Hanny's Voorwerp

[FaintFuzzies]

Hanny's Voorwerp is an O-III object - basically a huge galaxy sized object next to the galaxy....but it was determined (I think from Dr. Keel's paper/research) that it sits between 600-700k light years away...so the O-III lines of the object is red-shifted to about ~530nm from 501 and 496 nm...which is beyond the cutoff of traditional "nebular" filters, such as O-III, NPB, UGC, etc... The Sloan G filter passes everything from 400 to 550mn, while rejecting everything else...

When I observed it with Jimi's scope with and without the Sloan G filter - it was night and day.

I observed it for the first time without the filters back in 2009 as we tried various filters and all seemed to kill it. I don't remember if the CLS didn't completely extinguish it like the others or not. I'm at work, so I don't have my notes handy. Perhaps Jimi can comment.

[Howard B]

Thanks everyone, the Sloan G filter is on my list now! What other objects do well with this filter?

[Jimi Lowrey]

Howard, I used it on the faint outer halo of the ghost of Jupiter the other night it brought out the faint haze really well. I get some response to some PN and none in others . One thing that you will see is that how much it improves the contrast it dims down the sky brightness slightly and helps the contrast a lot.

[Marko]

From the details Alvin has brought out about the red-shift to about 530nm it would seem the Johnson/Cousins V filter may offer improved contrast for this object over the Sloan G given a large scope. The Sloan G is 150nm wide at that point with near 100% transmittance so it wins with transmitted light (important here of course). The Astrodon version of the V filter is by far much narrower in the 530 area and is tapering off in this range. The V is about 50nm wide but sloping off from it's peak of 94% at 520nm, 91% at 530nm, 86% at 540nm, 83% at 550nm where Sloan G drops like a rock. At 10% transmission the V is 140nm wide which approaches the Sloan G bandwidth of 50nm but is well down.

Marko