Object of the Week May 31, 2015 - NGC 4643 A Barred Polar Ring Galaxy

[Uwe Glahn]

NGC 4643, UGC 7895, PRC D-22

Type: SB(rs)0/a
RA: 12h43m20.1s
DEC: +01d58m42s

Size: 3.1’ x 2.5’
Mag: 11.7vmag (10.8bmag)

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I ran across this bright object when I scan the compilation of Whitmore et al (1990AJ....100.1489W) about polar ring galaxies. Instead of showing faint galaxies with superfaint polar ring structures the atlas shows an 11mag object. And the observation surprised me so much that I decided to choose it as an OOTW object.

To start at the beginning F.W. Herschel discovered the object in 1784 with his legendary 18.7 inch speculum reflecting telescope. He described it as very small but saw an elongation. And that is the first very astonishing detail – the bright and very dominant bar. The type of the galaxies says “SB(rs)0/a”. As repetition “SB” stands for “Spiral Barred” and “(rs)” for an intermediate characteristic between a spiral and ring notation. The ending “0/a” stands for an intermediate stage between “SB0” + “SBa” while “SB0” means an intermediate between the elliptical and spiral galaxies (where the Hubble fork split up) while SBa is the first step in the lower fork arm (earlier types) and describes a galaxy with “tightly-wound, smooth arms; large, bright central bulge”.

Back to the Polar Ring designation. While page 138 of the above-named paper shows nearly no clear structure, the AAO shows a very deep image from combined UK Schmidt plates. The Polar Ring is now visible as thin extensions along the long axis of the galaxy.

Now we know what should be visible but the “live observation” shows as often another picture. Yes, the bar is visible – and how! One of the most prominent bar examples I ever saw – and spectacular view. Next very interesting thing is the very faint disk around the bright bulge and prominent bar. The disk is huge and needs lower magnification like a fainter PNe. Next nice detail is an arrow-shaped asterism just NW of the galaxy. I did not look for the extremely faint polar ring extensions. Maybe the real challenge for large aperture?

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DSS 15'x15' blue
NGC4643_15b.gif

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deep picture of AAO
n4643_d.jpg

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sketch: 27", 172x-293x,
NELM 6m5+, seeing II
NGC4643.jpg
invertible version
(java on/mouse over)


"GIVE IT A GO AND LET US KNOW"

[BobbyD]

Ooo! I think I've seen this with my 8" dob. Can anyone confirm its visibility for me???

[wvreeven]

I have observed this object on May 15, 2015, under dark but windy circumstances with my 20" F/5 telescope. I only had a quick look and didn't look for a disk surrounding the galaxy. My notes read

At 83x (Nagler 31 mm) I can see NGCs 4636, 4624 and 4643 together in the same field of view. NGC 4643 is elongated without a clear core or brighter center.


Clear skies,

Wouter

[Howard B]

Hi BobbyD, I have one observation of 4643 with my 8 inch Newtonian from 1993 (!):

"Small round galaxy that brightens gradually towards its center. 105x"

Not much of a description but that's the only observation I have, so now I'm eager to have a go at it with my 28 inch - and thanks for the interesting OOTW Uwe.

[BobbyD]

Wow, Great, and thanks Howard! I really appreciate it. This is my first year of hardcore astronomatory action. Its been a blast! Its nice to have some confirmation, and its exciting to know something I stumbled on is this weeks ootw! Thanks again!

Clear skies!

[Ivan Maly]

Interesting structure for large apertures. The galaxy itself is visible even in 4" if the sky is dark.

[bladekeeper]

I caught this one on June 8th with my 12". Good stuff!