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A protoplanetary nebula or preplanetary nebula (Sahai, Sánchez Contreras & Morris 2005) (PPN) is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch (LAGB)[a] phase and the subsequent planetary nebula (PN) phase. A PPN emits strongly in infrared radiation, and is a kind of reflection nebula. It is the second-from-the-last high-luminosity evolution phase in the life cycle of intermediate-mass stars (1–8 M☉). (Kastner 2005)

Naming
Protoplanetary nebula IRAS 13208-6020 is formed from material that is shed by a central star.

The name protoplanetary nebula is an unfortunate choice due to the possibility of confusion with the same term being sometimes employed when discussing the unrelated concept of protoplanetary disks. The name protoplanetary nebula is a consequence of the older term planetary nebula, which was chosen due to early astronomers looking through telescopes and finding a similarity in appearance of planetary nebula to the gas giants such as Neptune and Uranus. To avoid any possible confusion, Sahai, Sánchez Contreras & Morris 2005 suggests employing a new term preplanetary nebula which does not overlap with any other disciplines of astronomy. They are often referred to as post-AGB stars, although that category also includes stars that will never ionize their ejected matter.
Evolution
Beginning

During the late asymptotic giant branch (LAGB)[a] phase, when mass loss reduces the hydrogen envelope's mass to around 10−2 M☉ for a core mass of 0.60 M☉, a star will begin to evolve towards the blue side of the Hertzsprung–Russell diagram. When the hydrogen envelope has been further reduced to around 10−3 M☉, the envelope will have been so disrupted that it is believed further significant mass loss is not possible. At this point, the effective temperature of the star, T*, will be around 5,000 K and it is defined to be the end of the LAGB and the beginning of the PPN. (Davis et al. 2005)
Protoplanetary nebula phase
Protoplanetary nebula known as Emperor Seiwa taken by Hubble's Advanced Camera for Surveys.

During the ensuing protoplanetary nebula phase, the central star's effective temperature will continue rising as a result of the envelope's mass loss as a consequence of the hydrogen shell's burning. During this phase, the central star is still too cool to ionize the slow-moving circumstellar shell ejected during the preceding AGB phase. However, the star does appear to drive high-velocity, collimated winds which shape and shock this shell, and almost certainly entrain slow-moving AGB ejecta to produce a fast molecular wind. Observations and high-resolution imaging studies from 1998 to 2001, demonstrate that the rapidly evolving PPN phase ultimately shapes the morphology of the subsequent PN. At a point during or soon after the AGB envelope detachment, the envelope shape changes from roughly spherically symmetric to axially symmetric. The resultant morphologies are bipolar, knotty jets and Herbig–Haro-like "bow shocks". These shapes appear even in relatively "young" PPN. (Davis et al. 2005)
End

The PPN phase continues until the central star reaches around 30,000 K and it is hot enough (producing enough ultraviolet radiation) to ionize the circumstellar nebula (ejected gases) and it becomes a kind of emission nebula called a PN. This transition must take place in less than around 10,000 years or else the density of the circumstellar envelope will fall below the PN formulation density threshold of around 100 per cm³ and no PN will result, such a case is sometimes referred to as a 'lazy planetary nebula'. (Volk & Kwok 1989)
Recent conjectures
An interstellar butterfly - protoplanetary nebula Roberts 22 [1]

In 2001, Bujarrabal et al. found that the "interacting stellar winds" model of Kwok et al. (1978) of radiatively-driven winds is insufficient to account for their CO observations of PPN fast winds which imply high momentum and energy inconsistent with that model. This has prompted theorists (Soker & Rappaport 2000; Frank & Blackmann 2004) to investigate whether an accretion disk scenario, similar to the model used to explain jets from active galactic nuclei and young stars, could account for both the point symmetry and the high degree of collimation seen in many PPN jets. In such a model, the accretion disk forms through binary interactions. Magneto-centrifugal launching from the disk surface is then a way to convert gravitational energy into the kinetic energy of a fast wind. If this model is correct and magneto-hydrodynamics (MHD) do determine the energetics and collimation of PPN outflows, then they will also determine physics of the shocks in these flows, and this can be confirmed with high-resolution pictures of the emission regions that go with the shocks. (Davis et al. 2005)
See also

Bipolar nebula
Bipolar outflow
List of protoplanetary nebulae
Planetary nebula

Notes

^ The late asymptotic giant branch begins at the point on the asymptotic giant branch (AGB) where a star is no longer observable in visible light and becomes an infrared object. (Volk & Kwok 1989)

References

"An interstellar butterfly". ESA / HUBBLE. Retrieved 11 March 2014.

