Object of the week May 13, 2012 - NGC 3664 = Arp 5

[Steve Gottlieb]

NGC 3664

Galaxy in Leo
11 24 24.8 +03 19 39 (J2000)
V = 12.8; Size 2.0'x1.9'; Surf Br = 14.1
Aliases: Arp 5 = VV 251 = UGC 6419 = VIII Zw 146 = MCG +01-29-041 = CGCG 039-170 = PGC 35041

This disrupted spiral was a fascinating sight last night in Jimi Lowrey's 48-inch. The brightest feature is a very knotty 1' irregular bar oriented SW-NE, with at least three brighter knots. The bar is brightest at the NE end with a very short offshoot to the north. Fainter haze surrounds the bar on the NW and SE sides.

The second brightest feature is a detached, mottled "arm segment" on the southwest side that's oddly cocked (NW-SE) perpendicular to the bar. As it appeared detached from the bar, it didn't look like part of a spiral arm, but this arm segment dims significantly and continues curving clockwise around the south and east side, making a low surface brightness outer loop or ring, all around to the other side of the bar! Now, I realized the bar was noticeably offset towards the NW side within a rounder 1.6' outline.

About 6' south is NGC 3664A, a much fainter disturbed companion that was likely involved in a train wreck with NGC 3664 during an earlier encounter. This 30" diameter galaxy has a fairly low surface brightness with a broad concentration, but it didn't reveal any irregular structure. UGC 6417, a more challenging edge on, is another 5' further south.

213

"GIVE IT A GO AND LET US KNOW"

GOOD LUCK AND GREAT VIEWING!

[Uwe Glahn]

Steve,

with 1/9 aperture the knotty structure was invisible but the brighter bar and the brightest part of the southern spiral arm, could also be detected. Cool object!
214

[Dave Tosteson]

Here is an observation of Arp 5 from my home with the 25"f5 in 1994: N3664 was moderately faint in surface brightness, 2' in size. At first it took averted vision, then was seen with direct vision. Appeared diffuse and was brighter to the middle. The offset nature of the bar was not noted. N3664A was faint, averted vision, had no detail, was round and small and not brighter to the middle. It took 2-3 minutes to find the smaller galaxy.

Dave Tosteson

[FaintFuzzies]

Here is my observation under NELM 6.5 skies...taken straight out of my book

22" (255 and 305x) - This is a weird galaxy in the eyepiece. Round even surface brightness patch with a broken up bar running across at a 45 degree angle about a third from the NW to SE edge. The 3 to 6 o’clock position of the edge is also brighter. A 16th magnitude star sits at the 10 o’clock position on the edge.