Object of the Week March 3, 2013 --- UGCA 258

[deepskytraveler]

Object of the Week March 3, 2013 UGCA 258

UGCA 258 PGC 037680 DDO 103 MCG-02-31-006

Ring Galaxy
Morphology: Im pec

Corvus

RA
11 58 25
DEC
-14 31 26

Size: 1.1’ x 1.0’ Mag: 14.6v (NED)

UGCA 258 is a collisional dwarf ring galaxy. First cataloged as DDO 103 in 1959 by Sidney van den Bergh in A Catalogue of Dwarf Galaxies. The galaxy received its UGCA 258 designation from a survey of the blue POSS plates by Peter Nilson in the Uppsala General Catalogue Addendum. The morphology classification of UGCA 258 is Im pec – Irregular Magellanic, peculiar. Surprisingly as a relative bright galaxy there is very little known about this unusual galaxy.


Here are my observing notes from my one and only observation so far of UGCA 258.
March 24, 2012 at the Cosmic Cowboy Observatory - Barbarella (Jimi’s 48” f/4)
Seeing above average, transparency 7/10, SQM 21.56
With ZAOII 10mm 488x
found 3 stars of nearly equal magnitude that form an equilateral triangle, they required averted vision and moments of good seeing
galaxy bisects the line between two of the stars
galaxy was visible with direct vision
slightly brighter denser portion, a knot, is on the inside side of this imaginary line, towards the center of the triangle
ring portion of the galaxy is outside the line of the triangle

491

492

I haven’t yet given this one a try with my 15”. However it’s on my list, as soon as the perpetual Ohio winter cloud cover gives way to some clear Spring time skies.

“GIVE IT A GO AND LET US KNOW”

GOOD LUCK AND GREAT VIEWING!

[Jimi Lowrey]

Nice one Mark!

This ring galaxy is one that is not much known. It is fairly bright for a ring galaxy and there has been little research on it.

If you like Ring Galaxies this is a link to my good friend Alvin Huey site were you can download my ring galaxy catalog.

http://www.faintfuzzies.com/DownloadableObservingGuides2.html

[Steve Gottlieb]

Fascinating looking object, whatever is going on! I'm surprised it didn't catch the attention of Vorontsov-Velyaminov or one of the main papers on collisional rings.

By the way, the De Vaucouleurs classification Im pec doesn't refer to "interacting merger - peculiar" -- though that may apply here -- but rather "Irregular Magellanic - peculiar"

[Jimi Lowrey]

What I don't understand is why this galaxy is in a Dwarf galaxy catalog?

[deepskytraveler]

Steve,

Thanks for your clarification on the de Vaucouleurs classification of Im pec. I will edit the original article to correct.

Galaxy classification is not for the faint of heart. :) As I researched this further today I came across a bewildering amount of information, which to a large extent confused me further. So in hopes of enlightening myself and others, I went right to the source, Dr. Stephen Odewahn, Resident Astronomer at McDonald Observatory, whose Ph.D. thesis was "Properties of the Magellanic-type galaxies". Here's what Steve shared with me.

"Im is a Magellanic Irregular. This is common to both the de Vaucouleurs and Sandage systems. So, the m stands purely for magellanic. There are many cases of merging Im galaxies though.

"The Magellanic galaxies are very late-type systems. This means they are disk dominated with little of no hint of a bulge. They often display an asymmetric optical structure, especially the SBm galaxies (barred magellanic spirals). The majority of Sm and Im galaxies are barred."

[Steve Gottlieb]

What I don't understand is why this galaxy is in a Dwarf galaxy catalog?

The DDO (David Dunlop Observatory) Dwarf catalogue by Sidney van den Bergh was based on their appearance on the POSS I and he used the following two criteria (I'm quoting) ---

1) Low surface brightness.
2) Little or no central concentration of light on the red prints. In view of the fact that these objects are found to be more frequent in clusters than in the general field, it is reasonable to assume that they are dwarf galaxies. This conclusion is supported by the similarity which many of these objects have to dwarf galaxies in the local group. Almost all objects which satisfy criteria A and B are probable dwarf galaxies. However, many galaxies which are known or probable dwarfs do not satisfy both criteria.

So, his criteria was really one of surface brightness or luminosity and limited by the quality of the POSS I plates.

[Steve Gottlieb]

I had an opportunity to take a look at this ring galaxy a week ago in Jimi's scope, along with Howard Banich, and its a good one!

48" (4/5/13): at 488x, this ring galaxy consists of several components. On the southeast end is the ring nucleus, which appeared as a very small, round, 12" knot of high surface brightness. A diffuse glow mainly northwest of the nucleus (about 0.4') contains three brighter knots forming a ring. A short, very thin extension to the west of the nucleus forms the brightest portion of the ring. Continuing counterclockise, there is a very small gap in the ring but on the west side is the second brightest and largest section (~15"x5") which forms roughly a 60° arc. After a small gap on the northwest side of the ring, a quasi-stellar knot defines the north end of the ring. There was another gap on the east side where the ring would attach to the nucleus.