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View Full Version : Object of the Week July 21, 2013 - NGC4656 The Hockey Stick



Dragan
July 22nd, 2013, 12:30 AM
NGC 4656 The Hockey Stick

Canes Venatici

12 43 57.7
32 10 05

Type: SB(s)m Pec IV

Mag: 11.0 Size: 9.1’x1.7’


So keeping with the spirit of my beloved Chicago Blackhawks winning the 2013 Stanley Cup last month, I thought it would be fitting to choose this object as an OOTW. Not only is it a great object, but it actually does tend to resemble its moniker.

I’ve been observing NGC 4656 regularly for quite a few years now and each time I return, I would take for granted what my Megastar & Uranometria would depict. And that was NGC4656 and 4657 were two separate galaxies. The assumption is that 4657 is interacting with 4656 causing the gravitational distortion that was creating the “blade” of the hockey stick. But once I started my research for this OOTW, I stumbled onto something. (This BTW, is one of the reasons why working on an OOTW is so great. You learn so much!) I found that this may not be the case.

What I stumbled upon was a few internet sources that made the claim that the nearby Whale Galaxy NGC 4631(worthy of its own OOTW if you ask me) was the one distorting NGC 4656 and not 4657. Redshift measurements of the two galaxies do clearly show that the two are part of the same galaxy group. But in those same papers and sources, I found no reference to 4657 being an interacting object. I did find various websites making the assumption that 4656 and 4657 were interacting, but I found no credible evidence to prove it. So it got me to digging. Was NGC4657 a real galaxy or was it a misidentification? Even Hyperleda comes back with 4656 when you do a search for 4657.

A quick search with the folks at Harvard revealed a paper (http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1983AJ.....88..602S&data_type=PDF_H IGH&whole_paper=YES&type=PRINTER&filetype=.pdf) from 1983. One of the intentions as stated in the abstract was to determine whether or not 4656 and 4657 were part of the same galaxy. Apparently even back then there was doubt. Unfortunately though, they were not able to come up with conclusive evidence. They do suggest at the end of the paper that their "results favor a single galaxy model of a tidally distorted variant of a Magellanic type system.” I’m sure some more research savvy DSF members than myself can come up with some newer evidence to prove one way or another.

Visually, the galaxy is fantastic in all size scopes. There are reports online of 4656 pairing nicely with 4631 in 100mm telescopes. In my 25” the shape of the hockey stick stands out nicely with a very apparent widening at the handle. Along the core of the galaxy mottling is very clearly seen as well as what appears to be HII regions.

One thing I did notice looking at many images while researching this OOTW is a faint band of stars extending away from the blade. I’ve looked at the hockey stick plenty of times with the 48” but I’ve never made note of it. Then again, I never knew to look. Has anyone seen this extension? Is it even visble? You can make it out in the images below. Next time out, I’ll be sure to look for it.

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Finally,

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

Marko
July 22nd, 2013, 01:08 AM
You have reminded me of this one which is a real favorite especially with the whale next door. My observation of 4646 in 18" does not mention the extension.
A semi-deep image of this pair that I enjoy so much is on my image site at http://astrospotter.zenfolio.com/p314501843/h806f361#h806f361 although I have seen better images ... this one was 'mine' and is a special visual area to me.

The Whale indeed deserves its own fame and together these too offer details each of their own for a great set of nearby observations. I too revisit this pair each year but will likely wait till next year to squeeze more details out of them when they return to higher ground.

Great info on the hocky stick. Thanks Dragan!

Uwe Glahn
July 22nd, 2013, 08:03 PM
Dragan,

I don't made a research but what I see on colored pictures is, that NGC 4657 is a part of NGC 4656 and most probable a result of the interaction with NGC 4631. The colors showed pink and blue tones which suggest star burst/formation.

For me it was always fun and challenge together to separate NGC 4657 into individual knots. With 16" I could pick up 4 knots within the hook and one more fainter knot 1' NW of NGC 4657. I don't try this with my 27" but I believe when the Seeing is steady enough NGC 4657 is extremely detailed. And no, I don't see the fainter extension to the NE.

779
16", 180x-257x, Seeing IV, NELM 6m5+

Dragan
July 22nd, 2013, 10:39 PM
Uwe,

In hi-res images, I always thought to myself that the hook was part of 4656. I never doubted that. But looking at different sources revealed that sometimes 4657 is depicted as a different galaxy, which I don't believe to be true.

Howard B
July 26th, 2013, 06:26 PM
Hi Dragan,

My most recent observation of 4656 is from May 2009 with my 28 inch:

" A terrific view of the Hockey Stick galaxy - a long, faint extension balances the bright areas nicely and is dramatically longer too. Some mottling in the core and "blade" area on the bright end is easily visible at 408x and detectable at 253x. 21.31 SQM"

786 787

Ivan Maly
April 18th, 2014, 08:51 PM
Only recently I got around to reobserve this object in detail. 12" SCT, 125-375x, SQM 21.78.

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