Omega Herculis

Lore & Background

The system bears the traditional name Cujam (also written as Cajam and Kajam), meaning 'club'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to standardize proper names for stars, and on February 1, 2017, the name Cujam was approved for the component Omega Herculis A. The system previously bore the Flamsteed designation 51 Serpentis before being added to Hercules. In Chinese astronomy, Omega Herculis is part of an asterism called 'Dipper for Liquid', which also includes 49 Serpentis, 13 Herculis, 29 Herculis, and 33 Herculis.

The primary, Omega Herculis A, is a chemically peculiar Ap star with a classification of A2 Vp CrSr, showing abnormally strong absorption lines of chromium and strontium and weak lines of calcium and magnesium. It is an Alpha2 Canum Venaticorum variable with a brightness amplitude of 0.4 magnitude and a 2.951-day phase that presumably matches its rotation period. The pattern of variation indicates regions on the star's surface with differing elemental concentrations, and it also displays short-period variations on the order of 2.5 hours. The secondary, Omega Herculis B, is a magnitude 11.5 companion star; as of 2010, it was located at an angular separation of 0.80 arc seconds along a position angle of 294°.

Reader's Guide

Omega Herculis is notable as a binary system whose primary is a chemically peculiar Ap star, a class of stars that exhibit strong magnetic fields and unusual surface abundances of elements such as chromium and strontium. Its variability as an Alpha2 Canum Venaticorum variable makes it a subject of interest for studies of stellar rotation and surface inhomogeneities, as the brightness changes are linked to the rotation of a star with uneven elemental distributions. The system's uncertain membership in the Ursa Major Moving Group places it in a broader context of stellar kinematics, though this association is not firmly established. The official naming of its primary component as Cujam by the IAU in 2017 reflects ongoing efforts to formalize traditional star names for individual stars within multiple systems. The system's history includes a change in constellation assignment, having once been designated 51 Serpentis before being moved to Hercules, illustrating the evolution of constellation boundaries and Bayer designations. Its Chinese asterism association adds a cultural dimension, linking it to a group of stars forming a 'Dipper for Liquid' in traditional Chinese astronomy.