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Looking oddly reminiscent of the “V” depicted in the logo for the sci-fi television series “V,” this has to be one of the strangest objects in space. It’s the Westbrook Nebula — also known as PK166-06, CRL 618 and AFGL 618 — and is a protoplanetary nebula. But this highly irregular bundle of disconnected jets and clouds is the result of a burst of a dying star expelling toxic gases such as carbon monoxide and hydrogen cyanide. Well, toxic to us, anyway, but maybe not to The Visitors!
There are only a few hundred protoplanetary nebulae known in the Milky Way. The appear during a star’s rapid stellar evolution between the late asymptotic giant branch phase and the subsequent planetary nebula phase.
But these short-lived clouds of gas are faint and very hard to see. They emit strong in infrared radiation, and are cool in temperature, so they emit small amounts of visible light. So, astronomers have a few tricks up their telescopic sleeves to try and get images of protoplanetary nebula, and the results are well worth it, as this image demonstrates.
This is a composite image where the astronomers have used exposures in visible light which shows light reflected from the cloud of gas, combined with other exposures in the near-infrared part of the spectrum, showing the dim glow, invisible to human eyes, that is coming from different elements deep in the cloud itself, so this is a kind of reflection nebula.
(See the “Light Echoes” podcast by Astronomy Cast for more information on reflected light.)
Hubble has taken images of the Westbrook Nebula before, but this new one is clearly sharper and provides more detail. See more info on what techniques were used at the Hubble ESA website.
Some Additional Information
This proto-planetary nebula, often abbreviated as PPN (plural PPNe) lies in Auriga. It is preferably named PN G166.4-06.5 from the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae. In 2001, T. Ueta called this object a “Molecular Gun”, with ‘bullets ‘ and ‘horns’, once mistaken for bipolar lobes, which might have a better title for the article here!
Some class this object, instead as a post-AGB (Asymptotic Giant Branch star). It is centred on the variable star V353 Aur (04h 42m 53.6s +36° 06′ 53″). The 15.5v to 19.2v variable star is of B0 spectral type and shows peculiar emission lines, while the highly red nebulosity on earlier images show just two peanut shaped nebulae. When first found it caused quote a stir in the astrophysical community as the object appeared in the earlier stages of planetary nebula evolution. The original paper is at; http://adsabs.harvard.edu/abs/1975ApJ…202..407W (it gives the “base data” on the object, but there have been 733 (according to the ADS) other interesting papers since this time. bout 80 directly relate to this object.)
Probably invisible to all amateur telescopes, this unusual 12 arcsec long object has been well studied since about 1975, when Westbrook et.al. discovered the object using rocket-launched infra-red observations during to so-called AFCRL Infra-red Sky Survey (Air Force Cambridge Research Observatories) [The CRL is just an alternative version of this catalogue with different numbering) This was object was primarily catalogued in 1975 and again then 1977 by Stephen Harris. The final catalogue of all objects and stars appear in 1981. At 1mm, the emission seen in this object is mostly from carbon monoxide (CO). [I think there is little hydrogen cyanide in this object, though.]
The velocity of Crl 618 the outer halo and the bipolar outflow is moving at about 340 km.s*-1 (huge in regards any ordinary planetary nebulae), whist the inner torus surround the central star (not seen in the HST image), is expanding at 17 km.s.^-1. According to Sanchez Contreras (Astrophys. J., 617, 1142-1156 (2004)) the nebula appeared just 2500 years ago (losing about one ten thousandth of a solar mass per year), while the central mass loss of the torus may have started just 400 years ago!
What is amazing in the HST image is that the nebulosity of the opposing ‘V’s defies the the so-called point symmetric property, where the direction of the rays are mirrored on the opposing side of the star. Very peculiar, and rather still unexplained.
Also, it is worth mentioning the famous Campbell’s Star in Cygnus or PK 64+5.1 around the star BD +303639 is the brightest of this early type planetary, and is was the first proto-planetary discovered. It too has small 8 arcsec shell with the nebula being 9.6v magnitude and the central star 10.03V magnitude. One of the interesting things about these PNe is that it is unusually weak in [O-III] filter but bright in Hydrogen-Beta filter.
Thanks for this article Nancy!!
The Sanchez Contreras paper “1” Resolution Mapping of the Molecular Envelope of the Protoplanetary nebula CRL 618″ can be freely downloaded at; http://iopscience.iop.org/0004-637X/617/2/1142/
Note: Page 1149 has a nice summary of the parameter data on this object, and a useful graphical map of the orientations of the bipolar outflow.
These higher resolution HST observation no doubt will improve our knowledge of this object significantly!
HSBC; Thanks, I didn’t have that paper in my group of 7 papers on CRL 618 from a year ago when doing an in-depth study on 40 PNe structures.
Initially I thought 618 was ‘uninteresting’ compared to other PNe, like; Red Square, Mz3, M2-9, etc. But after studying NGC 2440 and reading the APJ, 493:803-810, 1998 Feb 1 paper by J.A. Lopez w/ Meaburn, Bryce and Holloway; and specifically beginning to understand the inscruitability of Position Angle (PA) phenomena in regards to the central object and what could possibly account for massively powerful ejection phenomena at differing angles, I took a new look at CRL 618 and found a new interest in its structures.
The other PNe in the ‘P/A Series’ of photos during my presentation on PNe last October were: Calabash (aka: the Rotten Egg Nebula or OH231.8+4.2), NGC 6543 or Cat’s Eye, NGC 2440, Hubble 5 (a 1997 Hubble photo w/no papers or further info I could find about it), Eta Carinae w/Homunculus Nebula.
These all exhibit multiple ejections at differing angles of ejection. Eta Carinae’s are in its equatorial disc plane, each 120 degrees apart w/the third one obscured by eta itself.
[collecting the data is the first step, developing theories takes a backseat]
Eh? I read this through three times, and I still have little idea what you are talking about here.
López has published with many other astrophysicists, but as far as I know, there is absolutely no such thing as the “inscrutability of Position Angle (PA) phenomena” (I’m familiar with this paper, and is is not inferred at al especially in regards NGC 2440) I.e. So what exactly is so impossible about the position angle(s)? They might be misaligned to the symmetrical axis, but there are many other explanations for discordant outflows. (Rotation or precession, for example, could still explain it.)
Whilst there is some speculation this might be caused by difference in the magnetic and rotational axises, their is still really no direction observational evidence to support this idea.
Also I should add that eta Carinae is neither a planetary nebulae, a post-AGB star, nor pre-planetary nebula.
In this paper of CRL 618. the observations with the HST was with the unusual compounds making the nebulosity. Due to its distance and small size, much of the studies have been into the slight changes in the nebulosity structures to find clues to this unusual object.
[Much of what I know of this object is only the original observations that were made at 100 microns, as stated in the earlier post.])
It looks like the star has been split asunder, the two halves ejected into the void. But i wonder of the original star, does a remnant ever become a sun again, its dusty heavy matter freed to coalesce into new planets and begin anew.
I really wish the name of ‘Planetary Nebula’ was changed, (a 18th Century observational misnomer) Its only vaguely correct in as much as these events seed interstellar space with the heavy elements required for planets. Hows about “Stellar Remnant”?
Double opposite V.
How about supernova nebula?
How about calling them “Neons”?