Davis, C. J.; Smith, M. D.; Gledhill, T. M.; Varricatt, W. P. (2005), "Near-infrared echelle spectroscopy of protoplanetary nebulae: probing the fast wind in H2", Monthly Notices of the Royal Astronomical Society, 360 (1): 104–118, arXiv:astro-ph/0503327, Bibcode:2005MNRAS.360..104D, doi:10.1111/j.1365-2966.2005.09018.x.
Kastner, J. H. (2005), "Near-death Transformation: Mass Ejection in Planetary Nebulae and Protoplanetary Nebulae", American Astronomical Society Meeting 206, #28.04; Bulletin of the American Astronomical Society, 37: 469, Bibcode:2005AAS...206.2804K.
Sahai, Raghvendra; Sánchez Contreras, Carmen; Morris, Mark (2005), "A Starfish Preplanetary Nebula: IRAS 19024+0044" (PDF), The Astrophysical Journal, 620 (2): 948–960, Bibcode:2005ApJ...620..948S, doi:10.1086/426469.
Volk, Kevin M.; Kwok, Sun (July 1, 1989), "Evolution of protoplanetary nebulae", The Astrophysical Journal, 342: 345–363, Bibcode:1989ApJ...342..345V, doi:10.1086/167597.
Szczerba, Ryszard; Siódmiak, Natasza; Stasińska, Grażyna; Borkowski, Jerzy (April 23, 2007), "An evolutive catalogue of Galactic post-AGB and related objects", Astronomy and Astrophysics, 469 (2): 799–806, arXiv:astro-ph/0703717, Bibcode:2007A&A...469..799S, doi:10.1051/0004-6361:20067035.

vte

Stars
Formation

Accretion Molecular cloud Bok globule Young stellar object
Protostar Pre-main-sequence Herbig Ae/Be T Tauri FU Orionis Herbig–Haro object Hayashi track Henyey track

Evolution

Main sequence Red-giant branch Horizontal branch
Red clump Asymptotic giant branch
super-AGB Blue loop Protoplanetary nebula Planetary nebula PG1159 Dredge-up OH/IR Instability strip Luminous blue variable Blue straggler Stellar population Supernova Superluminous supernova / Hypernova

Spectral classification

Early Late Main sequence
O B A F G K M Brown dwarf WR OB Subdwarf
O B Subgiant Giant
Blue Red Yellow Bright giant Supergiant
Blue Red Yellow Hypergiant
Yellow Carbon
S CN CH White dwarf Chemically peculiar
Am Ap/Bp HgMn Helium-weak Barium Extreme helium Lambda Boötis Lead Technetium Be
Shell B[e]

Remnants

White dwarf
Helium planet Black dwarf Neutron
Radio-quiet Pulsar
Binary X-ray Magnetar Stellar black hole X-ray binary
Burster

Hypothetical

Blue dwarf Green Black dwarf Exotic
Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Gravastar Frozen Quasi-star Thorne–Żytkow object Iron Blitzar

Stellar nucleosynthesis

Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium flash Triple-alpha process Alpha process Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova
Symbiotic Remnant Luminous red nova

Structure

Core Convection zone
Microturbulence Oscillations Radiation zone Atmosphere
Photosphere Starspot Chromosphere Stellar corona Stellar wind
Bubble Bipolar outflow Accretion disk Asteroseismology
Helioseismology Eddington luminosity Kelvin–Helmholtz mechanism

Properties

Designation Dynamics Effective temperature Luminosity Kinematics Magnetic field Absolute magnitude Mass Metallicity Rotation Starlight Variable Photometric system Color index Hertzsprung–Russell diagram Color–color diagram

Star systems

Binary
Contact Common envelope Eclipsing Symbiotic Multiple Cluster
Open Globular Super Planetary system

Earth-centric
observations

Sun
Solar System Sunlight Pole star Circumpolar Constellation Asterism Magnitude
Apparent Extinction Photographic Radial velocity Proper motion Parallax Photometric-standard

Lists

Proper names
Arabic Chinese Extremes Most massive Highest temperature Lowest temperature Largest volume Smallest volume Brightest
Historical Most luminous Nearest
Nearest bright With exoplanets Brown dwarfs White dwarfs Milky Way novae Supernovae
Candidates Remnants Planetary nebulae Timeline of stellar astronomy

Related articles

Substellar object
Brown dwarf Sub-brown dwarf Planet Galactic year Galaxy Guest Gravity Intergalactic Planet-hosting stars Tidal disruption event

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