Object of the Week, September 4, 2022: NGC 7102 - Galaxy Pair in Pegasus

NGC 7102 (IC 5127) + PGC 214783 (2MFGC 16361)

RA: 21h 39m 44.5s
Dec: +06° 17’ 09”
Mag: 12.9vmag (NGC 7102), 16.9bmag (PGC 214783)

Today I want to pass the brighter nebulas within the milky way and leave the galactic latitudes to continue the galaxy dance of the always to short spring. The destination will be the nice galaxy pair NGC 7102 / PGC 214783 on the level of Messier 15 but 6° south.

The history is as often interesting. First discovered by the German astronomer Albert Marth in 1863 on Malta. As an assistant of William Lassell, he uses the famous and powerful 48" reflector with a speculum mirror and profited from the good skies. He describes the object as "faint, pretty large, round". Some years later in 1894 the French astronomer Guillaume Bigourdan discovered the same object with the 12.4" refractor at Paris observatory. He describes the galaxy as "extremely faint, pretty large, several extremely faint stars and nebulosity". He knows about the NGC designation but made a fault in the coordinates by using different offset stars and so measured the same galaxy twice. Both missed the PGC companion.

From the astrophysical aspect both galaxies seems to interact. NED gives distances of around 200 million light-years. Beside a recorded supernova in 2003 I could not find any scientific papers about the pair. Interestingly the fainter PGC also has a 2MFGC designation which stands for "2MASS Flat Galaxy Catalog".

In the telescope the main NGC is just visible in very small apertures. The PGC companion suggest a minimum aperture of around 16-inch. I recorded a "direct vision" and a "relative high surface brightness" in the 27-inch. Larger telescopes shows also a hint of the faint spiral structure of NGC 7102.

DSS blue 10'x10'
Attachment 4841

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PanSTARRS 4'x4'
Attachment 4842

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sketch: 27", 419x, NELM 6m5+, Seeing III
Attachment 4843
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As always, give it a go and let us know.

I can attest to the fact that the PGC requires a bit more aperture than the 12" I used 9 years ago. The NGC did not reveal any detail:

Only NGC7102 is visible, PGC214783 is not. An extremely faint, round glow, even in brightness, no difference with AV. To the SSE is a mag. 10.5 star.

Attachment 4845 Attachment 4844 Attachment 4846

Click here to download the guide.

I have an observation from August 1, 1995(!) on a night of average seeing conditions and a NELM of 6.0 at Sutton, Quebec. 15-inch f/5 Dobsonian at 146x:

“This is a fairly faint galaxy, ill-defined and gradually elongated SE/NW. The disk is hazy and fairly smooth in texture, just a little brighter to the middle. No core is visible.”

The PGC galaxy was not seen, or even suspected.

I've made three observations of NGC 7102. PGC 214783 wasn't noticed through my 17.5" back in 1986, though I doubt I was aware of its existence (not plotted on the Uranometria). Although challenging, it was visible the last two times, with my 24". These notes were taken from Yosemite in 2016 at an elevation of ~4400 ft.

24" (7/30/16): NGC 7102 appeared fairly faint, moderately large, roundish, fairly low overall surface brightness, broad weak concentration. On images NGC 7102 appears to be interacting with PGC 214783, an edge-on 1.1' SSW. At 220x, it was glimpsed several times in the same position but was too faint or fleeting for any definite details, including elongation, though appeared small.

I observed NGC 7102 for the first time just three weeks ago (Aug 18). I was using my 17.5 inch at our dark site house with 152x. Conditions were fairly good, with slightly below average transparency, and good seeing. I was unaware of PGC 214783.

It was easily picked up at 152x (Ethos 13mm), presenting a small and slightly dim smooth oval glow.

Last night I observed this galaxy with my 20" from Rio Hurtado, Chile. My notes read:

At 320x faint and elongated with occasionally a tiny stellar core. I think I see the central bar. Embedded in an exceedingly faint glow but I may be imagining that. At 427x I see PGC 214738 pop in and out of view as a very faint, long, oval glow almost pointing at a faint star.