A region of the Hertzsprung-Russell diagram populated by evolving low-mass to intermediate-mass stars. These stars have an electron degenerate core of carbon and oxygen surrounded by two burning shell
s of helium and hydrogen. The H and He-burning shells are activated alternately in the deep layers of the star. An extended and tenuous convection envelope, having a radius of 10^4 - 10^5 times the size of the core, lies above these shells. The loosely bound envelope is gradually eroded by the strong stellar wind, which forms a dusty circumstellar envelope out to several hundreds of stellar radii. The convective envelope, stellar atmosphere, and circumstellar envelope have a rich and changing chemical composition provided by nucleosynthesis processes in the burning shells in the deep interior.
A member of a class of near-Earth asteroids with perihelion distances between 0.983 and 1.0 astronomical units. It is estimated that 6% of the total number of NEAs are Atens.