NGC 3690 / IC 694 (Arp 299, UGC 6472 / UGC 6471) Galaxies in Ursa Major

Located at: RA 11 hours 28 minutes 33 seconds, Dec +58 degrees 33 minutes 56 seconds

Size: 1.5' x 1.0' / 1.1' x 0.9' Magnitude: 12.0 / 12.1 photographic Class: IBm pec (HII; LIRG)* / SBm? pec (Sbrst AGN)*

 North is up

West to the right


 14.5" f5 Newtonian reflector


  ST-8XME, self-guided, binned 1x1, temp -20, camera control MaxIm DL 4.56


Lumicon Red filter, 680 minutes (68 x 10 minute subs), 03/6/7/8/2017; FWHM 2.5-4.3 per CCDStack


CCDStack 2.93.6093.26774, Photoshop CS5.1


 Rolling Roof Observatory, Thousand Oaks, CA 91360 (+34d 13m 29s -118h 52m 20s)


As usual, with the near full moon brightening in the east (see NGC 3319), I have moved to the north to image ... this one had a tough background to process, as the nearly full moon almost shined down the tube the last two days of imaging. IC 694 is the smaller galaxy attached/below NGC 3690 ... the small galaxy northeast (upper left) of NGC 3690 / IC 694 is Arp 296 (0.7'x 0.4', mag 15.7; Cl: B).

From the NGC / IC Project:

NGC 3690 = Arp 299 = VV 118 = UGC 6471/2 = MCG +10-17-003/005 = CGCG 291-073 = Mrk 171a/b = Holm 256a/b = PGC 35321

11 28 32.3 +58 33 43

V = 11.5;  Size 2.9'x2.1';  Surf Br = 12.6;  PA = 50d


48" (5/12/12): at 488x, the southwest component (VV 118b) of NGC 3690 appeared as a very bright, elongated, irregular knot of high surface brightness.  Contains a very bright, quasi-stellar nucleus.  The northeast component (VV 118a) is the larger of the merged interacting pair and appeared bright, moderately large, ~1' diameter, small very bright core.  A very low surface, asymmetric halo extends on the northwest side of the bright pair.  The southwest component is generally misidentified as IC 694, which is described below.


VV 118d/e, probably HII regions, are just 45" NW of NGC 3690 (just outside the halo).  Occasionally an extremely faint and small glow popped in this position, 6"-8" diameter.  IC 694, ~1' NW of the bright pair, was easily visible as a fairly faint, slightly elongated glow, 15"x12", weak concentration.  PGC 35345 (the brighter component of Arp 296) lies 2.6' NE.  It was also a direct vision, fairly faint glow, fairly small, oval 4:3 NW-SE, 24"x18", increasing to a very small brighter core.


17.5" (4/1/95): NGC 3690 is a disrupted, interacting double system (Arp 299).  This unusual pair appears moderately bright, fairly small, elongated E-W.  The appearance is confusing with two very small "knots" in a common halo elongated E-W (20" between centers).  On the west side is a fairly bright virtually stellar "knot", which is probably the nucleus of the brighter member of NGC 3690.  There is a small fainter unconcentrated extension on the following end and the two components are not individually resolved.  With averted vision, IC 694 was barely glimpsed as an extremely faint spot about 1' NW.


17.5" (3/19/88): fairly bright, moderately large, elongated ~E-W, irregular, mottled appearance.  A mag 14 star is superimposed on the west side and an extremely faint mag 15.5 star or knot is involved.  This is a disrupted interacting system which includes IC 694.


WH discovered NGC 3690 = H I-247 = h896 on 18 Mar 1790 (sweep 951) and recorded "pB, lE, mbM."  On 9 Apr 1793 (sweep 1039) he logged "vB, pL, lE near the parallel, but a little from nf to sp."  JH reported "B; R; pgbM.  Query whether there be not a * excentric towards the south-following side." The "star" may refer to the companion on the south side.  On 27 Jan 1852, LdR's assistant Bindon Stoney described the system as "Neb div into two parts, faint appendage np about one dia distant."


Swift also noticed it was double in 1883, writing in Sidereal Messenger IV (p39), "mentioned to all observers as very little elongated.  Chancing to run across it with a power of 132, I immediately suspected it to be a close double, which suspicion a power of 200 confirmed.  It is probably the closest double nebula known."  Swift reobserved the galaxy on 18 Apr 1892 (list X) and noted "vs, close D with [NGC] 3690, suspected with 132, ver with 200".  This is nearly identical to his 1883 comments.  Dreyer entered Stoney's and Swift's second component as IC 694 -- but did they apply to the same object?


Usually, IC 694 is identified as the southwest component of the interacting double system NGC 3690 and this is likely what Swift resolved in his first observation.  But Stoney's earlier observation clearly resolved NGC 3690 into two components as well as picking up the extremely faint 16th mag galaxy (MCG +10-17-002a = VV 118c) "one diameter" NW of the NGC 3690 system.  Based on Stoney's observation, it is reasonable to assign IC 694 or IC 694B to MCG +10-17-002a = VV 118c.

*  NED classification.