Canes Venatici - Arp 269, 281 and SHK 71

[Mike JW]

After my trip into Ursa Major (see previous post) I wandered over the border in to CVn. I have chosen three highlights from a very productive 2 hour session.

Arp 269 – is an interacting galaxy pair that have had a cosmic collision, actually a near miss and are now moving apart. The result is a galactic carve up. The link between them is about 25,000 lyrs long and made up of hot gas and star forming regions (knots). NGC 4490 is known as the Cocoon Galaxy and a barred galaxy (SB pec). The smaller companion NGC 4485 is classified as IBm pec – an irregular barred galaxy – simply put, it is well and truly wrecked by the collision. I am pleased to have picked up the knots in 4490 and it appears that the left side as viewed has suffered the most disturbance, the side nearest the passing 4485. The bar can be seen in 4490.

 

Arp 281 is an interacting galaxy pair. The small NGC 4627 (17,000 lyrs across) is being pulled into the big 4631 (known as the Whale Galaxy, 116,000 lyrs across). NGC 4631 is an edge on barred spiral, with 400 or so billion stars in it. NGC 4627 and 4656 are thought to be part of the group.

SHK 71

I am a sucker for these very faint galaxy groups and this is where the 15" Dob and camera can really do the business in a short space of time. Obvious star drift on this shot but I was so excited to pick up this group that it does not bother me. A close look at the inset reveals a probable tally of 13, with some hot pixels and noise.

 

 

In the same session I did two other SHK groups and various other Arps - still to write them up. Shots have been cleaned up a bit in Photoshop.

Mike

 

 

 

[RobertI]

Nice session Mike,  the Whale and Cocoon are two of my favourites, particularly the latter with its knots and curves. Nicely captured galaxy group too.

[Martin Meredith]

Beautiful shots Mike and an interesting write-up (and kudos for braving the post-midnight temperatures!). Its remarkable what you can achieve in under 100s.  I'm looking forward to seeing your other Arps (second time round?). I was out looking at Arps over the weekend and Monday and a couple of Shakhbazians too which I'll post later. It is always fascinating to see what emerges as the stack progresses, especially for these ultra-faint galaxy groups. 

Martin

[Mike JW]

Hi Martin, At the risk of opening up the debate about what is "live" EAA, the advantage of using the 15" Dob is the speed of the view. Often in under 10 seconds. The stacking is really just to try to reduce the noise. Interestingly so with such large aperture it is better to use the "median" stacking rather than the "sum" for brighter DSOs. The advantage of my second tour of the Arps is that I am spending more time teasing out detail/more reading up. Looking forward to your next post.

I find the Pretty Deep Maps incredibly useful especially for the SHK groups.

I also fancy a peak at the Berkeleys with the 15 operating at f2.25.....there is no end to the targets!!

Mike