What characterizes optical doubles in astronomy?

Optical doubles in astronomy are characterized by the presence of two stars that appear close to each other in the sky but are not physically related. These stars are merely along the same line of sight from our perspective on Earth, which means they can be quite far apart in space and have no gravitational connection to one another. This concept is essential when distinguishing between optical doubles and true binary stars, which are gravitationally bound and significantly influence each other's motions.

In contrast, other options reflect characteristics that do not apply to optical doubles. Gravitationally bound pairs of stars indicate a binary system, where the stars exert mutual gravitational influence on each other. Being resolved independently is a trait found in both binary and multiple star systems, but it does not define optical doubles specifically. Lastly, while true doubles can be used to determine stellar masses through their orbital dynamics and interaction, optical doubles do not provide this capability since they are not related in a gravitational sense. This means the ability to analyze masses requires a different relationship between the stars than that of optical doubles.