- A Hipparcos Census of the Nearby OB Associations (iopscience.iop.org)
A comprehensive census of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes. It is a key part of a long-term project to study the formation, structure, and evolution of nearby young stellar groups and related star-forming regions. OB associations are unbound “moving groups,” which can be detected kinematically because of their small internal velocity dispersion. The nearby associations have a large extent on the sky, which traditionally has limited astrometric membership determination to bright stars (V ≲ 6 mag), with spectral types earlier than ∼B5. The Hipparcos measurements allow a major improvement in this situation.
- Silicate mineral (Wikipedia)
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth’s crust.