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 unrelated to ...
in the southern
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
of
Puppis
Puppis is a constellation in the southern sky. Puppis, the Latin translation of "poop deck", was originally part of an over-large constellation Argo Navis (the ship of Jason and the Argonauts), which centuries after its initial description, was ...
.
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...
measurements by
Gaia
In Greek mythology, Gaia (; from Ancient Greek , a poetical form of , 'land' or 'earth'),, , . also spelled Gaea , is the personification of the Earth and one of the Greek primordial deities. Gaia is the ancestral mother—sometimes parthenog ...
put the central star at a distance of roughly 1,370
light year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
s. It was discovered by
William Herschel
Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
on March 19, 1786. NGC 2438 appears to lie within the cluster M46, but it is most likely unrelated since it does not share the cluster's
radial velocity
The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
. The case is yet another example of a superposed pair, joining the famed case of
NGC 2818
NGC 2818 is a planetary nebula located in the southern constellation Pyxis (The Compass). It consists largely of glowing gases from the star's outer layers ejected during the final stages of its life when it had run out of the fuel necessary to s ...
.
This is a multi-shell planetary nebula with a bright inner nebula with a diameter of , consisting of two somewhat detached shells. It is expanding with a velocity of . The structure is surrounded by a fainter, mostly circular halo that is more visible on the western half, and has a diameter of . The mass of the main nebula is estimated at , while the shell has 0.5–. The main nebula has a temperature of about 10–13,000 K, rising to 15–17,000 K at the inner edge.
The nebula consists of material ejected from the central star during 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 ...
stage, beginning some 8,500 years ago. The main nebula was formed at about half that age. The central star of this planetary nebula is a 17.7-
magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...
, with surface temperature of about . It is one of the hottest stars known.
Gallery
File:NGC 2438 by Göran Nilsson & The Liverpool Telescope.jpg, HaRGB image of the planetary nebula NGC 2348, from the
Liverpool Telescope
The Liverpool Telescope (LT) is a two-metre-aperture robotic Ritchey–Chrétien telescope that observes autonomously (without human intervention). However professional astronomers, school groups and other credible registered users submit speci ...