Uwe Glahn
May 31st, 2015, 08:20 PM
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)
I ran across this bright object when I scan the compilation of Whitmore et al (1990AJ....100.1489W) (http://adsabs.harvard.edu/abs/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 (http://ftp.aao.gov.au/) 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?
DSS 15'x15' blue
1669
deep picture of AAO
1670
sketch: 27", 172x-293x,
NELM 6m5+, seeing II
1671
invertible version
(java on/mouse over) (http://www.deepsky-visuell.de/Zeichnungen/NGC4643.htm)
"GIVE IT A GO AND LET US KNOW"
Type: SB(rs)0/a
RA: 12h43m20.1s
DEC: +01d58m42s
Size: 3.1’ x 2.5’
Mag: 11.7vmag (10.8bmag)
I ran across this bright object when I scan the compilation of Whitmore et al (1990AJ....100.1489W) (http://adsabs.harvard.edu/abs/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 (http://ftp.aao.gov.au/) 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?
DSS 15'x15' blue
1669
deep picture of AAO
1670
sketch: 27", 172x-293x,
NELM 6m5+, seeing II
1671
invertible version
(java on/mouse over) (http://www.deepsky-visuell.de/Zeichnungen/NGC4643.htm)
"GIVE IT A GO AND LET US KNOW"