Object of the Week April 28, 2013 Keenan’s System
Keenan’s System, ARP 104, VV33
Ursa Major
NGC 5216, UGC 08528, MCG +11-17-004, CGCG 316-019, CGCG 316-019, PGC 47598
RA: 13 32 6.9
DEC: +62 42 03
Size: 1.9’x1.1’
Mag: 12.7V 13.6B
SB: 14.0
Morphology: E0 pec
NGC 5218, UGC 08529, MCG +11-17-005, CGCG 316-020, CGCG 317-003, PGC 47603
RA: 13 32 10.4
DEC: +62 46 04
Size: 1.8’x1.2’
Mag: 12.3V 13.1B
SB: 13.2
Morphology: SB(s)b? pec
Imagine this. Start with two relatively bright, undistinguished galaxies. Then separate them by 22,000 light-years. Finally throw in galactic debris connecting the two. The result is Keenan’s System, aka ARP 104 and VV33.
arp104_p.jpgarp104_n.jpg
The galaxies NGC 5216 and NGC 5218 were discovered and cataloged by William Herschel in 1790. Edwin Hubble studied them as Intergalactic Nebulae in 1926. Then in 1935 on a photograph taken with the Yerkes 24-inch reflector Philip C. Keenan noticed a “faint but definite band of nebulosity” connecting the two galaxies. He also noted a “short curved arm” continuing beyond the other side of NGC 5216. Keenan published a paper with his findings, however it received little notice for decades.
Keenan discovery article.jpgKeenan discovery plate.jpg
In 1958 this pair of galaxies was “rediscovered” by observers at Lick and Palomar Observatories. The pair was included in The Catalog of Interacting Galaxies as VV33, published by B.A.Vorontsov-Velyaminov in 1959. In 1966 they were included as Arp 104 into Halton Arp's Catalog of Peculiar Galaxies.
A recent study by Beverly Smith (et al) with the Spitzer Infrared and Galaxy Evolution Explorer UV Space Telescopes has shown the bridge to be a remarkable filament. It revealed "beads on a string" - a series of star-formation complexes. According to their findings, "Our model suggests that bridge material falling into the potential of the companion overshoots the companion. The gas then piles up at apogalacticon before falling back onto the companion, and star formation occurs in the pile-up."
Here are my somewhat sparse observation notes on Keenan’s System aka ARP 104
March 24/25, 2012 at the Cosmic Cowboy Observatory - Barbarella (Jimi’s 48” f/4)
Seeing above average, transparency 7/10, SQM 21.75
Brandon 24 at 203x and Ethos 13 at 375x
bridge between 2 galaxies [seen with] direct vision in both eyepieces
[E13] some brightening in bridge 1/3 way up from 5216
5216 condensed, stellar core
5218 elongated
In addition to the bridge both galaxies have a countertide - a fingerlike extension pointing in a different direction to the debris trail, a typical structure of interacting double galaxy systems. I have no recollection whether I saw either countertide – my sparse notes don’t make mention of either a positive or negative observation.
Observing the galactic bridge, in this case, was rather easy between 48 inches of aperture and the dark, transparent skies of southwest Texas. Once again the weather pattern this Spring in Ohio hasn’t given me a single night to observe with the Moon out of the way. I am patiently waiting to give Keenan’s System a go with my 15” scope, though this one might be a stretch. Meanwhile let us know your results with both the bridge and the countertides. Be sure to note your aperture and sky conditions.
Zwicky plate of Arp 104.jpg
“GIVE IT A GO AND LET US KNOW”
GOOD LUCK AND GREAT VIEWING!
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