Object of the Week, September 1, 2019 - NGC 317 A/B and PGC 3432

[Howard B]

Interacting galaxies

Andromeda

RA 00 57 41
DEC +43 47 28
Magnitude 13.9


NGC317DSS.JPG


NGC 317 A/B and PGC 3432 was suggested by Jimi as an interesting object at the 2019 Oregon Star Party – which had wonderfully dark and smoke-free skies this year. The main appeal of NGC 317 was that it’s a pair of beautiful interacting galaxies, with a PGC galaxy off to the side. It looked great on the DSS image on Jimi’s laptop, but what could we see with my 28-inch scope?

Quite a lot as it turned out. NGC 317 A (mag 13.86) is the bright elliptical galaxy just above the messed up looking edge-on spiral of NGC 317B (mag 13.95) below it. PGC 3432 is in the upper right corner of the DSS image, and all three were easy to see, even PGC 3432 (mag 16.7).

The spiral arm of 317B opposite of 317A was seen dramatically sweeping out into intergalactic space, and became quite long with averted vision. Beautiful.

The most difficult detail to see was a small knot in 317B’s other spiral arm, the one being directly pulled on by 317A. You can see it just left and slightly up of the NGC 317B label in the DSS image above. At the time Jimi and I thought it could be a star cloud or perhaps even a third galaxy caught up in the interaction. Without a decent internet connection we couldn’t go online and find out then.

So just now I looked up NGC 317 in the DR15 Navigate Tool (http://skyserver.sdss.org/dr15/en/tools/chart/navi.aspx) and quickly saw the knot was really three faint stars bunched together, so they’re simply a chance alignment of faint Milky Way stars.

NGC317A_B_SDSS.JPG

Out of curiosity I clicked on each of these stars to see what their magnitudes are, but it only gives the magnitude of the reddest star of the three, the one on the lower left in the image below. For some reason all three stars in the clump have been assigned the same magnitude as the reddest star. Astoundingly, it’s shown as magnitude 20.09!

No doubt all three stars together combine into a bright enough glow that experienced observers with a 28-inch scope can reasonably detect under dark skies, so I’m not suggesting that this “star-clump” is really magnitude 20.09. Based on experience, I’ll guess their combined glow is probably around 17-ish magnitude. Pretty cool even so.

NGC317clump.JPG

My observing notes from July 28, 2019:

“Fabulous field of view – NGC 317 A/B shows their connecting tidal tail and the opposite spiral arm being flung into space. Also saw a small knot in 317B, and PGC 3432 is surprisingly easy to see. 547x, 21.90 SQM.”

NGC317A_B_crop.JPG NGC317A_B_cropinvert.JPG

NGC 317 A/B and PGC 3432 are easily found just a few degrees northeast of M31, so give them a go and let us know!

[Jimi Lowrey]

I can still see the view of this interaction in my mind. This is another Lewis Swift find with his 16” Clark refractor.

It is to bad we did not know to look for PGC 3442. It looks like a small galaxy caught up in the cosmic crash with the larger galaxies. This gives me a good reason to revisit It

6F019DA7-A188-4EA5-BA85-48CB4414E7F5.jpeg

[obrazell]

Interestingly the pair is also in the extended VV catalogue as VV 928

Owen

[Uwe Glahn]

Nice unknown pair (KPG 19) Howard. It quickly looks familiar to me and indeed I found a 27-inch sketch of it. Also observed under dark skies but probably not the OSP sky you guys had.
Both spiral arms were visible easily but I missed the knot of the blurred star group (under average seeing).

sketch: 27", 419x-586x, NELM 7m0+; Seeing II-III
NGC317.jpg

[Ivan Maly]

Interesting object and inspiring observations above. Here is a new one (20" F/4, 4800 ft a.s.l.). In the sketch image, N up.

"NGC 317, VV 928 (OOTW). And. Visible in 13 mm as a close, rather compact double nebulosity paralleling the unequal star pair to its W.

"With 5.5 mm, the N core [NGC 317A] much brighter. The N component features a broad extension to NW, which has a comparatively well-defined edge like a CW arm. 3 stars to its E, unequal close star pair NW.

"On the line to the N core from said star pair there is a threshold object that appears unconcentrated and much larger than oh the DSS print [PGC 3432].

"The S component [NGC 317B] of the main galaxy pair has a core that is round and only marginally brighter than the similarly sized enhancement to its WNW, which is connected to the core on the S side. It is almost touching the N core. Fainter, longer extension in the S component from NE side of the core E, slightly curving S. Past it there is a faint, long segment pointing ESE (not continuing the described E extension). At its end, halfway to the bright star SE and as far as the fainter star to the S, is a hook-like nebulosity pointing S. It may be due to some unresolved stars in the area. SQM 21.74. Sketched."

NGC 317 2019-09-03 N up crop light 500w.jpg

[Steve Gottlieb]

Also nearby is CGCG 536-14 = PGC 3448, situated 5' south of the NGC 317 pair (KPG 19).

The trio forms KTG 2, the second of 82 northern triplets (also from Karachentsev) - an excellent, though little-known observing project!