Results 1 to 4 of 4

Hybrid View

  1. #1

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

    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

  2. #2

    Default

    Oops..of course I meant NGC 4517!!

  3. #3
    Join Date
    Nov 2005
    Location
    Virgil, NY
    Posts
    5,124

    Default

    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
    Attached Files Attached Files
    Dick
    www.VirgilObservatory.us
    Pier-mounted Meade 12-inch SCT "classic"
    w. focal reducer to f/5.3 ~ FL 1630mm
    Optec TCF-S focuser
    SBIG CFW-8A and ST7-XME
    FOV ~ 15' x 10'
    H-alpha, BVRI, RGB & Clear filters
    MaxIm and, of course, ACP!
    AAVSO Code: BRIC

  4. #4

    Default

    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

 

 

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. ACP and Astro-Physics startup and coordinate issues [SPLIT - new thread]
    By Michael Miller in forum Hardware/Software/Driver Topics Not Directly Related to Our Software
    Replies: 34
    Last Post: May 6, 2016, 02:51
  2. Flip confusion
    By Jeffrey Jongmans in forum Hardware/Software/Driver Topics Not Directly Related to Our Software
    Replies: 29
    Last Post: Feb 12, 2014, 00:43

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •