Object of the Week June 28, 2020 – Minkowski 2-9 "Butterfly Nebula"

[Uwe Glahn]

Min 2-9 (PNG 010.8+18.0; PK 010+18.2)
Constellation: Ophiuchus
Type: PPN
RA: 17h 05m 38s
DEC: -10° 08' 35"
Magnitude: 14.7v
Size: 115" x 18"

This unusual object was discovered in 1947 [1947PASP...59..257M] by astronomer Rudolph Minkowski and cataloged in his second compilation of new objects. Interestingly he found the nebula during the inspection of objective-prism survey plates through a 10-inch telescope. While the plates, which covers a larger field, shows stars as long and wide lines of their continuous spectra, the emission objects only shows their short emission lines (mostly Hα and [OIII] lines) and so they stand out very well within the field.

Physically the nebula belongs to the group of Proto-Planetary Nebula. The central star (AGB) is dying and produces stellar winds. The star itself is not hot enough to ionize the blown of material and "only" illuminate the gas similar to a reflection nebula. It is suspected, that the bipolar structure is formed by a binary and the gravity between the main red giant and a hot white dwarf. The former APOD (https://apod.nasa.gov/apod/ap070618.html) shows a spectacular animation of the very fast changes of the appearance of Min 2-9.

In the telescope the nebula is very small and only around 2' long. A 16-inch telescope shows both wings but under very good conditions the bipolar structure could be a target for a 12-inch telescope? What do you think?

I noted:
16", 360x, fst 7m0+, seeing II: small and faint appearance; CS easy and direct visible; faint and thin extensions to N and S, ~1' long
27", 837x, fst 6m5+, seeing III: already elongated object around bright CS with searching eyepiece (113x); with high magnification both wings not uniformly conical but bulgy with knots behind the widest position of the wings, brighter wing and knot to the N; faint but direct visible second star some arc seconds NW of the CS

DSS b, 10'x10'
3934

PanSTARRS g, 2'x2'
3935

sketch: 16", 360x, NELM 7m0+, Seeing III
3936

sketch: 27", 837x, NELM 6m5+, Seeing III
3937

As always, give it a go and let us know.

[wvreeven]

Great choice, Uwe, and very interesting background info. I only observed this nebula with my 12” telescope from a very dark site:

The famous Minkowski's Butterfly nebula. At 48x this nebula isn't visible. With UHC a faint smudge becomes visible. With OIII too but less prominent than with UHC. At 88x without filter I see a star to the west of where the nebula should be. With UHC the nebula becomes visible as a small line wich again is less visible with OIII. At 188x the same applies as at 88x but the nebula is much harder to see. I'll need to visit this nebula with a larger aperture.

[Raul Leon]

Hi here's my observation from 12/20/2011: Minkowski 2-9 aka Minkowski's butterfly in Ophiuchus; magnitude 14.7 ; size:114"x18" ; small ; two fairly bright lobes eminating from a bright central area. I used a 7mm Nagler at 200x with my 14.5 Starstructure Dob f/4.3 3938

[Steve Gottlieb]

Here's a diagram of the various parts of Minkowski's Butterfly. The two knots in Uwe's diagram are labelled on the diagram as N3 and S3.

I've seen N3 a couple of times in my 18" as a stellar point, once at 323x and another time at 435. It was clearly non-stellar using 500x in my 24" and sometimes it appeared as a short "bar" oriented perpendicular (east-west) to the major axis. S3 is smaller with a lower contrast and I missed it in my 24", though it was easy in Jimi's scope.

3939

[Bertrand Laville]

Hi All,

Very interesting object, and very interesting explanations.
Here are my drawings with T450 and T635.
Report: http://www.deepsky-drawings.com/pk-10182-2/dsdlang/fr

Clear skies
Bertrand
http://www.deepsky-drawings.com/

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[akarsh]

I have a question about this object: I was just looking over my notes made on Jimi’s 48” and using a DGM NPB filter shows two knots, sort of symmetrically on either lobe, and also enhances on of the edges of the bipolar nebula. So this must indicate some sort of ionization of hydrogen and/or oxygen. But typically in a Preplanetary Nebula like this, as Uwe points out in the post, no ionization is expected as the star is not yet hot enough to ionize the gas unlike in the case of a planetary nebula. Then what causes the ionization that results in the NPB filter response?

[Steve Gottlieb]

Minkowski's Butterfly is not a typical pre-planetary nebula -- strong evidence points to a symbiotic system. Here's what I wrote in the June '21 issue of Sky & Tel (which also includes the Egg Nebula and the Footprint Nebula, which are true PPNe).

Astronomers usually classify M 2-9 as a symbiotic nebula. In this scenario, the binary central star consists of a hot white dwarf and a Mira-type companion. The latter loses mass via its stellar wind or else transfers mass to the white dwarf when it overflows its Roche lobe. The white dwarf ionizes this gas, thus mimicking a young planetary nebula.

