A post-AGB star (pAGB, abbreviation of post-

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 ...

) is a type of luminous

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...

star of intermediate mass in a very late phase of

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...

. The post-AGB stage occurs after the

(AGB or second-ascent

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

) has ended. The stage sees the dying star, initially very cool and large, shrink and heat up. The duration of the post-AGB stage varies based on the star's initial mass, and can range from 100,000 years for a solar-mass star to just over 1,000 years for more massive stars. The timescale gets slightly shorter with lower

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

. Towards the end of this stage, post-AGB stars also tend to produce

protoplanetary nebula A protoplanetary nebula or preplanetary nebula (PPN, plural PPNe) is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch (LAGB) phase and the subsequent planetary ne ...

e as they shed their outer layers, and this creates a large infrared excess and obscures the stars in visible light. After reaching an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of about , the star is able to ionise its surrounding nebula, producing a true

planetary nebula A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...

Properties

Post-AGB stars span a large range of temperatures, as they are in the process of heating up from very cool temperatures ( or less) up to about . Technically, the post-AGB stage only ends when the star reaches its maximum temperature of 100-, but beyond , the star ionises the surrounding gas and would be considered a central star of a planetary nebula more often than a post-AGB star. On the other hand, the luminosity of post-AGB stars is usually constant throughout the post-AGB stage, and slightly dependent on the star’s core mass, and getting slightly brighter with lower metallicity.

Examples

Due to the dust usually obscuring them, many post-AGB stars are visually relatively dim. However there are still some post-AGB stars visible to the naked eye, the brightest of which is 89 Herculis. Other examples include: *

L2 Puppis L2 Puppis (also known as HD 56096) is a giant star in the constellation of Puppis and is located between the bright stars Canopus and Sirius. It is a Semiregular variable star, semi-regular pulsating star, and is intermittently visible ...

RV Tauri RV Tauri (''RV Tau'') is a star in the constellation Taurus (constellation), Taurus. It is a yellow supergiant and is the prototype of a class of pulsating variables known as RV Tauri variables. It is a post-AGB star and a spectroscopi ...

* R Scuti * U Monocerotis

References

{{Star Protoplanetary nebulae Star types Post-asymptotic-giant-branch stars