Here's a breakdown:
* Primary Star: The primary star, Alpha Librae A, is a subgiant star of spectral type F8IV. This means it's slightly cooler and larger than our Sun, and is in the process of evolving away from the main sequence.
* Secondary Star: The secondary star, Alpha Librae B, is a main sequence star of spectral type F9V. It's a bit cooler and smaller than our Sun.
While the primary star is considered a subgiant, it's still relatively young and bright. It's about 1.8 times the mass of the Sun and is about 200 times more luminous.
So, while Alpha Librae is technically a binary system, it's often referred to simply as a subgiant star because the primary star dominates the system's luminosity.