Arp 23

Arp 23 in Canes Venatici is a pair of one-armed spirals, the larger NGC 4618 and the smaller NGC 4625. This pair is also KPG 349. I first saw the Herschel 400 object NGC 4618 with 4” a few years ago. It is actually two Herschel objects, because he cataloged the core and the large enhancement in this galaxy separately. Vorontsov-Velyaminov adopted a similar view, cataloging the core as his #73b and the arm as 73a.


Recently I have sketched the entire field as it appeared in my 12” SCT. The galaxies could indeed be framed at a magnification that revealed their structure. I used the 8-24 mm Pentax zoom, which gives nominally 125-375x in this telescope and has an approximately constant true field within its range. In addition to the main part of the arm in NGC 4618, the proximal (E) and distal (W) parts of that arm were seen as detached enhancements. SQM 21.78.


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Fine detail with your 12" SCT Ivan. Here my attempt:

16", 225x, NELM 6m7
http://www.deepsky-visuell.de/Zeichn...18_NGC4625.jpg

NGC 4618 also has two IC numbers (3668, 3669) in his heavy arm. To my knowledge these details were discovered by Wolf with the big Bruce refractor.

Hi Ivan

Excellent observation and drawing from you. Especially are many similarities between your and Uwe `s drawing!

CS Hajü
www.astromerk.de

Superb drawings guys!!! and, of course, one more nice target for my next new moon observing list!!!

Here are my two Arp 23 observations and sketches - the first one is with my 28 inch and the second with Jimi's 48 inch:

"Nice! Funny how easy this was to find tonight and I mistook NGC 4485/90 for it last night. Arp 23 is every bit as interesting and certainly more unique looking with NGC 4618 having one big spiral arm - a fascinating sight. 327x, 21.12 SQM"
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"Woohoo! Great sight, both galaxies are curly cues with 4618 having several bright knots and a faint extension curving around its top. 375x, 21.62 SQM"
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Wonderful Obersavations and Drawings!! Great Respect!

CS Hajü

www.astromerk.de

Excellent sketches!! I'll throw in my visual notes for NGC 4618 with my 18-inch --

18" (5/15/10): This is a very unusual, asymmetric Arp galaxy with a single massive arm (similar to NGC 4027). At 220x it appeared bright, fairly large, obviously irregular, with a slightly elongated main body ~2'x1.5', extended 4:3 SW-NE. Within the main portion of the galaxy a brighter, elongated bar was visible, roughly 1.5'x0.5'. The central bar, though, is displaced to the NW side of entire glow as extending mostly to the south side is a faint, beefy arm that often appears detached and barely connected on the east end of the central region. This broad arm winds counterclockwise from east to south roughly 100° with IC 3668, the brightest region or knot near the south end of the arm, ~1.8' from the center of the bar. This single arm increases the overall size to ~3'x2'. IC 3369 refers to the brighter SE portion of the spiral arm.

And here is my visual rendition of Arp 23..... I guess I will be calli9ng it the "Horseshoe Galaxy" from now on!

Attachment 1187