Red Rectangle Nebula

High-resolution images of it in visible and near infrared light reveal a highly symmetric, compact bipolar nebula with X-shaped spikes which imply anisotropic dispersion of the circumstellar material. The central binary system is completely obscured, providing no direct light.{{cite web |first=Robert Roy |last=Britt |title=Mystery of Red Space Glow Solved |url=http://space.com/scienceastronomy/070406_red_rectangle.html |work=Space.com |date=April 6, 2007 |access-date=April 29, 2016}}

The Red Rectangle is known to be particularly rich in polycyclic aromatic hydrocarbons (PAHs).{{Cite journal|last1=Cohen|first1=M.|last2=Anderson|first2=C. M.|last3=Coyne|first3=G. V.|date=Feb 1975|title=The peculiar object HD 44179, 'The red rectangle'|journal=Astrophysical Journal|volume=196|page=179|doi= 10.1086/153403|bibcode = 1975ApJ...196..179C |display-authors=etal}}{{Cite journal|last1=Russell|first1=R. W.|last2=Soifer, B|first2=T.|last3=Willner|first3=S. P.|date=Mar 1978|title=The infrared spectra of CRL 618 and HD 44179|journal=Astrophysical Journal|volume=220|doi=10.1086/155937|bibcode=1978ApJ...220..568R|page=568|doi-access=free}}{{Cite journal|last1=Miyata|first1=T.|last2=KatazaH.; Okamoto, Y. K.|first2=H.|last3=Okamoto|first3=Y. K.|date=Feb 2004|title=Sub-arcsecond imaging and spectroscopic observations of the Red Rectangle in the N-band|journal=Astronomy and Astrophysics|volume=415|page=179|doi= 10.1051/0004-6361:20034601|bibcode = 2004A&A...415..179M |display-authors=etal|doi-access=free}} The presence of such carbon-bearing macromolecules in the X-shaped nebular component, while the equatorial regions are known to contain silicate-rich dust grains and O-bearing molecules,{{Cite journal |last1=Cava |first1=I. Gallardo |last2=Bujarrabal |first2=V. |last3=Alcolea |first3=J. |last4=Gómez-Garrido |first4=M. |last5=Santander-García |first5=M. |date=2022-03-01 |title=Chemistry of nebulae around binary post-AGB stars: A molecular survey of mm-wave lines |url=https://www.aanda.org/articles/aa/abs/2022/03/aa42339-21/aa42339-21.html |journal=Astronomy & Astrophysics |language=en |volume=659 |pages=A134 |doi=10.1051/0004-6361/202142339 |arxiv=2202.02106 |bibcode=2022A&A...659A.134G |issn=0004-6361|doi-access=free }} was interpreted as due to a change of the O/C abundance ratio of the primary star during its late evolution.{{Cite journal|last1=Waters|first1=L. B. F. M.|last2=Cami|first2=J.|last3=de Jong|first3=T.|date=Feb 1998|title=An oxygen-rich dust disk surrounding an evolved star in the Red Rectangle|journal=Nature|volume=391|issue=6670 |page=868|doi= 10.1038/36052|bibcode = 1998Natur.391..868W |s2cid=4373724 |display-authors=etal}} However, PAHs could also be formed as a result of the development of a central photodissociation region, a region in which a very active chemistry appears due to dissociation of stable molecules by the UV emission of the central stellar system. The Red Rectangle was the first nebula around an evolved star in which an equatorial disk in rotation was well identified (the existence of such disks has been demonstrated only in a few of these objects, only expansion is observed in most of them).{{Cite journal|last1=Bujarrabal|first1=V.|last2=Castro-Carrizo|first2=A.|last3=Alcolea|first3=J.|last4=Neri|first4=R.|date=Oct 2005|title=The orbiting gas disk in the Red Rectangle|journal=Astronomy and Astrophysics|volume=441|issue=3 |page=1031|doi= 10.1051/0004-6361:20053118|bibcode = 2005A&A...441.1031B |doi-access=free}} However, the disk absorbs the stellar light and is practically not seen in the beautiful optical image, which mainly represents a relatively diffuse outflow that is very probably formed of material extracted from the denser disk.{{Cite journal|last1=Bujarrabal|first1=V.|last2=Castro-Carrizo|first2=A.|last3=Alcolea|first3=J.|date=Sep 2013|display-authors=etal|title=ALMA observations of the Red Rectangle, a preliminary analysis|journal=Astronomy and Astrophysics|volume=557|page=L11|doi= 10.1051/0004-6361/201322232|arxiv = 1307.5959 |bibcode = 2013A&A...557L..11B |s2cid=119188468 }} The distinct rungs suggest several episodes of increased ejection rate.

Image:PIA04533.jpg

The Hubble Space Telescope has revealed a wealth of new features in the Red Rectangle that cannot be seen by ground-based telescopes looking through Earth's turbulent atmosphere. The origins of many of the features in this dying star, in particular its X-shaped image, still remain hidden or even outright mysterious. The presence of a conspicuous bipolar symmetry is usual in protoplanetary and planetary nebulae. Theorists, like Noam Soker, {{ill|Vincent Icke|nl}}, Adam Frank, and others, have shown that this axial symmetry can appear as a result of shocks due to interaction of different phases of the stellar winds (characteristic of the late stellar evolution), but its origin is still debated.{{Cite journal|last1=Balick|first1=Bruce|last2=Frank|first2=Adam|date=2002|title=Shapes and Shaping of Planetary Nebulae|journal=Annual Review of Astronomy and Astrophysics|volume=40|page=439|doi= 10.1146/annurev.astro.40.060401.093849|bibcode = 2002ARA&A..40..439B }} On the other hand, the X-like shape and the low velocity of the outflowing gas in the Red Rectangle are peculiar, probably because its origin (associated to a stable, extended disk) is different than for most protoplanetary nebulae. {{Clear}}

{{reflist|colwidth=25em}}

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• [http://www.esa.int/esaCP/SEMHBNGHZTD_FeatureWeek_0.html The remarkable Red Rectangle: A Stairway to Heaven?]
• [http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/11/ Dying Star Sculpts Rungs of Gas and Dust]
• [https://web.archive.org/web/20070731022458/http://spacescience.arc.nasa.gov/redglow/ Charged polycyclic aromatic hydrocarbon clusters and the galactic red emission], 2007.
• Astronomy Picture of the Day – [http://apod.nasa.gov/apod/ap100614.html The Red Rectangle Nebula from Hubble] (14 June 2010)
• [http://www.physics.usyd.edu.au/~gekko/redrect.html The Red Rectangle]

{{Sky|06|19|58.2160|-|10|38|14.691|100000000000}}

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Category:Protoplanetary nebulae

Category:Monoceros