Bruce Balick and collaborators’ recent model of M 2-9 using hydrodynamic simulations showed that a conical spray blasts out at an incredible 200 km/s (450,000 miles/hr) in the polar direction. The gas interacts with the pre-existing AGB wind that is slower and denser, forming and shaping a variety of features.

The Butterfly’s “proboscis” or outer lobe extends 1? in both directions, so the nebula’s total size is 120" x 12?". At the outer tips are blobs of compressed gas. The bright inner lobe is hourglass-shaped and nested with two separate shells: an inner “bulb” and a thin outer “sheath.” Two brighter knots, N3 and S3, are near the tips of the inner lobes and appear flattened in HST images. In Balick’s model, the knots formed in situ and were not ejected by the core.

A 2011 study by Romano Corradi (Instituto de Astrofísica de Canarias) and colleagues compared 12 years’ worth of observations and found dramatic changes in the Butterfly’s inner lobe. H_alpha and O III images showed the knot pairs S1/S2 and N1/N2 marching along the walls of the lobe from east to west. The knots rotate around the symmetry axis (the period is nearly one century) within a “lighthouse” jet from the central star. This pattern points to a symbiotic binary source, whose orbital period matches the rotation period of the knots. The phenomenon results from a collimated jet of high-velocity particles that shocks and excites the bulb walls on impact.

The thin equatorial region has two expanding, ring-shaped structures of molecular gas and dust with diameters of 2.5" and 7". A 2012 investigation headed by Arancha Castro-Carrizo (of the Institut de Radioastronomie Mil- limétrique in France) found these rings move in different directions, suggesting two mass-loss episodes occurred 900 and 1,400 years ago at distinct points in the binary star’s orbit.

[akarsh]

Minkowski's Butterfly is not a typical pre-planetary nebula -- strong evidence points to a symbiotic system. Here's what I wrote in the June '21 issue of Sky & Tel (which also includes the Egg Nebula and the Footprint Nebula, which are true PPNe).

Astronomers usually classify M 2-9 as a symbiotic nebula. In this scenario, the binary central star consists of a hot white dwarf and a Mira-type companion. The latter loses mass via its stellar wind or else transfers mass to the white dwarf when it overflows its Roche lobe. The white dwarf ionizes this gas, thus mimicking a young planetary nebula.

Bruce Balick and collaborators’ recent model of M 2-9 using hydrodynamic simulations showed that a conical spray blasts out at an incredible 200 km/s (450,000 miles/hr) in the polar direction. The gas interacts with the pre-existing AGB wind that is slower and denser, forming and shaping a variety of features.

The Butterfly’s “proboscis” or outer lobe extends 1? in both directions, so the nebula’s total size is 120" x 12?". At the outer tips are blobs of compressed gas. The bright inner lobe is hourglass-shaped and nested with two separate shells: an inner “bulb” and a thin outer “sheath.” Two brighter knots, N3 and S3, are near the tips of the inner lobes and appear flattened in HST images. In Balick’s model, the knots formed in situ and were not ejected by the core.

A 2011 study by Romano Corradi (Instituto de Astrofísica de Canarias) and colleagues compared 12 years’ worth of observations and found dramatic changes in the Butterfly’s inner lobe. H_alpha and O III images showed the knot pairs S1/S2 and N1/N2 marching along the walls of the lobe from east to west. The knots rotate around the symmetry axis (the period is nearly one century) within a “lighthouse” jet from the central star. This pattern points to a symbiotic binary source, whose orbital period matches the rotation period of the knots. The phenomenon results from a collimated jet of high-velocity particles that shocks and excites the bulb walls on impact.

The thin equatorial region has two expanding, ring-shaped structures of molecular gas and dust with diameters of 2.5" and 7". A 2012 investigation headed by Arancha Castro-Carrizo (of the Institut de Radioastronomie Mil- limétrique in France) found these rings move in different directions, suggesting two mass-loss episodes occurred 900 and 1,400 years ago at distinct points in the binary star’s orbit.


Steve, most of this material just flew over my head. So what I gather is that the Mira-type star, which is an AGB star that has not yet given up its planetary shell, is paired with a white dwarf. The mass flow from the Mira-type star to the white dwarf is ionized by the UV of the white dwarf, and the stellar wind from the system pushes it out in an outflow -- is that roughly accurate? I now realize that's exactly what Uwe's explanation in the main post says, but it didn't sink in.

Thanks for your reply. I realized that I had read your article, but did not follow enough of it to register the details. Tells me I should revisit it.

[akarsh]

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This figure from the paper https://arxiv.org/pdf/2203.00881.pdf seems helpful in understanding the deal with the knots and their motion. The introduction of the paper is also highly readable, which is refreshingly nice.

[Don Pensack]

Hi here's my observation from 12/20/2011: Minkowski 2-9 aka Minkowski's butterfly in Ophiuchus; magnitude 14.7 ; size:114"x18" ; small ; two fairly bright lobes eminating from a bright central area. I used a 7mm Nagler at 200x with my 14.5 Starstructure Dob f/4.3 3938

This is almost exactly the image I see in the 12.5" at 304x in skies of mag.21.4.