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View Full Version : Object of the Week, December 2, 2018 IC 298 and IC 298A – Arp 147



Howard B
December 2nd, 2018, 07:07 AM
Ring galaxy (IC 298) with collider (IC 298A)

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Cetus
RA 03 11 18.4
DEC +01 18 57
Magnitude 14.3(v)
Size: 0.5’ x 0.4’

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Discovered by French astronomer Stéphane Javelle in 1893, these two small and faint interacting galaxies are certainly photogenic, and are relatively well-known as a result.

IC 298 is the face-on ring galaxy on the right (west) side of the HST image, and IC 298A is the nearly edge on ring galaxy on the left. Evidently, IC 298 was a spiral galaxy that collided with elliptical galaxy IC 298A, and the resulting gravitational interactions made ring galaxies out them both. You can practically sense their relative motion by looking at the blue tendrils of stars trailing from IC 298 back toward 298A.

IC 298 is also a starburst galaxy as evidenced by it mostly blue-ish white color, and although is creating about 4.6 solar masses of stars now, its star forming rate peaked about 15 million years ago. The most massive stars quickly blew up as supernovae and left behind 9 black holes in the 10 to 20 solar mass range, along with less massive neutron stars.

The darker yellow-red area on its south-eastern border is probably the original central bulge of the galaxy as it contains 30 to 50 percent of its total mass. IC 298 is a relatively small galaxy at only about 30 thousand light years in diameter and is a mere 21 thousand light years from IC 298A.

But they’re located about 435 million light years away, so we can barely see any of this great stuff in our amateur-sized telescopes.

My best view so far was in 2005 and even so I could not see the entire ring of IC 298, and IC 298A was seen only as a faint edge-on galaxy. I had heard them called the “number 10 galaxies” but really this view made them look more like the “IC galaxies”.

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My brief notes from a dark and transparent night in 2005 using my 28-inch scope:

“Faint but unmistakable – the number “10”. Or maybe “IC” is better! 654x”

It’s time for another look – I’d love to see the entire ring of IC 298 – but that will take an exceptionally dark, transparent and steady night. What have you seen?

As always, give them a go!

kisspeter
December 2nd, 2018, 11:18 PM
Ah. When I bought the Arp book by Jeff Kanipe and Dennis Webb and browsed through the images this was No. 1 I wanted to take a look at. In September 2015 I pointed a 16" to IC 298 and was surprised not to see anything at first sight. Then I dedicated a lot of time to this and all I can say is that I saw "something". More precisely it was held ~80% of the time for a couple of minutes in at least 2 hours of observation. No details of course and pointless to draw it.

I hope, I'll have the possibility to take a look at IC 298 in a much bigger scope once.

Uwe Glahn
December 3rd, 2018, 08:07 PM
Wow Howard, for sure one of the most fascinating objects in large apertures.

Smallest used aperture was the 24-inch of a friend of mine during good transparency in 2006. I noted: IC 298A visible as a nonstellar patch with brighter nucleus, somewhat elongated; IC 298 much fainter, round, no ring structure
sketch: 24", 525x, NEM 6m5+, Seeing III
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In 2014 I did a second attempt on Arp 147 with my 27-inch and with a 33-inch of a friend of mine under very good transparency but soft seeing. I noted: 33": both faint, but steadily visible with averted vision; IC 298A 3:1 elongated and concentrated; IC 298 shows as a faint, round glow with darker center; E to NE ring fragment somewhat better defined, difficult observation; 27": similar results, a little bit fainter but both steadily visible with averted vision; again, E-NE segment of the ring visible as circle segment

Paul Alsing
December 4th, 2018, 03:55 AM
Wow Howard, for sure one of the most fascinating objects in large apertures.

Well, Uwe, you got that right!

This was one of the objects I viewed one weekend in 2006 using the 82" at McDonald Observatory in Texas, right up the road from Jimi's house in Texas. I didn't have too much to say about it, but here are my notes anyhow...

IC 298, Arp 147, Cetus
I wanted very much to look at these guys because the DSS shows them to look like the letters "I" and "C", and by golly, they do! Very cool.