NGC/IC Project Restoration Effort
(This is a very very beta version)
Location and Magnitude
Right Ascension: 10:51:31.2
Visual Magnitude: 13.6
Discoverer: Herschel W.
Year of discovery: 1789
Discovery aperture: 18.7
Summary description: vF, S, E, er
NGC 3398 = IC 644. Considerable confusion has surrounded the identification
of this object and its neighboring galaxies. The original observation is due
to William Herschel, who found a "vF, S, E 20deg sp nf, er" nebulae on 17
April 1789 2m 11s preceding, 0d 50' north of 44 UMa. Reducing these offsets,
taking the proper motion of 44 UMa into account, gives the position (for 1950)
10 48 24, +55 41.1.
There are four galaxies in the area that might be the one that Herschel saw.
Here are data for them:
RA (1950.0) Dec B_t PA Type MCG CGCG UGC IC
10 48 28.4 +55 39 23 14.55 73 SA:(rs:)ab? +09-18-038 267-18 5954 0644
* superposed 0.55 sp
10 48 32.1 +55 43 53 15.6 130 SA:(rs?)0^+ +09-18-039 267-19 -- 0646
10 48 44.8 +55 39 04 -- 55: E2/S0^-: +09-18-041 -- -- --
10 48 59.9 +55 51 56 14.82 20 SAB(s)cd III +09-18-043 267-22 5976 --
Sev F sts, knots, comps near
On the face of it, UGC 5976 is the most likely candidate: it is second
brightest, the position angle is correct, it is knotty, and it is the largest
of the galaxies in the area. However, its position is well off of Herschel's,
and it has the lowest surface brightness of any of the galaxies here. I think
it is doubtful that Herschel would have picked it up while sweeping.
Instead, Herschel's position falls near UGC 5954, the brightest galaxy of the
four, and also the one with the highest surface brightness. This means that
it is the one that Herschel would be most likely to see. The position angle
is at least in the correct quadrant, and Herschel's note "extremely mottled"
could well be due the presence of the star near south-preceding combined with
the galaxy's bright nucleus and pseudo-ring of uneven brightness.
Still, visual verification of this theory would be nice to have.
Finally, the identity of the two IC objects in the area -- I644 and I646 --
is unambiguous. While Swift's positions are often none too good, they are
at least adequate in this case. The offset in RA is about 12 time-seconds
for both, while the declinations are within a minute of arc. I644 turns out
to be identical to NGC 3398, while I646 is MCG +09-18-039.
17.5" (4/22/95): brighter of a pair of galaxies oriented N-S. NGC 3398 is a faint, narrow edge-on streak 4:1 E-W, 1.0'x0.25'. IC 646, 4.6' NNE, is very faint, small, slightly elongated NW-SE, 0.5'x0.4'. Located 4.7' NW of mag 8.1 SAO 27802.
Some catalogues refer to this galaxy as IC 644. UGC 5976 (identified as NGC 3398 in CGCG and UGC) lies 13' NNE (see observation).