catalog. As you discovered, 4437 and 4517 are actually the same object. The MiniSAC has it wrong in that it matches 4437 with 4417, again as you discovered. There are probably a few other errors in the MiniSAC, and most notable for me is that for M 67, MiniSAC does not point to what one would call the center of the cluster. There may have been a reason for that when the MiniSAC was first built, or when the source catalog used to create the MiniSAC was built, but that reason is probably forgotten.

Some research:

The first modern update of Dreyer's original NGC published in 1888 was done in 1973. ( Go to https://vizier.u-strasbg.fr/viz-bin/VizieR and search for "NGC") That catalog update marks NGC 4437 as "non-existent" and reassigns it (in error) as NGC 4417. This could have led to the error in the MiniSAC catalog. Here are four lines from that catalog - a bit difficult to unpack, but 4437 clearly says =4417. The digits 5 and 7 refer to "galaxy" and "non-existent" respectively. Following those numbers are the RA and Dec, followed by other designations relating to the Palomar Sky Survey used to update the original NGC.

1973Catalog.png

Now, from Dreyer's original 1888 catalog from (https://babel.hathitrust.org/cgi/pt?...view=1up&seq=7) (four attached images here), it shows that No. 4417, No. 4437 and No. 4517 were three different objects in this catalog, though 4437 and 4517 were very close to each other. Note that the coordinates are epoch 1860, and the declination is tabulated as North Polar Distance (= 90 - Dec). I've changed it to our conventional declination:

NGC 4417 12.329 10.360
NGC 4437 12.344 00.905
NGC 4517 12.434 00.852

[Roelof Platenkamp]

Hi David,

thanks for the additional information. I also use the SIMBAD database frequently (and Alladin, ViZer etc) as eminently reliable data sources. However, I had never seen Dreyer's original catalogue, thanks for sharing!
Given the enormous number of objects, we should not be surprised that even in the digital age occasionally errors do occur.

Kind regards, Roelof