NGC 3917 (UGC 6815) Group of Galaxies in Ursa Major

Center of field at approximately: RA 11 hours 50 minutes 25 seconds, Dec +51 degrees 56 minutes 57 seconds

Size: 5.1' x 1.2' Magnitude: 12.5 blue Class: SAcd: HII

North is up

West to the right

Telescope:

 8" f5 Newtonian reflector

Camera:

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

Image:

Lumicon Red filter, 470 minutes (47 x 10 minute subs), 04/3/4/6/2011; seeing 2.5-3.1 FWHM per CCDStack

Processing:

CCDStack 2.24.4110.20701, Photoshop 7.0

Location:

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

Notes: This galaxy group is just 39 minutes WSW of NGC 3953. The faint northeastern (upper left) most galaxy in this field is UGC 6840 (2.3' x 1.9', mag 14.3b; Cl: SB(rs)m) is also imaged with NGC 3953. The other galaxies (west to east <right to left>)  are UGC 6802 (2.4' x 0.3', mag 15.9, Cl: Scd), NGC 3917, and NGC 3931 (1.3' x 1.0', mag 14.4p, Cl: SA0-:).

From the NGC / IC Project:

Contemporary Visual Observation(s) for NGC 3917
NGC 3917 = UGC 06815 = MCG +09-20-008 = CGCG 268-093 = PGC 37036
11 50 45.4 +51 49 28
V = 11.8;  Size 5.1x1.3;  SB = 13.7;  PA = 77d

17.5": moderately bright, large, very elongated 4:1 WSW-ENE, broad concentration 
without a distinct nucleus.  Two stars are off the S edge; a mag 13.5 star 1.3' 
S and a mag 14 star 1.3' SE of center.  Forms a pair with the mag 16 edge-on 
galaxy U06802 6.2' WNW (not seen).

This nearly edge-on galaxy was found by WH (II 824) although his polar distance 
was in error by 1 degree.  The equivalence with JH's h994 was noted by Dreyer, 
so the identification N3917 = U06815 is certain.  The RA in the RNGC is 0.7 
tminutes following the correct place.  There is a similar offset for N3921 
located 3 degrees north.  Listed in RNGC Corrections #3.

- by Steve Gottlieb
Contemporary Visual Observation(s) for NGC 3931
NGC 3931 = UGC 06825 = MCG +09-20-011 = CGCG 268-096 = CGCG 269-009 = NPM1G 
+52.0151 =  RNGC 3917A = PGC 37073
11 51 13.4 +52 00 02
V = 13.3;  Size 1.1x0.9;  SB = 13.3;  PA = 160d

17.5": fairly faint, small, round, bright core.  Located 4.9' W of mag 8.6 SAO 
28166.  N3917 lies 11' NNE.

Discovered by WH (III 769).  The NGC position is 0.8 tmin E and 3' S of U06825 = 
M+09-20-011 = CGCG 268-096.  Assuming this identification is correct, CGCG 268-
096 and M+09-20-011 should be identified as N3931.  This galaxy was also 
identified by Keenan as N3917A.  The RNGC assigns the exact same coordinates to 
both N3931 and N3917A.  N3931 was not found by Bigourdan. See Catalogue  and 
CGCG Corrections, Thomson.

- by Steve Gottlieb
Historical Research Notes / Correction for NGC 3931
NGC 3931.  WH's RA is 1 minute too large.  This was first mentioned, as far as
I can determine, by Anders Reiz in his thesis published in the Lund Annals, 
No. 9, in 1941.  

Reinmuth took a much fainter galaxy closer to WH's position as N3931.  But 
even though it is a high-surface-brightness object, it is quite faint and very 
small.  If WH could have seen it, I think he would have simply counted it as a 
star.  Perhaps a visual investigation is in order, but this galaxy is so much
fainter than the one just a minute of time preceding, that I think that Reiz
must have chosen the correct object.

Here is a curious footnote.  Dreyer reports in his 1912 notes to WH's lists
that Bigourdan could not find NGC 3931.  However, looking at Bigourdan's big
published table, we find a "Nova" as the very next object following his entry
for NGC 3931.  He found it the same night that he searched for N3931.   
Bigourdan did not include this new nebula in any of his lists of new objects, 
so it has no IC number.  Reducing this observation, however, shows that it 
refers to the very object that Reiz picked up 40 years later. 

Finally, the number "NGC 3917A" is sometimes put on this object.  This was
first done by Philip Keenan in a 1935 paper (ApJ 82, 62); I've copied the 
number only to make it clear which galaxy Keenan actually listed.  Let's not
carry this any further, shall we? - Dr. Harold G. Corwin, Jr.