Are Wide Pre-Main-Sequence Binaries Coeval?

Hartigan, P. (UMass), Strom, K. (UMass) and Strom, S. (UMass)
We have observed a sample of 39 wide (projected separations 400 AU - 6000 AU) pre-main-sequence binary pairs spectroscopically and with optical and near-infrared images. The observations enable us to place 26 of the pairs in an HR-diagram and to determine masses and ages of the primary and secondary according to three sets of pre-main-sequence evolutionary tracks. In two-thirds of the cases the primary and secondary lie along the same isochrone to within the observational errors. However, real age differences appear for about one-third of our sample pairs - there is no set of non-intersecting theoretical isochrones that can make the primary and secondary have the same age for all pairs in our sample. In the cases where there are significant age differences between the component stars, the less massive star is usually younger than the more massive star. There is no correlation of the age differences with the presence or absence of accretion disks around the young stars. Hence, while disk accretion may affect the evolutionary tracks of pre-main-sequence stars HR-diagram, we see no clear evidence of this effect among the pairs in our sample. The age differences also do not depend systematically on the apparent separation, the mass ratio, or the ages of the stars.

Journal of publication: Ap J 427, 961, 1994.