Object of the Week, November 13, 2022 - Hickson 98 (NGC 7783 & friends)

Object of the Week, November 13, 2022 - Hickson 98 (NGC 7783 & friends) in Pisces
R.A.: 23h54m10.1s
Dec.: +00°22'58"
Size: 1.5'x 0.7'; Magnitude: 14.0B

Deb & I had the pleasure of spending a week last month with Connie and Jimi Lowrey at their home in Fort Davis, Texas… and between the great meals and the great conversations we also managed to get in some observing… imagine that! Observing was limited by various combinations of wind, rain, humidity, and poor seeing/transparency, but we managed to accumulate about 12 hours of quality eyepiece time over 3 different nights and came away happy… but the weather difficulties allowed us more time to visit, always a good thing.

We logged quite a number of objects, both deep-sky stinkers and spectacular eye-candy objects, and a lot of stuff in between those extremes. Today’s OOTW is a typical example of the latter category.

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Hickson 98 was one of several HCGs that we observed but it was the only one that had thus far escaped being featured here in the OOTW, so the timing was great for me. It is a group of (4) galaxies in Pisces, with the anchor galaxy being NGC 7783, HCG 98A (aka Arp 323, VV 208), a spiral S0-a galaxy of about mag 14B. It was easily seen directly as a 2:1 smudge about 30 arcseconds long with a star on the SE end. Directly on the other side of the star is HGC 98B (PGC 72808, MCG+0-60-59) almost in-line with the main galaxy but aiming a little more south. This member is round and dim, about 20” or so in diameter, and stated to be about mag 15B. Continuing in generally the same direction for a little over an arcminute brings us to HCG C (PGC 72810), yet another mag dimmer at about 16.3B… but it too was fairly easy to observe with direct vision. Going back to NGC 7783 and heading a little east of due north about 40 arcseconds brings us to the last member of this cluster, HGC D (PGC 72803, MCG+0-60-60) and this stinker is still another mag dimmer at 17.5B! However, with averted vision and patience at the eyepiece, it was definitely detectable in moments of steady seeing. By the way, component “D” is actually a background galaxy and therefore not a physical member of the others.

In doing my due diligence about this object I ran across an interesting paper specifically about this group of galaxies, which can be accessed here…

As a bonus object, going back to HCG component C, about 23 arcseconds SW is another dim galaxy, this being Mac 2354+0021, mag 17B… and we could detect this guy, too, in moments of good seeing. We really enjoyed this observation.

As always, give it a go and let us know!

Hi, here's my observation notes from last year in France (Bar-lès-Buzancy) SQM 21.4. With a 16" Sumerian Alkaid and Pentax XW 5mm at 362x

NGC 7783 is the brightest member, seen as a clear knot at the N side of a curved, nebulous glow. At the S side NGC 7783B is seen as a somewhat dimmer and smaller knot. Between these two galaxies a dim m14.9 is visible. Further S and fully separated from the above mentioned nebulosity, a very dim star and NGC 7783C are seen loose from each other. The galaxy is very hard to discern with averted vision. A bright m10 star nearby disturbs a bit and (partially) prevents the final member NGC 7783D from being seen, but perhaps it’s just too dim.

Attachment 4923


Martijn

The galaxy South West of C MAC 2354+0021 AKA SDSS J235412.56+002113.3 is far behind the Hickson group at Z=0.1143 which gives it a light travel time 1.48 Billion light years. On the night we observed this group it was direct vision at 610X. I was surprised the next day to discover it was that far away. Always fun to catch billion year + light.

I observed this group from Spain on November 8, 2015, almost 7 years ago to the day! My notes read:

At 545x I saw all four galaxies. NGC 7783A is visible as an elongated galaxy with a faint star at one side. B is visible next to the star. Another star lies south and south of that C. Between a bright star and A I sometimes see a very faint glow, which is D.

I missed D in my 18-inch many years ago and the nearby mag 9.4 star (1' N) sure doesn't help.

I also observed SDSS J235412.56+002113.3 in Jimi's scope back in 2014, though found it fairly tough at the time. Thanks for mentioning the high redshift!

D was visible as a very faint, popping in and out of view galaxy in my 16-inch. The 27-inch shows d steadily with averted vision.
Nice galaxy chain in mid size telescopes.

sketch: 16", 360x, Seeing II-III, NELM 6m5+
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I'll add that component D was tough, but I did it by positioning it so it would drift WITHOUT that "blazing" 10th mag star popping into the field. It helps to use a very narrow field eyepiece, such like what I used...a 4mm Supermono eyepiece. Notes below:

Almost stellar. Held most of the time with averted vision. There is an obnoxiously bright mag 10.1 star sitting 1.1’ north. The key to detection is to keep it off the field, so I used the 4mm Supermonocentric eyepiece giving 573x with a little 3.1’ field. Tracking was a little tough, but fortunately I was able to find a way for the field to drift without letting the star pop into the field.