Zeta Herculis Moving Group is a set of
star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s that share a common
motion through space.
The existence of this
moving group
In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space.
Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...
was first published in 1958 by
Olin J. Eggen. Based upon the high velocity motion of the star
Zeta Herculis through space, he searched for stars that were following a similar velocity and direction. A total of 22 candidate members were identified. Among the group members he included
β Hydri,
ρ Persei,
η Reticuli,
φ1 Lupi,
ζ Herculis and
ε Octantis. He estimated the group velocity at 74.5 km/s.
[
] In 1970, Richard Woolley refined the list to ten stars, including
φ2 Pavonis and
ζ1/
ζ2 Reticuli as members of this cluster.
[
]
The parallel motion of the stars in this group implies a common origin, and hence a similar age and composition. The membership of ζ Herculis and
HD 158614 came into question because their composition appeared to show they were much younger than other members of the group. The average age was estimated as 8.2 billion years, while ζ Herculis was estimated as 6.3 billion years in age.
However, a statistical analysis of the
metallicity
In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...
for stars in this group showed no difference from a comparison sample, indicating that it may not be possible to determine more information about this group based on the composition of its members.
References
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Moving groups