Object Of The Week August 27, 2023 - Robert's Quartet

[wvreeven]

Robert's Quartet, Phoenix Group, SCG2 0018-4854

Group of Galaxies

Phoenix

RA: 00 21 23.0
DEC: -48 38 20

Mag: 13.91 (B)

Arguably the best know list of galaxy groups probably is the Hickson Compact Groups list. But there are many others, including the SCG (Southern Compact Group) list, where the 2 refers to the second paper that was released regarding that topic. One of the groups in this list is Robert's Quartet, also known as the Phoenix Group. The group contains four galaxies: NGC 87, NGC 88, NGC 89 and NGC 92, which were discovered by John Herschel on 30 September 1834.

eso0535a.jpg
VLT image (credit: ESO).

In 1987 Halton Arp and Barry Madore compiled A Catalogue of Southern Peculiar Galaxies and Associations. Robert Freedman helped generate many updated positions for the catalogue so Arp and Madore named the group Robert's Quartet in honor of his work.

Visually the group is very tight. The four galaxies lie within a circle with a diameter of 3.2' which, at the distance of the group, corresponds to about 150,000 lightyears or about 1.5 times the size of our own Milky Way. Mutual interactions have malformed all four galaxies. Unfortunately, I didn't see much of that and I wonder what you make of it. My observations read:

NGC 87: At 320x oval with a stellar nucleus.
NGC 88: At 320x round and small with a stellar core.
NGC 89: At 320x oval about 2:1 with a central brighter region.
NGC 92: At 320x oval about 2:1 with a central brighter part. Occasionally an extension about the size of the major axis of the galaxy is visible.


As always,

"Give it a go and let us know!
Good luck and great viewing!"

[Steve Gottlieb]

If the Phoenix (Robert's) Quartet was further north, it would qualify as one of the better Hickson groups. It's actually a quintet if we include ESO 194-13. This latter galaxy was missed by Herschel, but it was discovered visually in 1887 with the 48-inch Great Melbourne Telescope when the quartet was observed. The discovery is buried, though, in the observer's notebook (Pietro Baracchi).

My observations were also made in Australia (Coonabarabran) with a 30-inch f/4.5 at 429x.

NGC 87: fairly faint, irregularly round, 0.7' diameter, low even surface brightness. Westernmost and second faintest in the compact Phoenix Quartet with NGC 88 1.5' SE, NGC 89 2.8' SE and NGC 92 2.9' E. The arrangement is distinctive with the three brighter galaxies (NGC 87/89/92) arranged in an equilateral triangle and NGC 88 at the center, forming a "Y" or propeller shape. ESO 194-13 lies 12' ENE of the quartet.

NGC 88: faint, small, slightly elongated NW-SE, very small bright core. An extremely faint star is attached at the SW end. This galaxy is the faintest in the quartet.

NGC 89: moderately bright, moderately large, elongated 2:1 NW-SE, 1.0'x0.5', very small slightly brighter core, faint stellar nucleus. Has a slightly higher surface brightness than NGC 92.

NGC 92: this galaxy is the brightest member and furthest east in the compact quartet. It appeared moderately bright, elongated 2:1 NW-SE, 1.2'x0.6', broad concentration to a bright core.

ESO 194-013, a fifth member of the group, lies 11' ENE of NGC 92. At 429x, it appeared moderately bright, elongated 4:3 SW-NE, 0.9'x0.7', broad concentration with a slightly brighter core but no distinct zones. A distinctive string of three mag 13 stars [length 1.4'] is centered 2' E.

[Uwe Glahn]

Found records with three different apertures. All made in Namibia.

12", 214x, NELM 7m0+: very nice, compact group; similar brightness in form of an triangle; four galaxies visible within 3,5'

17", 260x, NELM 7m0+: NGC 88 with bright nucleus; NGC 92 with elongated central part; NGC 89 3:2 NW-SE elongated; NGC 87 round with no structure
NGC92-Gruppe.jpg
home

24", 300x-400x, NELM 7m0+: NGC 92 with a very faint tidal tail, around 2' long to the SE; NGC 89 with two very tight and short spiral arms; NGC 87 totally mottled but without showing a clear structure