Object of the Week, Hickson 90 (NGC’s 7172, 7173, 7174, 7176)

[Paul Alsing]

R.A.: 22 02 01.7 Dec.: -31 52 18 (NGC 7172 = HCG 90A)
Size: 2.5'x1.4', Magnitude: V 11.9
Piscis Austrinus

Alternate ID’s (for the triplet) KTS 66 = VV 698 = Klemola 34

It is a lot of fun the track down the 100 objects in the Hickson catalogue, and Hickson 90 yet another fun object. It is available to observe using telescopes both large and small.

Here is a labeled screenshot from Megastar with a RealSky overlay…


5545

There are several challenging galaxies in the area, give them a go, too!


The Big Dog in this group is NGC 7172. It is clearly the largest galaxy in the group, and the only one with any discernable structure in my own experience, and that only being a much brighter core.

The other 3 galaxies in the group, NGC 7173, NGC 7174 and NGC 7176 are also catalogued as KTS 66A, B and C, with the KTS being the “Karachentseva Southern Isolated Triplets of Galaxies”. They are in a small tight group, with 2 of them being in contact. All are fairly easy to see.

There is, however, a fly in the ointment regarding my picture. Megastar is a very old program and got its data from the RNGC, but the RNGC had it wrong, and in Steve Gottlieb’s own words… “The RNGC reverses the identifications of NGC 7173 and 7174, making NGC 7173 and 7176 the contact pair. This misidentification is listed in my RNGC Corrections #1”

As usual, I check Steve’s NGC and IC notes because I often learn something I did not previously know. Thanks, Steve!

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

[Raul Leon]

Hi, here's my observation from 11/4/2013: four galaxies in Piscis Austrinus : ngc 7172 on bottom, brightest of the four, ngc 7174, ngc 7176 and ngc 7173. I used a 10mm Ethos at 198x with my 14.5 StarStructure f/4.35546

[lamperti]

Saw this grouping twice with an 18" at 256x and a 20" at 272x. Each was distinctively different.

[Uwe Glahn]

From Southern Germany (48°N) we had problems to see the group but the brighter members are reachable. I wrote:

8", 229x, fst 6m0+
compact part b-d visible even in the searching eyepiece as a faint smudge; with higher magnification, a, b and c are visible with direct vision; a visible as the faintest of all three, 1:2 elongated and somewhat concentrated; b and d together visible as a 1:2 elongated object with a peak at the position of b; c is fainter than b, but more compact and brighter surface brightness than a; nice group, also for an 8-inch

sketch:
5547
home (http://www.deepsky-visuell.de/Zeichnungen/HCG90.htm)

16", 180x, fst 7m0+
a visible as a striking 2:1 E-W elongated object with indicated dust lane; b visible as a bright round galaxy; d indicated as a single object and even separated directly west of b; c visible as a bright round and structureless glow

[wvreeven]

My observations with my 20" from central Spain on September 18, 2015, read:

Despite the low altitude this galaxy group proved to be very interesting.

NGC 7172: At 320x it is a faily oval patch of light with a stellar nucleus. It has a dust lane running along the major axis.
NGC 7173: At 320x it is a compact patch of light with fuzzy edges.
NGC 7174: At 320x it is a faily oval patch of light with a stellar nucleus. It is an elongated, slightly arced patch of light.
NGC 7176: At 320x it is a compact patch of light.