Colliding Galaxy pair NGC 3690 (aka Arp 299) and Spiral IC 694
with Supernova 2005U

CCD Image taken at 4:20 UT on Feb 6, 2005 using an SBIG STL-1301E camera thru Kopernik's 20 inch F/8.1 telescope. The exposure was 12 minutes. North at top; the field of view is about 13x12 arc minutes. The 1998 image is a 10 minute exposure with an SBIG ST-6 camera.

Supernova 2005 U:

        Galaxy Pair NGC-3690 (Arp 299):

        These two galaxies (NGC 3690, Arp 299, IC 694?) in Ursa Major are a colliding or merging pair that are a strong radio and infrared source.  They are a chaotic mix of intense star forming regions and dust clouds with no disk-like structure. This is one on the most intense star burst systems known. H. Arp included this galaxy pair in his catalog of oddly shaped galaxies as Arp 299.

NGC 3960 - Arp 299 has been host to perhaps six Supernovae in the past decade: 1990al, 1992bu, 1993G, 1998T, 1999D, and now 2005U. Supernova 1993G (Type II), 1998T (Type Ib/c), and 1999D (Type II) have been spectroscopically classified; the other two possible Supernovae (1990al and 1992bu) have been identified only in the radio and infrared, respectively.

Which Galaxy is IC-694?

IC 694 was discovered by Swift in 1893. His discovery description reads "close double with NGC 3690 = object 247 of list I of Sir William Herschel. Suspected at 132x magnification, verified at 200x." In the Index Catalogue of Nebulae (IC; Dreyer 1895) this becomes "very small, forms double nebula with no. 247 of list I of Sir William Herschel." The position for IC 694 is given as 11:20:44 +59:20 (epoch 1860) in the IC, while the NGC position for NGC 3690 is 11:20:45 +59:19; i.e., IC 694 lies approximately 1 arc minute to the northwest of NGC 3690. This seems to be pretty conclusive evidence that IC 694 refers to the spheroidal galaxy MCG 10-17-2A. However, Dreyer remarks in the introduction to the IC that Swift's positions are "generally reliable within one or two minutes of arc, but larger errors occur occasionally." We also learn from Dreyer that Swift's observations were taken through the 16-inch refractor at Rochester Observatory. Since the spheroidal galaxy is 3 magnitudes fainter than either of the disk galaxies, is it even possible for Swift to have seen it? If not, is it likely that he simply resolved NGC 3690 into two separate condensations of nearly equal luminosity, adding a separate catalogue entry for the second system? Recent attempts to repeat these observations with similar-sized telescopes by amateur astronomers suggest that (1) the second light concentration that we now associate with Arp 299 East is very easy to discern as distinct from Arp 299 West and (2) the spheroidal is indeed a very difficult, but not impossible object. Combined with the correct relative position of IC 694 given by Swift, it seems that there is strong evidence that IC 694 properly designates the northwest compact spheroidal. However, since these observations were made with prior knowledge of both the existence and location of the northwest spheroidal, this confirmation is not entirely independent. It is also possible that Swift actually saw barred spiral galaxy MCG 10-17-5.

Starting with Vorontsov-Velyaminov in 1959 modern professional astronomers began referring to the eastern member of the Arp 299 pair as “IC-694”, and this identification is used in most scientific papers.  Sulentic & Tift (1973) concluded that "any further question as to which objects Dreyer was referring to can only be of historical interest."

Info thanks to Harold Corwin, Steve Gottleib, Malcom Thomson, Bill Vacca, and Dennis Webb.

This is the data on Galaxies NGC 3690 and IC 694

NGC 3690

  • Magnitude: 12.1
  • RA: 11h 28m 33.6s
  • Dec: +58d 33' 52" Epoch 2000
  • Size (mins) 2.0 x 1.5
  • Constellation Ursa Major
  • Description
    Deep Sky Field Guide to Uranometria 2000:
    Disrupted double system in contact with IC 694;
    two very complex nuclei separated by 0.3 arc min.

de Vaucouleurs classification: I pec: Irregular, peculiarities.

IC 694

  • Magnitude: 12.1
  • RA: 11h 28m 31.3s
  • Dec: +58d 33' 28" Epoch 2000
  • Size (mins) 1.2 x 1.0
  • Constellation Ursa Major

de Vaucouleurs classification: SBm?: Barred Spiral (uncertain,
much doubt).

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George Normandin, KAS

February 11th, 2005