Hanny's Voorwerp

[Jimi Lowrey]

Howard the Sloan G passes 401/550 NM which from the spectral image of Hanny's Voorwerp is right in the Middle of the OIII line that the Voorwerp is strongest in.

Bill Keel or the University of Alabama who is the lead investigator on Hanny's Voorwerp suggested to me that the Sloan G filter should enhance the Voorwerp visually from his work on the spectra and as it turns out he was right on. you can get the Sloan filters at Astrodon.

http://www.astrodon.com/products/fil...trics_-_sloan/

[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