Planetary nebula luminosity function (PNLF) is a secondary
used in
astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
. It makes use of the
IIIλ5007
forbidden line found in all
planetary nebula
A planetary nebula (PN, plural PNe) 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 unrelate ...
(PNe) which are members of the old stellar populations (
Population II
During 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations.
In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926:
Baade noticed th ...
).
It can be used to determine distances to both
spiral
In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point.
Helices
Two major definitions of "spiral" in the American Heritage Dictionary are:[elliptical galaxies despite their completely different stellar populations and is part of the Extragalactic Distance Scale.]
Procedure
The distance estimate to a galaxy using the PNLF requires discovery of such an object in the target galaxy that is visible at λ5007 but not when the entire spectrum is considered. These points are candidate PNe, however, there are three other types of objects that would also exhibit such an emission line that must be filtered out: HII regions,