The disappearing Egg trick

[Steve Gottlieb]

One of my targets on Tuesday night at Lake Sonoma was the pre-planetary Egg Nebula in Cygnus (HST image from 2003), which shines by reflected light — roughly 50% of it polarized.  Although I’ve viewed it several times in the past, I brought along a polarizing filter to see if I could get to disappear by rotating the polarizing filter in the proper orientation.  This object is small — about 20” in length — and buried in a rich Milky Way field, but it stands out in 12” and larger scopes as a fuzzy mag 12/13.5 double “star”, at least at 200x or higher.  This unusual object has a high surface brightness, so can easily take very high magnification.

After identifying it in my 24” (an 8th magnitude star is 4’ to its west), I plopped the polarizing filter directly on top of a 10mm Zeiss Abbe. Holding the rim of the filter, I slowly rotated it around while peering through the filter. Sure enough the brightness dimmed significantly (at least a magnitude, probably more).  A nearby 12th magnitude star was a convenient reference to gauge the dimming.  Although the nebula never disappeared completely with the filter, the effect was quite noticeable, even dramatic.

Two other pre-PNe — Frosty Leo and Minkowski's Footprint also have polarized features, but as far as I know, the Egg Nebula is the only one that ‘responds’ significantly to a polarizing filter.

If anyone else gives it a try, I’d like to hear your results (I’m writing an article on this object for Sky & Tel).

Steve

[Steve Gottlieb]

Speaking of polarized deep sky objects, here’s an observing article by German amateur Reiner Vogel.  He experimented using a polarizing filter on several pre-planetary nebulae and also the Crab Nebula.  The Egg Nebula, by far, elicited the strongest response.

Steve

<Egg Nebula.jpg>

[Mark McCarthy]

The shape of the lives of the Butterfly and Minikowski’s footprint are very similar to Outers 4.  If it’s a proto Star maybe polarization would help?

Mark

Sent from my iPhone

On Jun 19, 2020, at 9:18 AM, Steve Gottlieb <astrog...@gmail.com> wrote:

Speaking of polarized deep sky objects, here’s an observing article by German amateur Reiner Vogel.  He experimented using a polarizing filter on several pre-planetary nebulae and also the Crab Nebula.  The Egg Nebula, by far, elicited the strongest response.

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[Steve Gottlieb]

There was a study of Outers 4 (called Ou4) in 2014 to determine the nature of this beast and the results weren’t definitive.  At the center is a young cluster including the massive triple star HR 8119 (type-B stars). The study concluded Ou4 was less likely to be a PN, partly because there's no identifiable central star.  Some of the gas is ionized, but shock-excited as it collides with denser material in Sh 2-129.

Given the apparent location of Ou4 in the sky, aligned with the young stellar cluster at the centre of the H II region Sh 2- 129 and the striking correspondence between the 22 μm and [O III] emission, it is reasonable to suppose that Ou4 is an outflow launched some 90,000 years ago from the massive triple system HR 8119. The location of the outflow, its radial velocities and extinction values are all consistent with such an hypothesis. Further support might come from the fact that the south bow-shock has an enhanced brightness in correspondence with a bright portion of Sh 2-129, as expected if it were impinging on a denser zone at the border of the H II region.

In the alternative scenario that Ou4 is a PN, its overall morphology would likely be the result of the expansion of a fast collimated wind from a yet unidentified central source through a relatively dense circumstellar medium.

I don’t know if there’s been any other work to figure out if the gas is outflow from blue main-sequence stars or from a star at or beyond the asymptotic giant branch stage.

Steve

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[Mark McCarthy]

Steve

You are probably already aware of this but in Kent Wallace's book p. 393 he says: "Observed the Egg Nebula at Navajo Flats California, using a polarizing filter on 11/21/98 with the 20" f/5 reflector.  At 245x, the Egg Nebula normally looks like two close blobs, one larger than the other.  When the polarizing filter is rotated around the field of view, the smaller blow almost disappears and the larger blob isn't as bright."

He also references a S&T article from Oct. 1998 where the author noted "if the Egg Nebula was turned 10 or 20 degrees, its central star, now blocked by a band of dust, would be a naked eye star and the nebula would be unobservable."

So much of what we can see is an accident of orientation!

Would a filter such as this be suitable for these observations?  Apparently you can split this filter in two and mount one at the telescope end of the eyepiece and one on the diagonal (or just one) and rotate as desired.

Mark

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[Peter Natscher]

On Friday, June 19, 2020 at 5:54:35 PM UTC-7, Mark McCarthy wrote:

So much of what we can see is an accident of orientation!

So are our lives   ; )

[Steve Gottlieb]

The filter you linked should work, though I just used a single 1.25” polarizing filter like this one from Lumicon and layed it directly on the top of a 1.25” eyepiece (ZAO) that has a flat top and square shoulders.  Just rotating the filter itself with two fingers did the trick.

Steve

Steve

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