Abell 39
Encyclopedia
Abell 39 is a low surface brightness
planetary nebula
in the constellation of Hercules
. It is the 39th entry in George Abell's
1966 Abell Catalog of Planetary Nebulae (and 27th in his 1955 catalog) of 86 old planetary nebulae which either Abell or Albert George Wilson
discovered before August 1955 as part of the National Geographic Society - Palomar Observatory Sky Survey
. It is estimated to be about 6,800 light-year
s from earth and 4,600 light-years above the Galactic plane
. It is almost perfectly spherical and also one of the largest known spheres with a radius of about 2.5 light-years.
is slightly west of center by about 2″ or 0.1 light-years. This offset does not appear to be due to interaction with the interstellar medium
, but instead, it is hypothesized that a small asymmetric
mass ejection has accelerated the central star. The mass of the central star is estimated to be about 0.61 M☉
with the material in the planetary nebula comprising an additional 0.6 M☉.
This planetary nebula has a nearly uniform spherical shell. However, the eastern limb
of the nebula is 50% more luminous than the western limb. Additionally, irregularities in the surface brightness are seen across the face of the shell. The source of the east-west asymmetry is not known but it could be related to the offset of the central star.
This planetary nebula has been expanding for an estimated 22,100 years, based on an assumed expansion velocity between 32 and 37 km/s and a 0.78 parsec radius.
Background galaxies
are visible near the nebula, and some can be seen through the translucent nebula.
Oxygen
is only about half as abundant in the nebula as it is in our own sun
.
Surface brightness
The overall brightness of an extended astronomical object such as a galaxy, star cluster, or nebula, can be measured by its total magnitude, integrated magnitude or integrated visual magnitude; a related concept is surface brightness, which specifies the brightness of a standard-sized piece of an...
planetary nebula
Planetary nebula
A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
in the constellation of Hercules
Hercules (constellation)
Hercules is a constellation named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. It is the 39th entry in George Abell's
George Ogden Abell
George Ogden Abell was an astronomer at UCLA. He worked as a research astronomer, teacher, administrator, popularizer of science and education, and skeptic. Abell received his B.S. , M.S. and Ph.D. from the California Institute of Technology...
1966 Abell Catalog of Planetary Nebulae (and 27th in his 1955 catalog) of 86 old planetary nebulae which either Abell or Albert George Wilson
Albert George Wilson
Albert George Wilson is an American astronomer.He was born in Houston, Texas. He received his Ph.D. in mathematics from Caltech in 1947; his thesis title was Axially Symmetric Thermal Stresses in a Semi-Infinite Solid....
discovered before August 1955 as part of the National Geographic Society - Palomar Observatory Sky Survey
National Geographic Society - Palomar Observatory Sky Survey
The National Geographic Society – Palomar Observatory Sky Survey is a major photographic survey of the night sky that was completed at Palomar Observatory in 1958.-Observations:...
. It is estimated to be about 6,800 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s from earth and 4,600 light-years above the Galactic plane
Galactic plane
The galactic plane is the plane in which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles...
. It is almost perfectly spherical and also one of the largest known spheres with a radius of about 2.5 light-years.
Central star
Its central starCentral Star
Central Star consists of four residential skyscrapers under construction in Busan, South Korea. The tallest landmark tower measures tall and has 58 floors. Ground was broken by POSCO E&C in 2007 and is completing in 2011....
is slightly west of center by about 2″ or 0.1 light-years. This offset does not appear to be due to interaction with the interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
, but instead, it is hypothesized that a small asymmetric
mass ejection has accelerated the central star. The mass of the central star is estimated to be about 0.61 M☉
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
with the material in the planetary nebula comprising an additional 0.6 M☉.
This planetary nebula has a nearly uniform spherical shell. However, the eastern limb
Limb
Limb can refer to:*Limb , an appendage of a human or animal*Limb darkening, in astronomy, the appearance of the border of the disk of a celestial body*Limb Music, a record label*Limb , a compilation album by Foetus...
of the nebula is 50% more luminous than the western limb. Additionally, irregularities in the surface brightness are seen across the face of the shell. The source of the east-west asymmetry is not known but it could be related to the offset of the central star.
Structure and composition
The bright rim of the planetary nebula has an average thickness of about 10″.1 or about 0.34 light-years. There is a faint halo that extends about 18″ beyond the bright rim giving a complete diameter of around 190″ under the assumption that this emission is uniform around the planetary nebula.This planetary nebula has been expanding for an estimated 22,100 years, based on an assumed expansion velocity between 32 and 37 km/s and a 0.78 parsec radius.
Background galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
are visible near the nebula, and some can be seen through the translucent nebula.
Oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
is only about half as abundant in the nebula as it is in our own sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
.