KjPn 8 is a bipolar planetary nebula which was discovered by M.A. Kazaryan and Eh. S. Parsamyan in 1971 and independently by Luboš Kohoutek in 1972. Very little was published about this nebula until 1995, when it was realized that KjPn 8 sits in the center of a very large filamentary nebula, 14 by 4 arc minutes in size. This is the largest known bipolar structure associated with a planetary nebula. Narrow band images centered at

Hα H-alpha (Hα) is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm in air and 656.46 nm in vacuum; it occurs when a hydrogen electron falls from its third to second lowest energy level. H-alpha ...

and

forbidden line In spectroscopy, a forbidden mechanism (forbidden transition or forbidden line) is a spectral line associated with absorption or emission of photons by atomic nuclei, atoms, or molecules which undergo a transition that is not allowed by a particu ...

transitions of nitrogen, sulphur, and oxygen reveal pairs of bow shocks at differing position angles, indicating the presence of episodic ejection of material along a precessing jet, similar to what is seen in

Fleming 1 Fleming 1 is an unusual planetary nebula situated in the Centaurus constellation. It has a pair of symmetrical jets spanning more than 2.8 pc and delineated with a number of knots. The jets and knots are moving away from the center of the nebula ...

, but much larger (in angular extent). The physical size of this extended nebula is approximately 4.1 by 1.2

parsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

, much larger than a typical planetary nebula, while the core nebula known prior to 1995 is only about 0.2 parsecs in diameter. The envelope of KjPn 8 is expanding rapidly enough to allow the

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

of features in the nebula to be measured. In 1997 John Meaburn compared images of the nebula taken in 1954 (as part of the Palomar Sky Survey) and 1991.He measured a proper motion of 34±3 milliarcseconds per year for two knots in the nebula. Combining this proper motion with an expansion velocity derived from spectral line profile widths allowed Meaburn to derive a distance to the nebula of 1600±230 parsecs, and a kinematic age of 3400±300 years. Microwave emission from

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

reveals the presence of a dense disk of molecular gas 30 arcseconds in diameter expanding at about 7 km/sec, with a mass ≥ 0.03 M_⊙. The disk is aligned with the youngest and fastest bipolar jet, which has an expansion velocity of about 300 km/sec. The central star has begun to ionize the central region of this disk.

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

observations suggest that KjPn 8 might be a very rare object, formed by a binary system in which both stars had similar masses, which reached the end of the

Asymptotic Giant Branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

phase within 10 to 20 thousand years of each other, and entered the planetary nebula formation stage nearly simultaneously.

References

{{reflist Planetary nebulae Cassiopeia (constellation)