Unresolved Pre-Main-Sequence Binaries in the HR Diagram

Hartigan, P. (Rice) and Kenyon, S. J. (CfA)

We consider how positions of unresolved pre-main-sequence binaries in the HR diagram compare with the positions of their corresponding primaries and secondaries. As one might expect from simple considerations, the composites appear younger than their components, and have masses intermediate between those of the two stars. However, the amount of the age difference between the composite and its components ranges from nearly zero to as much as an order of magnitude depending upon the specifics of the system such as the reddening and relative spectral types of the objects. We present four examples that illustrate these issues.

2000, I.A.U. Symp. 200, Formation and Evolution of Binary Stars, H. Zinnecker and R. Mathieu eds.