Object of the Week, June 20, 2021 – Arp 302, VV 340, UGC 9618

[Howard B]

Bootes
Galaxy pair interaction?
Magnitude (v): 15.3 and 15.7
RA: 14 56 54
Dec: +24 36 00

More popularly known as the Exclamation Mark Galaxy, I had this to say about the name when I observed this pair last summer with my 28-inch scope:

“The name is a bit confusing because the star between the two galaxies would seem to be the point of the exclamation mark. But it’s the two galaxies that inspire the name – an edge on and face on galaxy. Cool pair, 408x and 547x, 21.75 SQM.”

Arp302_negative.jpg Arp302_invert.jpg

Wikipedia indicates this pair has a light travel time of 470 million years, and seem rather bright for being that far away. Each galaxy is approximately mid-15th magnitude, but together they seem brighter. That’s good news for us, because they’re a pretty sight in the eyepiece.

The z of each galaxy doesn’t match up very well though. VV 340A - the edge on galaxy – translates to a light travel time of 246 million years, while the edge on galaxy, VV340B, seems a bit closer to the advertised light travel time with a z that works out to 450 million years. So perhaps these two galaxies are a line of sight coincidence.

The seeing was mush during my observation, and I’m hopeful to give it another shot this summer under sharper seeing conditions and try to detect the dark lane of VV 340A and perhaps a spiral arm or two in VV 340B - but I’ll probably be pushing my luck on both counts. I definitely won’t see them unless I try, so the effort will be worth it regardless of the outcome.

The background galaxies that appear so vividly in the HST image are all fainter than magnitude 18.3, so there’s an outside chance I might see the brightest one, but that’s the best I can hope for with my scope. How about you?

Give it a go and let us know!

720px-Hubble_Interacting_Galaxy_UGC_9618_(2008-04-24).jpg

[Clear Skies]

My final observation in the night of 8 april 2018 in dark northeast Germany. 14" SCT @ 168x / 29':

Without AV one north-south elongated glow is visible, with AV both galaxies are visible.
The southern galaxy MCG+04-35-018 (PGC53433, KPG 446A, VV' 340B) is a slightly north-south elongated, oval glow, brighter in a core that is clearly elongated in the same direction (notable).
The northern galaxy MCG+04-35-019 (PGC53432, KPG446B, VV' 340A) is just a bit to the NNE of the southern galaxy, a clearly north-south elongated streak, even in brightness, no detail visible.
With AV the mag. 14.5 star 4UCAC574-050606 in between the galaxies is visible.

This is 1 of 3 (that I know of) celestial exclamation marks. One of them is also in Boötes and is also an Arp: Arp 199. The other is Vorontsov-Vel'yaminov 912 in Phoenix. And then there's also the planetary nebula NGC6309 in Ophiuchus, more commonly known as the Box Nebula, that is sometimes dubbed the Exclamation Mark Nebula due to the star directly to its NNW.

Are there more out there?

[Dragan]

One of them is also in Boötes and is also an Arp: Arp 199.

I think 199 more commonly goes by a more, ummmm, perverted nickname

[Steve Gottlieb]

Nice "early stage" interacting pair! Here's an observation with my 18" from July 2011. I've also seen it a couple of times in my 24", but didn't really see any additional detail, except the edge-on was longer and thinner.

"At 285x, Arp 302 (double system) appeared as a fairly faint, very elongated glow oriented N-S, ~1.1'x0.3'. A mag 14.8 star is in the center. With careful viewing the two component galaxies were resolved [centers separated by 36"]. The northern galaxy (MCG +04-35-019) was longer and thinner and appeared barely detached from the star. The southern galaxy (MCG +04-35-018) seemed attached to the star and rounder.

LEDA 1713635, picked up 4.5' due north, was extremely faint and small, round, roughly 10" diameter."

[Uwe Glahn]

Recorded an old observation with my smaller 14.5-inch.

I wrote: 14.5", 404x, NELM 6m5+, Seeing III: faint overall duo but clear morphology of the system, both similar in brightness, northern galaxy somewhat larger and 1:2 elongated, star in the middle barely visible with direct vision

sketch:
UGC9618.jpg
home

[morsie]

I need to revisit this again from a dark sky location. I recorded both of these back on 7-28-1998 under 6+ NLEM skies at 450x in West Virginia. I used the PGC designations.

UGC 9618A
Very small and dim oval extended 1 1/2 to 1 with a slightly brighter core. Averted vision shows more size. PA = 115. About 1min N lies PGC 53432. ARP 302

UGC 9618B
Small dim slash elongated 3 to 1 with a slightly brighter extended core. PA = 10. PGC 53433 is 1min S.