Palomar 12
Encyclopedia
Palomar 12 is a globular cluster
in the constellation
Capricornus
that belongs to the halo of the Milky Way
galaxy. First discovered on the Palomar Survey Sky plates by Robert G. Harrington
and Fritz Zwicky
,
it was catalogued as a globular cluster. However Zwicky came to believe this was actually a nearby dwarf galaxy in the Local Group
. It is a relatively young cluster, being about 30% younger than most of the globular clusters in the Milky Way. It is metal-rich with a metallicity
of [Fe/H] ~= -0.8. It has an average luminosity distribution of Mv = -4.48.
Based on proper motion
studies, this cluster was first suspected in 2000 to have been captured from the Sagittarius dwarf galaxy
about 1.7 Ga ago. Its membership is now generally believed (Cohen 2004, Sbordone et al. 2006).
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Capricornus
Capricornus
Capricornus is one of the constellations of the zodiac; it is often called Capricorn, especially when referring to the corresponding astrological sign. Its name is Latin for "horned male goat" or "goat horn", and it is commonly represented in the form of a sea-goat: a mythical creature that is half...
that belongs to the halo of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy. First discovered on the Palomar Survey Sky plates by Robert G. Harrington
Robert G. Harrington
Robert G. Harrington was an American astronomer who worked at Palomar Observatory. He should not be confused with Robert Sutton Harrington, who was also an astronomer, but was born later and worked at the US Naval Observatory....
and Fritz Zwicky
Fritz Zwicky
Fritz Zwicky was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and observational astronomy.- Biography :Fritz Zwicky was born in Varna, Bulgaria to a Swiss father....
,
it was catalogued as a globular cluster. However Zwicky came to believe this was actually a nearby dwarf galaxy in the Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
. It is a relatively young cluster, being about 30% younger than most of the globular clusters in the Milky Way. It is metal-rich with a metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
of [Fe/H] ~= -0.8. It has an average luminosity distribution of Mv = -4.48.
Based on proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
studies, this cluster was first suspected in 2000 to have been captured from the Sagittarius dwarf galaxy
Sagittarius Dwarf Elliptical Galaxy
The Sagittarius Dwarf Elliptical Galaxy is an elliptical loop-shaped satellite galaxy of the Milky Way Galaxy. It consists of four globular clusters, the main cluster being discovered in 1994...
about 1.7 Ga ago. Its membership is now generally believed (Cohen 2004, Sbordone et al. 2006).